维持新生儿体外循环有氧代谢的足量氧供应下限

Background: The objective of cardiopulmonary bypass (CPB) is to maintain an adequate balance between oxygen delivery (ḊO₂) and consumption. The critical ḊO₂ is that at which consumption becomes supply dependent. This study aimed to identify the critical ḊO₂ in neonates, who have higher metabolic rates than adults.

Methods: In a retrospective cohort of neonates, ḊO₂ was calculated from CPB parameters recorded during aortic cross-clamping. High lactate concentration measured after aortic unclamping (lactOFF) was used to identify anaerobic metabolism. Data were analysed using mixed linear and proportional odds regression models. The relationship between ḊO₂ and temperature was analysed in a subgroup of patients with lactOFF <2.5 mM, thought to have had balanced oxygen delivery and consumption. The estimated regression coefficient was further used to adjust hypothetical ḊO₂ thresholds, and ḊO₂ excursions below the threshold were quantified as magnitude-durations. The lowest threshold that provided magnitude-durations and linked with an increase in lactOFF was used as the lowest suitable (critical) ḊO₂ at 37℃.

Results: Overall, 22 896 time points were analysed in 180 neonates. In 40 patients with lactOFF <2.5 mM, ḊO₂ varied by 22.87 (0.70) ml min^-1m^-2℃^-1. When varying the ḊO₂ threshold between 340 and 380 ml min^-1m^-2, excursions below the threshold were linked with incremental lactOFF. A 100 ml m^-2 excursion below the 340 ml min^-1m^-2 ḊO₂ threshold increased the risk of a 1 mM increment in lactOFF by 22% (odds ratio: 1.22; 95% confidence interval: 1.02~1.45).

Conclusions: It was found that 340 ml min^-1m^-2 is likely to represent the lowest suitable ḊO₂ required in neonates to maintain aerobic metabolism during normothermic CPB.