Measured versus estimated oxygen consumption in ventilated patients with congenital heart disease: The validity of predictive equations

Abstract

To determine the validity of predictive equations in calculating oxygen consumption (Vo(2)) in ventilated patients with congenital heart disease. Prospective study. Cardiac catheterization laboratories and intensive care units of two university teaching hospitals. A total of 126 patients with congenital heart disease were studied. Of these, 75 patients received anesthesia in the pediatric cardiac catheterization laboratory, and 51 were deeply sedated in the intensive care unit after open heart surgery. Vo(2) was measured directly in all patients using respiratory mass spectrometry. Estimated values for absolute Vo(2) (mL/min) and indexed Vo(2) (mL.min-1.m-2) were calculated from the four predictive equations published by LaFarge and Miettinen, Lundell et al., Wessel et al., and Lindahl. The agreement between measured and estimated Vo(2) was evaluated by calculating their bias and limits of agreement. A failure of agreement between measured and estimated Vo(2) was noted in both groups of patients, irrespective the equation used, and the agreement was poorer in patients in the intensive care unit. The equation by LaFarge and Miettinen produced the closest estimation in patients at cardiac catheterization with a bias of 4.5 mL/min for absolute Vo(2) and 6.9 mL.min-1.m-2 for indexed Vo(2). A systematic error of overestimating lower and underestimating higher indexed Vo(2) mL.min-1.m-2 was introduced in both groups. Predictive equations do not accurately estimate Vo(2) in ventilated patients with congenital heart disease.