Binder2

The components of an intra-arterial monitoring system can be viewed as three main parts:  The measuring apparatus  The transducer  The monitorThe measuring apparatus consists of an arterial cannula connected to tubing containing acontinuous column of saline. The pressure waveform of the arterial pulse is transmitted via thecolumn of fluid, to a pressure transducer, in the case of intra-arterial monitoring the transducerconsists of a flexible diaphragm which in turn moves strain gauges converting the pressurewaveform into an electrical signal. Monitors amplify the output signal from the transducer, filterthe noise and also display the arterial waveform in real time on a screen. They also usually givea digital numeric display of systolic, diastolic and mean arterial blood pressure (MAP).The arterial line is also connected to a flushing system consisting of a bag of saline pressurisedto 300 mm/Hg via a flushing device. Pressure Bag Pressure transducer & automatic flushing system Arterial line Saline filled tubing Fig 3 – Invasive Blood Pressure being monitored (Omron, 2015)For a pressure transducer to read accurately, atmospheric pressure must be discounted fromthe pressure measurement. This is done by exposing the transducer to atmospheric pressureand calibrating the pressure reading to zero. A transducer should be zeroed several times perday to eliminate any baseline drift.The pressure transducer must be set at the appropriate level in relation to the patient in orderto measure blood pressure correctly. This is usually taken to be level with the patient’s heart.Failure to do this results in an error due to hydrostatic pressure (the pressure exerted by acolumn of fluid – in this case, blood) being measured in addition to blood pressure. This can besignificant – every 10cm error in levelling will result in a 7.4mmHg error in the pressuremeasured; a transducer too low over reads, a transducer too high under reads.IBP monitoring has numerous advantages; IBP allows continuous ‘beat-to-beat’ blood pressuremonitoring. This is useful in patients who are likely to display sudden changes in blood pressure(e.g. vascular surgery), patients who require close control of blood pressure (e.g. head injuredpatients), or in patients receiving drugs to maintain blood pressure.The IBP technique also allows accurate blood pressure readings at very low pressures, forexample in shocked patients.An invasive blood pressure reading could also allow for improvement of patient comfort if bloodpressure monitoring is required for a long period of time. IBP monitoring avoids the trauma ofrepeated cuff inflations.Other advantages include that the arterial cannula is convenient for repeated arterial bloodsampling, for instance for arterial blood gases. (Jones, 2009)

Maintenance & Service ProceduresInvasive Blood PressureThis is checked using a patient simulator at various pressures, it is essential that a zeroingprocedure is performed before any measurements are taken.Respiration RateThis is also checked using a patient simulator at various rates to ensure accuracy.Capnography & Airways GasesCapnograpy can be tested by attaching an ETCO2 circuit and breathing into the airway adapter ata set rate, the rise and fall of the CO2 graph will be displayed on the monitor. The accuracy ofany measured airways gases is also to be checked by attaching a cylinder filled with variousgases such as; O2, CO2, nitrogen and typically an anaesthetic gas at set percentages. The monitorshould show the levels of the various gases, if the values displayed are not correct a calibrationprocedure should be carried out.BibliographyEBME, 2014. Capnography. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/16-capnometry-capnography[Accessed December 2015].Fukuda Denshi UK, 2014. DS-8500 System Maintenance Manual V.09 (2014). V 9 ed. Tokyo:Fukuda Denshi.Jones, A., 2009. Physical Principles of Intra-Arterial Blood Pressure Measurements, Salford: s.n.Mallett , J. & Dougherty, L., 2004. The Royal Marsden Hospital Manual of Clinical NursingProcedures. 6th ed. Oxford: Blackwell Science.Omron, 2015. Arterial Blood Pressure. [Online]Available at: http://omronbloodpressuremonitorpictures.blogspot.co.uk/2015/01/2015-arterial-blood-pressure-monitoring.html[Accessed 2015].Paramedicine, 2000. End Tidal CO2. [Online]Available at: http://www.paramedicine.com/pmc/End_Tidal_CO2.html[Accessed October 2015].Physio-Control, 2013. Lifepak® 20e Defibrillator Service/User manual.Tilakaratna, P., 2014. How Equipment Works. [Online]Available at: http://www.howequipmentworks.com/capnography/[Accessed December 2015].

12 Lead ECG Recorders Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Electrocardiography (ECG)The heart is responsible for pumping blood around the body by repeated, rhythmiccontractions. The functional unit of the heart is the cardiac muscle cell or cardiomyocyte. Eachcardiomyocyte maintains an electrical charge or potential across its cell membrane andcontracts when this potential is discharged. In order for all of the cardiomyocytes to contract atthe same time and produce an effective muscular contraction, the heart also maintains its ownelectrical conducting system which coordinates the electrical activity of the heart. Fig 1 – The Human Heart (EBME, 2011)The electrical impulses take a specialised conduction pathway.This pathway is made up of 5 elements: 1. The Sino-Atrial (SA) node 2. The Atrio-Ventricular (AV) node 3. The bundle of His 4. The left and right bundle branches 5. The Purkinje fibres Fig 2 – The Human Heart (The University of Nottingham, 2015)

The SA node is the natural pacemaker of the heart. Pacemakers and Temporary Pacing Wires(TPWs) are used when the SA node has ceased to function properly.The SA node releases electrical stimuli at a regular rate; this rate is dictated by the needs of thebody. Each stimulus passes through the myocardial cells of the atria creating a wave ofcontraction which spreads rapidly through both atria.The heart is made up of around half a billion cells; the majority of the cells make up theventricular walls. The rapidity of atrial contraction is such that around 100 million myocardialcells contract in less than one third of a second. The electrical stimulus from the SA nodeeventually reaches the AV node and is delayed briefly so that the contracting atria have enoughtime to pump all the blood into the ventricles. Once the atria are empty of blood the valvesbetween the atria and ventricles close. At this point the atria begin to refill and the electricalstimulus passes through the AV node and Bundle of His into the Bundle branches and Purkinjefibres.The Purkinje fibres spread widely across the ventricles. In this way all the cells in the ventriclesreceive an electrical stimulus causing them to contract.As the ventricles contract, the right ventricle pumps blood to the lungs where carbon dioxide isreleased and oxygen is absorbed, whilst the left ventricle pumps blood into the aorta fromwhere it passes into the coronary and arterial circulation.At this point the ventricles are empty, the atria are full and the valves between them are closed.The SA node is about to release another electrical stimulus and the process is about to repeatitself. The SA node recharges whilst the atria are refilling, and the AV node recharges when theventricles are refilling. In this way there is no need for a pause in heart function. Again, thisprocess takes less than one third of a second.The times given for the 3 different stages are based on a heart rate of 60 bpm, or 1 beat persecond.The term used for the release (discharge) of an electrical stimulus is \"depolarisation\", and theterm for recharging is \"repolarisation\".The sum total of the simultaneous electrical discharging and re-charging of all thecardiomyocytes in the heart is sufficient to be detected by sensing probes placed on the exteriorof the body at various positions around the heart. The ECG records the vector sum and producesa combined trace. This is the principle behind the electrocardiograph or ECG which can be usedto monitor the rhythm of the heart.Injured cardiomyocytes such as those suffering from lack of oxygen during a heart attack leakelectrical current rather than discharge it in a coordinated manner, the altered electrical signalof the injured heart results in a characteristic ECG pattern which can lead to the diagnosis ofacute myocardial infarction (Heart Attack).In contrast, dead cardiomyocytes or scarred cardiac muscle does not carry or maintain anelectrical charge, and this absence of electrical activity is also detectable by ECG. Therefore, apreviously unrecognised or \"silent\" heart attack can be diagnosed by electrocardiogram, andeven localised to a particular area of the heart by using multiple sensing probes or ECG leads. (EBME, 2011)An ECG trace may be obtained with the electrodes attached in a variety of positions, however,the system of positioning leads for performing a 12-lead ECG is universal. This helps to ensurethat, when a person's ECGs are compared, any changes on the ECG are due to cardiac injury, nota difference in placement of leads, this is extremely important with the increasing use of foreigntravel. There are universal standards in place throughout the world.

