Carbon Dioxide Elimination and Oxygen Consumption in Mechanically Ventilated Children

Abstract

BACKGROUND: Accurate measurement of carbon dioxide elimination (V CO 2 ) and oxygen consumption (V O 2 ) at the bedside may help titrate nutritional and respiratory support in mechanically ventilated patients. Continuous V CO 2 monitoring is now available with many ventilators. However, because normative data are sparsely available in the literature, we aimed to describe the range of V CO 2 and V O 2 values observed in mechanically ventilated children. We also aimed to examine the characteristics of V CO 2 values that are associated with standard steady state (5-min period when V CO 2 and V O 2 variability are < 10%). METHODS: Mechanically ventilated patients who underwent indirect calorimetry testing were eligible for inclusion, and subjects who achieved standard steady state were included. Normalized V CO 2 and V O 2 values (mL/kg/min) were modeled against subject height, and correlation coefficients were computed to quantify the goodness of fit. A steadystate definition using only V CO 2 was developed (V CO 2 variability of < 5% for a 5-min period) and tested against standard steady state using sensitivity and specificity. RESULTS: Steady-state data from 87 indirect calorimetry tests (in 70 subjects) were included. For age groups < 0.5, 0.5-8, and > 8 y, the mean V CO 2 values were 7.6, 5.8, and 3.5 mL/kg/min. Normalized V CO 2 and V O 2 values were inversely related to subject height and age. The relationships between normalized gas exchange values and height were demonstrated by the models: V CO 2 ‫؍‬ 115 ؋ (height in cm) ؊0.71 (R ‫؍‬ 0.61, P < .001) and V O 2 ‫؍‬ 130 ؋ (height in cm) ؊0.72 (R ‫؍‬ 0.61, P < .001). Steady-state V CO 2 predicted standard steady state (sensitivity of 0.84, specificity of 1.0, P < .01). CONCLUSIONS: V CO 2 and V O 2 measurements correlated with subject height and age. Smaller and younger subjects produced larger amounts of CO 2 and consumed more O 2 per unit of body weight. The use of a 5-min period when V CO 2 varied by < 5% predicted standard steady state. Our observations may facilitate greater utility of V CO 2 at the bedside in the pediatric ICU and thereby extend the benefits of metabolic monitoring to a larger group of patients.

Correlation between minute carbon dioxide elimination and pulmonary blood flow in single‐ventricle patients after stage 1 palliation and 2‐ventricle patients with intracardiac shunts: A pilot study

“…Alteration of minute ventilation changes EtCO 2 and VCO 2 in opposite directions, while changes in Qp or metabolism move EtCO 2 and VCO 2 in the same direction. However, in steady‐state conditions, when metabolism and minute ventilation are maintained at a constant, carbon dioxide elimination and, hence VCO 2 , represents an assessment of Q p and by extension CO in patients with normal cardiac physiology and anatomy . Among critically ill patients on mechanical ventilation and sedation, there may be very little variation in metabolic rate and minute ventilation at any given time within each individual patient.…”

Volumetric Capnography in Pediatric Extracorporeal Membrane Oxygenation: A Case Series

“…Under stable minute ventilation and metabolic conditions, VCO 2 becomes a very sensitive indirect indicator of Q p and by extension cardiac output in patients with normal cardiac physiology and anatomy. [8][9][10] Volumetric capnometry correlates well with Q p in patients with stable single ventricle physiology and with Q p and cardiac output in patients with structurally normal hearts. In contrast, poor correlation between cardiac output and VCO 2 is seen in patients with single ventricle physiology and significant intracardiac shunts.…”

Comparisons of Metabolic Load between Adaptive Support Ventilation and Pressure Support Ventilation in Mechanically Ventilated ICU Patients

“…e sample size was calculated according to a previous study [13], and assuming a middle effect size and an α error of 0.05, a sample size of 25 would have 80% power to detect the difference between the modes. Allowing for the 20% dropout rate, the sample size was increased to 30.…”

“…is approach assumes that the VO 2 of respiratory muscles varied with and without ventilatory support [11,12]. In addition, VCO 2 and VO 2 in mechanically ventilated patients can be measured using an indirect calorimeter [13]. A study reported significantly increased WOB in terms of energy expenditure (EE) and VO 2 during T-piece breathing compared with those in the PSV mode in critically ill patients [14].…”