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FIGURE 11.10 Boyle law (P1 V1 = P2 V2 or P1 /P2 = V1 V2 ). As altitude increases, barometric
pressure decreases and volume of gas increases. The diagram illustrates enclosed gas expansion
at specific altitudes. “Atmospheres” is compared with the amount of pressure exerted by an
overlying 1-square-in air column. At sea level, this equals 14.7 lb/square in (psi) and one-half
that amount (7.35 psi) at 18,000 ft. (From Woodward GA, Vernon DD. Aviation physiology in
pediatric transport. In: Jaimovich DG, Vidyasagar D, eds. Pediatric and Neonatal Transport
Medicine . Philadelphia, PA: Hanley and Belfus, Inc; 1995:40, with permission.)

These issues can be important during the air medical transport. Entrapped air, if
not vented, can be painful (middle ear sinus, teeth, bowel), annoying (flatus,
belching), and dangerous (pneumothorax). Use of tight-fitting earplugs in flight
can cause an artificial air pocket that may trigger similar consequences. More
significant air space issues include simple pneumothorax and pneumocephalus,
which can become symptomatic at high altitudes. Patients with bowel
obstructions may have increased gas volume, potentially leading to vomiting,
aspiration, and even ischemia. Inflation volume in air splints may vary with
altitude, as will the air in blood pressure cuffs, fluid bags, and pressure bags. Air
in endotracheal tube cuffs and Foley catheters may also be affected and might
need to be adjusted during flight (slightly deflated at higher altitudes). Patients
with air embolisms from diving injuries or other causes are especially prone to