Ventilatory and metabolic effects of glucose infusions

It has been demonstrated that total parenteral nutrition (TPN) results in increased O2 consumption (VO2), CO2 production (VCO2) and minute ventilation (VE). TPN consists of a mixture of glucose and amino acids. The individual role of each of these nutrients in mediating these changes has not been well established. To examine the effects of the individual nutrients, continuous infusions of glucose in hypo- and hypercaloric amounts were given to four normal volunteer subjects and four acutely ill patients for a six-day period, with three days on each dietary intake. After each three-day period, gas exchange, VO2, VCO2, and ventilatory variables (VE), tidal volume (VT), frequency (f), mean inspiratory flow (VT/TI), inspiratory time (TI) and expiratory time (TE) were measured. With the high carbohydrate diet, CO2 production increased 18 percent (p greater than .05) and 7 percent (p greater than .05) in the normal subjects and the patients, respectively. VO2 did not change, while the RQ rose. VE rose in parallel with VCO2, with no significant change in ventilatory sensitivity to CO2. In light of previous observations, these results suggest that during administration of TPN, the protein component plays a major role in the observed ventilatory changes: a) by bringing about a rise in VO2, which acts to magnify the effect of an increased RQ on VCO2, and b) by increasing ventilatory sensitivity to CO2.