Influence of Lumbosacral Cerebrospinal Fluid Density, Velocity, and Volume on Extent and Duration of Plain Bupivacaine Spinal Anesthesia

BACKGROUND: The current study was designed to investigate the influence of lumbosacral cerebrospinal fluid (CSF) density, velocity, and volume on the extent and duration of plain bupivacaine spinal anesthesia. METHODS: Forty-one patients scheduled to undergo orthopedic surgery with spinal block were enrolled. Lumbosacral CSF volumes were calculated from low thoracic, lumbar, and sacral axial magnetic resonance images. CSF velocity at the L3-L4 level was derived from phase-contrast magnetic resonance images. Spinal anesthesia was performed in the lateral decubitus position. CSF (2 ml) was sampled to measure CSF density before injection of 3 ml plain bupivacaine (0.5%). Statistical correlation coefficients (rho) between CSF characteristics and measurements of spinal anesthesia were assessed by Spearman rank correlation. In addition, stepwise multiple linear regression models were used to select important predictors of measures of spinal anesthesia. RESULTS: There was a significant correlation between CSF density and peak sensory block level (rho = 0.33, P = 0.034). Lumbosacral CSF volume inversely correlated with peak sensory block level (rho = -0.65, P < 0.0001) and positively correlated with onset time of complete motor block (rho = 0.42, P = 0.008). CSF volume also inversely correlated with time required for regression of the sensory block to L1 (rho = -0.35, P = 0.026) and L2 (rho = -0.33, P = 0.039). There was a significant inverse correlation between peak diastolic CSF velocity and duration of motor blockade (rho = -0.44, P = 0.005). Multiple regression analysis revealed that weight and CSF volume significantly contributed to the peak sensory block level (R2 = 0.46). CONCLUSIONS: These findings indicate that CSF density and volume influence the spread of spinal anesthesia with plain bupivacaine and that CSF volume also influences the duration of spinal anesthesia. CSF velocity might also influence the duration of plain bupivacaine spinal anesthesia.