Abstract
It has been suggested that malnourished patients respond to glucose intake in excess of energy needs by a rise in respiratory quotient (RQ) above 1.0, indicating net fat synthesis. This would represent inefficient utilization of glucose as an energy source. It is unclear, however, whether this also occurs when some of the energy source is provided as a fat emulsion.
Energy expenditure was measured by indirect calorimetry using a canopy hood and RQ, calculated from the analysis of 2 X 5 minute collections of expired air, were measured every 3rd day in two groups of surgical patients who received a 14-day course of intravenous nutrition [total parenteral nutrition (TPN)]. Group I (mean ± 1 S.D. 57.4 ± 15.4 yers, 9 females, 3 males) received glucose as the only source (46.6 ± 9.2 kilocalories per kilogram per day and group II (55.8 ± 14.2 years, 5 males, 3 females) 60% of their calories as fat (44.0 ± 7.5 kilocalories per kilogram per day). Both groups were given similar amounts of crystalline amino acid solution (0.34 ± 0.007, 0.32 ± 0.005 gram nitrogen per kilogram per day, respectively) and no other intake. There was no significant difference between the groups mean values of body weight (52.3 ± 7.9 versus 57.9 ± 12.5 kilograms) or energy expenditure before TPN commenced (31.3 ± 6.5, 32.3 ± 3.0 kilocalories per square meter per hour). In group I there was a persistent elevation (p < 0.001) of mean RQ above 1.0 from the 9th day of TPN, together with a significant increase (p < 0.001) in mean energy expenditure which attained the value of 38.0 ± 4.8 kilocalories per square meter per hour on the 14th day. In group II, the mean RQ never exceeded 1.0. The rise in the mean expenditure in group II was significantly less ( p < 0.02) than that observed in group I.
This study shows that the use of glucose as the only energy source during TPN is associated with a greater rise in energy expenditure than is observed with a glucose-fat regime and a persistent elevation of RQ above 1, indicating net lipogenesis. These results suggest, therefore, that complete oxidation of glucose occurs when it is the only source of nonprotein calories given during TPN.
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