Binder2

BibliographyBeevers DG, L. G. a. O. E., 2007. ABC of Hypertension. 5th ed. s.l.:Blackwell.DoH, 2012. Department of Health - Device Bulletin DB 2006(03) v2.0. [Online]Available at: http://www.dhsspsni.gov.uk/db2006_03_v2.pdf[Accessed March 2014].EBME, 2009. EBME - NIBP. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/70-noninvasive-blood-pressure-measurement[Accessed 2015].NICE, 2013. Hypertension: Clinical management of primary hypertension in adults. [Online]Available at: https://www.nice.org.uk/guidance/cg127[Accessed March 2014].

Apnoea Monitors Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Apnoea MonitorsIn a premature baby, the part of the central nervous system (brain and spinal cord) thatcontrols breathing is not yet mature enough to allow nonstop breathing. This causes largebursts of breath followed by periods of shallow breathing or stopped breathing. The medicalterm for this is Apnoea of prematurity, or AOP. Once off a mechanical ventilator and breathingon their own - with or without nasal CPAP - they are monitored continuously for any evidence ofApnoea. The cardiorespiratory monitor (also known as an Apnoea and bradycardia, or A/B,monitor) also tracks the infant's heart rate. An alarm on the monitor sounds if there's no breathfor a set number of seconds. When the monitor sounds, a nurse immediately checks the baby forsigns of distress. False alarms are not uncommon.If a baby doesn't begin to breathe again within 15 seconds, a nurse will rub the baby's back,arms, or legs to stimulate the breathing. Most of the time, babies with Apnoea of prematurityspells will begin breathing again on their own with this kind of stimulation. AOP can happenonce a day or many times a day. Doctors will closely evaluate the patient to make sure the apneaisn't due to another condition, such as infection.The MR10 is a single channel respiration monitor with a choice of a 10 or 20 second apnoeadelay. To work, the Monitor requires a Respiration Sensor. The soft, foam filled Sensor isattached to the baby's abdomen and is linked to the Monitor by a narrow tube. A breathingsignal is picked up by the Respiration Sensor attached to the infant's abdomen. Duringbreathing, expansion of the abdominal wall causes a small amount of air to pass through theSensor and tube to the Monitor. The signal that is received from the pressure transducer isfiltered to remove any unwanted components which could cause erroneous results. Duringbreathing the Monitor will also make an audible click and give a simultaneous visual indication.If the selected alarm time is breached (i.e. if no breath is detected after 20sec.) an audio visualalarm is triggered. (EBME, 2009) Fig 1 – MR10 Apnoea Monitor (EBME, 2009)The Monitor is powered by 4 LR6 (AA) alkaline batteries. A low battery indicator is included onthe main panel of the monitor.

Maintenance & Service ProceduresMR10 Monitors are serviced annually. This includes a visual inspection & functional checks.Using the dedicated test box checks are carried out including;Sensitivity, Apnoea delay, Audible and visual alarms, Alarm Resets and Low battery alerts. Thebatteries are then replaced and a ‘DO NOT USE AFTER’ label dated one year after service date isattached.BibliographyEBME, 2009. EBME. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/6-apnoea-alarms[Accessed March 2014].

Doppler Handheld Ultrasound Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Doppler Handheld UltrasoundDoppler handheld ultrasound devices all use a technique based on the Doppler principle fornon-invasively monitoring movement within the body.The Doppler Effect causes the received frequency of a source (how it is perceived when it gets toits destination) to differ from the sent frequency if there is motion that is increasing ordecreasing the distance between the source and the receiver. This effect is observable asvariation in the pitch of sound between a moving source and a stationary observer.The amount of frequency shift is proportional to the velocity of the reflector relative to thetransmitter/receiver.The most common example of the Doppler principle is a moving siren or train where thefrequency of the sound changes as the source approaches.As the sound source approaches the frequency increases, as the source moves away thefrequency decreases. Fig 1 – Doppler Effect (Broom, 2015)In the Dopplex range, a fixed frequency ultrasonic signal is transmitted from the probe into thebody. This is reflected from, for example, moving blood cells. The signal is reflected from thesecells and is received by the probe. Due to the movement of the blood cells, a frequency shiftresults which is proportional to the blood flow velocity. The Doppler shift is also affected by theangle between the probe and the direction of flow. The Doppler shift is greatest when the flowis directly towards, or away from, the probe.The Dopplex probe contains a transmitter and receiver. The probe sends out a continuousultrasonic signal (carrier), generated by the piezo-ceramic transmitter crystal, in the frequencyrange 2 to 10 MHz (depending on probe).This signal is scattered by blood cells or any other \"interface\" such as skin, muscle layers,organs, walls of vessels etc. A small proportion of the scattered signal will be reflected back anddetected by the receiver. By demodulating the received signal (removing the high frequencycarrier) the Doppler shifted component (the difference between the transmitted and receivedsignals) can be produced.With typical target velocities found in the human body, the Doppler shift signal falls within theaudio frequency range. It can therefore be amplified and heard through a loudspeaker.The sound heard is an artificial sound, the frequency (pitch) of which is proportional to thevelocity of the moving target. It is not the real sound made by blood rushing through an arteryor vein, or movement of the fetal heart.A Doppler ultrasound may help diagnose many conditions, including:  Blood clots  Heart valve defects and congenital heart disease  Decreased blood circulation into your legs (peripheral artery disease)  A blocked artery (arterial occlusion)  Narrowing of an artery, such as those in your neck (carotid artery stenosis)  Bulging arteries (aneurysms) (Huntleigh, 2004)

Advances in technology over the past 30 years now enable us to assess fetal health using safeand non-invasive ultrasound techniques. One such technique is fetal heart rate monitoring, andin pregnancies where there is fetal compromise the fetal heart rate contains crucial informationwith regard to the optimum timing of delivery. Fig 2 – Doppler Ultrasound effect (Huntleigh, 2004)The main difference between Obstetric and Vascular dopplers are the probe heads and theiroperational frequency. Obstetric probes have a larger diameter and operate at either 2 or 3MHz, Lower frequencies are able to penetrate deeper into the body and have a wider beamtherefore are more appropriate for fetal heart rate detection, vascular probes operate between4 to 10 MHz. Fig 2 – Various Probe Heads & Uses (Huntleigh, 2004)

Maintenance & Service ProceduresThe Doppler Handhelds are seen annually where a visual inspection is performed including themain body, probe cable, probe and crystal face. A check should also be done to confirm thevolume is adjustable and that the battery is still good. Obstetric probes can be checked bymoving them towards/away from a surface and vascular probes can be checked on self, bylistening to your pulse. Repairs such as probe replacement or case changes can be done on site.BibliographyBroom, M., 2015. Princeton Innovation. [Online]Available at: http://princetoninnovation.org/magazine/2015/12/09/redshift-universes-doppler-effect/[Accessed 2016].Huntleigh, 2004. Handheld Dopplers. [Online]Available at: http://iworx9.webxtra.net/~emedical/images/stories/pdf/726374-2_hand_held_dopplers_service-1.pdf[Accessed Febuary 2014].Pozniak, M. A., 2014. Clinical Doppler Ultrasound. 3rd ed. s.l.:Churchill Livingstone.Thilaganathan, B., 2005. Obstetric Ultrasound. 1st ed. s.l.:Churchill Livingstone.