These positions may differ slightly when a patient is on continuous cardiac monitoring. Theleads routinely attached to wrists and ankles will be placed on shoulders and lower abdomen sothat movement of limbs has minimal effect on the rhythm trace. These positions may also differif a patient is shaking (maybe due to Parkinson's disease or hypothermia) or has muscletremors. In this situation the leads may be moved onto the thighs and forearms.There are 10 wires on an ECG machine that are connected to specific parts of the body. Thesewires break down into 2 groups: 1. 6 chest leads 2. 4 limb or peripheral leads (one of these is \"neutral\") Fig 3 – 12 Lead ECG Placement (The University of Nottingham, 2015)The 6 leads are labelled as \"V\" leads and numbered V1 to V6. They are positioned in specificpositions on the rib cage.Limb leads are made up of 4 leads placed on the extremities: left and right wrist; left and rightankle. Fig 4 – ECG Placement on a patient lying down. (The University of Nottingham, 2015)

Each of the 12 leads represents a particular orientation in space, as indicated below (RA = rightarm; LA = left arm, LL = left foot):Bipolar limb leads (frontal plane):  Lead I: RA (-) to LA (+) (Right Left, or lateral)  Lead II: RA (-) to LL (+) (Superior Inferior)  Lead III: LA (-) to LL (+) (Superior Inferior)Augmented unipolar limb leads (frontal plane):  Lead aVR: RA (+) to [LA & LL] (-) (Rightward)  Lead aVL: LA (+) to [RA & LL] (-) (Leftward)  Lead aVF: LL (+) to [RA & LA] (-) (Inferior)Unipolar (+) chest leads (horizontal plane):  Leads V1, V2, V3: (Posterior Anterior)  Leads V4, V5, V6:(Right Left, or lateral)The \"aV\" stands for Augmented Vector, the last letter refers to a position, which are asfollows: aVR Augmented Vector Right Right wrist/shoulder aVL Augmented Vector Left Left wrist/shoulder aVF Augmented Vector Foot Left foot/lower abdomenThese 3 leads create a triangle with the heart in the middle, as below. The lines into the centreindicate the line of sight of these leads. Fig 5 – Einthoven’s Triangle. (The University of Nottingham, 2015)The 2 leads situated on the right and left wrist (or shoulders), aVR and aVL respectively, and thelead situated on the left ankle (or left lower abdomen) aVF, make up a triangle, known as\"Einthoven’s Triangle.

ECG Leads have colour coded bands so that they can be easily identified.The ECG below shows where these leads are when printed. Fig 6 – ECG Printout (Geeky Medics, 2015)The ECG is usually recorded on a time scale of 0.04 seconds/mm on the horizontal axis and avoltage sensitivity of 0.1mV/mm on the vertical axis.On standard ECG recording paper, 1 small square represents 0.04 seconds and one large square0.2 seconds.In the normal ECG waveform the P wave represents atrial depolarisation, the QRS complexventricular depolarisation and the T wave ventricular repolarisation.The P - R Interval is taken from the start of the P wave to the start of the QRS complex. The Q - Tinterval is taken from the start of the QRS complex to the end of the T wave. This represents thetime taken to depolarise and repolarise the ventricles. The S - T segment is the period betweenthe end of the QRS complex and the start of the T wave. All cells are normally depolarisedduring this phase.

Fig 7 – ECG Waveforms (Virinda Diagnostics, 2013)ECG Normal ValuesP - R interval - 0.12 - 0.2 seconds (3-5 small squares of standard ECG paper)QRS complex - duration less than or equal to 0.1 seconds (2.5 small squares)Q - T interval- corrected for heart rate (QTc) QTc = QT/ RR interval less than or equal to 0.44seconds. (EBME, 2012)InterferenceThere are a number of reasons for ECG rhythm disturbance, which could either be down to thepatient, the leads or down to the environment the patient is being nursed in.Muscle tremor is something that can occur for a number of reasons, such as:  Shivering due to cold  Rigors  Parkinson’s diseaseThis can cause the ECG trace to look like the below image. Fig 8 – ECG Trace showing Muscle Tremor (The University of Nottingham, 2015)

Another disturbance, emanating directly from the surrounding environment, is electricalinterference. The ECG machine is designed to pick up electrical activity within the heart butit could pick up electrical activity from other sources, causing a trace as below. Fig 9 – ECG Trace showing Electrical Interference (The University of Nottingham, 2015)Artefact is the name given to disturbances in rhythm monitoring caused by movement of theelectrodes Fig 10 -ECG Trace showing Artefact (The University of Nottingham, 2015)The movement can be caused in a number of ways.  If the electrodes have been in place for a prolonged period of time, the moist inner pad can dry up and the connection becomes poor.  The weight of the leads can pull the electrode away from the skin and contact is lost intermittently, such as when the patient leans or roles over.  The electrode has come away from the skin and is stuck to an item of clothing  The patient is fiddling with the electrodes.  When the skin is sweaty/dirty/hairy the electrodes may not stick well, resulting in an unstable traceHowever, the machine can also mistake artefact for fatal arrhythmias. In this case the machinewill release a \"fatal arrhythmia\" alarm.The cables from the electrodes terminate in a single cable, which is plugged into the port on theECG Monitor and are electrically isolated for patient safety. Circuitry also protects the monitorfrom any high voltages produced by a defibrillator or electro-cautery signals. The signal isfiltered, amplified, conditioned and processed for display. Pulse rate is also calculated anddisplayed, with high and low alarms set with the standard being 150bpm high, 50bpm low. (The University of Nottingham, 2015)

Maintenance and Service ProceduresFirstly check the ECG leads for noise, this is done by connecting the leads to a patient/ECGsimulator and gently flexing the leads while watching the screen carefully for any noise. If anynoise occurs the leads should be replaced.The lead select function must then be checked to ensure the monitor switches between allavailable leads.Lead fault detection must then be checked this is done by removing a lead from the simulator,the ECG machine must recognise this as a lead becoming detached and alarming this to ensureusers don’t mistake a lead becoming detached for a clinical problem.Check heart rate calibration, set simulator to various rates and ensure monitor reads withinspecification, Clinical engineering general specification is for rates under 160bpm ±2bpm andfor rates over 160bpm ±3bpm.Visually inspect screen gain and scroll rates, also perform a print out and check this.The 50Hz Filter is checked.The audible alarms are then checked by lowering and raising the rate on the simulator belowand above the heart rate limits to ensure all alarms are working as expected.If applicable pacer detection is checked, to do this heart activity and pacer signals are simulatedthe monitor should display the heart rate that has been applied and also the pacer signal shouldbe visible in the waveform. Then set the simulator to only give the pacer signal, the monitorshould recognise this as the pacer signal and heart rate should read as zero.An Electrical Safety Test is then carried out.

BibliographyEBME, 2011. EBME - Cardiology. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/10-cardiology[Accessed Febuary 2014].EBME, 2012. EBME - Cardiac Monitoring. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/20-cardiac-monitoring[Accessed March 2014].Geeky Medics, 2015. Understanding an ECG. [Online]Available at: http://geekymedics.com/understanding-an-ecg/[Accessed 2015].Jones, A., 2009. PHYSICAL PRINCIPLES OF INTRA-ARTERIAL BLOOD PRESURE MEASUREMENTS,s.l.: s.n.The University of Nottingham, 2015. Cardiology Teaching Resource. [Online]Available at:http://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/index.php[Accessed June 2015].Virinda Diagnostics, 2013. Virinda Diagnostics. [Online]Available at: http://www.vrindadiagnostic.com/tmt.html[Accessed 2015].

Video Stacks & Endoscopy Systems Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Endoscopy Systems & Video StacksEndoscopy is a minimally invasive medical procedure directly visualising any part of the insideof the body using an endoscope, this will be used with a stack containing various equipmentsuch as a monitor, light source, insufflator, camera, and printer all connected through anisolation transformer. These stacks are used in theatres and various clinics, such as Ear, Nose,and Throat (ENT).EndoscopesAn endoscope is a long, thin, rigid or flexible tube that consists of two or three main opticalcables, each of which comprises up to 50,000 separate optical fibres (made from optical-qualityglass or plastic). One or two of the cables carry light down into the patient's body; another onecarries reflected light (the image of the patient's body) back up to the physician's eyepiece (orinto a camera, which can display it on a monitor).The optics of an endoscope are similar to those in a telescope. At the remote (distal) end, thereis an objective lens, which links to one or more bendy sections of fibre-optic cable that carry thelight back out of the patient's body to a second lens in an eyepiece or to a camera, which can bemanipulated to adjust the focus.Endoscopes can be inserted into the body through a natural opening, such as the mouth anddown the throat, or through the anus. Alternatively, an endoscope can be inserted through asmall surgical cut made in the skin (known as keyhole surgery). Images of the inside of the bodyare relayed to a Monitor. The instrument may not only provide an image for visual inspectionand photography, but may also be capable of taking biopsies or the retrieval of foreign objects.Some of the most commonly used types of endoscope include:  Colonoscopes: used to examine the large intestine (colon).  Gastroscopes: used to examine the oesophagus and stomach.  Endoscopic Retrograde Cholangiopancreatography (ERCP): used to check for gallstones.  Broncoscopes: used to examine the lungs and airways.Other types of endoscope include:  Arthroscopes: used to examine joints.  Hysteroscopes: used to examine the womb (uterus).  Cystoscopes: used to examine the bladder.Endoscopy can involve;  The Gastrointestinal Tract (GI tract): oesophagus, stomach and duodenum (esophagogastroduodenoscopy), small intestine, colon, (colonoscopy, procto- sigmoidoscopy).  The Respiratory Tract: the nose (rhinoscopy), the lower respiratory tract (bronchoscopy), the urinary tract (cystoscopy).  The Female Reproductive System: The cervix (colposcopy), the uterus (hysteroscopy), the Fallopian tubes (Falloscopy).  Normally closed body cavities (through a small incision): the abdominal or pelvic cavity (laparoscopy), the interior of a joint (arthroscopy), Organs of the chest (thoracoscopy and mediastinoscopy).

