Objective: Renal dysfunction is among the most commonly occurring morbidities following descending thoracic and thoracoabdominal aortic repair. We hypothesized that myoglobin nephrotoxicity might arise from leg ischemia caused by femoral artery cannulation, which is required for distal aortic perfusion. Lacking complete historical laboratory data on myoglobinemia, we studied somatosensory evoked potential (SSEP) changes in the leg (a functional marker of leg ischemia), as a surrogate predictor of acute postoperative renal failure.
Methods: Intraoperative leg SSEP function and preoperative glomerular filtration rate (GFR - an essential covariate) were available for 299 patients. Change in SSEP was defined as 10% increase in latency or 50% decrease in amplitude. Postoperative renal dysfunction was 1mg/dl/day increase in creatinine for 2 days, clinical diagnosis of ARF or need for dialysis postoperatively.
Results: Change in SSEP in the cannulated leg occurred in 108/299 (36%) of cases intraoperatively. All recovered normal SSEP function at decannulation. Patients with SSEP changes had 41/108 (38%) postoperative renal failure compared to 49/191 (26%) without (odds ratio 1.8, p<0.03). Modeled with GFR, aneurysm extent, and chronic obstructive pulmonary disease (COPD), SSEP changes had an adjusted odds ratio of 1.9, p<0.03. Pre-op GFR was also a highly significant predictor of postoperative renal failure (OR 0.98/ml; p<0.0001).
Conclusion: This is the first study to show a relationship between intraoperative leg ischemia and postoperative renal failure. It provides epidemiological evidence that the ischemic leg may be an important contributor to rhabdomyolysis-like renal morbidity after thoracoabdominal aortic surgery.