Pulse Oximetry Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Pulse OximetryPulse oximetry is an important modern development that allows us to monitor the blood’ssaturation levels with the view of ensuring they don’t drop too low. Adequate oxygen levels inthe blood are crucial if the body is to function. Without enough oxygen, cells can becomedamaged and will eventually die. The purpose of pulse oximetry is to detect dangerously lowsaturation within the blood before there are even any visible signs of deficiency, at which pointthe body will already be in a dangerous condition.The body needs oxygen to survive and it is the haemoglobin molecule that transports theoxygen around the body. This molecule has four sites to which oxygen can become attached,when all four of these positions are full the haemoglobin is fully or 100% saturated.In an average human being, problems occur when arterial saturation of haemoglobin falls below90%. It is not until saturation falls below this point that obvious physical signs, such as the skinand mucous membranes taking on a bluish colour occurs, in a condition known as cyanosis.Therefore it is important to detect poor saturation before it falls to this level; consequently,pulse oximetry has been developed as a means of monitoring these levels.Pulse oximetry is a non-invasive procedure of measuring the arterial saturation of thehaemoglobin in red blood cells. A pulse oximeter uses a probe which can be attached to finger,ear, toe or multisite probes, special probes for neonates are also available which are designed tobe taped onto the foot to remain secure as the baby moves.On one side of this probe are two LED’s which shine different wave lengths of light, the fist avisible red beam at a wavelength of approximately 660nm and the second an invisible infraredbeam at an approximate wavelength of 900nm. On the other side of the probe there is aphotodiode to detect these light sources. (Masimo, 2012)The oxygen level of the blood effects howlight waves are absorbed. Blood rich inoxygen absorbs infrared light and lets redlight pass through; whilst the deoxygenatedblood absorbs red light and allows infraredlight to pass through. The ratio of the red toinfrared light is measured when the probeflashes light through a finger, ear or toe, thedetector, on the other side of the probe,receives this light and compares the ratio toa scale that is calibrated to each pulseoximeter to find the oxygen saturation level. Fig 1 – Pulse Oximetry (Masimo, 2012)Oxygen saturation levels must be taken from arterial blood, However, the light emitted by theoximeter and registered on the detector has not only passed through arteries, it will have alsopassed through tissue, bone and venous blood, where much of it is absorbed, these amounts ofabsorption do not change dramatically over short periods of time, but the amount of arterialblood pulses as the heart beats. As this is usually the only light absorbing component which isnoticeably changing, it can be isolated from the other components and an accurate reading canbe given.Oxygen saturation levels may be taken at a single time point, but this is an unreliable reading assaturation levels are constantly changing. More accurate information is gained by takingreadings over time and analysing the trends.

Pulse oximeters do have their disadvantages and can give unreliable readings due tocircumstances such as:  Incorrect sensor size: If a sensor is too big or too small, the LED and the light detector may not line up. If a finger is inserted too far into the sensor it may be squeezed, which causes venous pulsation. As I mentioned earlier the pulse oximeter recognises arterial blood by its pulsing motion, so in this case it could also measure venous blood, causing readings which are falsely low.  Movement: Patient movement can affect the readings and again give an inaccurate reading. During patient motion, the venous blood also moves, which causes conventional pulse oximetry to miss-read because it cannot distinguish between the arterial and venous blood. Although latest advances by Masimo have eliminated this problem using their SET (Signal Extraction Technology), signal processing identifies the venous blood signal, isolates it, and by using adaptive filters, cancels the noise and extracts the arterial signal, it still exists in other probes.  Weak Pulse: A poor perfusion index will cause the oximeter to have difficulty isolating its signal from those of the surrounding venous blood, bone, and tissue. Even cold hands can affect readings.  Nail Varnish: Studies suggest that certain colours (Green, Blue, and Black) can cause erroneous readings.  Carboxyhaemoglobin (COHb): Carbon Monoxide bound to Haemoglobin is indistinguishable from Oxyhaemoglobin , therefore, a patient suffering from high levels of Carbon Monoxide poisoning will have a false oxygen saturation reading. The latest advances by Masimo have overcome this with their rainbow technology., however, it is still a potential problem in older SPO2 monitors.Masimo rainbow is a non-invasive monitoring platform enabling the assessment of multipleblood constituents and physiologic parameters, that previously required invasive orcomplicated procedures including;  Total Hemoglobin (SpHb)  Carboxyhemoglobin (SpCO)  Methemoglobin (SpMet)  Oxygen Content (SpOC)  Acoustic Respiration Rate (RRa)  Pleth Variability Index (PVI) Fig 2 – Masimo Rainbow Technology (Masimo, 2012)Maintenance & Service proceduresA Visual Inspection of the unit and any probes and patient extension cables should be carriedout along with a functional check on self or using an appropriate simulator Ensure all alarmfunctions are working correctly, change internal battery as required (CEng protocol states thisto be every two years. Further testing on probes or their cables can be checked on a device suchas a Lightman, which performs checks on LED wavelengths, a reduced light output, or light thatis not the correct wavelength may cause incorrect absorption, which in turn will cause the bloodoxygen levels readout to be incorrect. Cable checks are also performed and can determine if theprobe is still within acceptable accuracy parameters. The unit is then tested for electrical safety.

BibliographyMasimo, 2012. Masimo - SPO2 Technology. [Online]Available at: http://www.masimo.co.uk/pdf/whitepaper/LAB1035R.PDF[Accessed March 2014].Hopkins Medicine,2012. Oximetry. [Online]Available at:http://www.hopkinsmedicine.org/healthlibrary/test_procedures/pulmonary/oximetry_92,P07754/[Accessed March 2014].Nursing Times, 2002. Pulse Oximetry. [Online]Available at: http://www.nursingtimes.net/the-correct-use-of-pulse-oximetry-in-measuring-oxygen-status/199984.article[Accessed March 2014].

Basic Observation Monitors Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Basic Observation MonitorsObservation monitors are used in a clinical environment for spot checks or continuousmonitoring of;Temperature – A stable core body temperature between 36.5°C and 37.5°C promotes properfunction of cells, tissues and organs.Non Invasive Blood Pressure (NIBP) - Measuring blood pressure can give information oncardiovascular status and assist in the diagnosis of disease or evaluation of treatment. Problemscan occur when either hypertension (high blood pressure) or hypotension (low blood pressure)are present.Pulse Oximetry (SPO2) – To assess a patients oxygen arterial saturation (percentage ofhaemoglobin saturated with oxygen) which gives an indication of a patient’s cardio-respiratorystatus, and if a hypoxic condition is developing.Electrocardiography (ECG) – Used to monitor electrical activity in the heart, helps to identifyreduced blood supply to the heart muscle, abnormal rhythms, abnormal rate, and conductiondisorders.These devices may also have a ‘memory’ facility which stores the last measurement andprevious readings.TemperatureMost basic observation monitors no longer contain a function for measuring temperature, as thecurrent trend is to use a stand-alone unit such as the ‘Welch Allyn- SureTemp contactthermometer’ models which do have this function have one or two probes, oral and rectal.Contact thermometers use a thermistor to measure resistance as the temperature changes.Once the probe is placed into a person's mouth, it heats up to the same temperature of themouth, the thermistor inside also warms up, increasing/decreasing its resistance. Amicrocontroller measures the resistance and converts it into a temperature and displays it onthe screen. (eHow, 2012)Non Invasive Blood Pressure (NIBP)Observation Monitors take measurements of blood pressure with some incorporating heartrate. An electrically-driven pump raises the pressure in the cuff. Devices may have a user-adjustable set inflation pressure or they will automatically inflate to the appropriate level,usually about 30mmHg above an estimated systolic reading. When started, the deviceautomatically inflates, then deflates the cuff and displays the systolic and diastolic values. Themajority calculate these values from data obtained during the deflation cycle, but there aresome that use data from the inflation cycle. If a BP reading cannot be taken, the cuff will inflateagain but to a higher pressure until a BP reading is recorded. Due to this feature the pressurecan become uncomfortable for some patients even causing injury. The pulse rate may also bedisplayed. The majority of non-invasive automated blood pressure measuring devices currentlyavailable use the oscillometric method.The oscillometric method relies on detection of variations in pressure oscillations due toarterial wall movement beneath an occluding cuff. Empirically derived algorithms areemployed, which calculate systolic, mean arterial (MAP) and diastolic blood pressure. (DoH, 2012)

