Reducing acute kidney injury in cardiac surgery: optimizing oxygen delivery and perioperative management

Acute kidney injury (AKI) is a prevalent and severe complication following cardiac surgery, especially in procedures involving cardiopulmonary bypass (CPB), such as coronary artery bypass grafting (CABG)[1,2]. The development of AKI is closely linked to increased morbidity, prolonged hospital stays, and higher mortality rates[3]. Furthermore, AKI can have long-term consequences, leading to chronic kidney disease (CKD) and a persistent decline in renal function[4,5]. Several factors contribute to the onset of AKI in this setting, including preoperative renal impairment, the inflammatory response triggered by CPB, and hemodynamic fluctuations during surgery. Addressing the modifiable risk factors associated with AKI has become a central focus in cardiac surgery to improve patient outcomes and reduce the incidence of renal complications. A recent study by Maruniak et al. evaluated 120 patients undergoing on-pump CABG to identify factors associated with AKI in the postoperative period[6]. The study revealed that 26% of the patients developed AKI, with preoperative renal dysfunction (elevated creatinine and urea), lower hemoglobin, and reduced albumin levels being significant contributors. The most critical intraoperative factor was oxygen delivery (DO2) during CPB, with lower DO2 levels correlating strongly with an increased risk of AKI (P = 0.030). The findings emphasize the importance of maintaining adequate oxygenation and hemodynamic stability during surgery to prevent renal injury, particularly in high-risk patients. AKI remains a significant concern in the context of cardiac surgery, with reported incidences ranging from 5% to over 40% depending on patient demographics and the specific procedure performed[1,2]. The kidneys are highly susceptible to ischemia and hypoperfusion during CPB, given their high metabolic demands and the systemic inflammatory response that often accompanies CPB. Even minor elevations in serum creatinine levels postoperatively can lead to significant increases in patient mortality and long-term morbidity [7]. In severe cases, patients may require renal replacement therapy (RRT), which further complicates recovery and impacts overall outcomes[8]. Previous studies have demonstrated that patients with preoperative renal dysfunction are at a higher risk of developing AKI, underscoring the importance of identifying and optimizing renal function before surgery [9-11]. Managing AKI risk factors preoperatively, including proper hydration and minimizing nephrotoxic medications, is essential for improving surgical outcomes. Several patient-related factors also contribute to the development of AKI in cardiac surgery. Age, diabetes, and chronic hypertension are well-established risk factors, with older patients and those with preexisting renal dysfunction being particularly vulnerable to postoperative renal complications[12]. Intraoperative factors, including the duration of CPB, the type of surgery, and the use of vasopressors, also play a role in determining AKI risk[13]. Identifying these risk factors allows clinicians to adopt preventive strategies, such as limiting CPB time and optimizing fluid management, to minimize the risk of renal injury. One of the most critical intraoperative factors contributing to AKI is the delivery of oxygen (DO2) to the kidneys and other vital organs during CPB. Hypoperfusion and ischemic injury to the kidneys during surgery can lead to irreversible damage, and studies have shown that maintaining a minimum DO2 threshold can significantly reduce the incidence of AKI[12,14]. Achieving this requires careful management of hemodynamics, including monitoring of blood flow, hemoglobin levels, and oxygen saturation throughout the procedure. Research suggests that a DO2 threshold below 272 mL/min/m2 during CPB is associated with a higher likelihood of AKI[15]. Maintaining adequate oxygen delivery through blood transfusions or increasing cardiac output can help prevent renal injury[16]. Advanced monitoring techniques, such as continuous cardiac output monitoring and near-infrared spectroscopy (NIRS), can be employed to provide real-time feedback on tissue oxygenation and guide interventions when DO2 levels drop below safe thresholds. In high-risk patients, the use of preoperative renal protective agents, such as N-acetylcysteine or bicarbonate, may offer additional benefits, although their use remains controversial and is not standard practice[17,18]. The prevention of AKI in cardiac surgery remains an ongoing challenge, with a need for continued research into strategies that can improve renal outcomes. Future studies should focus on refining goal-directed perfusion strategies and exploring the role of novel monitoring technologies that allow for more precise regulation of DO2 during CPB. Additionally, investigating the potential of pharmacologic interventions aimed at mitigating the inflammatory response to CPB and protecting renal function could lead to new approaches in managing AKI risk. Long-term follow-up of patients who develop AKI postoperatively is also essential to assess the impact of renal injury on chronic kidney disease progression and cardiovascular health. Understanding the long-term implications of AKI in cardiac surgery can help shape guidelines for postoperative care and the monitoring of kidney function in these patients. In conclusion, AKI is a significant and preventable complication in cardiac surgery, particularly in patients undergoing CABG with CPB. By focusing on hemodynamic management, maintaining adequate DO2, and addressing patient-specific risk factors, clinicians can improve surgical outcomes and reduce the burden of AKI in this high-risk population. Further research is needed to develop more effective strategies for preventing AKI and improving long-term renal outcomes in cardiac surgery patients.