An endoscopy procedure is normally carried out while a patient is conscious. It is not usuallypainful, but can be uncomfortable, so a local anaesthetic or sedative may be given.The exception is keyhole surgery, such as a laparoscopy or an arthroscopy, which are performedunder general anaesthetic. (Martin, 2014)Endoscopy procedures are usually safe, and the risk of serious complications is low. Possiblecomplications of an endoscopy include an infection in the part of the body that the endoscope isused to examine, damage to the body part which may in turn cause excessive bleeding.MonitorsMonitors used on modern video stacks are high quality high definition (HD) flat panel screens,with excellent colour reproduction and a wide viewing angle. Most will have various videoconnections on the back such as S-Video, BNC, DVI, HDMI, etc. Some older video stacks mayhave a non HD flat panel monitor or a CRT monitor.Light Source & LampsThe light source may form part of a video or endoscopic stack, be a stand-alone unit often usedin ENT procedures, or be attached to a microscope providing illumination to the area underinvestigation, the light is usually transmitted via a fibre optic cable to the lens end of a scope.High-Intensity Discharge LampsHigh Pressure Sodium (HPS), Metal Halide, Mercury Vapour and Self-Ballasted Mercury Lampsare all high intensity discharge lamps (HID). Compared to fluorescent and incandescent lamps,HID lamps produce a large quantity of light from a relatively small bulb.HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside aspecially designed inner glass tube. This tube is filled with both gas and metals. The gas aids inthe starting of the lamps, then, the metals produce the light once they are heated to a point ofevaporation. High intensity discharge lamps, such as xenon, are ubiquitous within the field ofendoscopy for minimally invasive surgery and diagnosis. Coupling light into a small diameterfibre bundle is difficult, so an extremely bright light source is required. Historically, the lightsource of choice has been the 180 to 300 W xenon lamp, which could deliver 1,000+ lumens oflight at the distal end of the fibre bundle. While xenon bulbs achieve the technical requirementsfor endoscopy, they have a very short life, 500 - 1,000 hours, and can be expensive.LED LightingThe medical device industry is constantly changing. New technologies and products enter themarket, replacing outdated or inefficient equipment. LED lighting is one of these, and there arenumerous benefits in using LEDs for medical illumination applications including; longer life, lessheat, dynamic control, lower energy consumption, and in many cases, lower cost. LEDtechnology has improved significantly over the years, and is currently being integrated intomedical devices, including surgical lighting, exam lights, phototherapy, and endoscopy. Ongoingadvancements in LEDs that are driving the technology’s use in medical devices includeimprovement in light intensity, product size and weight; long-term reliability, andheat/temperature management, a line of high performance LEDs optimised to displace xenontechnology for endoscopy have been developed.

Fibre OpticThe light in a fiber-optic cable travels through the core by constantly bouncing from thecladding (mirror-lined walls), a principle called total internal reflection. The cladding does notabsorb any light from the core, enabling the light wave to travel great distances. Fig 1 - Fibre Optic Cable (How Stuff Works, 2001)Light source intensity is either adjusted manually via a dial or slider on the unit. If a camera andprocessor are attached they can monitor the amount of light at the scope end and adjusts theintensity automatically.Different wavelengths of light are needed for different procedures;Auto Fluorescence Imaging (AFI) is based on the detection of natural tissue fluorescenceemitted by endogenous molecules (fluorophores) such as collagen, flavins, and porphyrins.After excitation by a short-wavelength light source, mucosal tissue emits a green fluorescence.A difference in the intensity of this fluorescence is seen between healthy and unhealthy tissue.These colour differences in fluorescence emission can be captured in real time duringendoscopy and used for lesion detection or characterisation.Narrow Band Imaging (NBI) is a powerful optical image enhancement technology thatimproves the visibility of blood vessels and other structures on the bladder mucosa. This makesit an excellent tool for diagnosing bladder cancer during cystoscopy.White light is composed of an equal mixture of wavelengths. The shorter wavelengths onlypenetrate the top layer of the mucosa, while the longer wavelengths penetrate deep into themucosa. NBI light is composed of just two specific wavelengths that are strongly absorbed byhaemoglobin.The shorter wavelength in NBI is 415 nm light, which only penetrates the superficial layers ofthe mucosa. This is absorbed by capillary vessels in the surface of the mucosa and shows upbrownish on the video image. This wavelength is particularly useful for detecting tumours,which are often highly vascularised. The second NBI wavelength is 540 nm light, whichpenetrates deeper than 415 nm light. It is absorbed by blood vessels located deeper within themucosal layer, and appears cyan on the NBI image. This wavelength allows a betterunderstanding of the vasculature of suspect lesions. (Olympus, 2014) Fig 2 – Absorption of Narrow Band Illumination (Olympus, 2014)

InsufflatorAn Insufflator provides distension of the required cavity for diagnostic or operative procedures.The insufflator pumps CO2 into the cavity to a set pressure, this stretches the area being workedon making it easier to manipulate tools, assess the surgical site or perform the operativeprocedure. The maximum pressures of cavity’s should be observed when using an insufflator toprevent any problems, for example, Prolonged intra-abdominal pressures greater than 20mmHgshould be avoided as they can cause any of the following problems;  Decreased respiration due to pressure on the diaphragm.  Decreased venous return.  Decreased Cardiac output.CO2 is now preferred over air as CO2 is absorbed 150 times faster than the nitrogen in air, and ispromptly eliminated via the lungs. This also means that patients are not subjected to extendeddiscomfort from bloating and cramping.Camera SystemThe camera on a video stack consists of two parts, the camera head, where scopes and lightguides are attached, and a processer unit which feeds the image taken by the camera to amonitor, image capture device or printer.The aperture opens and closes to control how much light travels from the subject through aseries of curved lens and through coloured filters focused on a digital sensor, which converts itinto a digital (numerical) format. This is then processed and fed to the image capture system,monitor and printer.Image Capture SystemImage capture systems are image management systems that have the ability to record imagesand videos to their internal hard drive. They can also be connected to the hospital networkwhere they can be integrated with PACS and other similar systems.Many image capture systems are generally windows based systems with a dedicated userinterface. Very little maintenance of this system is required, at ULHT the only thing in the wayservice and repair we carry out is to take an image of the hard-drive at acceptance in case of anyfaults during its life, functional and visual checks and electrical safety testing.Isolation TransformerAn isolation transformer is a transformer used to transfer electrical power from a source ofalternating current (AC) power to some equipment or device while isolating the powered devicefrom the power source, usually for safety reasons. Isolation transformers are used to protectagainst electric shock, to suppress electrical noise in sensitive devices, or to transfer powerbetween two circuits which must not be connected. All true transformers are isolating as theprimary and secondary are not connected physically but only by induction. However, in anisolation transformer the windings are completely insulated from each other to ensure goodisolation.

In a normal supply the earth conductor is referenced to the neutralconnector at source, which gives a potential voltage between liveand earth of 240V. This means that touching either the live orneutral makes you part of the return path and can result inelectrocution. Fig 1 – Normal supply (Computer Audiophile, 2015)With an isolation transformer the output voltage is not referencedto ground, so you could safely touch the live conductor and groundand not received a shock. This system is safer but if there is a fault,the operator touched both live and neutral connections or therewas capacitive coupling between the secondary windings andearth. This would allow current to flow from either of thesecondary connections through the operator/ patient to groundand electrocution could still occur. Fig 2 – Isolation transformer (Computer Audiophile, 2015)Maintenance & Service ProceduresEndoscopesThese are generally managed by the user, this includes cleaning.Cameras and Image Capture devicesCameras should have visual inspection and function test, checking image quality and focus alsoensuring the various buttons work as they should.Image capture devices should also be visually inspected paying attention to the screen and caseall functions should then be checked including the touch screen responds if applicable. Thisshould then be safety tested.Light SourcesA thorough visual inspection to include the case, mains lead, and the bulb for anydamage/pitting should be performed. A filter clean/change and an electrical safety test areoften all that is required.Light sources that used arc lamps or HID lamps require a scheduled lamp change, usually atapprox. 500 hours of use.Before HID lamps are disposed of in an appropriate manner the xenon gas should be discharged.InsufflatorsA Visual inspection should be performed taking special care to inspect any gas connections andhoses including the pin index.A Check of output pressure and flow rates for conformity and accuracy against manufacturer’sspecification. Check all controls work and that any alarms sound, including excess pressure andempty cylinder alarm.An Electrical Safety Test (EST) should then be completed to the appropriate standard.

BibliographyBlackwell Publishing, 2014. Basic Endoscopic Equipment. [Online]Available at: https://www.blackwellpublishing.com/xml/dtds/4-0/help/10003420_chapter_1.pdf[Accessed December 2015].Computer Audiophile, 2015. Computer Audiophile. [Online]Available at: http://www.computeraudiophile.com/f27-uptone-audio-sponsored/uptone-audio-regen-22803/index79.html[Accessed 2015].How Stuff Works, 2001. How Stuff Works. [Online]Available at: http://computer.howstuffworks.com/fiber-optic2.htm[Accessed Febuary 2014].Martin, T., 2014. Principles of Gastrointestinal Endoscopy. Surgery (Oxford), 32(3), pp. 139-144.Olympus, 2014. Olympus - Narrow Band Imaging. [Online]Available at:http://www.olympus.co.uk/medical/en/medical_systems/applications/urology/bladder/narrow_band_imaging__nbi_/narrow_band_imaging__nbi_.html[Accessed Febuary 2014].ustudy, 2011. Endoscopy Working Principle. [Online]Available at: http://www.ustudy.in/node/5066[Accessed December 2015].

