Gastric versus duodenal feeding and gastric tonometric measurements

Objective: To compare the influence of gastric and postpyloric enteral feed ing on the gastric tonometric PCO2 gap (tonometric PCO2 - PaCO2). Design: A prospective, clinical trial. Setting: Two intensive care units in a university hospital. Patients: Twenty patients undergoing mechanical ventilation and enteral fee ding without catecholamines, sepsis, or sign of hypoxia. Interventions: Patients were randomized to receive feeding through the tono meter (gastric group), or through a postpyloric tube (postpyloric group). Measurements and Main Results: The patients received tube feeding at a rate of 50 mL/hr during 4 hrs. Baseline measurements included: mean arterial pr essure, heart rate, tonometric parameters. arterial gases, and arterial lac tate concentration. Except for lactate concentration, these measurements we re repeated after 1 and 4 hrs of enteral feeding and 2 hrs after stopping e nteral feeding. During the study, arterial pH and Pace, did not change. Dur ing enteral feeding, the PCO2 gap increased in the gastric group from a mea n of 7 +/- 5 to 17 +/- 14 (SD) torr (0.9 +/- 0.7 to 2.3 +/- 1.9 kPa) (p < . 01) and did not change in the postpyloric group (5 +/- 5 to 3 +/- 1 torr [0 .7 +/- 0.7 to 0.4 +/- 0.1 kPa]). Two hours after stopping enteral feeding, the PCO2 gap was still increased in the gastric group (15 +/- 9 vs. 7 +/- 5 torr [2.0 +/- 1.2 vs. 0.9 +/- 0.7 kPa]) (p < .01). Conclusion: The results indicate that gastric enteral feeding increased the PCO2 gap. However, postpyloric enteral feeding does not interact with gast ric tonometric measurements and should be used when using gastric tonometry in enterally fed patients.