Ventilatory and metabolic effects of glucose infusions

It has been demonstrated that total parenteral nutrition (TPN) results in increased O₂ consumption (V̇O₂), CO₂ production (V̇CO₂) and minute ventilation (V̇E). 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 4 normal volunteer subjects and 4 acutely ill patients for a 6-day period, with 3 days on each dietary intake. After each 3-day period, gas exchange, V̇O₂, V̇CO₂, and ventilatory variables (V̇E), 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% (p>.05) and 7% (p>.05) in the normal subjects and the patients, respectively. V̇O₂ did not change, while the RQ rose. V̇E rose in parallel with V̇CO₂, 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 V̇O₂, which acts to magnify the effect of an increased RQ on V̇CO₂, and b) by increasing ventilatory sensitivity to CO₂.