Indirect Calorimetry: Is it Required to Maximize Patient Outcome from Nutrition Therapy?

Abstract

Nutrition support regimens which fail to meet caloric requirements may adversely affect morbidity. This study evaluated the importance of accuracy of nutritional regimens and whether indirect calorimetry (IC) is required to optimize patient response. Patients admitted to a long-term acute care hospital, on mechanical ventilation, made nil per os NPO and placed on enteral nutrition (EN), were enrolled. At baseline and weekly for 3 weeks, two experienced critical care physicians estimated caloric needs, followed by IC. Patients were randomized to receive EN determined by physician estimates or by IC. Accuracy of physician estimates and adequacy of nutrition therapy were the primary study endpoints. Results showed that while estimates of caloric requirements appeared to be accurate, averaging 109.3 ± 26 % of actual requirements measured by IC for all subjects (n = 27), there was wide variation above and below the mean. Only 32 % of estimated values were within 10 % of measured requirements. Delivery of nutrition in both groups was suboptimal, with all patients receiving only 82.0 ± 15.4 % of goal requirements. There were no differences between groups regarding outcome (duration mechanical ventilation, healing of pressure sores). Physiologic consequences to hypocaloric feeding were seen nonetheless, with adequacy of feeding correlating significantly (p < 0.05) to mean respiratory quotient (RQ), albumin, and prealbumin. Increasing BMI was shown to correlate significantly with a reduction in accuracy of physician estimates (p < 0.001). BMI was found to be inversely correlated with prealbumin level and RQ. While caloric requirements of critically ill patients can be estimated by predictive equations, estimates decrease in accuracy as BMI increases. In this experience, use of IC failed to improve clinical outcomes. Delivery of the prescribed EN regimen continues to be a limiting factor.