ORLANDO — Independent risk predictors have been identified that help to target the 1% of patients who develop acute renal failure following general surgery.
Eleven independent risk factors predicted acute renal failure in a logistic regression model performed by Dr. Sachin Kheterpal and his colleagues at the University of Michigan, Ann Arbor.
The researchers reviewed 150,490 operations in the American College of Surgeons' National Surgical Quality Improvement Program data set performed over a 1-year period (2005–2006) and calculated hazard ratios to compare the likelihood of acute renal failure between patients with and without each risk factor.
Preoperative renal insufficiency was associated with the greatest hazard ratio, 8.5. Other risk factors were heart failure (HR 7.6), ascites (HR 6.4), myocardial infarction within 6 months (HR 5.7), high-risk surgery (HR 3.8), aged 58 years or older (HR 3.2), hypertension requiring chronic medication (HR 3.1), male sex (HR 1.9), diabetes mellitus (HR 2.6), previous cardiac procedure (HR 2.2), and emergency surgery (HR 2.7), Dr. Kheterpal said during a poster discussion session at the annual meeting of the American Society of Anesthesiologists.
Dr. Kheterpal and his associates then took the list one step further.
They developed a “robust” risk-prediction model—an index based on the number of preoperative risk factors. The association between these risk factors and ARF incidence was as follows: one to two risk factors, 0.2% ARF incidence; three risk factors, 1% incidence; four factors, 2% incidence; five factors, 3.3% incidence; and six factors, 9% incidence.
“This is really surprising when you look at how many older patients we have, who are also men, and have hypertension and diabetes—[they] have a fairly good chance of acute renal failure,” Dr. Kheterpal said. The prediction index could be the foundation for informed consent in these patients, he added.
The investigators based their conclusions on information prospectively gathered by trained nurse data collectors from 121 centers, including community and academic centers.
“The data collection system is very detailed. It includes 30-day outcomes, even if the patient leaves and dies at another hospital,” said Dr. Kheterpal of the department of anesthesiology at the university.
Excluded from the study were patients with preexisting acute renal failure or those requiring dialysis; patients undergoing any nongeneral surgery procedures, including cases performed by vascular, cardiac, urology, ophthalmology, podiatry, or obstetric services; outpatients; and general surgery patients on whom concurrent urology procedures were performed.
Data for 68,147 operations were assessed further. Of these, 712 patients (1%) experienced acute renal failure (ARF) postoperatively. ARF was defined as progressive renal insufficiency—an increase in serum creatinine of 2 mg/dL or more above baseline—or a requirement for postoperative dialysis.
This 1% incidence of acute kidney injury is very close to a previously reported incidence of 0.8% (Anesthesiology 2007;107:892–902). The use of vasopressors and diuretics was among the factors associated with ARF in this single-center study of more than 65,000 noncardiac procedures. In addition, patients who experienced ARF had increased 30-day, 60-day, and 1-year all-cause mortality.
A meeting attendee asked Dr. Kheterpal if he and other physicians at the University of Michigan are doing anything different based on the study findings. “Yes, we are very aggressive now about hydration. And we're very aggressive now about not using diuretics intraoperatively. I've gotten into fights about that,” he said.
Having a study with nearly 70,000 general surgery cases allowed Dr. Kheterpal and his associates to do an internal validation study.
He acknowledged that there are also many limitations because the study is based on a national data set. For example, intraoperative data beyond length of each procedure were “very limited,” and there was no information on the use of preoperative medications.
“Next at our institution we will be looking at alternative serum and urinary biomarkers of ARF,” Dr. Kheterpal said.