Subarachnoid anaesthesia with 0.5% bupivacaine: effects of density.

The effects of subarachnoid administration of 0.5% bupivacaine 4 ml in 8%, 5% or 0% glucose were investigated in a double-blind study in 30 women undergoing laparotomy through a lower abdominal incision. The onset time for maximum segmental spread of analgesia was 10-15 min for all solutions. Cephalad segmental spread of analgesia was three to four segments higher with the hyperbaric solutions (T4-5 v. T7-8). Time of onset of complete motor blockade of the lower limbs was 5-10 min for all solutions. The glucose-free solution did not produce sufficient surgical anaesthesia because of too low cephalad spread. Duration of motor blockade generally decreased with increasing glucose concentration, only the hyperbaric solutions providing useful for abdominal surgery, with a duration of 1-1.5 h. Anaesthesia (halothane) was required in seven of 10 patients in the glucose-free group and in five of 20 in the hyperbaric groups. No occurrence of "post-spinal headache" was recorded in the study.