Some automated devices may use an electronic auscultatory method. These devices incorporatea microphone in the cuff and apply sound-based algorithms to calculate the systolic anddiastolic blood pressure. (EBME, 2009)SPO2Pulse oximetry is a non-invasive procedure of measuring the arterial saturation of thehaemoglobin in red blood cells. A pulse oximeter uses a probe which can be attached to finger,ear, toe or multisite probes, special probes for neonates are also available which are designed tobe taped onto the foot to remain secure as the baby moves.On one side of this probe are two LED’s which shine different wave lengths of light, the fist avisible red beam at a wavelength of approximately 660nm and the second an invisible infraredbeam at an approximate wavelength of 900nm. On the other side of the probe there is aphotodiode to detect these light sources. (Masimo, 2012) Fig 1 – Pulse Oximetry (Masimo, 2012)Unreliable readings could be displayed due to circumstances such as:  Incorrect sensor size: If a sensor is too big or too small, the LED and the light detector may not line up. If a finger is inserted too far into the sensor it may be squeezed, which causes venous pulsation. As I mentioned earlier the pulse oximeter recognises arterial blood by its pulsing motion, so in this case it could also measure venous blood, causing readings which are falsely low.  Movement: Patient movement can affect the readings and again give an inaccurate reading. During patient motion, the venous blood also moves, which causes conventional pulse oximetry to miss-read because it cannot distinguish between the arterial and venous blood. Although latest advances by Masimo have eliminated this problem using their SET (Signal Extraction Technology), signal processing identifies the venous blood signal, isolates it, and by using adaptive filters, cancels the noise and extracts the arterial signal, it still exists in other probes.  Weak Pulse: A poor perfusion index will cause the oximeter to have difficulty isolating its signal from those of the surrounding venous blood, bone, and tissue. Even cold hands can affect readings.  Nail Varnish: Studies suggest that certain colours (Green, Blue, and Black) can cause erroneous readings.  Carboxyhaemoglobin (COHb): Carbon Monoxide bound to Haemoglobin is indistinguishable from Oxyhaemoglobin , therefore, a patient suffering from high levels of Carbon Monoxide poisoning will have a false oxygen saturation reading. The latest advances by Masimo have overcome this with their rainbow technology; however, it is still a potential problem in older SPO2 monitors.

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 2 – The Human Heart (EBME, 2011)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,conventionally they are placed in a standard position each time so that abnormalities are easierto detect. Most basic observation monitors use a 3 lead system and they are connected asfollows:  Red - RA - right arm, or second intercostal space on the right of the sternum.  Yellow - LA - left arm or second intercostal space on the left of the sternum.  Green (or Black) - LL - left leg or more often in the region of the apex beat. Fig 3 – Placing of a 3 lead ECG set (University of Nottingham, 2015)This will allow the Lead I, II or III configurations to be selected on the ECG monitor.The term 'lead' when applied to the ECG does not describe the electrical cables connected to theelectrodes on the patient. Instead it refers to the positioning of the 2 electrodes being used todetect the electrical activity of the heart, the third electrode acts as a neutral. These leads arecalled bipolar leads as they measure the potential difference (electrical difference) between twoelectrodes. Electrical activity travelling towards an electrode is displayed as a positivedeflection on the screen, and electrical activity travelling away as a negative deflection. Theleads are described by convention as follows:  Lead I - Measures the potential difference between the right arm electrode and the left arm electrode.  Lead II - Measures the potential difference between the right arm and left leg electrode.  Lead III - Measures the potential difference between the left arm and left leg electrode.Most monitors can only show one lead at a time and therefore the lead that gives as muchinformation as possible should be chosen. The most commonly used is lead II. This is the mostuseful lead for detecting cardiac arrhythmias as it lies close to the cardiac axis (the overalldirection of electrical movement) and allows the best view of P and R waves.The cables from the electrodes terminate in a single cable, which is plugged into the port on theObservation Monitor and are electrically isolated for patient safety. Circuitry also protectsthe monitor from any high voltages produced by a defibrillator or electrocautery signals.The signal is filtered, amplified, conditioned and processed for display. Pulse rate is alsocalculated and displayed, with high and low alarms set with the standard being 150bpmhigh, 50bpm low. A good electrical connection between the patient and the electrodes isrequired to minimise the resistance of the skin. When the skin is sweaty/dirty/hairy theelectrodes may not stick well, resulting in an unstable trace.

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 4 – ECG Waveforms (University of Nottingham, 2015)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)

Maintenance & Service ProceduresMonitors have a factory default configuration but this must be checked and adjusted to complywith the location the monitor is being used, generally there are standard values for adult,paediatric and neonate alarms, initial inflation values, default patient size setting, but aparticular area or monitor may require a specific configuration and therefore must always bechecked. A visual inspection of the unit is performed looking for any damage, NIBP, and SPO2can be ‘checked on self’ to confirm the readings are as expected. An electrical safety test iscarried out.NIBPCuffs, hoses and tubing connectors should be checked as excessive air leakage from damage orgeneral wear and tear may reduce the accuracy of the readings. The device should be tested forleaks this can be done by attaching a test chamber to the monitor and building the pressure inthe chamber and monitoring the amount of pressure lost over time, or to inflate the cuff to acertain pressure and using a pressure monitors leak check function observe the pressure lostover a time period. CEng protocol states a value of no greater than 12mmHg over 60 seconds.Both disposable (single patient use) and re-usable cuffs are available. Re-usable cuffs should becleaned in accordance with the manufacturer’s instructions, ensuring that cleaning fluid doesnot enter the cuff bladder or hoses. Over pressure vent test needs to be carried out to ensurethe unit vents if an event occur which could cause harm to the patient. Inflation pressures needto be checked for accuracy using a calibrated pressure monitor.ECGAn ECG patient simulator is used to give various pulse rates and amplitudes, some will simulatecertain arrhythmias, and these are then checked for accuracy. The waveform is checked forexcessive noise, this can sometimes be traced to a particular patient lead, as the noise is oftenmore amplified when moving the lead. Leads are disconnected individually to ensure themonitor detects their removal. High and low alarms are checked.SPO2A simulator is used which gives set pulse rates and saturation levels, using this you can checkthe high and low alarms, and the displayed accuracy. The finger probe and patient extensioncables should be visually inspected as they are regularly and easily damaged by being trailedalong the floor or being wrapped too tightly around the stand. . Further testing on probes ortheir cables can be checked on a device such as a Lightman, which performs checks on LEDwavelengths and cable integrity.

BibliographyDoH, 2012. Department of Health - Device Bulletin DB 2006(03) v2.0. [Online]Available at: http://www.dhsspsni.gov.uk/db2006_03_v2.pdf[Accessed March 2014].EBME, 2009. EBME - NIBP. [Online]Available at: http://www.ebme.co.uk/articles/clinical-engineering/70-noninvasive-blood-pressure-measurement[Accessed 2015].EBME, 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].eHow, 2012. eHow. [Online]Available at: http://www.ehow.com/how-does_5162287_electronic-thermometer-work.html[Accessed November 2013].Masimo, 2012. Masimo - SPO2 Technology. [Online]Available at: http://www.masimo.co.uk/pdf/whitepaper/LAB1035R.PDF[Accessed March 2014].University of Nottingham, 2015. Cardiology. [Online]Available at:http://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/bipolar_leads.php[Accessed 2016].