Neonatal Incubators Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Neonatal IncubatorsA Neonatal Intensive Care Unit (NICU) also known as a Special Care Baby Unit (SCBU) is adepartment in a hospital specialising in the care of and providing a safe and stable environmentfor new-born infants, often those who were born prematurely or with an illness or disabilitywhich makes them especially vulnerable for the first several months of life.A neonatal incubator is a device consisting of a rigid box-like enclosure in which an infant maybe kept in a controlled environment for medical care. Incubators are fully temperaturecontrolled shielding infants from harmful low or high temperatures; they provide insulationfrom outside noise, making it easier for them to get plenty of comfortable rest. Incubatorenvironments can be kept sterile, protecting infants from germs and minimising the risk ofinfection. The enclosure also keeps out all airborne irritants like dust and other allergens. Thecradle of the incubator is a roomy and comfortable surface, so it's possible to leave the infant inplace while many examinations and even simple medical procedures are administered. Thisprotects infants from too much handling, which can be a concern due to the transfer of bacteriaor viruses.The device may include an AC-powered heater, a fan to circulate the warmed air, a container forwater to add humidity, a system for increasing and monitoring the oxygen level, skintemperature probes controlling the air temperature ensuring the infants’ temperature remainsat the desired level, weighing scales and access ports for nursing care.Some neonates need respiratory support ranging from extra oxygen (by head hood or nasalcannula) to continuous positive airway pressure (CPAP) or mechanical ventilation.One of the most important elements in a new-born’s survival is temperature regulation.Humans have the advantage of being homeotherms, meaning that they are able to produce heat,allowing us to maintain a constant body temperature. A new born baby has all the capabilitiesof a mature homeotherm but the range of temperature which an infant can operate successfullyin is severely restricted.A neonate has several disadvantages in terms of thermal regulation; they have a relatively largesurface area, poor thermal insulation and a small amount of mass to act as a heat sink. A new-born has little ability to conserve heat by changing posture or to adjust clothing in a response totemperature change.Babies born more than 8 weeks before term have virtually no ability to sweat, even in a babyborn only 3 weeks early sweating is severely limited and confined to the head and face. Sweatproduction matures relatively quickly in the pre-term baby after delivery, allowing the infant tobe placed in a regular crib. In the case of cold environmental temperatures, the infant mayproduce heat by shivering and other muscular activity. (Sandham, 2008)In infants born before 31 weeks gestation, evaporative water loss is the single most importantchannel of heat loss. This is due to inadequate keratinisation of the skin, which allows a highpermeability of water. The permeability drops rapidly in the first 7 to 10 days after birth unlessthe skin becomes traumatised or secondarily infected. In that 7 to 10 day period, the absolutehumidity must be monitored so that evaporative heat loss is kept to a minimum as well as waterloss through the skin. (Sandham, 2008)It is for these reasons that such a high importance is placed on the incubators temperature &humidity being accurate.

TemperatureThe adjustment of the air temperature in an incubator is achieved by the use of a heaterelement; the heated air around the element is circulated by the use of an electric fan. Airtemperature can be controlled manually, set to a prescribed level by the nursing staff or by useof a skin temperature probe attached to the infant, the heater output is controlled to maintainthe infants skin temperature at a pre-selected level.HumidityThe humidity in an incubator can also be adjusted; this is achieved by the use of a heaterelement, a water bath and a humidity sensor. When the humidity drops below the set level theheater element switches on causing the water to evaporate therefore increasing the humidity,the heater is switched off once the humidity returns to the set level.Sensors based on capacitive effectHumidity sensors relying on this principle consists of a hygroscopic dielectric material, whichhas the ability to attract and hold water molecules from the surrounding environment,sandwiched between a pair of electrodes forming a small capacitor. Most capacitive sensors usea plastic or polymer as the dielectric material. The dielectric absorbs and releases waterproportional to the relative humidity, which changes the capacitance of the sensor; this ismeasured by another circuit. (Engineers Garage, 2015) Polymeric humidity sensing film Lower electrode Upper electrode Alumina substrate Base electrode Connection terminal Fig 1 - Basic structure of capacitive type humidity sensor (Engineers Garage, 2015).Sensors based on resistive effectResistive type humidity sensors pick up changes in the resistance value of the sensor element inresponse to the change in the humidity Polymeric humidity sensing film Comb electrode Alumina substrate Base electrode Connection terminal Fig 2 - Basic structure of resistive type humidity sensor (Engineers Garage, 2015)

ScalesThe majority of weigh scales used in the hospital environment are electronic. Electronic scalesuse strain gauges, a length of resistive metal that stretches or compresses as a load is applied toit, attached to a load cell that deflects as a load is applied to it. As the metal stretches andlengthens the resistance increases, and when the metal compresses and shortens the resistancedecreases. The scales then calculate the weight applied from the change in resistance. (Load Star Sensors, 2012)HazardsDeaths and injuries to neonates in incubators have been linked to thermostat failure, causingover/under heating of the infant. Inaccurate readings from the skin temperature probe can alsolead to incorrect heating; this may be caused by inadequate probe contact with the skin.Periodic checks of sensor placement should be carried out. Inadequate control oversupplemental oxygen delivered can cause side effects such as; hyperoxia (excessive oxygen inbody tissues) or hypoxia (inadequate oxygen in body tissue), excessive oxygen can contribute toretrolental fibroplasia, which is a formation of fibrous tissue behind the lens leading todetachment of the retina and be detrimental to the growth of the eye.Due to their construction, external noise around the incubators such as slamming a porthole,taping on the hood or having equipment vibrating against the incubator i.e. a nebuliser canproduce excessive internal noise, which can adversely affect infant hearing.Maintenance & Service ProceduresThe maintenance and service procedures performed on an incubator are staggered as partsneed replacing/servicing at differing intervals.Six monthly:At six monthly intervals the relevant filters should be replaced.Annually:Annually the O2 sensors should be replaced along with any filters, functional checks should becarried out and the temperature, humidity and the scales should be checked for accuracy.Finally an electrical safety test should be performed.Two – Four Yearly:Batteries should be replaced every two years or at the manufacturer recommended interval.Oxygen hoses should be replaced at four yearly intervals.

BibliographyBliss, 2016. Neonatal Care. [Online]Available at: http://www.bliss.org.uk/about-neonatal-care[Accessed June 2016].Engineers Garage, 2015. Humidity Sensors. [Online]Available at: http://www.engineersgarage.com/articles/humidity-sensor[Accessed August 2015].Load Star Sensors, 2012. Load Star Sensors. [Online]Available at: http://www.loadstarsensors.com/technology.html[Accessed January 2013].NHS Choices, 2015. NHS Choices. [Online]Available at: http://www.nhs.uk/conditions/pregnancy-and-baby/pages/baby-special-intensive-care.aspx[Accessed June 2016].Sandham, J., 2008. EBME - Baby Incubation. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/9-baby-incubation[Accessed August 2015].

Neonatal Phototherapy Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Neonatal PhototherapyJaundice is one of the most common conditions needing medical attention in newborn babies.Jaundice refers to yellow colouration of the skin and the sclerae (white outer coat of theeyeball). The yellow coloration of the skin and sclera in newborns with jaundice is the result ofan accumulation of unconjugated bilirubin. In most infants, unconjugated bilirubin reflects anormal transitional phenomenon. However, in some infants, serum bilirubin levels may riseexcessively, a condition known as hyper-bilirubinaemia, which can be cause for concernbecause unconjugated bilirubin is neurotoxic and can cause death in newborns and lifelongneurologic complications (bilirubin encephalopathy) in infants who survive. The termkernicterus is used to denote the clinical features of acute or chronic bilirubin encephalopathy.Newborns are especially vulnerable to hyper-bilirubinemia induced neurological damage andtherefore must be carefully monitored for alterations in their serum bilirubin levels. (GOSH,2014)Neonatal phototherapy is a widely used and accepted form of treatment for neonatal hyper-bilirubinaemia. Effective phototherapy needs to satisfy three important criteria; effectivespectrum, sufficiently high irradiance and large effective treatment area. The aim ofphototherapy is to lower the concentration of circulating bilirubin or keep it from increasing.Phototherapy achieves this by using light energy to change the shape and structure of bilirubin,converting it to molecules that can be easily excreted.Spectrum of Light Increasing skin transmittanceBlue most effective Wavelength (nm)(especially around 460-490)Structural isomers Configurational isomersBile, Urine Bile Urine O2 Colourless oxidation products Fig 1 – Effect of Blue Light on Bilirubin (Medscape, 2014)Bilirubin absorbs light most strongly in the blue region of the spectrum near 460nm. Onlywavelengths that penetrate tissue and are absorbed by bilirubin have a phototherapeutic effect.Phototherapy units with outputs predominantly in the 460-490nm blue region of the spectrumare the most effective for treating hyper-bilirubinaemia.Blue light (400-490nm) has the potential to cause photochemical induced retinal injury, usuallyduring therapy the neonate’s eyes will be covered using commercial or in-house eye protection.The baby’s temperature must also be carefully monitored during treatment because there maybe increased heat from the phototherapy lamps. (Wentworth, 2005)

