Influence of septic shock on energy expenditure in critically ill ICU patients, estimated with indirect calorimetry

Introduction

Energy requirements of critically ill septic shock patients treated in the ICU are particularly difficult to determine. Recent research shows that energy expenditure (EE) in those patients may be smaller than it was previously believed. EE values in this group are affected by the severity of the disease process as well as by administered treatment (sedation, inactivity of skeletal and respiratory muscles, fighting fever). The purpose of this study was to establish the influence of septic shock on EE in sedated and mechanically ventilated patients treated in the ICU. Using indirect calorimetry, we assessed EE in those patients and compared results with basal energy expenditure calculated according to the Harris-Benedict equation (BEE), and with EE values in patients subjected to general anesthesia.

Methods

Two groups of patients were studied with regard to EE measured by means of indirect calorimetry. Group I consisted of 50 critically ill patients treated in the ICU for septic shock. They were evaluated using the APACHE II and SOFA scores, taking into account the 28-day mortality. EE was measured continuously over the first 24 hours of treatment by means of the Datex-Ohmeda M-COVX indirect calorimeter. Group II comprised 50 patients (ASA I and II), whose energy expenditure was measured under general anesthesia in surgical treatment of disc herniation. Energy expenditure measurements were taken with the use of the Datex-Ohmeda E-CAiOVX indirect calorimeter, adapted to work in an atmosphere containing anesthetic gases.

Results

The mean EE value measured with a calorimeter (CEE) in septic shock patients (CEE group I) was 1,467 ± 304 kcal/day or 20 ± 4 kcal/kg/day. Their mean APACHE II score was 30.2, SOFA was 10.8. CEE in group I amounted to 67 to 137% of BEE (mean 101% of BEE) and to 121% of average CEE in anesthetized patients (CEE group II). Statistical dependence between mortality and CEE was demonstrated. CEE in surviving patients (APACHE: 26.8, SOFA: 8.1) amounted to 91 to 137% of BEE (mean 114% of BEE) and to 139% of average CEE in group II. CEE in deceased patients (APACHE: 32.9, SOFA: 13) amounted to 67 to 121% of BEE (mean 94% of BEE) and to 111% of average CEE in group II.

Conclusions

A decrease in the total metabolic rate of patients with severe sepsis and septic shock can constitute a prognostic indicator of heightened death risk in this group of ICU-treated patients.