Acute reduction of cerebrospinal fluid volume prior to spinal anesthesia: implications for sensory block extent

BACKGROUND: Multiple patient and clinical characteristics contribute to the variable outcome of spinal anesthesia (SPA). Acute reduction of cerebrospinal fluid (CSF) volume may alter the effect of SPA. The objective of the present study was to test if aspiration of 10 mL CSF immediately prior to SPA is associated with higher extent of sensory block. METHODS: Interventional cohort study. One hundred and two patients undergoing total hip arthroplasty (THA) were included. Fifty-one patients underwent sampling of 10 mL CSF prior to SPA (CSF aspiration group); 51 consecutive patients were used as controls. The primary outcome was the extent of sensory block to cold stimulus 20 minutes after injection of hyperbaric bupivacaine. Secondary outcome measures included duration of motor block and incidence of failed SPA. RESULTS: Acute reduction of CSF volume by 10 mL increased the extent of sensory anesthesia (mean thoracic level [T] 4.3±2.4 vs. 7.1±2.6, P<0.001). There were no significant between-group differences regarding motor block duration (P≥0.30) or failed SPA (three of 51 [CSF aspiration group] vs. one of 51 [control group], P=0.31). In a retrospective data analysis, 10 of 13 patients in the CSF aspiration group who had previously received SPA had a higher sensory block after 10 mL CSF aspiration compared to the previous SPA (T4.1 [range, 0-11] vs. T8.2 [4-10], P<0.01). CONCLUSIONS: Acute reduction of CSF volume by 10 mL prior to SPA leads to a higher thoracic level of sensory block.