Anesthetic requirements and stress hormone responses in chronic spinal cord-injured patients undergoing surgery below the level of injury: nitrous oxide vs remifentanil

BACKGROUND: Nitrous oxide (N(2)O) and remifentanil both have anesthetic-reducing and antinociceptive effects. We aimed to determine the anesthetic requirements and stress hormone responses in spinal cord-injured (SCI) patients undergoing surgery under sevoflurane anesthesia with or without pharmacodynamically equivalent doses of N(2)O or remifentanil. METHODS: Forty-five chronic, complete SCI patients undergoing surgery below the level of injury were randomly allocated to receive sevoflurane alone (control, n = 15), or in combination with 67% N(2)O (n = 15) or target-controlled infusion of 1.37 ng/ml remifentanil (n = 15). Sevoflurane concentrations were titrated to maintain a Bispectral Index (BIS) value between 40 and 50. Measurements included end-tidal sevoflurane concentrations, mean arterial blood pressure (MAP), heart rate (HR), and plasma catecholamine and cortisol concentrations. RESULTS: During surgery, MAP, HR, and BIS did not differ among the groups. Sevoflurane concentrations were lower in the N(2)O group (0.94 ± 0.30%) and the remifentanil group (1.06 ± 0.29%) than in the control group (1.55 ± 0.34%) (P < 0.001, both). Plasma concentrations of norepinephrine remained unchanged compared to baseline values in each group, with no significant differences among groups throughout the study. Cortisol levels decreased during surgery as compared to baseline values, and returned to levels higher than baseline at 1 h after surgery (P < 0.05) without inter-group differences. CONCLUSIONS: Remifentanil (1.37 ng/ml) and N(2)O (67%) reduced the sevoflurane requirements similarly by 31-39%, with no significant differences in hemodynamic and neuroendocrine responses. Either remifentanil or N(2)O can be used as an anesthetic adjuvant during sevoflurane anesthesia in SCI patients undergoing surgery below the level of injury.