Basic Medical Gas Equipment Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Medical Gas EquipmentMedical gases are used for a number of reasons within the clinical environment; the main gasesand their uses are;Medical Carbon Dioxide (CO2)Carbon dioxide is commonly used as an insufflation gas for minimal invasive surgery(laparoscopy, endoscopy, and arthroscopy) to enlarge and stabilize body cavities to providebetter visibility of the surgical area.It can also be used for Cryotherapy, where temperatures of -76° C, can be achieved. Using thistechnique body cells are destroyed by the process of crystallisation. This may include theremoval of wart, moles and skin tags.Medical AirMedical air cylinders are used to supply air to the patient where pipelines supplies are notavailable. The main uses of medical air in the hospital are, driving ventilators and incubators,where it provides uncontaminated and controlled air flows helping to reduce highconcentration of oxygen exposure, as a carrier gas for anaesthetic agents and as a power sourcefor driving surgical tools in the operating theatre.HELIOX21 (79% helium and 21% oxygen)Original research undertaken in the 1950’s was for use in lower airways. In the past ten yearsfurther interest has been shown in using HELIOX21 therapy in the treatment of asthma andCOPD. HELIOX21 is typically three times less dense than air and this property allows patientswith respiratory conditions to breathe more freely reducing their work of breathing andimproving their comfort.Medical Nitrous Oxide (N2O)Medical Nitrous Oxide is a liquefied medicinal gas, supplied in cylinders filled to a high pressure.Medical Nitrous Oxide is used for; anaesthesia, pain relief, inflating the abdominal cavitiesduring a laparoscopy (an investigative operation), as a refrigerant in cryosurgery (a treatmentusing extreme cold to remove warts/verruca’s etc.).ENTONOX (Medical Nitrous Oxide and Oxygen Mixture)ENTONOX is a ready-to-use medical gas mixture consisting of 50% nitrous oxide and 50%oxygen for use in all situations where analgesia and sedation with rapid onset and offset issought. It is widely used by midwives, hospitals and the ambulance service. It is usedexclusively for short-term procedures inevitably involving pain, including (but not limited to):  Acute trauma  Tooth extraction and other brief procedures in dental work  Wound and burn dressing, wound debridement and suturing  Fracture and joint manipulation  Colonoscopy  Venopuncture  Labour

Medical Oxygen (O2)Oxygen is widely used in every healthcare setting, with applications from resuscitation toinhalation therapy.Medical oxygen is used to:  Provide a basis for virtually all modern anaesthetic techniques  Restore tissue oxygen tension by improving oxygen availability in a wide range of conditions such as COPD, cyanosis, shock, severe hemorrhage, carbon monoxide poisoning, major trauma, cardiac/respiratory arrest  Aid resuscitation  Provide life support for artificially ventilated patients  Reduce incidence of surgical wound infection  Aid cardiovascular stability (BOC, 2011)The medicines act 1968 states that each medical gas listed above must have a licence to besupplied. These licences are obtained from the medicine and healthcare products agency of thedepartment of health.Medical gases are controlled by pharmacy and are kept in secure locked stores and should neverbe left unattended. Medical gases should only be prescribed to patients by medical practitioners.Cylinder Size Guide Fig 1 – Cylinder Size Guide (BOC, 2011)

Cylinder & Hose ColoursOxygen Nitrous Suction Air Oxide Fig 2 – Cylinder & Hose Colours (BOC, 2011)Cylinder Collar LabelAuthorisation Name & Chemical Number Symbol Cylinder Unique Weight BarcodeCylinder Size Contact & Pressure Numbers Directions for Hazard Use Warnings Quality Control Label Fig 3 – Cylinder Collar Label (BOC, 2011)

Cylinder ValvesHand Wheel Pin Index Combi Bull Nose Side SpindleValve Valve Valve Pin Index Valve Valve Fig 4 – Cylinder Valves (BOC, 2011)Pin Index SystemThis system complies with EN ISO 407 and was introduced to prevent gas cylinders beingconnected incorrectly to the wrong devices. It consists of a combination of locating pins on theregulator, at a set radius from the gas outlet, which fit into corresponding holes on the cylindervalve.Nitrous Oxygen Entonox Air Carbon Oxide Dioxide Fig 5 – Pin Index System (BOC, 2011)To ensure an air tight seal between the yoke and pin index valve a Bodok seal is used. TheBodok seal consists of a neoprene washer with a peripheral metal reinforcing ring whichprevents splaying of the washer. The seal is incombustible and resistant to the high pressuresimposed upon it by cylinder gases.

FlowmetersA variable area meter (rotameter) is a flow meter that measures volumetric flow of gases. Itsoperation is based on the variable area principle, where flow raises a float in a tapered tube.The float is pushed up by the flow of the gas, and pulled down by gravity, the flow rate is thenread from either a scale next to the tube or a scale on the tube.A change in flow rate upsets this force balance and the float will move up or down until it againreaches a position where the forces are in balance. The rotameter is popular because it has alinear scale, a relatively long measurement range, and low pressure drop. It is simple to installand maintain. (Omega, 2014)The forces or influences involved in the rotameter can be seen in the diagram below.Regulators Fig 6 – Forces in a variable flow meter (Omega, 2014)Regulators are used to allow high-pressure to be reduced to safe and/or usable pressures forvarious applications.In the diagram of the regulator, a force balanceis used on the diaphragm to control a valve inorder to regulate pressure. With no inletpressure, the spring above the diaphragmpushes it down on the valve, holding it open.Once inlet pressure is introduced, the openvalve allows flow to the diaphragm andpressure in the upper chamber increases untilthe diaphragm is pushed upward against the Fig 7 – Diagram of a Regulator (Broady, 2013)spring, causing the valve to reduce flow, finallystopping further increase of pressure. By adjusting the top screw, the downward pressure onthe diaphragm can be increased, requiring more pressure in the upper chamber to maintainequilibrium. In this way, the outlet pressure of the regulator is controlled.All regulators have a pressure relief valve for safety to ensure the regulated pressure doesnot go above a certain threshold. (Broady, 2013)

SuctionSuction is supplied at the wall outlet; a suction controller is connected directly to thewall/pendant outlet and is used to regulate the suction pressure. Suction controllers workin the same was as a pressure regulator only the forces are opposite. The spring pulls thediaphragm up opening the valve, the suction pressure draws the diaphragm down, as thesuction pressure drops the spring overcomes the force of the suction and the valve isopened again. A hydrophobic filter (allowing the passage of air but not liquid) prevents anyliquid or debris entering the regulator or main vacuum system.Maintenance & Service ProceduresAll medical gas equipment must be tested and serviced to a regular schedule to ensure theyperforms as required and remain in a safe condition.Medical gases can pose many hazards, most gases, including inert ones; carry the risk ofasphyxia (suffocation due to exclusion of oxygen)Another hazard to be aware of is the risk of oxygen combustion from alcohol, oils and grease.Any of these substances can ignite in oxygen enriched atmospheres and lead to serious fires. Itis important that only certified products are used when servicing equipment, and ensure handsare clean and dry.Care should be taken to release pressure in a controlled manner, and away from anybody toprevent injury, gas cylinders can be heavy, and should only be moved in a suitable cylindertrolley.BibliographyBOC, 2011. BOC - Medical Gases. [Online]Available at: http://www.bochealthcare.co.uk/en/Products-and-services/Products-and-services-by-category/Medical-gases/medical-gases.html[Accessed March 2014].Broady, 2013. Valve Theory. [Online]Available at: www.broady.co.uk/valve-theory[Accessed March 2014].Division of Research Safety, 2015. Division of Research Safety. [Online]Available at: http://www.drs.illinois.edu/SafetyLibrary/CompressedGasCylinderSafety/[Accessed March 2014].Omega, 2014. Rotameters. [Online]Available at: www.omega.co.uk/prodinfo/rotameters.html[Accessed March 2014].

