Modular indirect calorimeter suitable for long-term measurements in multipatient intensive care units.

Abstract

The construction of an indirect calorimeter capable of long-term automated sequential monitoring of multiple patients in adult and pediatric ICUs. A prototype system utilizing modular engineering principles, including central respiratory mass spectrometer; validation by organic solvent combustion and nitrogen dilution methods, and Tissot spirometer. Surgical and pediatric ICUs in a tertiary care university hospital. When expired minute volume was measured over a range of 4 to 28 L in six intubated patients, expired minute volume measured by the prototype system demonstrated a correlation coefficient of .998 compared with simultaneous expired minute volume measured by a Tissot spirometer. Organic solvent combustion demonstrated a maximum error of 3.8% for oxygen consumption (VO2) and an average error of 1.73 +/- 1.25% (SEM). The maximum error for the respiratory quotient was 3.0%, with an average error of 1.75 +/- 1.07%. VO2 (predicted) vs. VO2 (measured) demonstrated a correlation coefficient of .997. Validation with the nitrogen dilution method over a range of FIO2 from 0.21 to 0.60 demonstrated a maximum error of 7.9%, with an average error of -1.72 +/- 1.1% (n = 51). Indirect calorimetry by means of a shared system for measurements in multiple patients in ICUs is feasible and cost effective utilizing modular principles and a centralized respiratory gas analyzer.