# New Oxygen Consumption Formula for Congenital Heart Disease | Journal Scan

## Study Questions:

Is there a more accurate alternative to existing formulas to predict oxygen consumption (VO2) in children and adults with congenital and acquired heart disease?

## Methods:

A retrospective review was performed at a single center of 502 consecutive patients undergoing cardiac catheterization with measured VO2 (M-VO2). M-VO2 was compared with VO2 predicted by the LaFarge equations (LF-VO2). Patients were divided into those <3 years of age (group 1) and those ≥3 years of age (group 2). The data from the retrospective analysis were used to develop a new predictive equation, which was subsequently validated prospectively in 100 consecutive patients.

## Results:

LF-VO2 was inaccurate in the younger patients (42%), but performed better in the older patients (inaccurate in 13%). Multivariable predictors of inaccurate LF-VO2 included age (odds ratio (OR), 0.41; p = 0.01) and single-ventricle anatomy (OR, 2.98, p = 0.03) in group 1 and anemia (OR, 0.84; p < 0.001) in group 2. Critical illness was borderline significant in both age groups. The new predictive equation is: VO2 = 242.1 + [9.7 x ln Age] – [34 x ln Weight] – [9.6 x Single Ventricle] – [11.2 x Critical Illness] where critical illness and single-ventricle anatomy are dichotomous variables, with 1 used if present and 0 if absent. Intraclass correlation between M-VO2 and the new equation was good (r = 0.52), whereas LF- VO2 was not (r = 0.17). Bland-Altman analysis comparing M-VO2 with the new equation and with LF-VO2 demonstrated superiority of the new equation (mean bias 2.5 ml/min/m2 vs. -5.0 ml/min/m2; limits of agreement -51.6, 56.5 vs. -82.1, 72).

## Conclusions:

The authors concluded that VO2 derived from the LaFarge equation is inaccurate, particularly in younger patients. The authors proposed a new prospectively validated VO2 predictive equation for patients of all ages with congenital and acquired heart disease.

## Perspective:

There have been significant changes in the field of congenital heart disease since the LaFarge equation was proposed in 1970, particularly the greater number of interventions performed in the neonatal period and the increasing numbers of patients with single-ventricle anatomy. The proposed equation takes into account single-ventricle anatomy, as well as critical illness. As all patients in the study underwent general anesthesia with an artificial airway, the proposed equation may not be generalizable to patients with different anesthetic approaches.

Keywords: Anemia, Anesthesia, General, Cardiac Catheterization, Child, Critical Illness, Heart Defects, Congenital, Heart Diseases, Oxygen Consumption, Retrospective Studies

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