Oxygen Analysers Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Oxygen AnalysersOxygen analysers are intended for spot-checking the concentration of oxygen in gas mixturesused in applications such as anaesthesia gas delivery to ensure oxygen levels are correct toensure the patient is receiving the correct concentration of oxygen, or monitoring theoxygen concentration in an environment such as a neonatal incubator. They areintended for adult, paediatric and neonatal patients.Many items of equipment have built in oxygen analysers and have user configurable alarmsetting for situations where constant monitoring is required; the high and low alarms are set tothe desired level.There is no one universal oxygen analyser type, but the main ones used at ULHT are theParamagnetic Oxygen Sensor and the Fuel Cell or Electro-Galvanic Sensor.Fuel CellMost fuel cells that are used in oxygen analysers are electro-galvanic. A chemical reactionoccurs when the potassium hydroxide in the cell comes into contact with oxygen. Oxygenmolecules diffuse through a semi permeable membrane installed on one side of the sensor. Asthe molecules flow past the cathode they become negatively charged ions. These ions migratethrough the electrolyte to the anode where an oxidation reaction takes place, electrons arereleased which produce an electrical current proportional to the oxygen concentration in thegasElectro-galvanic fuel cells have a limited lifetime which is reduced by exposure to oxygen. Thismeans that as soon as an oxygen sensor is installed it is constantly being depleted, with thespeed increasing as the concentration of oxygen does.Paramagnetic SensorsOxygen has a relatively high magnetic susceptibility as compared to other gases such asnitrogen, helium, argon, etc. and displays a paramagnetic behaviour. The paramagnetic oxygensensor consists of a cylindrical shaped container inside of which is placed a small glassdumbbell. The dumbbell is filled with an inert gas such as nitrogen and suspended on a tautplatinum wire within a non-uniform magnetic field. The dumbbell is designed to move freely asit is suspended from the wire. When a sample gas containing oxygen is processed through thesensor, the oxygen molecules are attracted to the stronger of the two magnetic fields. Thiscauses a displacement of the dumbbell resulting in it rotating. A precision optical systemconsisting of a light source, photodiode, and amplifier circuit is used to measure the degree ofrotation of the dumbbell. In some paramagnetic oxygen sensor designs, an opposing current isapplied to restore the dumbbell to its normal position. Paramagnetic oxygen sensors offer verygood response time characteristics and use no consumable parts, making sensor life, undernormal conditions, quite good. They also offer precision over a range of 1% to 100% oxygen.However, other gases that exhibit a magnetic susceptibility can produce sizeable measurementerrors. The sensor is quite delicate and is sensitive to vibration and/or position. Due to the lossin measurement sensitivity, in general, the paramagnetic oxygen sensor is not recommended fortrace oxygen measurements.

A focused magnetic field is Two nitrogen filled glass created. Any Oxygen spheres are mounted on a rotating suspension withinpresent is attracted to thestrongest part of the field. the magnetic field. A mirror is mounted centrally on the The signal generated by the photocells is suspension. Light is shone onto the mirror, passed to a feedback system. The feedback which is reflected onto a pair of photocells. system will pass a current around a wireOxygen attracted into the magnetic field will mounted on the suspension. This causes adisplace spheres, causing them to rotate. The photocells will detect the movement and motor effect, which will keep the suspension in its original position. The current generate a signal. measured flowing around the wire will be directly proportional to the concentration of oxygen within the gas mixtureModern systems have moved away from the suspended dumbbell design and now use aswitched electromagnetic field and pressure transducer. The electromagnetic field is generatedat approximately 110 Hz. This creates a pressure differential between the reference sample(usually clean air) and the patient’s sample. A sensitive transducer detects the pressurefluctuations and converts them to a DC voltage, which is directly proportional to theconcentration of oxygen. (Servomex, 2013)

Maintenance & Service ProceduresAlthough there is no PPM schedule set for this equipment Oxygen Analysers should be seen on ayearly basis where a visual inspection is carried out to include case and screen. A check that thebatteries are in good condition and performance levels (this can be checked by pressing the ‘BatTest’ button on the front of some models). CAL checks at 21% can be performed in the room. Ifthe unit comes in for repair further CAL checks can be performed at 100% oxygen by placing thesensor in the flow from an O2 outlet using a T-piece, ensuring it returns to 21% within a set timewhen removed from the flow. Hi/Low and sensor off alarms are also checked.The depleted oxygen sensors are bagged up with their serial numbers recorded and then sentback to the supplier for correct disposal.

BibliographyMustafa Technologist, 2010. Slide Share. [Online]Available at: http://www.slideshare.net/Mustafa_Technologist/oxygen-analyzer[Accessed April 2014].Oxford Journals, 2011. Oxygen Analysis. [Online]Available at: http://ceaccp.oxfordjournals.org/content/9/1/19.full[Accessed April 2014].Servomex, 2013. Paramagnetic Oxygen Analysis. [Online]Available at: https://www.servomex.com/servomex/web/web.nsf/en/paramagnetic-oxygen-analysis[Accessed April 2014].

Volumetric Infusion Pumps Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Volumetric Infusion PumpsAn infusion system is a device, and any associated disposables, used to deliver fluids or drugs insolution to the patient.The simplest devices, gravity controllers, employ a clamping action to vary the flow of liquidunder the force of gravity. More complex systems use a positive pumping action for infusion.The simplest of these is an elastomeric pump which has a balloon reservoir which contractsdelivering the infusion at a constant rate. Powered volumetric infusion pumps, together with anappropriate administration set, are intended to provide an accurate flow of fluids over aprescribed period. Volumetric pumps may employ a peristaltic pumping mechanism applied tothe infusion tubing or ‘giving set’, or use a special cassette within the set. Fig 1 – A Giving Set Correctly Installed (Fresenius Kabi, 2014)The giving set consists of a container filled with fluid, a chamber and a length of tube (seen inFig 1.). The tube will have connections on it to fit the specific volumetric pump being used andwill contain a clamping mechanism. Fully opening the clamp on the giving set will permit all thefluid and any air in the bag to infuse into the patient. To prevent this happening when fitting orremoving the set, the clamp will, when installed into the pump, open when the pump door isclosed and the tubing is compressed against the back plate and close again when the door isopened this prevents any unwanted delivery of fluid.Most Volumetric pumps have a peristaltic mechanism. The Volumat MC Agilia (the current truststandard) uses linear peristalsis which consists of finger like projections that sequentiallycompress the intravenous tubing against a stationary back plate, moving the fluid in onedirection. Rotator peristaltic pumps have rollers on a wheel which compress the tubing andmove fluid in the tubing towards the patient.Due to various programming modes, infusion modes, customisation capabilities and extensivegiving set ranges, modern volumetric pumps can be used in any unit of the hospital: generalwards, paediatric wards, intensive care, oncology, etc. They are generally used for theadministration of drugs, solutions, fluids and parenteral nutrition, either;

