Increased Lipid Fuel Dependence in the Critically 111 Septic Patient

Abstract

The effect of sepsis in modifying post-surgical fuel utilization in critically ill patients was determined from 374 observations (246 septic (S) and 128 nonseptic (N) in 12 intubated intensive care unit patients studied serially). Patients received total parenteral nutrition (values/24 h; S, N2, 9.1 .+-. 2.2 gm; glucose, 543 .+-. 211 kcal/m2; N, N2, 8.3 .+-. 3.6 gm; glucose, 550 .+-. 346 kcal/m2). In some periods, i.v. lipid (L) was given to raise total caloric intake to 826 .+-. 223 kcal/24 h/m2. The .ovrhdot.VO2 [O2 intake], .ovrhdot.VCO2 [CO2 production], respiratory rate, minute vol and blood gas levels were measured, and respiratory quotient (RQ) and metabolic rate (MR) computed. Statistics were performed by 2-way ANOVA and analysis of covariance. Without L, mean .ovrhdot.VCO2 for S (126 ml/min/m2) and N (128 ml/min/m2) were not significantly different; .ovrhdot.VO2 in S (146 ml/min/m2) and N (132 ml/min/m2) and the RQ values S (0.88) and N (0.97), were different (P < 0.0001). In 360 studies RQ was shown to be increased by the total caloric intake, but reduced in the presence of sepsis. Administered glucose and L calories contributed to the RQ in sepsis. Sepsis increased .ovrhdot.VO2 with little change in .ovrhdot.VCO2, thus RQ fell, suggesting increased use of L fuels for oxidation. During hypercaloric L infusion in septic patients (SL) .ovrhdot.VO2 and .ovrhdot.VCO2 increased but .ovrhdot.VO2 was still greater, so RQ remained low (SL RQ = 0.89). As sepsis worsened .ovrhdot.VO2 remained high but .ovrhdot.VCO2 fell producing RQ < 0.8; while plasma glucose levels were increased. Evidently, septic patients are more dependent than nonseptics on L fuels for oxidative metabolism; i.v. L can be used to increase oxidative metabolism in sepsis at a time when glucose metabolism appears reduced.