MEA Altitude Physiology and Stressors of Flight

Commercial Medical Escort Altitude Physiology and Stressors of FlightPurpose/GoalsThe purpose of this course is to assist the registered nurse and paramedic in understanding the effectsthat atmospheric pressure has on the human body.ObjectivesAfter completing this course, the healthcare professional will be able to:  Identify problems associated with changes in atmospheric pressure.  Describe the effects that the cabin environment has on the human body.  Discuss the difference between Boyle's Law and Dalton's Law and the effects each one has on the human body at altitude.Introduction Fundamental principles of flight physiology include the effects of flight stressors, atmospheric pressure changes, and aircraft motion on the human body. Understanding these principles will serve to expand the critical thinking ability of the clinician and assist him/her in anticipating the potential problems that high altitude transport may bring. Cabin air pressure changes greatly during 15-30 minutes after take-off and before landing; gas expansion and contraction can cause pain and pressure effects. In-flight medical emergencies are increasing due to the steadily rising number of air travelers, the aging of the US and European populations, and the increasing mobility of people with acute and chronic illnesses. There are NO universal guidelines for managing in-flight medical emergencies, but there are unique considerations.Topics that will be reviewed are:  Epidemiology  Stressors of Flight  Cabin Environment1 Medical Escort Association ©Copyright 2015

EpidemiologyThere are an estimated two billion travelers per year (United States and overseas):  In-flight medical emergencies occur at a rate of 20 to 100 per million passengers.  A death rate of 0.1 to 1 per million.Most in-flight medical events are not serious and handled adequately by airline crew members. Themost common medical complaints include:  Gastrointestinal  Traumatic  Cardiac  Neurological  RespiratoryCardiac, neurologic and respiratory complaints comprise the more serious emergencies, as defined byaircraft diversion or use of ground-based medical assistance. Among these, cardiac emergencies aremost common and account for the largest number of deaths.  A medical professional is present for 40-70% of in-flight medical emergencies  A doctor is present in 30-60%These numbers may be higher; fear of liability prevents some healthcare professionals fromintervening.Stressors of FlightThe primary stressors of flying in an aircraft can be somewhat mitigated by adjustments within theaircraft during flight, but these stressors become more exacerbated the longer the flight. Awarenessof them will assist flight personnel in paying attention to their own needs, as well as the patient's needs.Flight stressors include, but are not limited to the following:  Decreased PO2 levels with greater altitude  Pressure changes  Temperature changes  Vibration  Decreased humidity  Noise  Fatigue  Weather changes  Vertigo / spatial disorientation  Exposure to fuel vapors2 Medical Escort Association ©Copyright 2015

Aggravating FactorsProlonged flights can expose the patient to low humidity causing or exacerbatingdehydration. Attention should be paid to oral intake and urine output when appropriate. Additionally,respiratory secretions may become thick, resulting in less efficient gas exchange and contributing tohypoxia. The intake of large amounts of caffeine or alcohol can also cause dehydration and increasethe risk of blood clots. Alcohol and smoking also inhibit the body's ability to utilize and transportoxygen.Hypoglycemia from a poor diet (too high in carbohydrates or too low in protein) or failing to eat anddrink fluids regularly can exacerbate feeling of nausea and motion sickness, as well as interfere withconcentration.Other factors such as emotions, extreme life stressors, or obesity can decrease the effective functionof transport personnel.Cabin EnvironmentIn-flight medical emergencies may occur because the unique physiological stresses of air travel,including those caused by the conditions of the aircraft cabin.Although an aircraft cabin is pressurized, that pressure (barometric pressure) is less than that on theground. For most flights, the cabin pressure is the same as that at 5,000 – 8,000 feet above sea level.In other words, when you are flying on a commercial airline, the atmosphere within the aircraft is thesame as if you were standing on the peak of a small mountain that is approximately 5,000 to 8,000feet high. This has two effects:  There is less oxygen available because the pressure of oxygen becomes lower.  Gas within our body cavities expands.The pressure inside a commercial aircraft cabin will not exceed 8,000 feet above sea level orapproximately 2,500 meters. Barometric pressure will decline from 760mmHg at sea level to a minimumof about 550mgHg at maximum cabin altitude.In a normal individual, this would cause arterial oxygen saturation to fall from 98% to88%.Additional concerns in flight include:  Vibration  Turbulence  Noise  Barometric pressure changes3 Medical Escort Association ©Copyright 2015

