CAUSES AND PREDICTION OF MALDISTRIBUTION DURING CONTINUOUS SPINAL-ANESTHESIA WITH ISOBARIC OR HYPERBARIC BUPIVACAINE

Background: Many cases of cauda equina syndrome after maldistribution of local anesthetics during continuous spinal anesthesia have been rep orted. In experiments, a caudad route of catheter travel and the use o f hyperbaric agents have been shown to induce these limited blocks. Th e aim of this clinical study was to verify this hypothesis and seek a predictive factor for the maldistribution of bupivacaine, Method: Cont inuous spinal anesthesia via a 19-gauge end port spinal catheter was p erformed in 80 elderly patients randomly assigned to receive either is obaric or hyperbaric solutions. Successive injections of 2.5 mg bupiva caine were per formed at 5-min intervals until a sensory level at or c ranial to T8 was obtained. Maldistribution was defined by a sensory le vel caudal to T12 despite a total dose of 17.5 mg of either isobaric o r hyperbaric bupivacaine. After surgery, all catheters were injected w ith contrast media and examined radiographically, Results: The frequen cy of maldistribution was not significantly different in the isobaric and hyperbaric groups. A caudally oriented catheter tip was found to b e a major cause of maldistribution (P < 10(-5)). A thoracic sensory le vel could be reached in all patients presenting a limited block by sim ply changing the baricity of the bupivacaine, the position of the pati ent, or both. The sensory level obtained 10 min after the first inject ion of 2.5 mg isobaric or hyperbaric bupivacaine was found to be a pre dictive factor of maldistribution. Conclusions: Hyperbaric solutions d o not appear to be a clinical factor in the development of limited blo ck. The principle factor causing the maldistribution of bupivacaine is the caudal orientation of the tip of the end-hole catheter rather tha n its level or the route of catheter travel.