Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.
Postoperative acute kidney injury (AKI) is a deterioration in kidney function that occurs after surgery. AKI is diagnosed when serum creatinine increases by at least 0.3 mg/dL within 48 hours, rises to at least 1.5 times baseline within 7 days, or urine output falls below 0.5 mL/kg/h for at least 6 hours. In the postoperative context, it is associated with longer hospitalization, higher mortality, and an increased risk of chronic kidney disease (1). Identifying the risk factors for postoperative acute kidney injury can help healthcare providers recognize high-risk patients and inform strategies for prevention and early intervention.
Pre-existing kidney disease is one of the most important risk factors for postoperative AKI. Kidney function is commonly assessed using the estimated glomerular filtration rate (eGFR), which estimates the volume of blood filtered by the kidneys each minute. A lower eGFR indicates reduced kidney function and is associated with a greater risk of postoperative AKI (1). Patients with chronic kidney disease have less renal reserve and are more susceptible to reductions in renal blood flow during surgery.
Advanced age is also an established risk factor for postoperative AKI. Kidney function gradually declines with age because of structural changes within the kidneys, including loss of functioning nephrons and reduced renal blood flow. Older adults also have a higher prevalence of comorbidities that increase the risk of kidney injury, such as diabetes and hypertension, which can cause progressive renal vascular damage. Heart failure further increases risk because reduced forward cardiac output can decrease renal perfusion and interfere with glomerular filtration (2).
The type and urgency of surgery also influence the risk of postoperative acute kidney injury. Cardiac surgery carries a particularly high risk. During cardiopulmonary bypass, blood circulates through an external circuit that produces nonpulsatile flow and may reduce renal blood flow, particularly when perfusion pressures are low or bypass is prolonged. The circuit can also trigger systemic inflammation and cause hemolysis, releasing free hemoglobin that may contribute to renal tubular injury. Major abdominal surgery also carries substantial risk because blood loss and fluid shifts can reduce circulating volume and compromise renal perfusion (3). Emergency surgery further increases risk because any sepsis or blood-related issues may not be fully corrected before surgery.
Additionally, intraoperative hypotension is an important risk factor for postoperative AKI. The kidneys normally maintain renal blood flow during changes in systemic blood pressure through autoregulation. When arterial pressure falls sufficiently, this response may no longer maintain adequate renal perfusion (4). Chronic hypertension can shift the autoregulatory range toward higher pressures, making some patients less tolerant of hypotension.
Nephrotoxic medications provide another potentially modifiable source of risk. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and ketorolac, are commonly used for perioperative analgesia but can reduce renal blood flow by inhibiting renal prostaglandin synthesis (1). Aminoglycoside antibiotics, such as gentamicin, are used for serious gram-negative infections and can accumulate within proximal tubular cells, causing direct tubular injury. Vancomycin, which is used for serious gram-positive infections, including those caused by methicillin-resistant Staphylococcus aureus, has also been associated with nephrotoxicity (1). Avoiding unnecessary nephrotoxic medications is particularly important in patients with other risk factors for postoperative acute kidney injury. Because postoperative AKI often results from several contributing factors, recognizing high-risk patients and limiting modifiable exposures remain important components of perioperative care.
References
- Boyer N, Eldridge J, Prowle JR, Forni LG. Postoperative Acute Kidney Injury. Clin J Am Soc Nephrol. 2022;17(10):1535-1545. doi:10.2215/CJN.16541221
- Prowle JR, Forni LG, Bell M, et al. Postoperative acute kidney injury in adult non-cardiac surgery: joint consensus report of the Acute Disease Quality Initiative and PeriOperative Quality Initiative. Nat Rev Nephrol. 2021;17(9):605-618. doi:10.1038/s41581-021-00418-2
- Gameiro J, Fonseca JA, Neves M, Jorge S, Lopes JA. Acute kidney injury in major abdominal surgery: incidence, risk factors, pathogenesis and outcomes. Ann Intensive Care. 2018;8(1):22. Published 2018 Feb 9. doi:10.1186/s13613-018-0369-7
- Wesselink EM, Kappen TH, Torn HM, Slooter AJC, van Klei WA. Intraoperative hypotension and the risk of postoperative adverse outcomes: a systematic review. Br J Anaesth. 2018;121(4):706-721. doi:10.1016/j.bja.2018.04.036
