Kheterpal et al identified a group of 15,102 patients out of a population of 65,043 cases who underwent major, non cardiac surgery and who had an estimated pre operative creatinine clearance greater than 80 ml/min. Of this group 9,078 patients had a creatinine measured during the first seven post operative days and formed the basis of this study. 121 patients developed acute renal failure (0.8%, ARF)) defined as an estimated creatinine clearance of 50 ml/min or less. Of this group 14 patients (0.1%) required renal replacement therapy such as dialysis. A significant portion of the ARF group had undergone vascular or general surgery procedures. Independent pre operative predictors of post operative ARF included age greater than or equal to 59, emergency surgery, liver disease, body mass index greater than or equal to 32, high risk surgery, peripheral vascular occlusive disease, and chronic obstructive pulmonary disease requiring bronchodilators. The risk of post operative ARF increased from 0.3% to 4.3% as the number of preoperative risk factors increased from zero to 3 or more. Intraoperative variables associated with post operative ARF included the use of vasopressors, furosemide, or mannitol. Thirty day, sixty day and one year all cause mortality was significantly higher in the patients who developed post operative ARF. For example at one year all cause mortality was 15% in the normal renal function group and 31% in the ARF group. In their discussion the authors note that post operative ARF in cardiac surgery patients is considerably higher (17%). Intraoperative oliguria (urine output less than 0.5 ml/kg/h) was not associated with ARF. The mean urine output was 1.0 ml/kg/h in both normal and ARF groups. Recognize that this was a retrospective study using clinically available data. Also note that this study provides no information on how to prevent or decrease the incidence of ARF. However this study does provide information on incidence, patients at risk and may thus stimulate prospective hypothesis testing that may lead to a better understanding of this problem. Even though the incidence appears low, the consequences in increased hospital stay, increased costs of care and poorer survival are significant. Finally this study could only be done because of the availability of an electronic anesthesia record and pre operative data collection instrument that allowed electronic searching. Ref: Predictors of postoperative acute renal failure after noncardiac surgery in patients with previously normal renal function. Anesthesiology. 2007;107:892-902.
David S. Smith, M.D., Ph.D.