Preoperative Urinary pH is Associated with Acute Kidney Injury After Cardiac Surgery in Non-Diabetic Patients

Abstract

Background: Acute kidney injury is a common complication of cardiac surgery that increases morbidity and mortality. The present study aims to analyze the association of preoperative urinary pH with acute kidney injury after isolated coronary artery bypass graft surgery (CABG). Methods: We retrospectively reviewed the data of 270 adult non-diabetic patients who underwent isolated CABG surgery with normal renal function. The perioperative data of the patients included demographic data, laboratory findings, morbidity, and mortality. The patient population was divided into four groups: Group I, patients with preoperative urinary pH=5; Group II, patients with preoperative urinary pH=5.5; Group III, patients with preoperative urinary pH=6-6.5; and Group IV, patients with preoperative urinary pH ≥ 7.0. Kidney injury was interpreted according to the Kidney Disease: Improving Global Outcomes (KDIGO). Results: There were 108 patients (40%) in Group I, 44 patients (16.3%) in Group II, 78 patients (28.9%) in Group III, and 40 patients (14.8%) in Group IV. Postoperative acute kidney injury (AKI) occurred in 39 patients (36.1%) in Group I, 4 patients (9.1%) in Group II, and 2 patients (2,5%) in Group III. None of the patients developed AKI in Group IV. Renal replacement therapy was required in 8 patients (2.3%) (6 patients from Group I; 2 patients from Group II; P = .016). Thirty-day mortality occurred in 5 patients (1.9%) (5 patients from Group I; none from other groups; P =  .017). All of the patients required renal replacement therapy. Logistic regression analysis revealing the presence of lower pH levels preoperatively was shown to be associated with increased incidence of postoperative AKI (OR: 0.193; 95% CI: 0.103-0.361; P < .001). Conclusion: Low preoperative urinary pH (≤5.5) results in severe acute kidney injury and increases the rate of morbidity and mortality after isolated CABG.