Influence of sex on cerebrospinal fluid density in adults.

The extent of sensory block during spinal anaesthesia is unpredictable and is influenced by many factors, mainly patient position, site of injection, baricity and the dose of drug injected. Among other factors, cerebrospinal fluid (CSF) density has been advocated to affect subarachnoid distribution of local anaesthetics. In this study, we have investigated the influence of patient characteristics such as sex, age, weight and height on variations in the density of CSF in more than 46 consecutive patients undergoing spinal anaesthesia. CSF 2 ml was obtained after spinal puncture and before injection of local anaesthetic. Mean CSF density measured at 37 degrees C was mean 1.00054 (SD 0.00017) g ml-1, with significantly lower CSF densities in women (1.00049 (0.00011) g ml-1) than in men (1.00058 (0.00011) g ml-1) (P = 0.024). In contrast, there was no correlation between age, weight or height, and CSF density. These results suggest that sex significantly influenced CSF density and may therefore modify subarachnoid distribution of local anaesthetics.