Introduction

Acute kidney injury (AKI) is a well-known serious complication of cardiopulmonary bypass (CPB) surgery and one of the significant risk factors for mortality, prolonged hospital stay, and additional cost. Patients having preexisting kidney dysfunction are more likely to develop AKI in the perioperative period. The complexity of CPB surgery often leads to AKI. Mechanisms of AKI include kidney hypoperfusion due to low-pressure blood flow. The nonpulsatile perfusion of the kidney, hypothermia, and inflammatory milieu, which causes afferent arteriolar constriction, contribute to AKI. The early postoperative period is characterized by a low cardiac output state, which gradually surpasses kidney compensatory mechanisms and filtration reserve. Various indigenous and infused vasopressors cause markedly elevated afferent arteriolar resistance, leading to a drop in glomerular filtration rate (GFR). Several studies have assessed the value of risk factors and their association with AKI after cardiac surgery. The evidence was mixed, with some showing a positive association. With an aim to clarify this relationship further, especially in the Indian population, we tried to study the incidence and clinical profile of AKI and its correlation with functional and clinical outcomes. We also tried to look for any diagnostic markers of AKI in the setting of cardiac surgery.

Methodology

The study was conducted among patients attending the Department of General Medicine and Cardiology at a tertiary care hospital in Delhi. It was a prospective longitudinal observational study conducted between March 2022 and February 2024.

Around 200 patients underwent cardiac surgery using a cardiopulmonary bypass machine at the study center during the study period. History, including comorbidities such as transient ischemic attacks, previous stroke, coronary artery disease, diabetes mellitus, hypertension, chronic obstructive pulmonary disease (COPD), and complete physical examination, were recorded. Patients were followed up preoperatively and postoperatively up to day 28. Preoperative details such as hemoglobin, serum creatinine, blood transfusion, and urine output were recorded. Intraoperative details such as duration of surgery, ACC (aortic cross-clamp) duration, hypotension, vasopressor use, and re-exploration were recorded. Postoperative findings such as urine output and serial kidney function tests on day 3, day 7, and day 28 were documented.

Results

Among 200 subjects, 99 patients had hypertension, and 70 patients developed AKI. Older age (>60 years) was significantly associated with AKI ( p -value 0.04367). Comorbid conditions such as T2DM, hypertension, dyslipidemia, and COPD were significantly associated with AKI as compared to those without comorbidities (Chi-squared test, p -value < 0.0001). In the study, there was no association between the type of surgery and the development of AKI (Chi-squared test, p -value 0.07). There was no relationship between AKI severity and cardiopulmonary bypass (CPB) duration. Similarly, there was no association between the severity of AKI and ACC duration. Intraoperative hypotension was significantly associated with AKI. About 53% of hypotensive patients developed AKI during surgery as compared to 19.44% of normotensive patients ( p -value < 0.0001, Chi-squared test). AKI was linked with a significantly prolonged hospital stay. A prolonged stay of >3 weeks was seen in 8.5% (6 out of 70) of patients who developed AKI as compared to 2.3% (3 out of 130) of patients without AKI. Most patients with AKI (57%) recovered within 1 week, and 24.28% recovered between 1 and 4 weeks. In the study, 8 patients (11.2%) developed acute kidney disease (AKD), and 5 patients (7%) died.

Conclusion

This prospective study concluded that AKI is a common complication in the perioperative period of cardiopulmonary bypass surgery. Older age, comorbid conditions, and intraoperative hypotension were significantly associated with AKI. AKI was linked with extended hospital stay and longer recovery times. Severe grades of AKI were associated with progression to AKD, need for dialysis, and higher mortality. It is imperative to focus on interventions to minimize and address the risk factors to reduce morbidity and mortality associated with AKI in CPB surgery.