The thermodilution technique for measuring resting energy expenditure does not agree with indirect calorimetry for...

The complications associated with overfeeding critically ill patients are well documented. Indirect calorimetry is touted as the gold standard for measuring resting energy expenditure (REE). Unfortunately, the device is expensive, and many centers do not have this technology. The thermodilution technique for measuring cardiac output and calculating REE using the Fick equation has been reported to be an acceptable alternative. This study compared these techniques in a critically ill population.

Forty consecutive patients with indwelling Swan-Ganz catheters in the surgical intensive care unit were prospectively studied while under the consultative care of the nutrition support service. REE was determined in all patients by both techniques within a 2-hour period. An error of 5% (approximately+/-100 kcal/d) between the two methods was deemed acceptable for clinical use.

Mean values for REE were 1928+/-558 vs 1898+/-518 kcal/d for the indirect calorimetry and thermodilution methods, respectively, and were not significantly different. However, there was great variation between the two techniques for the majority of patients such that REE determinations did not agree (t = 6.8; p < .0005). In 70% of the patients, REE determinations differed by > or =20% and in 10% of the patients by 50%. Additionally, the greater the difference between the two methods, the more the thermodilution method tended to overestimate REE.

When compared with indirect calorimetry in a critically ill population, the thermodilution method demonstrated an intersubject variability that is unacceptable for clinical use.