The effects of prehydration on the properties of cerebrospinal fluid and the spread of isobaric spinal anesthetic drug

BACKGROUND: In a two-part clinical study, we investigated the effect of the administration of fluids "prehydration" on the physical properties of cerebrospinal fluid (CSF) and intrathecal spread of local anesthetics. METHODS: First, in the clinical spinal anesthesia study, 68 patients were allocated randomly into the prehydration or nonprehydration groups. One group was prehydrated with 10 mL/kg of lactated Ringer's solution, and spinal anesthesia was performed with 12 mg of 0.5% isobaric tetracaine in all patients at the lumbar level. The arterial blood pressure, heart rate, and sensory block level were assessed. Second, in a magnetic resonance image study, 24 male volunteers were enrolled. CSF motion variables were measured after infusion of 10 mL/kg of lactated Ringer's solution to examine the net flow and volume displacement of the CSF at the L2-3 disk level. RESULTS: In the clinical study, there were no significant differences in arterial blood pressure, heart rate, and median peak sensory block level between the two groups, but the median time to reach peak sensory block level (26.4 ± 15.7 vs 16.5 ± 9.2 min, P < 0.05) was longer in group P. In posthydration magnetic resonance images, the CSF regurgitant fraction (caudal flow) was significantly increased after hydration, but the stroke volume, absolute stroke volume, mean flux, stroke distance, and mean velocity in the cranial direction were significantly decreased. CONCLUSIONS: Rapid crystalloid prehydration can affect CSF flow in the lumbar region, reducing cephalic spread of 0.5% isobaric tetracaine and delaying the time to reach the peak sensory level.