In critically ill patients undergoing emergency surgery, the following were identified to be independent risk factors of postoperative acute kidney injury (AKI): postoperative reoperation, postoperative Acute Physiology and Chronic Health Evaluation (APACHE II) score, and postoperative serum lactic acid (LAC).

• In this prospective observational study, 383 critically ill patients undergoing emergency surgery were included.

• Postoperative AKI occurred in 151 (39.4%) patients.

• Independent risk factors for postoperative AKI included: postoperative reoperation, postoperative APACHE II score, and postoperative LAC, with adjusted odds ratio (ORadj) of 1.854, 1.059, and 1.239, respectively.

• Duration of mechanical ventilation, renal replacement therapy, ICU and hospital mortality, ICU and hospital length of stay, total ICU and hospital costs were found to be higher in the AKI group vs the non-AKI group.