Anesthetic requirements and stress hormone responses in spinal cord-injured patients undergoing surgery below the level of injury

Neuraxial anesthesia decreases the minimum alveolar concentration. We determined the effects of spinal cord injury (SCI) on sevoflurane requirements and stress hormone response. Twenty-two chronic SCI patients undergoing surgery below the level of the injury were enrolled in the study, and 15 patients without cord injury served as control patients. Bispectral index score was maintained at 40-50. Measurements included end-tidal sevoflurane concentrations, systolic arterial blood pressure, heart rate, and plasma catecholamine and cortisol concentrations. During surgery, systolic arterial blood pressure, heart rate, and Bispectral index were comparable between SCI and control groups. However, end-tidal sevoflurane concentration was significantly smaller in the SCI (0.81%-1.06%) versus control (1.28%-1.31%) patients. In the control group, plasma norepinephrine and cortisol concentrations were significantly increased during and 1 h after surgery compared with awake baseline values. In the SCI group, the sympathoadrenal and cortisol responses were virtually abolished. We conclude that SCI reduces the anesthetic requirement by 20%-39% during surgery below the level of injury, in association with blunted sympathoadrenal and cortisol responses.