Measurement of Oxygen Consumption in Critically Ill Children: Breath-by-Breath Method vs Mass Spectrometry

BACKGROUND: Measurement of oxygen consumption (Vȯ2) is difficult in children but is essential to calculate cardiac index and systemic vascular resistance. OBJECTIVE: To compare measurements of Vȯ2 using respiratory mass spec trometry and the breath-by-breath method. METHODS: Vȯ2 was measured simultaneously and continuously for 10 minutes by using respiratory mass spectrometry and the breath-by-breath method in children receiving mechanical ventilation via cuffed endotracheal tubes. RESULTS: Sixteen children (7 boys; median [range]: age, 1.5 [0.2-6] years; weight, 11.5 [2.8-23.5] kg; body surface area, 0.55 [0.18-0.98] m(2)) were studied. The correlation between measurements of Vȯ2 by the 2 methods was good (R = 0.924). Mean Vȯ2 measured by mass spectrometry was 63 (95% CI, 47-78) mL/min vs 65 (95% CI, 47-83) mL/min measured by the breath-by-breath method. The mean Vȯ2 difference between the 2 methods was 3 (95% CI, -9 to 5) mL/min and statistically insignificant. Bland-Altman analysis showed that the 95% limits of agreement were between -28 and +23. Cardiac index did not differ significantly when calculated using Vȯ2 measured with one method or the other (mean difference, 0.1; 95% CI, -0.2 to 0.3). CONCLUSIONS: Measurements of Vȯ2 did not differ between mass spectrometry and the breath-by-breath method. Use of the breath-by-breath method may facilitate calculation of cardiac index and systemic vascular resistance in critically ill children.