We determined the effect of spinal cord injury (SCI) on sevoflurane requirements and stress hormone responses, and sevoflurane concentration to block autonomic hyperreflexia (AHR) in SCI patients.

In the first series, sevoflurane concentrations to maintain bispectral index score (BIS) at 40-50 and stress hormone response were examined in 27 SCI patients undergoing surgery below the level of injury. Fifteen patients without SCI served as control. Measurements included end-tidal sevoflurane concentrations (ET_SEVO), systolic blood pressure (SBP), heart rate (HR), catecholamines, vasopressin, and cortisol concentrations. In the second series, sevoflurane concentration to block AHR was examined in 31 SCI patients undergoing transurethral litholapaxy. When a patient developed an episode of AHR, the target sevoflurane concentration was maintained for 10 min, and then the procedure was repeated. Each target concentration was determined by up-down method based on SBP.

During surgery, SBP, HR, and BIS were comparable between SCI and control. However, ET_SEVO was significantly smaller in the SCI than the control. Plasma concentrations of norepinephrine, epinephrine and cortisol were significantly lower in the SCI than the control. SBP rose by 67 ± 31 mmHg, whereas HR fell by 13 ± 8 bpm during the 1st trial in the SCI (P < 0.01). Hypertensive events were associated with increases of norepinephrine concentrations. ET_SEVO required to prevent AHR were 3.12% in 50% of patients, 3.83% in 95% of patients.

SCI reduces the anesthetic requirement by 39%, and decreases stress hormone responses during surgery below the level of injury. To prevent AHR in 95% of SCI patients undergoing litholapaxy, ET_SEVO 3.83% may be required.