A physiologic basis for the provision of fuel mixtures in normal and stressed patients

It has been suggested that lipid is a preferred fuel in stressed patients. We evaluated glucose oxidation in 20 patients (sepsis, cancer of the colon, multiple trauma, controls) while they received TPN (5.65 mg glucose/kg/min). Respiratory quotient (RQ) was measured by indirect calorimetry and the percent VCO2 arising from the oxidation of glucose was measured using [U-14C] glucose. Since RQs were 1.0 or greater in all patients, the nonprotein energy utilized by them was calculated to be derived completely from glucose. However, the kinetic data showed that glucose contributed only 55-60% of the VCO2. Protein oxidation contributed less than 20% of the VCO2, as calculated from urinary nitrogen. The difference must have been derived from fatty acid oxidation. The glucose turnover that was not oxidized was presumed to be converted to lipid at an RQ of 8.6. The net oxygen consumption and carbon dioxide production from this overall distribution resulted in an RQ of about 1.0 with only 60% coming from glucose oxidation. Since all patients responded in the same manner, it appears that the proper ratio of glucose and lipid was dictated on a physiologic basis and not on the type of disease.