Variability of intrinsic positive end-expiratory pressure in patients receiving mechanical ventilation

Since variations in breathing pattern may affect the level of intrinsic positive end-expiratory pressure (PEEP), breath-to-breath variation of intrinsic PEEP was assessed.

Descriptive and prospective study.

Medical intensive care unit of a university teaching hospital.

Thirty-four patients requiring mechanical ventilation for a period of time due to respiratory failure.

Intrinsic PEEP was determined using simultaneous recordings of the esophageal pressure and airflow. The breath-to-breath intrinsic PEEP, respiratory rate, tidal volume, inspiratory time, and fractional inspiratory time were measured. Intrinsic PEEP was noted in 33 of 34 patients. For all patients, the mean intrinsic PEEP was 3.59 cm H2O. The group mean standard deviation (SD) of the intrinsic PEEP over 35 breaths was 2.68 cm H2O. In 17 chronic obstructive pulmonary disease patients, the mean intrinsic PEEP was 4.69 cm H2O and the group mean SD of the intrinsic PEEP was 3.19 cm H2O. In the subgroup of patients with significant intrinsic PEEP, the mean intrinsic PEEP was 6.69 cm H2O and the group mean SD was 4.29 cm H2O. The group mean coefficient of variation of intrinsic PEEP for all 34 patients was 123%. Among the 15 patients with clinically significant intrinsic PEEP, the coefficient of variation was smaller (74%). We did not find significant correlation between the coefficients of variation of breathing pattern parameters and the coefficients of variation of intrinsic PEEP.

We conclude that the occurrence rate of intrinsic PEEP in mechanically ventilated patients is high. The degree of variability in intrinsic PEEP on a breath-to-breath basis is also high. It may be difficult to find a specific level of intrinsic PEEP. Addition of external positive end-expiratory pressure without considering the breath-to-breath variability may lead to overdistention of the lung.