Influence of prone position on gastric mucosal-arterial PCO₂ gradients

Abstract.

Objective: To evaluate the effects of mechanical ventilation in the prone position on gastric mucosal-arterial PCO₂ gradients. Design: Prospective clinical study. Setting: Intensive care unit in a university clinic. Patients: Twenty-five patients requiring mechanical ventilation. The physician in charge indicated the turning manoeuver for the individual patient. Measurements/results: In addition to routine measurements of global hemodynamics and gas exchange we determined: 1) intragastric pressure; and 2) gastric mucosal-arterial PCO₂ difference. After a baseline measurement in the supine position patients were turned to the prone position. After 60', 120', a median of 6.5 h (2–10 h) in the prone position, and again after 60' in the supine position, all measurements were repeated. Global hemodynamics remained unaltered throughout the study. While gastric mucosal-arterial PCO₂ gradients did not change significantly during the first 60 min in the prone position, they significantly increased during the following 60 min [median/percentile: baseline: 6 (1 to –3); 60': 7 (15–5); 120': 13 (20–8) mmHg]. The median intragastric pressure was not significantly affected [baseline: 10 (13–5); 60': 12 (16–8); 120': 11 (13–7) mmHg], but 9 of the 11 patients in whom intragastric pressure increased during the first 60 min in the prone position also showed significantly increased PCO₂ gradients (P<0.01). Conclusion: Mechanical ventilation in the prone position may be affiliated with increased tonometric gastric mucosal-arterial PCO₂ gradients depending on the effect on intraabdominal pressure. Measuring intraabdominal pressure and/or gastric mucosal PCO₂ via a nasogastric tube therefore may help to detect adverse effects of this ventilatory strategy.