Maintenance and Service ProceduresPhototherapy units require a thorough visual inspection, a light output check every 3-6 monthsand a filter clean and electrical safety test. During service or maintenance procedures it isimportant to wear the correct PPE; in this case the most important piece is the correct eyeprotection, and safety glasses that block the blue light from entering the eye should be worn. Fig 2 – Example of Blue Light Blocking Glasses (Amber Lens) (Safety Supplies, 2016)BibliographyGOSH, 2014. Neonatal jaundice & Phottherapy. [Online]Available at: http://www.gosh.nhs.uk/health-professionals/clinical-guidelines/neonatal-jaundice-and-phototherapy[Accessed August 2015].Medscape, 2014. Phototherapy for Jaundice. [Online]Available at: http://emedicine.medscape.com/article/1894477-overview[Accessed 2015].NHS, 2013. Jaundice Newborns & Phottherapy. [Online]Available at: http://www.nhs.uk/conditions/jaundice-newborn/pages/treatment.aspx[Accessed August 2015].NICE, 2014. NICE Guidance. [Online]Available at: https://www.nice.org.uk/guidance/cg98/chapter/Introduction[Accessed August 2015].Safety Supplies, 2016. Protective Eyewear. [Online]Available at: http://www.safetysupplies.co.uk/trolleyed/protective-eyewear/uv-safety-glasses/[Accessed 2015].Wentworth, S. D., 2005. Neonatal Phototherapy, Cardiff: Rookwood.

Defibrillators Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

DefibrillationElectrical cardioversion and defibrillation have become routine procedures in the managementof patients with cardiac arrhythmias. Cardioversion is the delivery of energy that issynchronised to the QRS complex, while defibrillation is the non-synchronised delivery of ashock randomly during the cardiac cycle.Most defibrillators are energy-based, meaning that the device charges a capacitor to a selectedvoltage and then rapidly delivers a pre-specified amount of energy in joules (J) to themyocardium to treat cardiac arrhythmias. The capacitance of a capacitor is the amount ofelectric charge it can store for every volt applied to it. With regard to defibrillators the amountof energy stored in a capacitor is very important. It can be calculated using the formulaE = ½CV2, where E is the energy in joules, C the capacitance in farads and V the voltagemeasured in volts. This energy is dissipated in the patient’s body over a small time interval,about 10 milliseconds or one hundredth of a second.If the capacitance is 1000 μF and the voltage is 500 V then the stored energy is 125J. [E = ½ CV2]  E= ½ (1000 × 10-6) x (5002 ) = 125 J.Current European Society of Cardiology (ESC) and American Heart Association (AHA) guidelinessuggest the following initial energy selection for specific arrhythmias:  For atrial fibrillation, 120 to 200 joules for biphasic devices and 200 joules for monophasic devices.  For atrial flutter, 50 to 100 joules for biphasic devices and 100 joules for monophasic devices.  For ventricular tachycardia with a pulse, 100 joules for biphasic devices and 200 joules for monophasic devices.  For ventricular fibrillation or pulseless ventricular tachycardia, at least 150 joules for biphasic devices and 360 joules for monophasic devices. (European Society of Cardiology, 2015)They also incorporate an inductor to prolong the duration of the delivered current, and arectifier to convert alternating current (AC) to direct current (DC). (Knight, 2014)A defibrillator can deliver a controlled electrical shock to a heart that has a life-threateningrhythm, such as ventricular fibrillation (VF). In VF, the heart's chaotic activity prevents bloodfrom pumping adequately or at all. Voltage stored by the defibrillator conducts electricalcurrent (a shock) through the chest by way of electrodes or paddles placed on the chest. Thisbrief pulse of current halts the chaotic activity of heart, by depolarising a large part of the heartmuscle terminating the dysrhythmia allowing normal sinus rhythm to be re-established by thebody’s internal pace maker located in the sinoatrial node of the heart, giving the heart a chanceto re-start with a normal rhythm.Many factors affect the chance of defibrillation success including; placement of the electrodepads, time elapsed before the first shock is given, and certain health conditions. Successfuldefibrillation requires that enough current be delivered to the heart muscle during the shock. Ifthe transthoracic impedance level is high the heart may not receive enough current fordefibrillation to be successful. Impedance is the body's resistance to the flow of current; somepeople naturally have higher impedance than others. Therefore, it may take more current, alonger shock duration, and/or increased voltage to ensure success. (EBME, 2003)

The shock is delivered via two electrode pads/paddles placed as shown below. Fig 1 – Placement of Electrode Pads/Paddles (Physio-Control, 2013)Modern defibrillators may be manual or automated; they generally produce biphasic waveformsas opposed to monophasic waveforms, which increase safety and efficacy. Miniatureimplantable cardioverter-defibrillators (ICD) may be used in patients with recurrent life-threatening arrhythmias. (Chaudhari, 2005)Monophasic WaveformsThis is a type of defibrillation waveform where current flows in one direction. In this waveform,there is no ability to adjust for patient impedance, and it is generally recommended that allmonophasic defibrillators deliver 200 - 300 J of energy to a maximum of 360J, applied to adultpatients with the assumed average impedance of 50 ohms, to ensure maximum current isdelivered which in the graph below is ≈ 45 amps. Fig 2 – Graphical representation of a Monophasic Waveform (Physio-Control, 2013)Biphasic WaveformsWith biphasic shocks, the direction of current flow is reversed near the halfway point of theelectrical defibrillation cycle. Biphasic waveforms were initially developed for use inimplantable defibrillators and have since become the standard in external defibrillators. Withbiphasic waveforms there is a lower defibrillation threshold (DFT) that allows reductions of theenergy levels administrated and may cause less myocardial damage.While all biphasic waveforms have been shown to allow termination of VF at lower current thanmonophasic defibrillators, there are two types of waveforms used in external defibrillators.

The waveforms are shown below and will have the desired effect at current values ranging fromapprox. 15 – 35 amps. Fig 3 – Graphical representation of two Biphasic Waveforms (Physio-Control, 2013)Types of DefibrillatorAutomated External Defibrillator (AED)AEDs are highly sophisticated, microprocessor-based devices that analyse multiple features ofthe surface ECG signal including frequency, amplitude, slope and wave morphology. Theycontain various filters for QRS signals, radio transmission and other interferences, as well as forpoor electrode contact. Some devices are programmed to detect patient movement.The typical controls on an AED include a power button, a display screen on which trainedrescuers can check the heart rhythm and a discharge button. Certain defibrillators have specialcontrols for internal paddles or disposable electrodes.In AED Mode, the Defibrillator analyses the patient’s ECG and advises you whether or not todeliver a shock. Voice prompts guide you through the defibrillation process by providinginstructions and patient information. Voice prompts are reinforced by messages/pictures thatappear on the display. (Lozano, 2013)Manual DefibrillatorManual defibrillators are designed to give full control to the clinical users. The defibrillatorrecords the patients ECG, the user then assess the ECG and selects the appropriate level ofenergy for defibrillation.CapnographyCapnography is the measurement of carbon dioxide (CO2) in exhaled breath; capnography givesmedical professionals another tool for determining whether blood is flowing to vital organs likethe heart and brain. CO2 levels reflect cardiac output and pulmonary blood flow; as the gas istransported by the venous system to the right side of the heart and then pumped to the lungs bythe right ventricles. When CO2 diffuses out of the lungs into the exhaled air, a device called acapnometer measures the partial pressure or maximal concentration of CO2 at the end ofexhalation.

The two primary methods used for measuring CO2 in expired air are mass spectroscopy andinfrared spectroscopy. In mass spectroscopy gases and vapours of different molecular weightsare separated and a breakdown of what gases and percentages can be displayed.End tidal Carbon Dioxide (EtCO2) is the partial pressure or maximal concentration of carbondioxide at the end of an exhaled breath, which is expressed as a percentage of CO2 or in mmHg.Infrared (IR) spectroscopy uses an EtCO2 sensor to continuously monitor the carbon dioxidethat is inspired and exhaled by the patient. It is usually presented as a graph of expiratory CO2against time, or less commonly against expired volume.The EtCO2 sensor consists of an infrared source, a chamber through which the gas samplepasses, and a photo-detector. When the expired CO2 passes between the beam of infrared lightand photo-detector it leads to a reduction in the amount of light falling on the sensor, this is dueto the principle that CO2 absorbs infrared radiation. The absorbance is proportional to theconcentration of CO2 in the gas sample. (Physio-Control, 2013)Capnometers can be categorised based on the sensing device location. The gas samples can beanalysed by mainstream or side-stream techniques.During CPR, the amount of CO2 excreted by the lungs is proportional to the amount ofpulmonary blood flow; therefore capnography can be used to monitor the effectiveness of CPRand as an early indication of the Return of Spontaneous Circulation (ROSC).It has been shown that when a patient experiences ROSC the first indication is often a suddenrise in EtCO2 as the rush of circulation washes un-transported CO2 from tissues, likewise asudden drop in EtCO2 may indicate that the patient has lost pulse and CPR may need to berestarted. (Paramedicine, 2000)Maintenance & Service ProceduresDefibrillators are serviced annually, during the service functional checks of all controls, displaysand sound outputs are performed. ECG functions are checked including heart rate calibrationand lead off detection, most defibrillators can detect whether the paddles/pads are connectedor disconnected and this should also be checked.An analyser is used to ensure output energy levels are within specification and a check of allfunctions/analysis is performed when in AED mode.Pacer function and pacer detection are both tested, a functional check of the capnography (ifapplicable) and finally an electrical safety test is performed.There is also scheduled battery and patient lead replacement, the expiry dates on the padsshould be checked to ensure they are still ok to use. If they are past there expiry date the wardstaff should be informed and the pads removed from use and replaced.During maintenance & service procedures it is vital to ensure a defibrillator is never left alonecharged. When repairing or opening the case for any reason it is important to follow themanufacturer’s guidelines for discharging the capacitor to ensure no harm comes to yourself orothers.

