Boyle's law acts to increase the pressure of air-filled endotracheal cuffs as an air transport vehicle ascends. Most airplanes are pressurized to 8000 feet and helicopters can reach a similar altitude during transit. The authors cited 30 cm of H2O as a pressure where tracheal mucosal perfusion is reduced and 50 cm of H2O where perfusion is obstructed. This experimental study seeks to define the relationship between altitude and pressure of an air-filled endotracheal cuff.
Size 6.0 and 7.5 endotracheal cuffs were inflated to a standard pressure and connected to a calibrated manometer. This closed system was then transported to 7900 feet, recording pressure every 1000 feet. A comparison group used endotracheal tubes filled with water, and another group confined them in plastic tubes, simulating the constricted environment of a trachea.
A linear relationship existed between altitude and pressure in the cuff. As compared to unrestricted cuffs, the cuffs enclosed in a tube showed a steeper rate of pressure increase with altitude. In a 6.5-sized endotracheal tube, the critical value of 50 cm H2O was exceeded at 1300 feet when located within a plastic tube and at 2000 feet when not confined. Though low transport altitudes and cabin pressurization to lower altitude is possible, the authors suggest using water-filled endotracheal tubes to avoid complications.
(Ped Emerg Care. 2011;27:1–4) RM Miyashiro, LG Yamamoto.
Prepared by Anil Menon, MD, UTMB/NASA Aerospace Medicine Fellow, Galveston, TX, USA