Time–dose response of oxygen delivery during cardiopulmonary bypass predicts acute kidney injury

Abstract

Objective: Previous studies have reported that nadir oxygen delivery during cardiopulmonary bypass is associated with the occurrence of postoperative acute kidney injury (AKI). However, these measurements only considered the bottom point of the oxygen delivery (DO 2 ) but did not consider the duration of DO 2 . We aimed to examine whether the time-dose response of DO 2 during cardiopulmonary bypass can be used to estimate the risk for postoperative AKI.Methods: We evaluated 112 patients who underwent cardiac surgeries with cardiopulmonary bypass. We analyzed the perfusion parameters recorded every 20 seconds. To obtain time-dose response of DO 2 index (DO 2 i), the area under the curve was calculated as below the 300 mL/min/m 2 threshold, which accounts for depth and duration of cumulative oxygen debt. In addition, the cumulative time below DO 2 i 300 mL/min/m 2 was also calculated. Receiver operating characteristic analysis, univariate regression analysis, and multivariate regression analysis were used to evaluate associations between perioperative variables and postoperative AKI.Results: Patients who developed AKI had larger area under the curve below the 300 mL/min/m 2 threshold (1581 vs 632; P<.01) and cumulative time below DO 2 i 300 mL/min/m 2 (34.7 vs 15.3 minutes; P<.01). Nadir DO 2 i was not significantly different between the non-AKI and AKI groups (263.4 vs 247.0 mL/min/m 2 ; P ¼ .291). Conclusions:The time-dose response of DO 2 i during cardiopulmonary bypass is a better indicator than nadir DO 2 i in evaluating AKI risk. Maintaining DO 2 i levels >300 mL/min/m 2 may result in decreased risk for postoperative AKI.

Duration of critically low oxygen delivery is associated with acute kidney injury after cardiac surgery

“…In the present study, we found that the frequency of AKI was 29.3% and the need for RRT was 2.9%, similar to previous studies. Overall, the occurrence of all three outcomes increased with the duration of DO 2 below the critical level.…”

“…Furthermore, association between AKI and duration of a low DO 2 at various thresholds has shown high individual variability. At threshold levels below 300 and 280 mL min −1 m −2 , the median (IQR) duration of a low DO 2 among patients with AKI was 34.7 (16.0‐61.0) minutes and 7.7 (1.6‐28.0) minutes respectively. These observations clearly demonstrate the multifactorial aetiology underlying the pathophysiology of AKI following cardiac surgery.…”

“…The two studies did not calculate the mean of low DO 2 values, but used the single lowest DO 2 measurement. Recently, Mukaida et al demonstrated that the integral of duration and severity of a DO 2 <300 mL min −1 m −2 was an independent predictor of AKI. In the present study, we took advantage of the continuous data recordings every minute from the bypass machine’s monitoring system, making it possible to investigate the impact of a DO 2 <272 mL .…”

“…Observational studies have shown that a DO 2 below a critical threshold ranging between 225 mL min −1 m −2 and 272 mL min −1 m −2 is associated with an increased risk of post‐operative AKI, and in the largest retrospective study comprising more than 19 000 cardiac surgery patients, the critical cut‐off point was found at approximately 270 mL min −1 m −2 . Furthermore, the integral of amount and time below the critical DO 2 limit has been associated with an increased risk of AKI. Indeed, in a newly published randomised controlled trial, patients randomised to maintain DO 2 above 280 mL min −1 m −2 had a reduced rate of AKIN stage I injury.…”

Commentary: Avoiding acute kidney injury after cardiac operations: Searching for the holy grail is not easy

“…Mukaida and colleagues 7 used measurements of oxygen delivery (DO 2 ) during CPB to develop receiver operating characteristic curves and measures of the time that DO 2 falls below a critical value to reflect relationships between DO 2 and AKI. In qualitative terms, Mukaida and colleagues 7 found that the longer that DO 2 levels during CPB were below a critical threshold, the more likely was the chance of AKI. Mukaida and colleagues 7 developed receiver operating characteristic curves with 3 different critical thresholds for DO 2 (300, 280, and 260 mL/min/m 2 ).…”