Sevoflurane concentrations required to block autonomic hyperreflexia during transurethral litholapaxy in patients with complete spinal cord injury.

BACKGROUND

Autonomic hyperreflexia (AHR) is a potentially life-threatening hypertensive condition that occurs in patients with high spinal cord injury (SCI). The current study was aimed to determine sevoflurane concentrations that block AHR in SCI patients.

METHODS

The study involved 28 patients with chronic, complete SCI scheduled to undergo transurethral litholapaxy during general anesthesia. Nine patients without SCI served as controls post hoc. Anesthesia was induced with thiopental, and sevoflurane concentrations in 50% nitrous oxide were adjusted to maintain a Bispectral Index of 40-50. When a patient developed AHR during bladder distension, the target sevoflurane concentration was maintained for at least 10 min, and then the procedure was resumed. Systolic blood pressure, heart rate, and Bispectral Index as well as plasma concentrations of catecholamines and arginine vasopressin were measured before and during the bladder distension. Each target concentration was determined by the up-and-down method based on changes (15% increase or more) of systolic blood pressure in response to bladder distension.

RESULTS

In SCI, systolic pressure increased by 67 +/- 33 mmHg, whereas heart rate decreased by 13 +/- 8 beats/min during the first trial (P < 0.01). The hypertensive event was associated with increases of norepinephrine concentrations, but not of epinephrine or vasopressin concentrations. Systolic pressure, heart rate, and norepinephrine concentrations did not change significantly in the control patients. The end-tidal concentrations of sevoflurane to prevent AHR were EC50 of 3.12% and EC95 of 3.83%.

CONCLUSION

The EC95 for sevoflurane in 50% nitrous oxide to block AHR during transurethral litholapaxy in patients with SCI was 3.83%.