Summary

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 12 h (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), 8 h (r2 = 0.26, P = 0.04) and 12 h (r2 = 0.31, P = 0.03), aldosterone at 6 h (r2 = 0.54, P = 0.001), 8 h (r2 = 0.40, P = 0.01) and 12 h (r2 = 0.32, P = 0.03), ADH at 24 h (r2 = 0.38, P = 0.01) and ANF at 6 h (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.