Erratum

Abstract

In acute lung injury (ALI), controlled mechanical ventilation with decelerating inspiratory flow (V dec ) has been suggested to improve oxygenation when compared with constant flow (V con ) by improving the distribution of ventilation and perfusion (V A /Q ). We performed the present study to test this hypothesis in an animal model of ALI. Furthermore, the effects of combined decelerating and constant flow (V deco ) were evaluated. Thus, 18 pigs with experimental ALI were randomized to receive mechanical ventilation with either V con , V dec or a fixed combination of both flow wave forms (V deco ) at the same tidal volume and positive end-expiratory pressure level for 6 h. Hemodynamics, gas exchange, and V A /Q distribution were determined. The results revealed an improvement of oxygenation resulting from a decrease of pulmonary shunt within each group (P Ͻ 0.05). However, blood flow to lung areas with a normal V A /Q distribution increased only during ventilation with V con (P Ͻ 0.05). Accordingly, Pao 2 was higher with V con than with V dec and V deco (P Ͻ 0.05). We conclude that contrary to the hypothesis, V con provides a more favorable V A /Q distribution, and hence better oxygenation, when compared with V dec and V deco in this model of ALI.(Anesth Analg 2004;98:211-9) I n acute lung injury (ALI), the efficiency of mechanical ventilation to provide adequate pulmonary gas exchange depends mainly on the homogeneity of alveolar ventilation distribution in lung areas with different alveolar opening pressures, thereby determining the ratio of ventilation and perfusion (V A /Q ). According to a mathematical lung model, decelerating inspiratory flow (V dec ) has been suggested to provide a more uniform distribution of inspired gas when compared with constant inspiratory flow (V con ) (1). These assumptions were confirmed by Abraham and Yoshihara (2) in a clinical study comparing volume-controlled mechanical ventilation (VCV) with V con and pressure-controlled mechanical ventilation (PCV) with V dec at equal tidal volumes (Vt) in patients with ALI. The authors demonstrated that changing from V con to V dec may be associated with increased oxygenation. In contrast, other clinical trials revealed a more homogeneous gas distribution but failed to prove an increase of oxygenation from V dec in ALI (3-8). However, previous studies evaluated hemodynamics and conventional gas exchange but did not determine changes of V A /Q distribution. Furthermore, most of them revealed short-term effects of 30 -60 min of experimental intervention (3,5-8). Thus, the potential benefits of PCV with V dec in ALI are still under debate (9). In particular, prolonged effects of different flow patterns on V A /Q distribution in ALI remain unclear.This study was performed to compare V A /Q distribution in experimental ALI in relation to V con during VCV, V dec during PCV and a fixed combination of both flow patterns (V deco ) provided by volume-assured pressure support (VAPS), a dual mode where pressure-controlled inspiration with V dec may be ...