The European respiratory journal : official journal of the European Society for Clinical Respiratory Physiology
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The aim of the study was to assess the impact of the intrinsic positive end-expiratory pressure (PEEPi) on pulmonary gas exchange in mechanically-ventilated patients, by comparing the effects of similar levels (0.8-0.9 kPa) of positive end-expiratory pressure (PEEP) and PEEPi. Ten patients with acute respiratory failure, without chronic airway disease, were studied with three ventilatory modes: 1) intermittent positive pressure ventilation with zero end-expiratory pressure (ZEEP mode); 2) continuous positive pressure ventilation with PEEP set by the ventilator (PEEP mode); and 3) intrinsic PEEP elicited by adequate shortening of the expiratory time (PEEPi mode). ⋯ However, the improvement of PaO2 was more consistent (8 out of 10 patients), and larger (+2.1 kPa, on average, p < 0.05) with PEEP than with PEEPi (5 out of 10 patients, and +1.4 kPa, on average, NS). Since the effects of PEEP and PEEPi on ventilation, lung volume, compliance, cardiac output (QT), mixed venous oxygen tension (PvO2) and oxygen consumption (VO2) were similar, we attributed the less favourable impact of PEEPi on PaO2 to a less homogeneous distribution of PEEPi between lung units with different time constant, and hence to a more uneven distribution of the inspired gas.