Extradural block with bupivacaine: influence of dose, volume, concentration and patient characteristics

In a randomized, double-blind study the influences of the characteristics of both solution (dose, volume, concentration) and patient (age, weight, height, body mass index) on the development of extradural blockade produced by a low lumbar injection of bupivacaine were investigated. Thirty patients aged between 20 and 50 yr received one of three solutions (groups I-III, respectively): 0.75% 10 ml (75 mg); 0.5% 15 ml (75 mg); 0.75% 15 ml (112.5 mg). A further 20 patients older than 50 yr received 0.75% bupivacaine 10 ml (group IV, n = 10) or 15 ml (group V, n = 10). The number of segments blocked at maximal extent of block was virtually the same in each group: group I (0.75% 10 ml) 13.3 (SD 1.4); group II (0.5% 15 ml) 14.1 (2.9); group III (0.75% 15 ml) 13.8 (2.2); group IV (0.75% 10 ml) 14.2 (2.1); group V (0.75% 15 ml) 16.7 (3.1). The larger dose of bupivacaine (112.5 mg) produced the fastest onset and longest duration of block. Onset and recovery intervals were similar with 0.75% and 0.5% solutions when administered at the same dose (75 mg in 10 ml or 15 ml). There was no correlation between the level of block and the age, weight and height of the patient. In patients who received 15-ml injections, there was a positive association between the upper level of block and body mass index.