Oxygen consumption after cardiopulmonary bypass surgery in children: Determinants and implications

Objective: We sought to assess oxygen consumption and its determinants in c hildren shortly after undergoing cardiopulmonary bypass operations, Methods : Twenty children, aged 2 months to 15 years (median, 3.75 Sears), undergoi ng hypothermic cardiopulmonary bypass operations were studied during the fi rst 4 hours after arrival in the intensive care unit. Central and periphera l temperatures were monitored. Oxygen consumption was continuously measured by using respiratory mass spectrometry, Oxygen delivery was calculated fro m oxygen consumption and arterial and mixed venous oxygen contents, which w ere sampled every 30 minutes. Oxygen extraction was derived by the ratio of oxygen consumption and oxygen delivery. Arterial blood lactate levels were measured every 30 minutes. Results: There was a correlation between oxygen consumption and age in patients older than 3 months (r = -0.76). Mean oxyg en consumption increased by 14.7% during the study The increase in oxygen c onsumption was correlated with the increase in central temperature (r = 0.7 3). Nine patients had an arterial lactate level above 2 mmol/L on arrival. There mere no significant differences in oxygen consumption, oxygen deliver y, and oxygen extraction between the group with lactate levels between 2 an d 3 mmol/L and the groups with normal lactate levels both on arrival and at 2 hours. One patient with a peak lactate level of 6.8 mmol/L had initially low oxygen delivery (241.3 mL . min(-1) . m(-2)). Conclusions: During the early hours after a pediatric cardiac operation, the increase in oxygen con sumption is mainly attributed to the increase in central temperature. Oxyge n consumption is negatively related to age, Mild lactatemia is common and d oes not appear to reflect oxygen delivery or oxygen consumption or a more c omplicated recovery.