Metabolic and respiratory effects of enteral nutrition in patients during mechanical ventilation

The effect of enteral feeding on O2-consumption (VO2) and CO2-production (VCO2) was studied in 9 ventilator-dependent patients, who were in a stable condition without signs of hypermetabolism. Resting energy expenditure (REE) in postabsorptive state was assessed and enteral feeding was started by continuous drip (480 kcal carbohydrate, 360 kcal vegetable fat and 160 kcal milkprotein: 6.4 g Nitrogen/1000 ml). Patients were given a moderate and a high caloric intake: 1.5 and 2.0 times REE. VO2 and VCO2 were measured for a 24 h period, beginning 7 h after the start of the dietary intake. Significant greater increases in VO2, VCO2 and RQ were found during high caloric intake compared with the moderate caloric intake. VO2, VCO2 and arterial blood-gases were measured in 4 patients during weaning from the ventilator. The increase in VCO2 induced by the high caloric feeding resulted in a rise in arterial CO2 tension (PaCO2) and respiratory distress. High caloric enteral nutrition can cause a significant increase in VCO2 inducing respiratory distress during weaning from the ventilator in patients with limited pulmonary reserves. Moderate caloric nutrition will be preferable to these patients in order to facilitate the weaning.