What Is the Effect of Enteral Nutrition with a Raised Fat or Carbohydrate Content on Gas Exchange and Metabolism of Critically ill Patients with Acute Respiratory Failure?
Authors: Höltermann W. , Lukasewitz P. , Krämer M. , van Wickern M. , Leuchter L. , Lennartz H. 
Published: June 2009

<i>Objective: </i>Qualitative and quantitative description of gas exchange and metabolism of critically ill patients with complete enteral feeding on two formula diets with a different percentage of fat and carbohydrates. In particular, the study investigated whether carbon dioxide formation can be reduced and the burden on pulmonary ventilation can be lightened by reducing the proportion of carbohydrate. <i>Design: </i>Prospective, randomized study. <i>Setting: </i>Intensive-care unit of a university hospital in which mainly adults with acute respiratory failure are treated. <i>Patients: </i>Sixteen patients with acute respiratory failure of various etiology who were mechanically, ventilated (FIO<sub>2 </sub>≧ 0.3 and PEEP ≧ 8 cm H<sub>2</sub>O). Eight of these patients had another acute disturbance of organ function. <i>Interventions: </i>Two groups of 8 patients received either high-carbohydrate (50% of the total calories were carbohydrates) or a high-fat (50% of the total calories were fat) feeding over a period of 7 days. The parameters investigated were oxygen uptake, carbon dioxide release, respiratory quotient, respiratory minute volume, and partial pressure of carbon dioxide in the arterial blood. The time curves of these parameters were analyzed and compared between the two groups. Moreover, the rate of urea production and protein metabolism were calculated. Clinical chemical parameters in the serum which were relevant to metabolism (concentration of glucose, lac-tate, triglycerides, total protein, urea, and creatinine) were also measured. The severity of the clinical picture was established by determining the APACHE II score and the sepsis score of ELEBUTE and STONER. <i>Results: </i>The results do not reveal an unequivocal reduction of carbon dioxide release when the proportion of carbohydrates in the enteral diet of critically ill patients is lowered. With the percentage of fat to carbohydrate used (50% versus 30%), there were also no significant changes in the respiratory minute volume and in the partial pressure of carbon dioxide in the arterial blood. The different characteristics of oxygen uptake (significantly higher values were found on the high-fat diet) and thus the respiratory quotient can be explained by a more favorable relationship between the amount of calories administered and the energy consumption as well as by factors specific to the disease. An effect on protein metabolism and metabolic parameters which can be detected by clinical chemical tests was not found. <i>Conclusion: </i>In homogeneously defined patient groups, the gas exchange of these patients might be expected to alter if the proportion of carbohydrate in the enteral nutrition is reduced in favor of fat. However, the present study in critically ill patients indicates that an increase in the percentage of fat from 30% to 50% of the total calories does not appear to be of substantial clinical significance.