BACKGROUND: Even though the effect of prehydration on the spinal anesthesia-induced hypotension has not yet been concluded, prehydration prior to spinal anesthesia is recommended in order to reduce the incidence and severity of hypotension. We investigated the effects of prehydration on hemodynamic change during spinal anesthesia with isobaric 0.5% tetracaine.

METHODS: We prospectively performed this study on 96 patients who underwent elective transurethral surgery from October 2002 to January 2004. Patients were randomly allocated to receive either no prehydration or 10 ml/kg crystalloids administered over 10 15 min prior to spinal anesthesia. We compared dermatomal spreads of spinal anesthesia, hemodynamic parameters (blood pressure, heart rate), incidences of hypotension and bradycardia between two groups.

RESULTS: Hemodynamic parameters, incidences of hypotension and bradycardia showed no statistically significant differences during spinal anesthesia between two groups. There were statistically significant differences in the dermatomal spread of sensory levels between two groups from 5 to 90 min after spinal anesthesia. Sensory block levels in prehydration group were statistically lower than no prehydration group.

CONCLUSION: We hypothesized that prehydration can be one of factors that influence on dermatomal spread of local anesthetics in isobaric spinal anesthesia. The difference of dermatomal spread between two groups may be caused by brain blood barrier (BBB)-freely passing crystalloids, which may influence on the volume and density of cerebrospinal fluids. To verify this phenomenon found in our study, further investigation is still warranted.