Activation of the renin–angiotensin system contributes significantly to the pathophysiology of oliguria in patients undergoing posterior spinal fusion

BACKGROUND AND OBJECTIVE: This study was undertaken to investigate the role played by antidiuretic hormone (ADH), the renin-angiotensin system and atrial natriuretic factor (ANF) in the oliguria in patients undergoing spinal fusion. METHODS: Sixteen patients undergoing posterior spinal fusion using isoflurane and fentanyl (n = 8) or sufentanil (n = 8) had renin, aldosterone, ADH and ANF measurements. RESULTS: Compared to the non-oliguric patients, the oliguric patients had a higher number of fused vertebrae 10.5 +/- 1.3 vs. 9.0 +/- 0.5 (P = 0.01) and higher renin values at 12h (3.3 +/- 3.2 vs. 0.7 +/- 0.6 ng L(-1) s(-1), P = 0.04). Hormonal values that had a significant correlation with intraoperative diuresis were: renin at 0.5 h (r2 = 0.26, P = 0.04), aldosterone at 0.5 h (r2 = 0.30, P = 0.03) and ANF at 0.5 h (r2 = 0.32, P = 0.02). Those that had a significant correlation with the mean postoperative diuresis were: renin at 6 h (r2 = 0.29, P = 0.03), 8h (r2 = 0.26, P = 0.04) and 12h (r2 = 0.31, P = 0.03), aldosterone at 6h (r2 = 0.54, P = 0.001), 8h (r2 = 0.40, P = 0.01) and 12h (r2 = 0.32, P = 0.03), ADH at 24h (r2 = 0.38, P = 0.01) and ANF at 6h (r2 = 0.26, P = 0.045). Using stepwise regression, excluding hormonal values, only two continuous variables had a significant correlation with the mean postoperative diuresis: the number of fused vertebrae (P = 0.02) and the length of surgery (P = 0.02). CONCLUSION: Activation of the renin-angiotensin system is the major cause of the early intraoperative oliguria. ADH and the renin-angiotensin system are both involved in the pathophysiology of postoperative oliguria in patients undergoing spinal fusion.