BibliographyChaudhari, M., 2005. Anaesthesia Journal. [Online]Available at: http://www.anaesthesiajournal.co.uk/article/S1472-0299(06)00175-5/abstract[Accessed September 2015].EBME, 2003. EBME - Biphasic Defibrillator. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/12-biphasic-defibrillation?showall=&start=3[Accessed September 2015].European Society of Cardiology, 2015. European Society of Cardiology. [Online]Available at: https://www.escardio.org/Guidelines-&-Education/Clinical-Practice-Guidelines/listing[Accessed October 2015].Knight, B. P., 2014. UpToDate. [Online]Available at: http://www.uptodate.com/contents/basic-principles-and-technique-of-cardioversion-and-defibrillation[Accessed September 2015].Lozano, I. F., 2013. Principles of External defibrillators. [Online]Available at: http://www.heartrhythmcharity.org.uk/www/media/files/InTech-Principles_of_external_defibrillators.pdf[Accessed September 2015].Paramedicine, 2000. End Tidal CO2. [Online]Available at: http://www.paramedicine.com/pmc/End_Tidal_CO2.html[Accessed October 2015].Phillps Medical Systems, 2005. M4735A (ELD) Heartstream XL Defibrillator Service/User Manual,s.l.: s.n.Physio-Control, 2013. Lifepak® 20e Defibrillator Service/User manual.

Diagnostic Ultrasound Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Diagnostic UltrasoundUltrasound is acoustic (sound) energy in the form of waves having a frequency above the humanhearing range. The highest frequency that the human ear can detect is approximately 20thousand cycles per second (20,000 Hz). This is where the sonic range ends, and where theultrasonic range begins.Diagnostic ultrasound is an imaging technique used for visualising all body regions that are notsituated behind expanses of bone or air-containing tissue, such as the lungs. Examinationsthrough thin, flat bones are possible at lower frequencies. Frequencies of 2–20 Megahertz(MHz) are typical used. It is also possible to bypass obstacles with endoscopes (endoscopicsonography).Diagnostic ultrasound imaging depends on the computerised analysis of reflected ultrasoundwaves, which non-invasively build up fine images of internal body structures.Higher frequencies have a shorter wavelength and are therefore capable of reflecting andscattering off smaller structures giving higher resolution, however, the use of high frequenciesis limited by their greater attenuation (loss of signal strength) in tissue and thus shorter depthof penetration limiting the depth when producing an image. Lower frequencies produce lessresolution but image deeper into the body. For this reason, different ranges of frequency areused for examining different parts of the body values typically used are: 2.5 MHz - deep abdomen, obstetric and gynaecological imaging 3.5 MHz - general abdomen, obstetric and gynaecological imaging 5.0 MHz - vascular, breast, pelvic imaging 7.5 MHz - breast, thyroid 10.0 MHz - breast, thyroid, superficial veins, superficial masses, musculoskeletal imaging. 15.0 MHz - superficial structures, musculoskeletal imaging.Transcutaneous ultrasound is used mainly for evaluating: (Morgan, 2015) Neck: thyroid gland, lymph nodes, abscesses, vessels (angiology). Chest: wall, pleura, peripherally situated disorders of the lung, mediastinal tumours (The mediastinum is the cavity that separates the lungs from the rest of the chest. It contains the heart, esophagus, trachea, thymus, and aorta), and the heart as a whole (echocardiography). Abdomen: The abdominal cavity is the space bounded by the vertebrae, abdominal muscles, diaphragm, and pelvic floor. The intraperitoneal space located within the abdominal cavity, but wrapped in peritoneum (membrane that forms the lining of the abdominal cavity). The structures within the intraperitoneal space e.g. the stomach. The structures in the abdominal cavity that are located behind the intraperitoneal space \"retroperitoneal\" e.g. the kidneys, and those structures below the intraperitoneal space called \"subperitoneal\" or \"infraperitoneal\" e.g. the bladder and small pelvis: organs, fluid containing structures, gastrointestinal tract, great vessels and lymph nodes, tumours and abnormal fluid collections. Extremities (joints, muscles and connective tissue, vessels). Obstetric sonography is commonly used during pregnancy.

TransducerUltrasound waves are produced by a transducer (a hand-held probe), which can both emitultrasound waves, as well as detect the ultrasound echoes reflected back. The probe producesthe ultrasound waves and receives the echoes using a principle called the piezoelectric effect.Inside the probe there are one or more piezoelectric crystals, piezoelectric crystals are able toproduce sound waves when an electric current passes through them, but can also workin reverse, producing electricity when a sound wave hits them. This happens as the mechanicaland electrical energy causes them to change shape, by contracting or expanding.When used in an ultrasound scanner, the transducer sends out a directed beam of sound wavesinto the body, and the sound waves are reflected back to the transducer from the tissues andorgans in the path of the beam. When these echoes hit the transducer, they generate electricalsignals that the ultrasound scanner converts into images of the tissues and organs.The probe has a sound absorbing substance to eliminate back reflections from the probe itself,and an acoustic lens to help focus the emitted ultrasound waves.Ultrasound TechniquesThe echo principle forms the basis of all common ultrasound techniques. The distance betweenthe transducer and the reflector or scatterer in the tissue is measured by the time between theemission of a pulse and reception of its echo. Additionally, the intensity of the echo can bemeasured. With Doppler techniques, comparison of the Doppler shift of the echo with theemitted frequency gives information about any movement of the reflector. The variousultrasound techniques used are described below.A-modeA-mode (A-scan, amplitude modulation) is a one-dimensional examination technique in which atransducer with a single crystal is used. The echoes are displayed on the screen along a time(distance) axis as peaks proportional to the intensity (amplitude) of each signal. The method israrely used today, as it conveys limited information, e.g. measurement of distances. For anexample, ophthalmologists can use it to measure the diameter of the eye ballB-modeB-mode (brightness modulation) is a similar technique, but the echoes are displayed as points ofdifferent grey-scale brightness corresponding to the intensity (amplitude) of each signal.B-scan, 2DThe arrangement of many (e.g. 256) one-dimensional lines in one plane makes it possible tobuild up a two-dimensional (2D) ultrasound image (2D B-scan). The single lines are generatedone after the other by moving (rotating or swinging) transducers or by electronic multi-elementtransducers.Electronic transducers are made from a large number of separate elements arranged on a plane(linear array) or a curved surface (curved array). A group of elements is triggeredsimultaneously to form a single composite ultrasound beam that will generate one line of theimage. The whole two-dimensional image is constructed step-by-step, by stimulating one groupafter the other over the whole array.The lines can run parallel to form a rectangular (linear array) or a divergent image (curvedarray)

Three- and four-dimensional techniquesThe main prerequisite for construction of three-dimensional (3D) ultrasound images is very fastdata acquisition. The transducer is moved by hand or mechanically perpendicular to thescanning plane over the region of interest.The collected data are processed at high speed, so that real-time presentation on the screen ispossible. This is called the four-dimensional (4D) technique (4D = 3D + real time). The 3D imagecan be displayed in various ways, such as transparent views of the entire volume of interest orimages of surfaces, as used in obstetrics and not only for medical purposes. It is also possible toselect two-dimensional images in any plane, especially those that cannot be obtained by a 2D B-scan. Fig 1 - 3D Ultrasound scan Image (NIBI, 2012)M-mode or TM-modeM-mode or TM-mode (time motion) is used to analyse moving structures, such as heart valves.The echoes generated by a stationary transducer (one-dimensional B-mode) are recordedcontinuously over time.The ultrasound images can show:  Presence, position, size and shape of organs.  Stasis, concretions and dysfunction of hollow organs and structures.  Tumour diagnosis and differentiation of focal lesions.  Inflammatory diseases.  Metabolic diseases causing macroscopic alterations of organs.  Abnormal fluid collection in body cavities or organs, including ultrasound-guided diagnostic and therapeutic interventions;  Evaluating transplants;  Diagnosis of congenital defects and malformations.Additionally, ultrasound is particularly suitable for checks in the management of chronicdiseases and for screening, because it is low risk, comfortable for patients and cheaper thanother imaging modalities. (World Health Organization, 2011)Signal Processing and image captureThe main ultrasound system takes care of processing signals from the ultrasound probe andcapturing and recording images. The computer based system runs dedicated software thatcontrols the ultrasound probes, processes the signal returned from the probe, displays theimage and allows the image to be captured on internal storage or sent through the hospitalnetwork