Reduced OxygenCommercial aircraft is pressurized during flight because passengers could not survive the lowatmospheric pressure at the usual cruising altitude, which is commonly maintained at 30,000 to 40,000feet.  United States Federal Aviation Administration (FAA) specifies that an 8000-foot environment be maintained even at the highest operating altitude.At 8000 feet, the barometric pressure drops from a normal sea level value of 760mmHg toapproximately 560mmHg. As a result:  PaO2 in a normal individual drops from a baseline of around 95mmHg at sea level to a PaO2 of 50-60mmHg in a pressured cabin of 8000 feet.In a study, the oxygen saturation of healthy passengers were measured and showed a decline from99% O2 saturation before take-off to 94% O2 saturation during flight.Passengers may respond to this relatively hypoxic environment by increasing their:  Heart rate  Cardiac output  Respiratory rate and valueIn individuals with cardiopulmonary disease (example: COPD), compensation can be sufficient.Physics of the AtmosphereOne of the primary problems of flight related to physiology has to do with the fact that the pressure ofgases in the atmosphere change as we ascend and descend. It is essential that we have anunderstanding of the gases found in the atmosphere and their effects upon the body. Other factors,such as temperature change, also need to be understood so we can protect our patients from thesepotential hazards.Air PressureFlight nurses should be familiar with gas laws that can affect the safety of the patient. These gas lawsdescribe how altitude and pressure changes affect their characteristics. Some of these gas laws overlapone another in their descriptions, but there are two laws that are particularly important to the flightnurse.Physical Gas LawsPrior to working and caring for patients on a commercial airline, it is important to understand thephysical gas laws: Boyle's and Dalton.Boyle’s Law describes the effect that pressure has on a dry gas. It states that at a fixed temperature,the volume and pressure of a gas are inversely proportionate (760mmHg). However, if pressure of a4 Medical Escort Association ©Copyright 2015

gas decreases, then the volume (space between molecules) will increase and if the volume (spacebetween molecules) decreases, the pressure of the gas inside that space will increase.In flight terms, as the aircraft ascends, increasing in altitude, the barometric pressure diminishes. Anygas within an enclosed space will expand. Alternatively, as the aircraft descends and barometricpressure increases, the gas will contract.Example: A balloon inflated at least sea-levelAt 18,000 feet, this balloon will be approximately twice its sea-level volume, and at 25,000 feet, itwould be approximately three times its original volume. Landing at sea level would return the balloonto its original volume.Sea Level 5,000-8,000 Feet 18,000 Feet 25,000 FeetClinically, it is prudent for the medical escort to realize that any piece of equipment or body cavitycontaining gas will be subject to the effects of that gas’ expansion with ascent and contraction upondescent.Boyle’s Law (P x V = P1x V1) explains how a set amount of air trapped in a container or viscous willexpand to occupy more space at a lower barometric pressure.A medical emergency can ensue if the expanding gas is constrained within a confined space such asthe pleural cavity, the middle ear, sinuses, a medical device, or another body cavity after surgery.  Colostomy Bag: At 8000 feet, the Barometric Pressure ↓ to 540mmHg causing air (gas) trapped in a colostomy bag to expand. REMEMBER: If pressure of a gas decreases (760 to 540mmHg), the volume (space between molecules) will increase causing the colostomy bag to become grossly enlarged. Because of the drop in atmospheric pressure at altitudes greater than 30005 Medical Escort Association ©Copyright 2015

