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Category: EMS Operations

Topic: Flight Physics

Level: Critical Care

Next Unit: Physiologic Effects of Flight

16 minute read

Anatomic Effects of Flight

The psychological and physiological stressors of flight have many effects on both patients and providers. This section will review the primary mental and physical stressors common to flight and provide essential strategies for working around and through them.


Environmental Stressors

The decreased partial pressure of oxygen, barometric pressure changes, temperature changes, vibration, and noise are just a few stressors from a flight in an aircraft. The effect is more prevalent with rotor-wing aircraft than fixed-wing aircraft. From before takeoff to after the landing, our bodies are subjected to more stress than we realize. Yes, you feel that turbulence as you ascend above a ridge or across a waterway. Still, it's the stressors that we don't give much thought to that, added together, can make a significant impact not just on your body but on your cognitive abilities and critical thinking.

The following are Primary Stressors of Flight:

  • Thermal changes constantly occur in flight medicine. Freezing temperatures and significant heat can tax the body and increase the oxygen demand. For every 100 meters (330ft) increase in altitude, there is a 1 degree Celsius decrease in temperature.
  • Vibrations place additional stress on the body, which can cause an increase in body temperature and fatigue.
  • Decreased humidity is present as you pull away from the earth's surface. The higher the altitude, the less humidity in the air, which, over time, can cause cracking of mucous membranes, chapped lips, and dehydration. This stressor can be compounded in patients receiving oxygen therapy or positive pressure ventilation.
  • Noise from the aircraft, the equipment, and the patient can be significant. The average noise level of a helicopter is around 105 decibels but can be louder depending on the aircraft type. Sound levels over 140 decibels can lead to immediate hearing loss. Sustained noise levels over 120 decibels will also lead to hearing loss.
  • Fatigue worsens via a lack of restful sleep, aircraft vibrations, poor diet, and long flights: 1 hour or more in a rotor-wing aircraft or 3 or more hours in a fixed-wing aircraft.
  • Gravitational Forces, both negative and positive, cause stress on the body. This stress is only a minor annoyance for most. However, acute conditions worsen in critically ill patients with reduced cardiac function and increased intracranial pressure with the gravitational effects of takeoff and landings and sudden changes in flight such as loss of altitude due to turbulence or sudden banking turns.
  • Flicker Vertigo. The Flight Safety Foundation defines flicker vertigo as "an imbalance in brain cell activity caused by exposure to low-frequency flickering or flashing of a relatively bright light." This is most commonly the result of sunlight and turning rotor-blades on a helicopter and can affect all on the aircraft. Symptoms can range from seizures to nausea and headaches. People who have a history of seizures should be especially vigilant if working rotor-wing.
  • Fuel vapors can cause nausea, dizziness, and headaches with significant exposure. Be mindful of your location on the tarmac or helipad during aircraft refueling.
  • Weather primarily causes flight planning issues but can also lead to health issues. Rain, snow, and lightning can cause hazards while on the scene or preparing for a flight. The extremes in temperature and waterlogging of clothing can also contribute to stress.
  • The anxiety of the call, the flight time while caring for a sick patient, and even the flight itself can cause undue stress.
  • Night flying is more dangerous because of limited visibility even with the aid of night-vision goggles (NVGs). This demands consistent situational awareness, which can add to fatigue and stress, especially in unfamiliar terrain.


Personal and Psychological Stressors

Human Factors Affect Tolerance of Flight Stressors

The mnemonic IM SAFE is commonly used to remember the adverse effect of flight on patients and providers.

  • Illness has to do with your well-being. Going to work sick will significantly add stress to your shift in the air and compromise the quality of care you provide and the team's safety. A physician must clear you to return to fly.
  • Medication can cause certain undesired side effects. Knowing how your prescribed medication will interact with in-flight situations is essential and can make a significant difference when combating in-flight stressors.
  • Stressful life events such as a recent relationship break-up or a family member in the hospital can and will directly increase your stress at work. Taking care of yourself is essential before caring for others in such a high-stress career. If your head is not in the right place, the right place for you is not in the air
  • Alcohol can be a retreat for some as they encounter stress on the job. It is a temporary fix for a long-term problem. The post-intoxication effects of alcohol may still decrease performance and lead to safety concerns even if you are not clinically intoxicated. It also affects your body's ability to fight off infection and illness. 
  • Fatigue results from back-to-back shifts and exposure to the aforementioned flight-related stressors. Know your limits and never demand more than you know you can handle.
  • Emotion is something everyone handles differently. We all have emotions, and all express them differently depending on the circumstances. Knowing how to respond emotionally can either escalate an already stressful situation or put one at ease from anger to grief. Keeping your emotions in check on a flight is not only important but expected. You are a professional and should carry yourself in that manner, putting your crew and your patient above your feelings.

Space and Resources

Unlike a ground ambulance, the typical helicopter emergency medical service unit has very little room once all crew members are on board and the patient is loaded correctly. This in itself can bring about anxiety in an already stressful situation. Understanding the spatial limits of the aircraft is important. Most services can carry some of the most advanced equipment available in the prehospital setting, such as point of care lab machines, a transport ventilator, and ultrasound. Some can even transport extracorporeal membrane oxygenation (ECMO) patients! These items are fantastic assets, but utilizing them and monitoring them can add stress to the whole equation.