VARIABILITY OF INTRINSIC POSITIVE END-EXPIRATORY PRESSURE IN PATIENTSRECEIVING MECHANICAL VENTILATION

Objective: 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. Design: Descriptive and pro spective study. Setting: Medical intensive care unit of a university t eaching hospital. Patients: Thirty-four patients requiring mechanical ventilation for a period of time due to respiratory failure. Measureme nts and Main Results: Intrinsic PEEP was determined using simultaneous recordings of the esophageal pressure and airflow. The breath-to-brea th intrinsic PEEP, respiratory rate, tidal volume, inspiratory time, a nd 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 (so) of the intrinsic PE EP over 35 breaths was 2.68 cm H2O. In 17 chronic obstructive pulmonar y disease patients, the mean intrinsic PEEP was 4.69 cm H2O and the gr oup mean SD of the intrinsic PEEP was 3.19 cm H2O.In the subgroup of p atients with significant intrinsic PEEP, the mean intrinsic PEEP was 6 .69 cm H2O and the group mean so was 4.29 cm H2O. The group mean coeff icient of variation of intrinsic PEEP for all 34 patients was 123%, Am ong the 15 patients with clinically significant intrinsic PEEP, the co efficient 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. Concl usions: We conclude that the occurrence rate of intrinsic PEEP in mech anically ventilated patients is high, The degree of variability in int rinsic PEEP on a breath-to-breath basis is also high. It may be diffic ult to find a specific level of intrinsic PEEP. Addition of external p ositive end-expiratory pressure without considering the breath-to-brea th variability may lead to overdistention of the lung.