The Ornge Comparison of Tracheal Occlusion Pressures to Ensure Safety (OCTOPUS) Trial

Introduction Air medical services routinely transport patients who are intubated and mechanically ventilated. Transporting this patient population is safe but patients subject to changes in barometric pressure in flight. Aircraft used typically maintain a cabin pressures of 3000 to 7000 feet above sea level. This compares to commercial aircraft that maintain cabin pressures of 5000 to 8000 feet. A known volume of gas will expand as the ambient pressure decreases. If the gas cannot expand, pressure exerted by the gas in an enclosed space will increase. An aircraft cabin with an ambient pressure of 3000 to 7000 feet altitude results in a 9 to 23% decrease in ambient pressure compared to sea level. Tracheal tube cuffs are subject to changes in ambient pressure that occur in transport. Tracheal tube cuffs minimize the risk of tracheal mucosal injury, but high pressures occur. A recent series of intubated adult patients undergoing transfer by helicopter showed that 58% had initial pressures greater than 40 cm H2O . A subsequent study revealed pressures exceeding 40 cm H2O in two thirds of patients and 30 cm H2O in nearly three quarters. There is a risk because tracheal mucosa blood flow is compromised at 30 cm H2O, and ceases at lateral wall pressures of 50 cm H2O. These high pressures can result in complications ranging from sore throat to major complications such as tracheal ischemia and fistula formation. To avoid tracheal injury and related complications, tracheal tube cuff pressures should be maintained at less than 30 cm H2O.

Sterile saline to inflate the cuff can decrease risk because it is not compressible or subject to atmospheric pressure changes as much as gases. Saline causes less cuff pressure increase and tracheal morbidity in the operating room, avoids excessive pressure due to changes in altitude, and is safe in transport. However, the ability of saline to prevent increases in cuff pressure in air medical transport and the safety profile of this use have not been studied.

Objectives Compare the tracheal tube cuff pressures, filled with either air or sterile saline, at altitudes routinely encountered when intubated and mechanically ventilated adult patients undergoing air medical transport.

Methods Study design Conduct a prospective, randomized, blinded study of tracheal tube cuff pressures, filled with either air or sterile saline, on pressurized fixed wing and unpressurized rotor wing aircraft to determine impact of cuff content (air versus saline) and altitude on cuff pressure in flight.

Study setting and population Ontario is a large Canadian province with a mix of urban, suburban, rural, and remote areas. Ornge Transport Medicine is the publicly funded air medical transport system providing all air medical patient transfers in Ontario. Ornge carries out approximately 19,000 patient transports annually, of which approximately 1,000 are intubated.