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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