Influence of obesity on spinal analgesia with isobaric 0.5% bupivacaine.

In an unblinded study 50 patients undergoing cystoscopic procedures received a spinal anaesthetic of plain 0.5% bupivacaine 4 ml administered in the sitting position at the L3-4 space. There was a correlation between the height of blockade assessed by pinprick analgesia and the degree of obesity of the patients measured by weight, weight/height, and weight/height2. Using this dose of spinal anaesthetic agent, high blockade may be anticipated in obese patients.