Effect of adding sodium bicarbonate to bupivacaine for spinal anesthesia in elderly patients

The effect of added sodium bicarbonate on plain bupivacaine spinal anesthesia is unknown. Forty patients aged 75 years or older, ASA II or III, undergoing orthopedic lower limb surgery under spinal anesthesia were randomly classified into two groups. Just before injection, either 0.2 ml normal saline (group I) or 0.2 ml 0.42% NaHCO3 solution (group II) was added to 20 ml 0.5% bupivacaine hydrochloride. All patients then received intrathecally 3 ml (14.85 mg) of the bupivacaine solution in the lateral decubitus position. The segmental level of sensory loss was tested using forceps. The median time required to achieve maximal height of the sensory blockade and the median highest level of sensory anesthesia did not differ in the two groups. Alkalinized bupivacaine increased significantly the median times for regression to the T12 and L2 segments by 15 and 25 minutes, and the duration of complete motor block by 15 minutes, as compared to the hydrochloride salt. The clinical importance of such modest prolongations seems limited.