Objective: To evaluate a new and simple method for the measurement of intrinsic positive end-expiratory pressure during controlled and assisted modes of mechanical ventilation.
Design: Prospective study.
Setting: Three university hospital medical ICUs.
Patients: A total of 13 intubated, mechanically ventilated patients with severe airway obstruction.
Interventions: Airway occlusions reproducibly timed to occur coincidently with end-expiration were obtained by: a) manipulation of a three-way manual valve placed in the inspiratory limb of the external ventilator circuit (manual valve method) and b) activation of the expiratory pause hold function of the mechanical ventilator (Siemens 900C).
Measurements and main results: Airway pressure, flow, and volume were recorded during controlled and assisted modes of mechanical ventilation. Intrinsic positive end-expiratory pressure was determined from the plateau in airway pressure, which was developed during end-expiratory occlusions. For controlled mechanical ventilation, intrinsic positive end-expiratory pressure averaged 11.42 +/- 0.77 (SEM) cm H2O with the manual valve method, compared with 11.38 +/- 0.70 cm H2O, using the ventilator expiratory pause hold function. There was close correlation between results over the wide range of intrinsic positive end-expiratory pressure observed, which varied from approximately 5 to 22 cm H2O (y = 1.08x - 0.92; r2 = .99). Values of intrinsic positive end-expiratory pressure were comparable for the two methods during assist-control ventilation, pressure support ventilation, and spontaneous breathing through the ventilator circuit. The manual valve method was also effective when tested with different mechanical ventilators using a mechanical lung model.
Conclusions: The manual valve method can be used to determine intrinsic positive end-expiratory pressure during controlled and assisted modes of ventilatory support with current ventilators. The availability of such an approach should facilitate the routine monitoring of intrinsic positive end-expiratory pressure in mechanically ventilated patients, thereby aiding clinical decision-making and management in these critically ill individuals.