Intraoperative Arterial Pressure Variability and Postoperative Acute Kidney Injury

Abstract

Background and objectives: High BP variability may cause AKI because of inappropriate kidney perfusion. This study aimed to investigate the association between intraoperative BP variability and postoperative AKI in patients who underwent noncardiac surgery.

Design, setting, participants, & measurements: We performed a cohort study of adults undergoing noncardiac surgery in hospitals in South Korea. We studied three cohorts using the following recording windows for intraoperative BP: discovery cohort, 1-minute intervals; first validation cohort, 5-minute intervals; and second validation cohort, 2-second intervals. We calculated four variability parameters (SD, coefficient of variation, variation independent of mean, and average real variability) based on the measured mean arterial pressure values. The primary outcomes were postoperative AKI (defined by the Kidney Disease Improving Global Outcomes serum creatinine cutoffs) and critical AKI (consisting of stage 2 or higher AKI and post-AKI death or dialysis within 90 days).

Results: In the three cohorts, 45,520, 29,704, and 7435 patients were analyzed, each with 2230 (443 critical), 1552 (444 critical), and 300 (91 critical) postoperative AKI events, respectively. In the discovery cohort, all variability parameters were significantly associated with risk of AKI, even after adjusting for intraoperative hypotension. For example, average real variability was associated with higher risks of postoperative AKI (adjusted odds ratio, 1.13 per 1 SD increment; 95% CI, 1.07 to 1.19) and critical AKI (adjusted odds ratio, 1.13 per 1 SD increment; 95% CI, 1.02 to 1.26). Associations were evident predominantly among patients who also experienced intraoperative hypotension. In the validation analysis with 5-minute-interval BP records, all four variability parameters were associated with the risk of postoperative AKI or critical AKI. In the validation cohort with 2-second-interval BP records, average real variability was the only significant variability parameter.

Conclusions: Higher intraoperative BP variability is associated with higher risks of postoperative AKI after noncardiac surgery, independent of hypotension and other clinical characteristics.

Keywords: acute kidney injury; blood pressure; variability.

Graphical abstract

Figure 1.

Study population. Cr, creatinine; intraOp, intraoperative; SNUBH, Seoul National University Bundang Hospital; SNUH, Seoul National University Hospital; SPARK, simple postoperative AKI risk; V/S, vital sign.

Figure 2.

Significant correlations were identified between the studied BP parameters in the SPARK-discovery cohort. Correlation analysis was done using the Spearman test, and the squares show the correlation index between the variables according to row and column. The significant correlations (P<0.05) are colored, with red showing positive correlations and blue showing negative correlations. AUC, area under curve; MAP, mean arterial pressure.

Figure 3.

The lowest mean arterial pressure value of 65 mmHg was identified as a valid threshold to determine intraoperative hypotension related to a higher risk of postoperative AKI or critical AKI. We constructed generalized additive models, including preoperative and/postoperative AKI risk factors and the corresponding BP values. The predicted values are from the smoothing function of the explanatory variables and are centered to zero. The solid lines indicate the predicted values and the dotted lines indicate the 95% confidence intervals. The included preoperative/postoperative AKI risk factors were age, sex, eGFR (continuous, ml/min per 1.73 m²), diabetes mellitus, surgery duration (continuous, hours), emergency operation, usage of renin-angiotensin-aldosterone blockades, dipstick albuminuria, anemia (<13 g/dl for men, <12 g/dl for women), hypoalbuminemia (<3.5 g/dl), and hyponatremia (<135 mEq/L).

Figure 4.

Higher intraoperative BP variability parameters were associated with higher risks of postoperative AKI or critical AKI. We constructed generalized additive models, including preoperative postoperative AKI risk factors, hypotensive parameters, and the corresponding BP values. The predicted values are from the smoothing function of the explanatory variables and are centered to zero. The solid lines indicate the predicted values and the dotted lines indicate the 95% confidence intervals. The analysis included variability ranges from the fifth to the 95th percentiles of each parameter. The adjusted variables were age, sex, eGFR (continuous, ml/min per 1.73 m²), diabetes mellitus, surgery duration (continuous, hours), emergency operation, usage of renin-angiotensin-aldosterone blockades, dipstick albuminuria, anemia (<13 g/dl for male, <12 g/dl for female), hypoalbuminemia (<3.5 g/dl), hyponatremia (<135 mEq/L), the lowest mean arterial pressure values, and area under curve under the mean arterial pressure of 65 mm Hg. ARV, average real variability; CV, coefficient of variation; VIM, variation independent of mean.