 Intravenously - directly into the vein,  Subcutaneous - into the subcutaneous tissue,  Intra Arterial - into a blood vessel carrying blood away from the heart  Epidural where an anaesthetic or analgesic is infused directly into the epidural space, inside the spinal canal of the central nervous system, which is commonly used during childbirthAll these types of therapy need to be administered at a precise flow rate over a set time, usuallycalculated in ml/hr, administering the infusion manually would be difficult or not possible. Thisml/hr rate can be calculated by entering a volume to be infused (VTBI) and the duration overwhich it is to be infused.Once switched on most pumps perform an auto-test, this checks the functionality of the pump.Once the auto-test is complete, you can install the giving set.Alarms & Safety FeaturesConditions that could trigger an alarm in volumetric infusion pumps include;  Excessive upstream or downstream pressure - Any blockage/occlusion of the giving pathway causes the downstream line pressure to increase to the pumps occlusion alarm/ pressure limit. Clearing the occlusion by opening the tap, roller clamp, kinked tubing could infuse a bolus into the patient. The higher the occlusion alarm/ pressure limit is set the larger the bolus. Infusion pumps have a system to prevent this and the pump ‘backs off’ to release the occlusion pressure. The maximum bolus delivered after occlusion are; for rates of less than 100 ml/h a bolus of less than 0.2 ml will be delivered and at rates greater then 100 ml/h a bolus of less than 0.3 ml will be delivered.  Air in line - International Standards require all general-purpose pumps to have air embolus protection capable of detecting single bubbles of about 0.1ml. If the tubing is not pushed firmly into the detector slot or there are any small particles on the tubing or the detector it may respond with a false air-in-line alarm. Solutions prone to frothing will also activate the air sensor.  Low battery and disconnection from mains supply.  Infusion complete/ Near end. Once an infusion is finished the pump automatically switches to Keep Vein Open (KVO) Mode.If an alarm occurs, the infusion stops, and in most pumps visual and audible signals are emittedand a message is expressed by means of words and/or pictograms detailing the fault. When thecause of the alarm has been fixed, the alarms are silenced some pumps may still give a visualindication that there has been a fault for a period after the fault has been cleared.Many thousands of infusion devices are now in use in hospitals and in the community and thereis an identifiable mortality and morbidity associated with their use. In the five years between2005 and 2010 the MHRA investigated 1,085 incidents involving infusion pumps alone in theUK.The majority of serious problems relate to over-infusion of drugs. In most fatal incidents nofault has been found with the infusion device, suggesting that user error is the most significantcontributing factor or that some form of tampering could have taken place.The trust have standardised on the Volumat MC Agilia, standardisation is important with highrisk equipment such as infusion pumps as, shown in the MHRA investigation user errors whenentering infusion rates or volumes to be infused can cause death. If all departments and wardsuse the same pump, there will be less chance of staff making errors.

Maintenance & Service ProceduresThe pumps (Volumat MC Agilia) have a visual inspection and safety test on an annual basis, witha full service and battery change every three years. During the service the pump membrane ischanged, the pump is then connected to a PC and using the specific software various checks arecarried out including;  Checking the configuration  Ensuring the clamp motor is effective and can detect the giving set  Downstream/Upstream Pressure occlusion tests  Air Bubble detection & any other alarms  Flow rate accuracy checkingAn electrical safety test is carried out and after the service is complete a certificate of conformityis printed.BibliographyFresenius Kabi, 2014. Volumat MC Agilia Technical Manual. 1st ed. Brezins: Fresenius Vial.MHRA, 2013. Infusion Systems. [Online]Available at: http://www.mhra.gov.uk/home/groups/dts-iac/documents/publication/con007322.pdf[Accessed December 2014].Nursing Times, 2013. Infusion Devices. [Online]Available at: http://www.nursingtimes.net/infusion-pumps-how-to-pick-the-best-pump-for-the-delivery-of-fluids/200125.article[Accessed December 2014].

Syringe Drivers Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Syringe DriversA syringe driver is a small, battery powered portable pump that can be used to give acontinuous subcutaneous infusion of drugs such as; analgesics (pain relief), anti-emetics(nausea relief), sedatives or anticholinergics (blocks nerve impulses) through a syringe. Thepump delivers the infusion through central, peripheral venous, epidural, intra-arterial orsubcutaneous routes. The syringe is drawn up with a single drug or combination of drugs andadministered at a constant rate over a set period of time (usually 24 hours). It is attached by atube to a fine needle or cannula that is placed just under the skin. A small dose of the drug isthen released at a constant rate for as long as needed. This prevents periods during whichmedication levels in the blood are either too low or too high. It is suitable for adults or forpaediatric use. The syringe is usually changed every 24 hours by a nurse. A compact lockbox isavailable to protect against damage to or tampering with the pump or displacement of thesyringe.A syringe driver is an alternative route for drug delivery and is useful if the patient has; • Persistent nausea and vomiting • Intestinal obstruction • Difficulty in swallowing • Sleepiness / coma • Poor alimentary absorption (rare) • Intractable painThe cannula can be placed in various sites as seen in Fig 1. Where it is necessary to use morethan one syringe driver due to drug incompatibility issues these should ideally be sited ondifferent sides of the body or in different limbs.Where it is necessary to site both drivers in the same limb due to patient mobility or patientchoice the drivers should be placed as far apart as is practicable. This is due to the risk of thedrugs coming into contact subcutaneously and causing irritation. (Macmillan, 2013) Fig 1 - Cannula Placement sites (Macmillan, 2013)

The mechanism driving the pump is a lead screw, rotated either by a stepper motor or by apermanent-magnet motor with a gearbox, in a Permanent Magnet motor a coil of wire (calledthe armature) is arranged in the magnetic field of a permanent magnet in such a way that itrotates when a current is passed through it. The T34 uses a permanent-magnet motor, whichcan deliver the same torque as a stepper motor but from a much smaller unit. Motor rotation ismonitored by an optical shaft encoder and a rotating magnet, a microprocessor uses data fromboth to confirm the motor speed. Lead Screw position is monitored by a slotted disc on the endof the lead screw together with an IR LED and photodiode, driving the pump actuator andsyringe plunger forward at a controlled rate. This rate is adjustable from 0.1 to 1000 ml/h inincrements of 0.1 ml/h up to 100 ml and 1 ml from 100 to 1000 ml/h. To keep battery sizedown the T34 does not use a strain gauge to measure occlusion force; instead, the motorcurrent is monitored by a linear amplifier. (McKinley, 2012) Fig 2 –T34 Syringe Driver (McKinley, 2012)T34s have 3 point syringe detection enabling the pump to identify all commonly used (orprogrammed) syringe brands & sizes. This feature ensures the pump can make volume & ratecalculations, minimising the risk of user programming errors. The sensors also activate analarm if the syringe is removed or partially displaced during infusion.

Fig 3 – An Exploded view of a T34 Syringe Driver (McKinley, 2012)The pump can be configured (and locked) to one of three modes of operation;Lock on - is delivering the contents of a syringe over a fixed duration (pump default 24 hours).The pump automatically calculates the ml/h rate based on the fixed duration (lock on) and theconfirmed deliver-able volume.Lock off - is delivering the contents of a syringe over the default duration or a duration inputtedby the user. The pump automatically calculates the ml/h rate based on the confirmed durationand the confirmed deliverable volume.Rate mode - is delivering the contents of a syringe by ml/h as inputted by the user. The pumpcalculates the duration from the entered ml/h rate and the syringe volume detected by thepump.The T34 can be configured to deliver a KVO infusion to commence at END PROGRAM, withKVO enabled T34 applies the KVO rate set until the syringe is empty. (McKinley, 2012)Maintenance & Service ProceduresA visual inspection is carried out; the driver is then placed in the docking station and onceconnected to the Bodycomm software the events log can be checked for any significant errors.The test configuration is then uploaded to the pump.The syringe diameter calibration test is performed, the keypad, display, acoustic alarm, batteryvoltage, syringe sensor, diameter and travel tests are performed. Syringe recognition is testedfollowed by occlusion alarm limits and volume delivered.All of these measurements can be made using inbuilt test routines accessed via the TechnicianMode menu.Following the technician menu checks the ‘pump unattended’ alarm and ‘syringe displaced’alarms are checked. Near End and End Programme alerts are also checked.After servicing he pump must be placed into the docking station and have the relevantconfiguration uploaded dependant on the location. The pump settings are printed out andchecked against the relevant config. Each pump must be clearly labelled with the location.