feet above sea level, any air trapped within a fixed space will attempt to expand and create increased pressure within that fixed space.STOP: Remember to take your patient to the restroom before boarding a plane andempty the patient’s colostomy bag.  Pneumothorax can be caused by the expansion of trapped gas in the lungs, especially in individuals with COPD, cystic fibrosis, or recent thoracic surgery. Patients should be able to fly one week after a CXR confirming resolution, or after two weeks in the case of a traumatic pneumothorax.  Abdominal distention, pain, and nausea can be caused by pressure that has been built up in the hollow organs of the GI tract.  Expanding intestinal gas may cause dehiscence of surgical wounds, hemorrhage, or bowel perforation while in flight in individuals with recent abdominal surgery complicated by ileus or those with small or large bowel obstruction.  Urinary catheters should be filled with 0.9% NS or sterile water before boarding a plane. Most catheters used in the United States utilize 0.9% NS. The bulb of the urinary catheter will enlarge if filled with air instead of water due to the decreased barometric pressure.  Tracheostomy tube can be affected due to the air-filled cuff. Instilling water instead of air can avert this problem. Enlarged air-filled cuff can compromise the patient’s airway when the barometric pressure decreases.  Feeding tube must be capped off during ascent and descent to prevent introducing air into a hollow viscous.STOP: If your patient has a urinary catheter, remember to check it before leaving to go tothe airport.Dalton’s Law states, “The total pressure of a gas mixture is the sum of the individual pressures orpartial pressure of all the gases in the mixture.”In flight terms, oxygen is “thinner” in the upper atmosphere.Why is this? At sea level, the barometric pressure is 760mmHg, and the atmosphere is composed of20.95% oxygen. As altitude increases, the barometric pressure decreases, and the molecules in theatmosphere move farther apart. While oxygen still comprises 20.95% of the atmosphere, there areless oxygen particles per cubic millimeter to be utilized.Clinically, an increase in altitude diminishes the oxygen available to the body and can result inhypoxia. For instance, at 12,000 feet the barometric pressure decreases to 483mmHg. Thecomposition of the atmosphere remains the same, and so the percentage of oxygen remains at20.95%. However, the partial pressure of oxygen will decrease to 101.19mmHg.6 Medical Escort Association ©Copyright 2015

 At sea level: PO2= 20.95% x 760mmHg = 159.22mmHg  At 12,000 feet: PO2= 20.95% x 483mmHg = 101.19mmHgWith less oxygen available to breathe, hypoxia can result. One study of air medical evaluation showeda decrease in PaO2 of 20% in those patients flow at low altitude (3,000-3,800 feet) and a decrease of32-35% in those patients flow at high altitude (6,000 - 7,500 feet).Air QualityCommercial airliners use pressurized cabins and supply the air by pumping in outside air, either by aseparate pumping mechanism or bleeding the air off the compressor section of the jet engines poweringthe aircraft. As a result, the supplied air inside commercial airliners is extremely clean and dry. For example, an aircraft flying at 37,000 feet would provide air to a cabin that has a relative humidity of only 1-2%, but is biologically virtually sterile. The temperature constraints inside most commercial cabins during flight are in the 65-75F range and air quality content is regulated so that an entire turnover of the air inside the cabin occurs every 3-5 minutes. Some of this air may be recycled, but if recycling occurs, it is passed through high efficiency particulate air filters (HEPA), which remove any biological content added by the occupants of the cabin. In aircraft where smoking is prohibited (this includes all U.S. commercial flights), environmental tobacco smoke is not a significant consideration and the only source for biological contaminants will include exhaled products of occupants, such as viruses and bacteria, or clothing contaminants, such as fungi and dander, particularly cat and dog dander.Cabin air is very dry, usually between 10-20% humidity; optimal humidity ranges from 40-70%.  Low humidity can dry the skin, corneas, and airway passages, triggering respiratory problems, especially in patients with asthma or COPD.  Insensible water loss in the desiccated cabin environment, combined with diminished fluid intake during a long flight, can cause dehydration.  Thick mucus in patients with a tracheostomy tube can be contributed to dehydration during a long flight.STOP: Encourage your patient to drink water at least every 2 hours during a lengthy flightwhile awake to prevent dehydration.7 Medical Escort Association ©Copyright 2015