• P Kiefer, A Morin, C Putzke, H Wiedeck, M Georgieff, and P Radermacher.
• Universität Ulm, Universitätsklinik für Anästhesiologie, Donau, Germany. Peter.Kiefer@medizin.uni-ulm.de
• Intensive Care Med. 2001 Jul 1; 27 (7): 1227-30.

ObjectiveTo evaluate the effects of mechanical ventilation in the prone position on gastric mucosal-arterial PCO2 gradients.DesignProspective clinical study.SettingIntensive care unit in a university clinic.PatientsTwenty-five patients requiring mechanical ventilation. The physician in charge indicated the turning manoeuver for the individual patient.Measurements/ResultsIn 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).ConclusionMechanical 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.

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