BibliographyMacmillan, 2013. Cancer Information. [Online]Available at:http://www.macmillan.org.uk/Cancerinformation/Livingwithandaftercancer/Symptomssideeffects/Pain/Syringedrivers.aspx[Accessed April 2014].McKinley, 2012. McKinley T34 Guidelines. [Online]Available at: http://www.nht.nhs.uk/mediaFiles/downloads/82339879/MMG005-%20Guidelines%20for%20Use%20of%20McKinley%20T34%20(Apr12-Apr14).pdf[Accessed April 2014].McKinley, 2012. T34 Service Manual. [Online]Available at: http://ems-l1/documents/model/servicemanuals/6567.pdf[Accessed April 2014].McKinley, 2012. T34 User Manual. [Online]Available at: http://ems-l1/documents/model/usermanuals/T34%20User%20Manual.pdf[Accessed April 2014].

Syringe Pumps Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Syringe PumpsA syringe pump is a medical device, mains or battery operated, used to deliver feed to a neonate,nutrients or medications, such as insulin or other hormones, antibiotics, chemotherapy drugs,and pain relievers into a patient’s body in a controlled manner. Administering the drug orallymay not be possible, particularly if the patient has trouble swallowing. Using a syringe pumpthe drug can be administered intravenously, intra-arterially, or subcutaneously. The drug canbe delivered at a very low flow rate, over a long period of time, at a high rate, or very quickly butat a precise rate. Administering the drug manually would be difficult. All syringe pumps arecapable of delivering fatal doses of drug concentrations, or causing severe injury due toincorrect infusion procedures.To try to prevent this, the pumps used at ULHT have safety features incorporated; Self-testroutines check the pump when it is switched on, the mode of infusion, duration, volume, thesyringe type being used and (optionally) the drug being administered are displayed forconfirmation at each stage of an infusion. Levels of access to the pump can be configured fromvery restrictive - effectively a single type of infusion with the syringe under a locked cover - upto the most flexible, with clinicians able to choose from and combine a wide range of infusionmodes, drug types and delivery options. Users are warned of incidents like occlusions or powerfailure by both visible and audible alarms. In addition to standard occlusion sensing measuredagainst the syringe plunger, optional in-line pressure sensing is available for applications whereocclusion pressure needs to be monitored very precisely, for example in a Neonatal unit. This isused with a special extension set, which includes a pressure sensing disc, to monitor occlusionpressure in the infusion line while the pump is running. With either type of sensing, it ispossible to adjust the trigger pressure either to block out unwanted occlusion alarms orincrease sensitivity.The pump stores a historical database of its own operation as each event takes place; it recordsthe most recent events, logging them by date and time, this can be viewed either via the display,or in detail using the Syringe Pump Technician software package and a PC.Pumps are used in a variety of environments. They are designed mainly for stationary use at apatient’s bedside. Others, however, called ambulatory infusion pumps, are designed to beportable or wearable.Syringe pumps are designed to mechanically hold a syringe in place, whilst a piston drives thesyringe plunger at a pre-determined infusion rate. This infusion rate can either be entereddirectly or by keying in a volume and time limit, when these parameters are entered theinfusion rate is calculated by the pump. The pumps can be programmed to give a dose ofmedication which is expressed as a mass unit, rather than volume to be infused over a period oftime.The mechanism to drive the syringe plunger is commonly a stepper motor which causes a leadscrew to rotate. The lead screw drives the syringe plunger clamp to carry out the infusion. Amicrocomputer controls the speed of the motor and subsequently the distance travelled by thepusher in a given time. The pumps will also feature a bolus function. Bolus delivery is a fastdelivery of the drug into the patient to increase concentration in the blood stream, these can beperformed manually or a pre-determined volume can be set. Occlusions are detected either by apressure transducer monitoring the pressure exerted on the plunger, or by monitoring thecurrent needed to drive the plunger. A safety feature should an occlusion be detected is toreverse the motor this will reduce the pressure in the line preventing an inadvertent boluswhen the source of the occlusion is cleared. If any alarms are trigged the infusion will stop, andremain this way until restarted by clinical staff.Some pumps have a lockable cover; this may be useful in clinical areas where it is necessary toprevent the syringe from being removed easily and to prevent any change to the flow rate forthe infusion.

Graseby Omnifuse Fig 1 – Graseby Omnifuse (Graseby, 2005)Omnifuse syringe pumps have been designed to meet the growing needs of the clinicalenvironment.They are suitable for the administration of drugs or other parenteral fluids by or under thesupervision of healthcare professionals such as physicians and nurses. The pump offers aContinuous infusion mode as well as other modes for specialised infusions: Preset Volume,Preset Time, Intermittent and Circadian Rhythm (different rates over a period of time).The pump features an easily viewable LCD display which, together with an array of LEDs andsound signals, allows the pump’s operation to be monitored from anywhere within sight andhearing range. The pump is controlled via a soft-touch keypad and a rotary command wheel thatallows the user to select options from a succession of screen menus.The drug filled syringe is loaded into the syringe mechanism, which consists of a slot for thesyringe ear, a barrel clamp and a syringe plunger clamp which senses the syringe size andbrand. As the clamp rotates, a flag on its swivelling end interacts with an opto sensor to reportthe clamp's final resting point as one of seven positions corresponding to seven possible syringecapacities between 2 ml and 50/60 ml. If a syringe does not correspond to one of thesecapacities or has been incorrectly loaded an INVALID SYRINGE alarm is given. Syringe Barrel Clamp Fig 2 – Syringe clamp mechanism (Graseby, 2005)The pump asks for confirmation of the syringe size and brand, and which type of infusion is tobe performed (continuous or pre-set volume). The infusion rate is then requested and a valuebetween 0.1 - 200 ml/h (Adult config.) and 0.1 – 50 mm/h (Neonate config.) can be entered.The pump will also indicate when it is nearing end of delivery and will reduce the delivery rateto a minimal level (0.1ml/h) and indicate this by displaying KVO (Keep Vein Open). The syringesensors trigger an alarm if the barrel clamp is lifted during an infusion. (Graseby, 2005)

B.Braun Perfusor Space Syringe Pump Fig. 3 – B.Braun Perfusor Space Syringe Pump (B.Braun, 2011)The system is intended for use on adults, paediatrics, and neonates for the intermittent orcontinuous delivery of parenteral and enteral fluids. The system is used for the delivery ofmedications indicated for infusion therapy including drugs like anaesthetics, sedatives,analgesics, catecholamines, anticoagulants etc., blood and blood components, Total ParenteralNutrition (TPN), lipids, and enteral fluids.The Space system is a modular design, up to three pumps can be connected togethermechanically using ‘L rails’ on the bottom of the unit and grooves on the top. They can then befastened to a drip stand or appropriate rail using the pole clamp.The SpaceControl module can be used to extend operation. Up to four pumps can be installed inevery SpaceStation, up to six SpaceStations can be set-up as a column with a total of 24 pumps.Alarms are signalled by a row of LEDs and a loudspeaker in the SpaceCover Comfort. Fig 4 – Space station (B.Braun, 2011)The pump cover door is opened and the syringe inserted, the syringe size detection isperformed via the syringe holder. This is connected to a potentiometer and syringe size isdetermined from the resistance of this. The syringe is fixed with the syringe holder and theaxial fastening device. The syringe piston is fastened with two claws in the drive head. Afterconfirmation of the brand and size of the syringe the type of infusion is confirmed and theinfusion rate is set. An alarm signals the end of the infusion or the pump reaching a preselectedvolume to be infused (VTBI) or time, the pump can continue the infusion with a predefinedKVO-rate.At Lincoln County Hospital, this pump is mainly used in the ICU. (B.Braun, 2011)

