Effects of positive end-expiratory pressure on lung ventilation/ perfusion matching: a clinical study

Abstract

Introduction Positive end-expiratory pressure (PEEP) exerts multiple protective effects in hypoxemic critically ill patients: PEEP can increase end-expiratory lung volume (EELV) and induce recruitment, thus reducing lung strain and opening and closing of alveoli and potentially improving the ventilation/perfusion matching. In particular, estimation of PEEP-induced ventilation/perfusion matching might help identify the optimal PEEP setting, but bedside non-invasive methods are few and complex to be applied in daily clinical practice. Electrical impedance tomography (EIT) is a non-invasive bedside technique that claims to track global and regional changes in perfusion and ventilation over time. In the present study we aimed at verifying the effects of PEEP on ventilation/perfusion matching, as assessed by EIT, in acute respiratory failure patients. Methods We enrolled 20 intubated critically ill patients undergoing controlled mechanical ventilation, sedated, paralyzed and with PaO2 /FiO2 5 cmH2O. We started EIT monitoring (Pulmovista500; Drager Medical GmbH, Lubeck, Germany) and applied two PEEP levels (clinical and clinical + 5 cmH2O) for 20 minutes each. We collected ventilatory and EIT parameters and, by offline analysis, we calculated the increase of EELV at higher PEEP and the EITbased indexes of ventilation heterogeneity (VtHetend-insp) and of the regional homogeneity of ventilation/perfusion matching (HA/P). Results Patients were 62 +/- 12 years old, mean PaO2 /FiO2 was 197 +/- 52, lower PEEP level was 7 (7 to 9) cmH2O, while higher PEEP was 12 (12 to 14) cmH2O (P O (P O (P O (P O (P 16%) had higher baseline VtHetend-insp (2.6 (2.3 to 4.8) vs. 1.9 (1.5 to 2.1), P 16%) had higher baseline VtHetend-insp (2.6 (2.3 to 4.8) vs. 1.9 (1.5 to 2.1), P 2O vs. 18 +/- 6 ml/cmH2O, P <0.05), as compared with patients with smaller improvement. Conclusion EIT might represent a feasible, bedside method to estimate PEEP-induced improvement in ventilation/perfusion matching. Assessing regional ventilation and mechanical lung properties might help identify patients who would benefit more from higher PEEP.