Maintenance & Service ProceduresA visual inspection paying attention to the case, cables, any foot pedals and the ultrasoundprobe should be carried out, also checking that any ventilation grilles are free from dust/debris.The ultrasound system should be running quietly when switched on and a check that all thebuttons are functioning and the screen displays a clear image.Check for ‘dropout’ (i.e. crystal failure) on all probes using a paperclip ensuring that it isdisplayed as expected. If an ultrasound phantom is available confirm the following;  Image quality (uniformity, no axial banding, excessive noise etc.)  Ultrasound phantom targets imaged as expected.An EST should then be performed on the system with the probe placed in a saline solution withthe applied part lead.BibliographyMorgan, D. M. A., 2015. Ultrasound Frequencies, s.l.: NIBIB.NIBI, 2012. National Institute of Biomedical Imaging. [Online]Available at: http://www.nibib.nih.gov/science-education/science-topics/ultrasound[Accessed 2016].Stern, B., 2016. Basic Concepts of Utrasound Scanning. [Online]Available at: http://www.yale.edu/ynhti/curriculum/units/1983/7/83.07.05.x.html[Accessed 2016].World Health Organization, 2011. Manual of Diagnostic Ultrasound. 2nd ed. Geneva: WHO Press.

Ventilators Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

VentilatorsVentilators are used when a patient’s spontaneous breathing is inadequate to maintain life dueto ineffective gas exchange in the lungs. (Hoesch, et al, 2012)Depending on the patient’s condition mechanical ventilation can support or completely controlthe breathing process. Breath sequences can be classified as either;  Continuous mandatory ventilation (CMV) – the clinical intent is to make every inspiration a mandatory breath (Ventilator Initiated).  Intermittent Mandatory Ventilation (IMV) - a combination of mandatory and spontaneous breaths (Patient Initiated).  Continuous Spontaneous Ventilation (CSV) - where every breath is spontaneous i.e., patient triggered and patient cycled with ventilator support. (Chatburn, 2007)It is important to remember mechanical ventilation only serves to control or assist breathingand does not cure the underlying problems; the patients underlying conditions should becorrectable and resolvable over a period of time. (Cambrini, 2011)The breathing process consists of taking in oxygen and expelling carbon dioxide. Duringinspiration, air rich with oxygen flows through the mouth/nose, down the trachea to the lungsfilling the alveoli.Alveoli, the air sacs in the lungs, transfer oxygen to the blood, whilst carbon dioxide in thebloodstream is transferred to the alveoli. Therefore, when you expire, the carbon dioxide andother gaseous wastes are expelled from your body.The exchange of oxygen and carbon dioxide between the bloodstream and the lungs worksby diffusion and requires no external work; however, air must be moved into and out ofthe lungs to make it available to the gas exchange process.In spontaneous breathing, a negative pressure is created in the pleural cavity (the spacebetween the outside of the lung and inside of the chest wall) by the muscles of respiration.The muscles of respiration include inspiratory muscles which cause the thoracic cavity toexpand and induce inhalation while expiratory muscles compress the thoracic cavity and induceexhalation.The major muscle responsible for helping us breathe is the diaphragm, it separates the thoracicand abdominal cavity by its thin and dome shaped structure. When the diaphragm contracts thecentral portion moves downwards and the sides move upwards, aided by the intercostalmuscles the volume of the thoracic cavity is increased. The increased volume reduces intra-thoracic pressure causing air to be drawn into the lungs (inhalation). The opposite actioncauses exhalation. Fig 1 - Diaphragm and Ribs during Inspiration & Expiration (Coskun, 2016)

Intercostal muscles run between the ribs, helping expand and shrink the size of the chest cavityto facilitate breathing. The external intercostal muscles are placed in such a manner that whenthey contract the ribs are raised assisting inhalation, the internal intercostal muscles areresponsible for the depression of the ribs and bending them inward, which with the relaxationof the diaphragm and elastic recoil of the lungs aids expiration.Negative Pressure VentilationThe first generation of ventilators used negative pressure; in negative pressure ventilation thepatient’s body was enclosed in an airtight chamber with just the head exposed; this device iscommonly known as an Iron Lung. The pressure inside the Iron Lung is reduced by means of apump removing the air until a negative pressure is created. This negative pressure leads to anexpansion of the chest causing air to be drawn into the patient’s lungs. As the vacuum isreleased, the pressure inside the tank equalizes to that of the ambient pressure, and the elasticre-coil of the chest and lungs leads to passive exhalation. This method mimics the naturalbreathing process.The Iron Lung was further developed into a device called the Cuirass or chest shell; this is ashell-like unit, creating negative pressure only to the chest using a combination of a fitting shelland a soft bladder. A vacuum is created between the shell and the chest wall, as with the IronLung this vacuum causes the chest to expand, drawing air into the lungs. This method ofventilation is no longer widely used.Positive Pressure VentilationPositive pressure ventilation is commonly used these days and there are two main types,invasive and non-invasive. In non-invasive ventilation a tight fitting mask is placed over themouth and nose of the patient and air is forced into the lungs by the mechanical ventilator.Invasive ventilation requires either a tracheostomy tube inserted through an artificial openingin the trachea via the throat or an endotracheal tube being inserted down the trachea(intubation), in order to provide air to the lungs. The endotracheal tube may have markings onone end to show where the vocal chords should be positioned; it will also show the length incentimetres and the internal and external diameter in millimetres.At the end which is inserted into the patients trachea is an inflatable balloon, this is inflated viaa pilot balloon (shown in blue in Fig 2) using a syringe or dedicated cuff inflator. The balloonprotects the lungs from contamination by gastric contents and nasopharyngeal matter such asblood. Fig 2 – Endotracheal tube, cuff inflator & Placement (Aegis Anesthesia Partners, 2016)Modern ventilators consist of a turbine, air and oxygen supplies, various valves, tubes, filtersand a disposable or re-useable patient circuit. The turbine pushes the air through the ventilator,a flow valve opens and closes to adjust pressure/volume/breath rate to meet the patientspecific needs. When the positive pressure is released the patient will exhale passively due tothe lungs elasticity. The pressure left in the patient lungs, after exhalation can also be set by theventilator and is known as Positive End Expiratory Pressure or PEEP.

The exhaled air is released through the patient circuit and ventilator where the expiratoryvolume is measured.There are four phases to a mechanical breath: initiation phase, inspiratory phase, plateau phase,and expiratory phase.Depicted below is the pressure waveform of a ventilator breath. Fig 3 – Waveform of a Ventilator Breath (Deranged Physiology, 2015)  Initiation phase - This starts at the end of expiration. At this stage, the breath is \"triggered\" (initiated) either by the machine or by the patient.  Inspiratory phase - Once the breath is triggered, the inspiratory flow begins. This phase is defined by air flow into the patient.  Plateau phase - There may be an inspiratory pause, which would allow a plateau phase to form. This phase is defined by the absence of air flow.  Expiratory phase - The ventilator cycles from inspiration to expiration; the expiratory valve opens, and the patient exhales passively. This phase is defined by air flow out of the patient.The pressure which remains behind is the PEEP (Positive End Expiratory Pressure).Patient circuitThe patient circuit comprises the components external to the ventilator that route gas betweenthe ventilator and the patient.These components include: • An inspiratory filter that protects against contamination between the patient and ventilator. • A humidification device (optional) in line with the patient circuit. • The inspiratory and expiratory limbs of the patient circuit that conduct the breathing gas to and from the patient. • A collector vial that protects the expiratory pneumatics from moisture in the exhaled gas. • An expiratory filter that limits the escape of microorganisms and particulates in the patient’s exhaled gas into the room air or inside the ventilator exhalation pneumatics.

Fig 4 – Patient Circuit with Humidifier (Humiaide, 2016)The exhalation system monitors the exhaled gas leaving the patient circuit for spirometry.Throughout the respiratory cycle, pressure transducers monitor inspiratory, expiratory, andatmospheric pressures. The temperature of the exhaled gas is heated to a temperature above itsdew point to prevent condensation in the exhalation compartment.Compliance CompensationVentilator hoses & patient circuits are compliant and absorb some of the tidal volume intendedfor the patient.The error caused by the machine and circuits compliance is greater at higher inspiratorypressures, for example those encountered if the patient has very stiff lungs.Modern ventilators can determine their own compliance; before being connected to a patientthe users must block the end of the patient circuit, the ventilator then pressurises the system.The ventilator monitors the pressure and volume and calculates the system compliance.Now the system knows its own compliance it calculates how much additional gas it needs topush into the circuit to ensure the patient actually receives the settings requested by theoperator.Once the system is connected to the patient and running, the compliance compensation ismonitored and adjusted dynamically on a breath by breath basis.Modes & SettingsWhen a patient is put on a ventilator, numerous settings including; respiratory rate, fraction ofinspired oxygen (FiO2), trigger & cycle, volume or pressure control, volume and/or pressuresupport, PEEP etc. can be selected depending on which ventilation mode is chosen. Limits canbe set for each breath delivered, either or a mix of pressure, flow or volume to prevent patientinjury.TriggerThe trigger setting on the ventilator determines how the mechanical breath is initiated; whetherthe timer initiates the breath, or whether the patient indicates their intention to breathe bymaking some sort of inspiratory effort, a change in flow, pressure or volume can initiate abreath.

