Hypercapnic acidosis induced by nutrition in mechanically ventilated patients: glucose versus fat.

Total parenteral nutrition (TPN) increases CO2 production (VCO2) in patients on intermittent positive-pressure ventilation who cannot match their CO2 excretion to the CO2 load, leading to an increase in PaCO2. We studied gas exchange and blood gas values in six patients with chronic respiratory failure, who were ventilated at low (6 +/- .7 L/min) and high (10 +/- 2 L/min) minute ventilation during three randomized nutritional regimens: control (255 kcal/day), glucose TPN (2550 kcal/day), and lipid TPN (3000 kcal/day). At the two levels of ventilation, TPN compared to control increased VCO2 and PaCO2 (p less than .01) and decreased pH (p less than .001). At low minute ventilation, the increase in VCO2 and the hypercapnic acidosis were less with lipid than with glucose TPN (p less than .05 and p less than .01, respectively). These results indicate that the risk of TPN-induced CO2 retention is lower if minute ventilation is increased before beginning TPN. Conversely, in patients with compromised ventilatory function, this risk could be higher during intermittent mandatory ventilation or weaning from the ventilator.