Is glucose-free bupivacaine isobaric or hypobaric?

Spinal anesthesia with 0.5% glucose-free bupivacaine was given to 20 patients lying in the lateral decubitus position during lumbar injection and for 30 minutes after. The mean maximum level of anesthesia after 30 minutes was Th:8 in the nondependent side and Th:9 in the dependent side. The difference in cephalad level of analgesia between the two sides during the initial 30 minutes was significant. Fourteen patients experienced some degree of hypoalgesia during the initial 30 minutes in the dependent side but not in the nondependent side. The degree of motor blockade also showed significant difference between the dependent and nondependent side except at five minutes. These findings indicate glucose-free bupivacaine 0.5% is hypobaric in clinical conditions.