EMS should be aware of the risks involved and carefully observe for symptoms of ear barotrauma, especially in susceptible patients, as some presentations may mimic other severe pathologies. However, patients critical enough to require air travel are often not alert and able to follow commands nor able to avoid the additional risk factors of high altitude transport for ear barotrauma, including upper respiratory infection or otitis media. In emergent EMS travel, conscious or alert patients may receive instruction on middle ear pressure equalization techniques. Flyers should also avoid air travel when they have signs or symptoms or an upper respiratory tract infection. In commercial flying, ways to prevent barotrauma include the Valsalva maneuver, chewing mints or gum, or swallowing to equalize the inner ear pressure with the outer ear. įlying is the most cited cause of ear barotrauma. This risk increases in patients with underlying eustachian tube dysfunction, either via structural disease or inflammatory process. When gas expansion builds up in the middle ear via decreased atmospheric pressure (as seen with altitude increases), or by direct compression from increased pressure externally compressing the TM (as in landing), barotrauma to the TM may result. These open during yawning or swallowing, or during Valsalva maneuvers (forcing positive pressure to open the eustachian tube by blowing against a closed nasopharynx). The Eustachian tube helps equilibrate the pressure in the middle ear with the external atmosphere via the levator and tensor veli palati muscles. Posterior to this is an ossicular structure that remains open. The anterior aspect is a mucosa-lined structure adjacent to the nasopharynx that is flat at rest. This anatomy further divides into two separate parts. The middle ear begins behind the tympanic membrane (TM) and communicates via the eustachian tube with the nasopharynx. The middle and inner ear are air-filled spaces that are essential for both hearing and spatial orientation. Such areas include the inner ear, lungs (specifically relative to pneumothoraces), and potentially any air-filled instruments like a balloon cuff on an endotracheal tube (ET). The increase in the volume occupied by gas at higher altitudes can have adverse effects on various body sites sensitive to changes in air volume and pressure. An understanding of flight physiology is essential, as even an increase of 1000 to 1500 feet above sea level can cause gas expansion leading to clinical significance in the critically ill. Additional physiological factors of high altitude transport, the details of which are beyond the scope of this discussion, include decreasing temperatures, dehydration, and gravitational forces.Ī typical helicopter pre-hospital transport reaches altitudes of 1000 to 3500 feet above ground level, while airplane transport typically transports at altitudes of 10000 to 40000 ft above sea level. In-flight hypoxia as altitude increases can have a marked clinical significance in the transport of the critically ill. One report demonstrated a decrease of 32 mm Hg, from 159 at sea level to 127 at the height of 6200 feet. Īnother physiological factor that changes with altitude is the decrease in the partial pressure of oxygen as height above sea level increases this leads to a reduction in FiO2 (fraction of inspired oxygen) at a higher altitude compared to sea level. Fortunately, acceptable cabin altitude levels, or the atmospheric height experienced inside a flight cabin, have been safely increased over time due to aircraft and technologic improvements. This setting is possible through in-cabin pressurization, thereby decreasing barotraumatic risks that would be in effect at higher altitudes. Federal regulations, such as those promulgated by the FAA, require cabin pressure to be below atmospheric pressure equal to the pressure at 8000 feet above sea level. These physiological factors affect both helicopter pre-hospital transport and aeromedical airplane transport. These changes are demonstrated by the fact that atmospheric pressure at 10000 feet is 10.1 pounds per square inch (psi) (68 kPa), compared to 14.7 psi (101 kPa) at ground level. Boyle’s law explains that “the volume of a gas is inversely proportional to the pressure to which it is subjected.” Based on this law, pressure decreases with increased altitude, thereby causing an increase in the volume of gas. An understanding of flight and altitude physiology is essential to prevent pre-hospital fight-induced barotrauma. Physiologic parameters at high altitudes vary from those at sea level.
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