Abstract
IntroductionAcute kidney injury (AKI) is common after cardiac operations. There are different risk factors or determinants of AKI, and some are related to cardiopulmonary bypass (CPB). In this study, we explored the association between metabolic parameters (oxygen delivery (DO2) and carbon dioxide production (VCO2)) during CPB with postoperative AKI.MethodsWe conducted a retrospective analysis of prospectively collected data at two different institutions. The study population included 359 adult patients. The DO2 and VCO2 levels of each patient were monitored during CPB. Outcome variables were related to kidney function (peak postoperative serum creatinine increase and AKI stage 1 or 2). The experimental hypothesis was that nadir DO2 values and nadir DO2/VCO2 ratios during CPB would be independent predictors of AKI. Multivariable logistic regression models were built to detect the independent predictors of AKI and any kind of kidney function damage.ResultsA nadir DO2 level < 262 mL/minute/m2 and a nadir DO2/VCO2 ratio < 5.3 were independently associated with AKI within a model including EuroSCORE and CPB duration. Patients with nadir DO2 levels and nadir DO2/VCO2 ratios below the identified cutoff values during CPB had a significantly higher rate of AKI stage 2 (odds ratios 3.1 and 2.9, respectively). The negative predictive power of both variables exceeded 90%. The most accurate predictor of AKI stage 2 postoperative status was the nadir DO2 level.ConclusionsThe nadir DO2 level during CPB is independently associated with postoperative AKI. The measurement of VCO2-related variables does not add accuracy to the AKI prediction. Since DO2 during CPB is a modifiable factor (through pump flow adjustments), this study generates the hypothesis that goal-directed perfusion management aimed at maintaining the DO2 level above the identified critical value might limit the incidence of postoperative AKI.
Highlights
Acute kidney injury (AKI) is common after cardiac operations
In the present dual-centre large series of patients where these values were routinely monitored during cardiopulmonary bypass (CPB), we investigated the hypothesis that oxygen delivery (DO2) and carbon dioxide production (VCO2) during CPB might be independently associated with postoperative AKI
The primary end point of this study was the determination whether the nadir DO2 value and DO2/VCO2 ratio and the VCO2 peak value during CPB are independently associated with postoperative renal function impairment, which we defined as the peak postoperative serum creatinine value and the presence of AKI according to the AKI Network (AKIN) criteria [15]
Summary
Acute kidney injury (AKI) is common after cardiac operations. There are different risk factors or determinants of AKI, and some are related to cardiopulmonary bypass (CPB). The early mortality rate in patients with AKI is around 5% but climbs to 50% when renal replacement therapy during CPB were associated with increased lactate formation [12] and that hyperlactatemia was associated with decreased DO2 levels and an increased CO2 production (VCO2) during CPB, with critical values settled at a VCO2 > 60 mL/minute/m2 and a DO2/VCO2 ratio < 5.0 [13] These data generate the hypothesis that when the DO2 during CPB falls below a critical value (in the range of 260 to 270 mL/minute/m2), organ dysoxia may be triggered, with consequent tissue acidosis leading to increased VCO2, and that this mechanism may be a determinant of impaired postoperative renal function. The finding that low DO2 during CPB is an independent determinant of postoperative AKI is still based on a single-centre observation
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