Effects of tidal volume reduction in acute respiratory distress syndrome on gastric mucosal perfusion

Objective: This study was conducted with the aim of testing the effects of a reduction in tidal volume (V_T) on gastric mucosal perfusion using laser-Doppler flowmetry in patients with acute respiratory distress syndrome (ARDS). Design: It was designed as a prospective study. Patients: Seventeen patients with ARDS were enrolled in the study. All patients were mechanically ventilated in volume-controlled mode. Before the start of the protocol, V_T was set at 9 ml/kg body weight. Intervention: V_T was reduced to 6 ml/kg body weight. Measurements and results: Measurements of systemic hemodynamic parameters and gastric mucosal blood flow (GMBF) were obtained before and after reduction of V_T. Cardiac index, heaart rate and pulmonary arterial pressure increased significantly after V_T reduction. The increase in cardiac output was observed in all patients. However, despite a mean 25% increase in cardiac output after V_T reduction, no significant increase in mean GMBF was observed, and individual GMBF responses were heterogeneous. Conclusion: V_T reduction in patients with ARDS, despite resulting in an increase in cardiac output, did not change gastric mucosal perfusion. The heterogeneity in the individual response of GMBF to V_T reduction could be due to opposite direct (i.e., local vasodilatory effect) and indirect (i.e., global sympathetic stimulation) effects of hypercapnia on gut vessels.