Indirect Calorimetry Overestimates Oxygen Consumption in Young Children: Caution is Advised Using Direct Fick Method as a Reference Method in Cardiac Output Comparison Studies

Abstract

Direct Fick method is considered a standard reference method for estimation of cardiac output. It relies on indirect calorimetry to measure oxygen consumption. This is important as only a minor measurement error in oxygen consumption can result in false estimation of cardiac output. A number of studies have shown that indirect calorimetry overestimates oxygen consumption in adults. The aim of this prospective single center observational method comparison study was to compare the determination of oxygen consumption by indirect calorimetry and reverse Fick method in pediatric patients. Forty-two children mean age 352 days (range 30 to 1303 days) and mean weight 7.1 kg (range 2.7-13.6 kg) undergoing corrective cardiac surgery were included in the study. The mean (standard deviation) oxygen consumption by reverse Fick method was 43.5 (16.2) ml/min and by indirect calorimetry 49.9 (18.8) ml/min (p < 0.001). Indirect calorimetry overestimated the reverse Fick oxygen consumption by 14.7%. Bias between methods was 6.5 (11.3) ml/min, limits of agreement (LOA) − 15.7 and 28.7 ml/min and percentage error of 47.7%. A significant bias and large percentage error indicates that the methods are not interchangeable. Indirect calorimetry and the direct Fick method should be used with caution as a reference method in cardiac output comparison studies in young children.

Long-Term Outcomes in Adult Patients With Pulmonary Hypertension After Percutaneous Closure of Atrial Septal Defects

“…Typically, in most adult catheterization laboratories, patients are treated awake and oxygen consumption is estimated as opposed to measured. Past studies noted >25% error rate when comparing estimated oxygen consumption with directly measured values using an analyzer, 39,40 potentially skewing the pulmonary vascular resistance method substantially. In practice, if the PAP is <50% to 55% of the systemic blood pressure and Qp:Qs >1.5:1, ASD closure is performed.…”

Methods recently used for the assessment of physical activity in children and adolescents

“…They require expensive devices or room calorimeters for their measurement [6]. Moreover, indirect calorimetry should be used with caution as it may overestimate oxygen consumption in children [13].…”

Measured Oxygen Consumption During Pediatric Cardiac Catheterization is More Accurate than Assumed Oxygen Consumption

“…Direct measurement of oxygen consumption during cardiac catheterization has historically been di cult, requiring large, cumbersome equipment and an open circuit with spontaneously-breathing patients [9,23]. However, advancements in technology have allowed for the measurement of VO 2 with progressively more compact, automated equipment that can be incorporated into a ventilator circuit for mechanically ventilated patients [4,8,10,13,15,18,20,[24][25][26][27][28][29][30][31][32][33].…”

“…The CARESCAPE series of respiratory modules including the E-CAiOV and the E-sCAiOVX (GE Healthcare, Madison, WI, USA) use side-stream sampling and paramagnetic oxygen sensors to measure VO 2 . This technology has been validated using the reverse Fick method in small samples of adults [25] and pediatric patients undergoing cardiac surgery [33], as well as pediatric patients under the age of 3 with structurally normal hearts undergoing cardiac catheterization [8]. Older devices no longer in production that use similar indirect calorimetric technology and real-time gas analysis such as the Deltatrac (Datex-Ohmeda) and the Capnomac Ultima (Datex-Ohmeda) have been more extensively studied and validated in the congenital heart disease population [4,11,18,24,26,28,30,32].…”