Gastric mucosal pH and blood flow during weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease

To determine if gastric intramucosal pH changes during weaning from mechanical ventilation are related to gastric mucosal blood flow modifications, we studied 16 ventilator-supported patients with chronic obstructive pulmonary disease (COPD) who tolerated a 2-h trial of spontaneous breathing with pressure support ventilation and were successfully extubated and 11 patients with COPD who failed such a trial. Gastric mucosal perfusion was assessed using gastric intramucosal pH (pH) by tonometry and laser-Doppler flowmetry. During the weaning attempt, the failure weaning group developed a rapid, shallow breathing pattern with acute respiratory acidosis. The pH(i) was lower and gastric intramucosal Pco(2), (Pco(2)im) was higher in the failure weaning group than in the successful weaning group (p < 0.05). No change in gastric intramucosal-arterial Pco(2) difference was observed and a linear correlation was found between arterial Pco(2) and Pco(2)im (r(2) = 0.70; p < 0.001). Cardiac index increased in the failure group (p < 0.05) and remained stable in the success group whereas gastric mucosal blood flow decreased in the failure group (H-120 min-22 +/- 11% from baseline; p < 0.05) and increased in the success group (H-120 min: 85 +/- 27% from baseline; p < 0.05). We conclude that gastric intramucosal pH changes during a 2-h weaning trial are mainly due to arterial Pco(2), variations. Nevertheless, gastric mucosal blood flow changes do occur and differ according to the weaning success or failure.