Heterogeneity in ventilation during positive end-expiratory pressure

Excerpt

We read with interest the commentary 'Can heterogeneity in ventilation be good' [1] and the related article by Zhao and colleagues [2]. We agree with the comments that instead of incremental positive end-expiratory pressure (PEEP) levels, a decremented PEEP titration might be an attractive option for determining optimal PEEP [1, 3]. However, we feel that physiological inhomogeneity in ventilation and perfusion related to the gravitational effect in normal lungs occurs during spontaneous breathing, and during spontaneous breathing a negative alveolar pressure develops during inspiration and facilitates pulmonary blood flow. Contrary to when applying PEEP, the positive pressure remains throughout respiration and paradoxically affects the pulmonary flow. We feel that it would be wiser not to compare the physiological inhomogeneity in ventilation with PEEP-related inhomogenous ventilation. PEEP is a slow recruitment technique for aerating collapsed alveoli, which can happen in a non-uniform fashion. Hence, anticipating any good effect of inhomogeneity of ventilation during PEEP may give a false impression to physicians regarding mechanically ventilated patients in the ICU. …