Respiratory RateThis setting simply refers to the number of breaths per minute that the ventilator delivers. Atypical respiratory rate is 8 -12 breaths per minute (BPM). (Joyce, 2005)Depending on the mode selected all of the patient's ventilation can be provided, or the patientmay be able to breathe spontaneously between ventilator initiated breaths.FiO2This indicates the amount of oxygen the ventilator delivers, expressed as a percentage or anumber between zero and one. FiO2 varies widely depending on the patient's condition; roomair is 21% (0.21). While some patients might be adequately oxygenated with an FiO2 of less than40% (0.40), someone with severe hypoxemia, for example, might need an initial FiO2 setting of100% (1.00). Arterial blood gases and pulse oximetry values will help determine FiO2 settings.Positive End-Expiratory Pressure (PEEP)PEEP can be used to increase oxygenation in, a small amount of applied PEEP (4–5cm/H2O) isused in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse, thishelps improve oxygenation as the alveoli stay open and are therefore easier to inflate. Somepatients, such as those with acute respiratory distress syndrome (ARDS) or other conditionsthat make lungs stiff, require higher levels of PEEP to keep alveoli from collapsing. PEEP shouldnot exceed 20cm/H2O; higher settings increase the risk of severe lung damage, subcutaneousemphysema (Air in tissue under the skin), and pneumothorax (Collapsed Lung), this occurswhen air leaks into the space between the lung and chest wall. This air pushes on the outside ofthe lung causing collapse. (Manzano, et al., 2008).Continuous Mandatory Ventilation (CMV) or Assist Control (AC)The ventilator supports every breath; whether it's initiated by the patient or the ventilator theoperator inputted values are delivered. This high level of respiratory support is frequentlyrequired in patients who have been resuscitated, have acute respiratory distress syndrome(ARDS), are paralyzed or sedated.Continuous Spontaneous Ventilation (CSV)Where every breath is spontaneous, patient triggered by either pressure or flow, breaths maybe volume or pressure supported. An operator can also initiate a manual inspiration, but theventilator cannot initiate a breath.Intermittent Mandatory Ventilation (IMV) or Synchronized IMV (SIMV)In IMV, a mandatory breath initiated by the ventilator with values pre-set by the operator isgiven, while additional breaths initiated by the patient can be pressure/volume supported.Dependent on settings not all spontaneous breaths have to be supported, leaving the patient todraw some breaths on their own. Synchronization (SIMV) between pre-set mandatory breathsand the patient's spontaneous breaths, attempts to limit barotrauma that may occur with IMVwhen a pre-set mandatory breath is delivered to a patient who is already maximally inhaled(breath stacking) or is forcefully exhaling.There are several advantages to this mode, for patients who can tolerate it, as this helpspreserve the strength of the respiratory musculature, decreases the risk of hyperventilation andbarotrauma (damage to the lung due to pressure), and facilitates weaning. Weaning can be doneby gradually decreasing the percentage of machine-assisted ventilation. (Tobin, 2013)

Automatic VentilationSome ventilators will automatically start ventilating when a patient is connected to thebreathing circuit. To sense a patient the ventilator delivers a low flow of gas to the patientconnection at the end of the breathing circuit, which mainly flows out to atmosphere. When thepatient is connected this small flow returns down the other limb of the breathing circuit to theexpiratory flow sensor, when a large enough flow is detected at the flow sensor the ventilatorwill start, if no settings have been entered for the patient, default settings are used.Volume Control (VC)On this setting the ventilator is programmed to deliver a pre-set volume of oxygen and air,called the tidal volume (VT), regardless of the amount of pressure required to deliver thevolume.Peak pressure can vary from breath to breath depending on the patient's lung compliance(ability to expand) and resistance. If the lung compliance reduces or resistance increases thepeak pressures will increase to ensure the set tidal volume is achieved. This volume would bedelivered with each breath regardless of the pressure required so it is very important to checkthe upper pressure alarm limit is at a suitable value to protect the patient's lungs. Fig 5 – Volume Controlled Waveform (Deranged Physiology, 2015)

Pressure Control (PC)An alternative to volume control, in pressure control pressure is the endpoint rather thanvolume. There is a set pressure; once reached it is maintained for the duration of theinspiratory phase. Flow starts high (to reach the desired pressure) and decreases on a slope, asthe lungs fill with air they stretch and become less compliant so less flow is required to maintainthe same pressure.Inspiration ends when a pre-set pressure is reached, regardless of the volume delivered.The advantage of this mode is that it allows the volume to change in response to intrathoracicpressure. The goal is to increase mean airway pressure by prolonging inspiration, ideallyrecruiting more alveoli than volume control ventilation. By limiting pressure there is less risk ofpressure-related injury. PEEP is set to prevent the alveoli collapsing making them easier toinflate. Fig 6 – Pressure Controlled Waveform (Deranged Physiology, 2015)Pressure-Regulated Volume Control (PRVC)PRVC is an alternative to strict pressure control, representing an attempt to obtain the best ofboth volume and pressure control. PRVC adapts to changing compliance of the lungs adjustinginspiratory time and pressure to maintain a pre-set tidal volume (VT).Pressure Support (PS)Pressure support provides a small amount of pressure during inspiration to help the patientdraw in a spontaneous breath. The patient initiates the breath and the ventilator deliverssupport, this makes it easier for the patient to overcome the resistance of the ET tube and isoften used during weaning because it reduces the work of breathing. This setting is often usedwith SIMV.Volume Support (VS)Volume support works in a very similar way to pressure support but the tidal volume and PEEPare set rather than the pressure. The patient initiates the breath and the ventilator deliverssupport in proportion to the inspiratory effort and the target volume. The set tidal volume isdelivered to the patient with different support from the ventilator depending on the patient'sactivity. (Covidien, 2011)

High Frequency Oscillatory Ventilation (HFOV)High frequency oscillatory ventilation (HFOV) is a method of ventilating patients using ultra-high respiratory rates, up to 600 breaths per minute verses up to 40 breaths per minute inconventional ventilation; this allows the use of tidal volumes that with conventional ventilationwould lead to rising CO2 levels.The role of HFOV is to achieve and maintain optimal lung inflation through maximum alveolarrecruitment, increasing functional residual capacity. This is achieved through a continuous flowof gas producing a pressurised circuit. The gas is oscillated using a driven piston with adiaphragm unit. Inspiration and expiration are active, therefore reducing the likelihood of gastrapping.HFOV is thought to be responsible for decreasing the incidence and severity of ventilatorinduced lung injury when compared with conventional ventilation.This is a commonly accepted ventilator setting for premature infants and has now also beenused in small critical care unit studies on patients with ARDS, with reports of improvingoxygenation and lung recruitment.The use of HFOV in adults is currently reserved for patients unresponsive to standardventilation, or patients in whom standard ventilation is likely to become increasingly difficultrequiring high ventilation pressures or levels of oxygenation.The side effects of HFOV may include cardiovascular instability and barotrauma from the highairway pressures. (T. Bachman, 2013)

Maintenance & Service ProceduresMany ventilators have 6 monthly, annual and biannual service schedules as well as gas hosechanges every 4 years.Below lists the basic service schedule for Puritan Bennett 840 ventilators as used in theIntensive care unit at Lincoln County Hospital.Short Self-Test (SST)SST is a short (about 2 to 3 minutes) and simple sequence of tests that verifies proper operationof breath delivery hardware (including pressure and flow sensors), checks the patient circuit(including tubing, humidification device, and filters) for leaks, and measures the circuitcompliance and resistance. SST also checks the resistance of the exhalation filter.Covidien recommends you run the SST every 15 days, between patients, and when you changethe patient circuit or its configuration.Extended Self-Test (EST)EST verifies the integrity of the Puritan Bennett™ 840 Ventilators subsystems using operatorparticipation. EST requires a “gold standard” test circuit. A Single test EST feature allowsindividual EST tests to be run in any order, but the full suite of EST tests must successfully passbefore the ventilator can be used on a patient.EST checks the pneumatics system , including gas supplies, proportional solenoid (PSOL) valves,flow sensors, circuit pressure accuracy, safety valve, and exhalation valve, memory, safetysystem, front panel controls and indicators, power supplies, transducers, and options. EST canrun only when the ventilator is in service mode.Air and oxygen supplies are required (the compressor can supply the air source).EST is a comprehensive ventilator test designed to be run by qualified service personnel forperiodic and corrective maintenance, in Clinical Engineering we run this test every 6 months.Annual ServiceDuring the annual service the Extended Self-Test is carried out as above, in addition the O2sensors are replaced and a calibration is performed on the expiratory valve, flow sensors andpressure sensors.2 Yearly ServiceThe annual service tests are carried out followed by the performance verification tests whichinclude the regulator setting check, exhalation port test, volume performance test and O2performance test. (Covidien, 2011)

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Electro-Surgery Equipment Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust