Subglottic positive end-expiratory pressure in extubated patients recovering from acute lung injury

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Abstract

Objective:

To examine the glottic function in extubated patients recovering from acute lung injury by simultaneous measurement of airway opening and subglottic airway pressures while patients are breathing at ambient pressure and receiving continuous positive airway pressure by a face mask.

Design:

Descriptive, prospective study.

Setting:

Intensive care unit at a university hospital.

Patients:

Ten patients who required continuous positive airway pressure of at least 7 cm H2O in order to restore gas exchange after mechanical ventilation for acute lung injury.

Interventions:

Spontaneous breathing at ambient airway pressure and with continuous positive airway pressures of 5 and 10 cm H20 via face mask.

Measurements and Main Results:

Intratracheal pressure, airway opening pressure, and airflow at the airway opening were measured. Breathing at ambient pressure resulted in significantly higher end-expiratory intratracheal pressure than end-expiratory airway opening pressure (p< .01). No significant differences between endexpiratory intratracheal pressure and end-expiratory airway opening pressure were observed during breathing with continuous positive airway pressures of 5 and 10 cm H2O. A significant end-expiratory airflow at the airway opening (p< .01), observed during ambient pressure breathing, was not detectable while the patient received mask continuous positive airway pressure. The partial pressure of oxygen in the arterial blood (Pao2) increased significantly while patients breathed with 10 cm H20, but not while patients breathed 5 cm HˆO continuous positive airway pressure compared with breathing at ambient pressure (p < .05).

Conclusions:

Our data imply that patients recovering from acute lung injury create an intratracheal positive end-expiratory pressure by braking the expiratory airflow, probably by glottic narrowing. Despite compensatory glottic narrowing, extubated patients with reduced lung function may benefit from higher levels of continuous positive airway pressure. (Crit Care Med 1994; 22:67-73)

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