The Laryngeal Mask Airway at Altitude

Laryngeal Cuff Force Application Modeling During Air Medical Evacuation Simulation

Endotracheal tubes are intended to protect the airway and assist with mechanical ventilation in sedated patients. The blood vessels of the tracheal mucosa can be compressed by high tracheal tube cuff pressures (> 30 cm H2O), leading to reduced mucosal blood flow with resulting ischemia and morbidity. Previous research showed a direct correlation between aircraft pressure altitude and the pressure reading from the tracheal cuff, with resulting pressures > 80 cm H2O at 10,000 ft. Standard practice is to periodically remove air from the cuff during ascent based on assumed increased pressure on the adjacent tracheal mucosa. Using a vacuum chamber and a direct reading micropressure sensor in a 22-mm-diameter semirigid tube, we assessed the direct force applied by the tracheal cuff against the laryngeal tube analog. Standard tracheal cuffs showed direct force/pressure relationships when properly inflated to 20 cm H2O but much less than reported in the literature. Current literature reports values of 55 to 150 cm H2O at 5,000 ft, whereas we report 23 to 25 cm H2O. Our data indicate that a properly inflated cuff does not exceed the critical pressure of 30 cm H2O until the altitude exceeds 8,000 ft. Thus, the standard practice of deflating the laryngeal cuff on ascent should be reconsidered because it may be counterproductive to patient safety.

Managing endotracheal tube cuff pressure at altitude: a comparison of four methods

BACKGROUND

Ascent to altitude results in the expansion of gases in closed spaces. The management of overinflation of the endotracheal tube (ETT) cuff at altitude is critical to prevent mucosal injury.

METHODS

We continuously measured ETT cuff pressures during a Critical Care Air Transport Team training flight to 8,000-ft cabin pressure using four methods of cuff pressure management. ETTs were placed in a tracheal model, and mechanical ventilation was performed. In the control ETT, the cuff was inflated to 20 mm Hg to 22 mm Hg and not manipulated. The manual method used a pressure manometer to adjust pressure at cruising altitude and after landing. A PressureEasy device was connected to the pilot balloon of the third tube and set to a pressure of 20 mm Hg to 22 mm Hg. The final method filled the balloon with 10 mL of saline. Both size 8.0-mm and 7.5-mm ETT were studied during three flights.

RESULTS

In the control tube, pressure exceeded 70 mm Hg at cruising altitude. Manual management corrected for pressure at altitude but resulted in low cuff pressures upon landing (<10 mm Hg). The PressureEasy reduced the pressure change to a maximum of 36 mm Hg, but on landing, cuff pressures were less than 15 mm Hg. Saline inflation ameliorated cuff pressure changes at altitude, but initial pressures were 40 mm Hg.

CONCLUSION

None of the three methods using air inflation managed to maintain cuff pressures below those associated with tracheal damage at altitude or above pressures associated with secretion aspiration during descent. Saline inflation minimizes altitude-related alteration in cuff pressure but creates excessive pressures at sea level. New techniques need to be developed.

Endotracheal tube cuff pressures in pediatric patients intubated before aeromedical transport

OBJECTIVES

Prolonged endotracheal tube cuff pressures (ETTCPs) greater than 30 cm H2O can cause complications. With increasing utilization of cuffed endotracheal tubes (ETTs) in pediatric patients comes the risk of overinflation. We evaluated the incidence of elevated ETTCP in pediatric patients intubated with cuffed ETTs, transported by a critical-care transport service and attempted to identify whether elevated ETTCP was associated with factors such as patient demographics, diagnostic category, and intubator credentials.

METHODS

In this prospective study, assessment of ETTCP was made upon transport crew arrival at the bedside. The study focused on a consecutive sample of pediatric patients undergoing transport with cuffed ETTs placed before transport team arrival. All patients had cuff pressures assessed by the same cuff manometry device. Pressures found to be greater than 30 cm H2O were corrected immediately.

RESULTS

Forty-one percent of cases met the a priori defined cutoff for elevated ETTCP of 30 cm H2O; 30% of those elevated cuff pressures were twice that cutoff (>60 cm H2O). There were no associations between high ETTCP and any of the following independent variables: demographics, physician versus nonphysician intubator, and intubation location (ie, scene vs emergency department vs intensive care unit).

CONCLUSIONS

A significant number of pediatric patients transported by a critical-care transport service had elevated ETTCP. Furthermore, there was no clear risk factor for elevated cuff pressures. This is further evidence that cuff pressures should be measured in all patients. Further research should focus on the effect of educational intervention and on the possible clinical results of elevated ETTCPs.