Background and Objectives Many factors have an impact on the outcome of continuous spinal anesthesia (CSA) with small-bore catheters. Recent publications of neurologic complications after CSA suggest that the local anesthetic as well as the microspinal catheter influence the analgesic effect in CSA. This prospective study was designed to evaluate the influence of the subarachnoid position of 28-gauge spinal catheters on the speed of onset of analgesia and on the dose of plain bupivacaine 0.5% required for a block at the level of T-10 in CSA.

Methods Sixty-eight patients (mean age 61.7 ± 6.4 years) received CSA using a 22-gauge Quincke needle (Kendall, Mansfield, MA) and a 28-gauge spinal catheter. After initial injection of 2.5 mL (minimum) up to a maximum of 5 mL of supplemental doses of plain bupivacaine 0.5%, the time of onset of analgesia at the level of T-10 and the dose of local anesthetics required for this block were determined. The subarachnoid catheter position was examined radiographically by a dye supported conventional anteroposterior roentgenogram of the lumbar spine on the first day after the operation.

Results The onset time of analgesia and the dose of plain bupivacaine 0.5% required for the block at the level of T-10 were significantly dependent on the subarachnoid position of the microcatheters (P < .01), but not on the level of the lumbar dural puncture (P = .29, P = .69). In patients with cranially running catheters or catheters with the tip at the level of the puncture site, analgesia onset was faster and required doses of bupivacaine were smaller than in patients with caudally running catheters.

Conclusions The subarachnoid position of a 28-gauge microcatheter is an important factor with regard to the effectiveness (e.g., onset time of analgesia and dose requirement) of CSA using plain bupivacaine 0.5%.