Intrinsic PEEP determined by static pressure-volume curves : application of a novel automated occlusion method

Evaluation of new computer-controlled occlusion procedure for determination of intrinsic PEEP in mechanically ventilated patients and comparison with the standard end-expiratory occlusion method. Prospective controlled study. Intensive care unit of a university hospital. 16 patients with acute respiratory failure of different degree and etiology. All patients were mechanically ventilated, heavily sedated and muscle paralyzed (non-depolarising relaxants). The type of ventilator, the inspiration/expiration ratio, FIO2 and PEEP were selected by the attending clinicians according to the patients' need and independently from the study. Static compliance of the respiratory system (Cstat) was determined at varying external end-expiratory pressure settings: ZEEP (= ambient pressure), PEEP of 5 cmH2O and 10 cmH2O. All other ventilator settings were kept constant during the entire procedure. A computer-controlled occlusion method (SCASS) was used for determination of Cstat. Intrinsic PEEP was determined by SCASS as the extrapolated zero-volume intercept of the regression line of multiple pressure/volume data pairs (PEEPSCASSinspir and PEEPSCASSexpir). Directly thereafter intrinsic PEEP in this particular ventilatory setting was determined by end-expiratory occlusions (PEPPEEO). The intrinsic PEEP values of the different methods were nearly identical with a significant correlation (p < 0.0001). Mean values +/- SD: PEEPSCASSinspir 7.1 +/- 4.3 cmH2O; PEEPSCASSexpir 7.1 +/- 4.5 cmH2O; PEEPEEO 7.1 +/- 4.2 cmH2O. Since no significant difference between PEEPi values measured by the inspiratory and expiratory occlusion method (SCASS) was seen, this indicates that no alveolar recruitment occurred during the respiratory cycle. This study demonstrates that the automated occlusion method for measuring Cstat system can also be used with high accuracy for determination of intrinsic PEEP in mechanically ventilated patients.