Effects of isoenergetic glucose-based or lipid-based parenteral nutrition on glucose metabolism, de novo lipogenesis, and respiratory gas exchanges in critically ill patients

Abstract

Objective 

To compare the effects of isocaloric, isonitrogenous carbohydrate nutrition vs. lipid-based total parenteral nutrition on respiratory gas exchange and intermediary metabolism in critically ill patients.

Design 

Prospective, clinical trial.

Setting 

Surgical intensive care unit in a major university hospital in Switzerland.

Patients 

Sixteen patients admitted to the surgical intensive care unit.

Interventions 

Patients were randomized to receive isocaloric isonitrogenous total parenteral nutrition (TPN) containing 75% (TPN-glucose) or 15% (TPN-lipid) glucose over a 5-day period.

Measurements and Main Results 

Indirect glucose metabolism was assessed from plasma carbon-13 (¹³) C)-labeled glucose and¹³ C-labeled CO₂ production during a tracer infusion of uniformly¹³ C-labeled glucose, and de novo lipogenesis was estimated from the incorporation of¹³ C into palmitate-very low density lipoproteins (VLDL) during a tracer infusion of 1-(¹³) C acetate.

Compared with TPN-lipid, TPN-glucose increased plasma glucose more (by 26% vs. 7%, p < .05), increased insulin more (by 284% vs. 40%, p < .01), and increased total CO₂ more (by 15% vs. 0%, p < .01). Both nutrient mixtures failed to inhibit endogenous glucose production and net protein oxidation, suggesting absence of suppression of gluconeogenesis. Fractional de novo lipogenesis was markedly increased by TPN-glucose to 17.4% vs. 3.3% with TPN lipids.

Conclusions 

The rate of glucose administration commonly used during TPN of critically ill patients does not suppress endogenous glucose production or net protein loss, but markedly stimulates de novo lipogenesis and CO₂ production. Increasing the proportion of fat may be beneficial, provided that lipid emulsion has no adverse effects. (Crit Care Med 1998; 26:860-867)