INTRINSIC PEEP DETERMINED BY STATIC PRESSURE-VOLUME CURVES - APPLICATION OF A NOVEL AUTOMATED OCCLUSION METHOD

Objective: Evaluation of new computer-controlled occlusion procedure f or determination of intrinsic PEEP in mechanically ventilated patients and comparison with the standard end-expiratory occlusion method. Des ign: Prospective controlled study. Setting: Intensive care unit of a u niversity hospital. Patients: 16 patients with acute respiratory failu re of different degree and etiology. All patients were mechanically ve ntilated, heavily sedated and muscle paralyzed (non-depolarising relax ants). The type of ventilator, the inspiration/expiration ratio, FIO2 and PEEP were selected by the attending clinicians according to the pa tients' need and independently from the study. Interventions: Static c ompliance of the respiratory system (C(stat)) was determined at varyin g external end-expiratory pressure settings: ZEEP (= ambient pressure) , PEEP of 5 cmH2O and 10 cmH2O. All other ventilator settings were kep t constant during the entire procedure. Measurements and results: A co mputer-controlled occlusion method (SCASS) was used for determination of C(stat). Intrinsic PEEP was determined by SCASS as the extrapolated zero-volume intercept of the regression line of multiple pressure/vol ume data pairs (PEEP(SCASSinspir) and PEEP(SCASSexpir)). Directly ther eafter intrinsic PEEP in this particular ventilatory setting was deter mined by end-expiratory occlusions (PEPP(EEO)). The intrinsic PEEP val ues of the different methods were nearly identical with a significant correlation (p<0.0001). Mean values+/-SD: PEEP(SCASSinspir) 7.1+/-4.3 cmH2O; PEEP(SCASSexpir) 7.1+/-4.5 cmH2O; PEEP(EEO) 7.1+/-4.2 cmH2O. Co nclusion: Since no significant difference between PEEP(i) values measu red by the inspiratory and expiratory occlusion method (SCASS) was see n, this indicates that no alveolar recruitment occurred during the res piratory cycle. This study demonstrates that the automated occlusion m ethod for measuring C(stat) system can also be used with high accuracy for determination of intrinsic PEEP in mechanically ventilated patien ts.