Oxygen Delivery, Oxygen Consumption and Decreased Kidney Function After Cardiopulmonary Bypass

Introduction

Low oxygen delivery during cardiopulmonary bypass is related to a range of adverse outcomes. Previous research specified certain critical oxygen delivery levels associated with acute kidney injury. However, a single universal critical oxygen delivery value is not sensible, as oxygen consumption has to be considered when determining critical delivery values. This study examined the associations between oxygen delivery and oxygen consumption and between oxygen delivery and kidney function in patients undergoing cardiopulmonary bypass.

Methods

Oxygen delivery, oxygen consumption and kidney function decrease were retrospectively studied in 65 adult patients.

Results

Mean oxygen consumption was 56 ± 8 ml/min/m², mean oxygen delivery was 281 ± 39 ml/min/m². Twenty-seven patients (42%) had an oxygen delivery lower than the previously mentioned critical value of 272 ml/min/m². None of the patients developed acute kidney injury according to RIFLE criteria. However, in 10 patients (15%) a decrease in the estimated glomerular filtration rate of more than 10% was noted, which was not associated with oxygen delivery lower than 272 ml/min/m². Eighteen patients had a strong correlation (r >0.500) between DO₂ and VO₂, but this was not related to low oxygen delivery. Central venous oxygen saturation (77 ± 3%), oxygen extraction ratio (21 ± 3%) and blood lactate levels at the end of surgery (1.2 ± 0.3 mmol/l) showed not to be indicative of insufficient oxygen delivery either.

Conclusions

This study could not confirm an evident correlation between O₂ delivery and O₂ consumption or kidney function decrease, even at values below previously specified critical levels. The variability in O₂ consumption however, is an indication that every patient has individual O₂ needs, advocating for an individualized O₂ delivery goal.