Maintenance & Service ProceduresSyringe pumps have their batteries changed and are serviced every 2 years. A visual inspectionis carried out including the case, mains lead, syringe sensors, pole clamp and lockable cover iffitted.Using technician software and a PC, the pump is then tested to ensure the keypad and displayare functioning correctly, different size syringes are recognised, the load and unload sensors arefunctioning, the bolus operation is good, the volume being delivered is accurate, occlusionpressures are accurate and all the alarms are functioning.Following service the pump needs to be configured correctly for the area of use, and shouldhave its flow rate and volume set to minimum. An electrical safety test should be performedto the relevant class.BibliographyB.Braun, 2011. Perfusor Space Syringe Pump Service Manual. [Online]Available at: http://ems-l1/documents/model/servicemanuals/6774_3.pdf[Accessed March 2014].Graseby, 2005. Omnifuse Service Manual. [Online]Available at: http://ems-l1/documents/model/servicemanuals/Graseby%20Omnifuse%20Service%20Manual.pdf[Accessed Febuary 2014].

Multi-Parameter Monitoring Steven Lewis Clinical Engineering United Lincolnshire Hospital Trust

Multi-parameter MonitorsMulti-parameter Monitors are intended to be used for monitoring, displaying, reviewing, storingand the transferring of multiple physiological parameters including, ECG, heart rate (HR),respiration (Resp), temperature (Temp), SPO2 (pulse oxygen saturation), pulse rate (PR), non-invasive blood pressure (NIBP), invasive blood pressure (IBP), cardiac output (C.O.), airwaysgases such as; carbon dioxide (CO2), oxygen (O2), anaesthetic gas (AG).Monitoring vital signs for example; a patient’s blood pressure, pulse rate, and respiration rate isa crucial aspect of patient care in hospital. Vital signs indicate a patient’s clinical condition, arenecessary to calculate national early warning scores (NEWS) and used to determine themonitoring, escalation and interventions that are required subsequently.In a hospital setting, patient monitoring is used in operating theatres, intensive care and criticalcare units, and many other critical and non-critical areas.Continuous multi-parameter monitoring has shown to be an effective mechanism for triggeringearly detection of changes in a patient’s condition by notifying the nursing staff that the patientneeds attention. This is beneficial as by assessing the situation sooner and making the rightclinical decision to intervene as appropriate.In addition to monitoring patients on an individual basis, the remote observation of multiplepatients is possible through central patient monitoring systems. These monitoring systems aretypically made up of networked machines consisting of one or more sensors, display devices,processing components, and communication links for displaying or recording the resultselsewhere through the network. For portable monitors or in areas where a hard wired networkis not practical wireless monitors are used, the signal is sent from the telemetry unit and pickedup by aerial’s located around the hospital. This is particularly useful for areas such as Accident &Emergency and Coronary Care Unit or where multiple areas need to monitor the same patient atthe same time or while a patient is being transported from one area to another.In non-critical areas the signs being monitored will predominantly be Heart Rate, SPO2, BloodPressure and ECG. In a critical care area such as ICU or an operating theatre, further signs willbe monitored these may include; Invasive Blood Pressure (IBP), Respiration Rate and airwaysgases such as CO2, O2, and other gases that may be respired such as anaesthetic gases during asurgical procedure.Respiration RateThe function of the respiratory system is to supply adequate oxygen to the tissues and toremove the waste product carbon dioxide. This is achieved with the inspiration and expirationof air. With each breath there is a pause after expiration. The rate of respiration will vary withage and gender. A respiratory rate of 12-18 breaths per minute in a healthy adult is considerednormal. Rates outside of this normal range can be classed as;  Tachypnoea: the rate is regular but over 20 breaths per minute.  Bradypnoea: the rate is regular but less than 12 breaths per minute.  Apnoea: there is an absence of respiration for several seconds - this can lead to respiratory arrest.  Dyspnoea: difficulty in breathing, the patient gasps for air.  Cheyne-Stokes respiration: the breathing gets increasingly deeper then shallower, very slow and laboured with periods of apnoea. This type of breathing is often seen in the dying patient.

 Hyperventilation: patients may breathe rapidly due to a physical or psychological cause, for example if they are in pain or panicking. Hyperventilation reduces the carbon dioxide levels in the blood, causing tingling and numbness in the hands; this may cause further distress. In adults, more than 20 breaths a minute is considered moderate, more than 30 breaths is severe. (Mallett & Dougherty, 2004)Multi-parameter monitors have a function to measure the respiration rate of the patient. This isthe number of breaths the patient takes per minute. Most multi-parameter monitors record thisby monitoring the resistance between two ECG electrodes connected to the patient. As thepatient breaths in and the chest expands the resistance between the two electrodes increasesand then decreases as the patient exhales and the chest contracts. Others ways to monitorrespiration could be using capnography which involves CO2 measurements, referred to as EtCO2or end-tidal carbon dioxide concentration. The respiratory rate monitored as such is calledAWRR or airway respiratory rate. Other monitors may record spirometry flow volume loops,which will show the flow, volume and time taken to inhale and exhale, or it may be monitoredby simply counting the number of breaths in one minute by recording how many times the chestrises.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.Capnography is particularly important during surgery, where patients are continuouslymonitored while under anaesthesia to ensure safety. In addition to its use in surgical settings,capnography can help physicians and emergency medical personnel determine whether apatient is having a heart attack or hyperventilating. It can also help them determine whetherCPR is working.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.

Mainstream capnometers are in-line with the patient tubing; the housing is heated to preventcondensation. The advantage of mainstream analysis is that it gives a real-time measurement(i.e., an immediate response rate of <100 milliseconds). However, there are disadvantages tomainstream capnometry, such as the excessive dead space in the patient breathing circuitproduced by the sensing chamber can lead to false readings and the weight of the device cancause kinking of the tube. ETCO2 Sensor Equipment SidePatient Side Y- Piece Airway Adapter Fig 1 – Mainstream Method (Fukuda Denshi UK, 2014)Side-stream capnometers withdraw a continuous sample of gas through a capillary tube whichis placed between the endotracheal tube and breathing circuit, because of this the displayedlevel of CO2 takes 2-3 seconds to catch up as the CO2 has to travel down the sampling tube first.A water trap should be utilised to remove particles of water in the breath sample beforemeasurement takes place. Fig 2 – Side-Stream Method (Fukuda Denshi UK, 2014)Invasive Blood Pressure (IBP)Invasive (intra-arterial) blood pressure (IBP) monitoring is a commonly used technique in theIntensive Care Unit (ICU) and is also often used in the operating theatre, it may also be usefulwhere NIBP measurement is difficult e.g. burns or obesity.This technique involves direct measurement of arterial pressure by inserting a cannula needlein a suitable artery (usually radial, femoral, dorsalis pedis or brachial). The cannula must beconnected to a sterile, fluid-filled system, which is connected to an electronic patient monitor.The advantage of this system is that a patient’s blood pressure is constantly monitored beat-by-beat, and a waveform (a graph of pressure against time) can be displayed.