A Valve System for the Accurate Measurement of Energy Expenditure in Mechanically Ventilated Patients

Abstract

Current interest in nutritional support of patients with compromised respiratory function has led to increased use of indirect calorimetry. In patients receiving mechanical ventilation, the determination of energy expenditure by indirect calorimetry may be inaccurate if the inspired oxygen concentration (FIO2) is not measured correctly. Because the oxygen concentration delivered from both external and internal oxygen sources fluctuates, the calculation of oxygen consumption is subject to substantial error. We have devised a valve system that permits direct measurement of FIO2, minimizing the chance of this error and, in turn, providing a more reliable estimate of energy expenditure. The system is constructed of components available in most respiratory care and pulmonary function departments, and it is compatible with standard ventilator circuits and most metabolic measurement systems. (Respir Care 1985;30:969-973)