Venous blood concentrations after subarachnoid administration of bupivacaine.

Peripheral venous blood concentrations of bupivacaine were measured in 51 patients given 0.5% (4 ml, 20 mg) or 0.75% (3 ml, 22.5 mg) bupivacaine, both solutions with or without glucose, for spinal anesthesia. The initial absorption of bupivacaine, as measured in peripheral venous blood, was rapid, although the blood concentrations were low. The mean peak concentration (Cmax) did not differ when glucose was added to 0.5 or 0.75% bupivacaine. When glucose-free and glucose-containing bupivacaine groups were combined, 22.5 mg bupivacaine give a significantly higher venous blood concentration than 20 mg of the solution. The mean time between subarachnoid injection and the time when Cmax was reached (tpeak) was influenced by the density of bupivacaine, i.e., the tpeak of bupivacaine with glucose was significantly shorter than with glucose-free solution (35 min; P less than 0.05). No correlation was found between Cmax and the age, height, or weight of the patients, or between Cmax and the maximum cephalad level of analgesia in the different groups. In addition, there was no correlation between tpeak and the age, height, or weight of the patients. The maximal cephalad level of analgesia did not influence tpeak in the different groups (the correlation coefficients less than 0.3).

A double-blind study of motor blockade in the lower limbs. Studies during spinal anaesthesia with hyperbaric and glucose-free 0.5% bupivacaine.

Sensory and motor blockade were studied double-blind during spinal anaesthesia in 20 urology patients who received 0.5% bupivacaine solution 4 ml with or without glucose. Using a new method for determining muscle strength, motor blockade during anaesthesia was recorded quantitatively for flexion of the hip, extension of the knee and plantar flexion of the big toe. Movements of the lower part of the thoracic cage were recorded at the same time. Complete motor blockade of longer duration was observed for all three movements following the administration of the glucose-free solution compared with the solution containing glucose. During the regression phase, the muscle strength returned significantly later (knee extension and hip flexion) when glucose-free bupivacaine solution was given. There was no significant difference between the two anaesthetic solutions regarding plantar flexion of the big toe during this phase. For hip flexion (L1-L3) there was no noteworthy difference between the levels of analgesia and the motor blockade, whereas for plantar flexion of the big toe (L5-S2) the level of analgesia was 2-3 segments higher than the level of motor blockade. Thoracic movements (maximal inspiration to normal expiration) did not appear to be notably influenced by the level of analgesia. Complete regression of motor blockade was not observed for any of the movements at grade O of a modified Bromage scale. Not until 1.5-2 h after the attainment of this grade was the muscle strength of all movements restored (90% of control value).

Spinal anaesthesia with hyperbaric 0.5% bupivacaine: effects of volume.

Different volumes (1.5, 2, 3 and 4 ml) of hyperbaric 0.5% bupivacaine (8% glucose) were compared in spinal anaesthesia for urological surgery in 40 patients. The blockade was given with the patient in the sitting position. Two minutes after the injection the patient was placed in the lithotomy position. The time required for maximum cephalad spread of analgesia was about 20 min for all volumes. The maximum cephalad spread was directly related to log volume of the local anaesthetic solution. The onset time for motor blockade of the lower limbs decreased and the frequency increased with increasing volume. Four ml produced complete blockade in all patients. The duration of analgesia increased with increasing volume: 3-4 ml produced analgesia at T8 for 1.5-2.5 h and at L1 for 2-3 h. With this volume, complete motor blockade was obtained for 1.5-2.5 h. Satisfactory surgical anaesthesia for transurethral resection was obtained with 3-4 ml of the local anaesthetic solution.