CONTINUOUS SPINAL-ANESTHESIA - WHERE DO SPINAL CATHETERS GO

The purpose of this study was to investigate the incidence of technica l problems encountered when performing continuous spinal anesthesia an d the influence of catheter tip position on block height following inj ection of a hypobaric spinal anesthetic. Twenty-nine elderly patients undergoing hip surgery were studied. Lumbar puncture was performed wit h an 18-gauge Tuohy needle at the L3-4 (or L2-3) interspace. Threading was defined as easy if a 20-gauge catheter was inserted on the first try, 3-4 cm cephalad. Threading was considered difficult if cephalad i nsertion of the catheter was impossible on the first try; the Tuohy ne edle was then rotated with its bevel facing caudally, the catheter ins erted for 1-2 mm, and the needle turned back cephalad together with th e catheter partially threaded, for further cephalad insertion up to 4 cm. All patients received 7.5 mg of hypobaric bupivacaine or tetracain e in the lateral decubitus position and sensory levels were determined by pinprick. After surgery all catheters were injected with radiograp hic dye and examined by radiograph for verification of position. The d etermination of the level of lumbar puncture was falsely judged in 59% of cases, the puncture being performed 1 or 2 spaces higher than assu med. Although threading difficulties were encountered in 4/28 cases, t here was a 100% success rate in catheter insertion. One catheter displ acement into the epidural space was noted. Twenty of twenty-eight cath eters took a cephalad direction, 6 remained coiled in a horizontal pos ition, and 2 took a caudal direction. Finally, no correlation was foun d between the position of the tip of the catheter and the sensory leve ls achieved with the same dose of local anesthetic. We conclude that t he direction taken by the catheter cannot be anticipated, and that the final position of its tip does not influence the distribution of hypo baric local anesthetics in the subarachnoid space. However, the high i ncidence of inadequate determination of the level of lumbar puncture, associated with the cephalad threading of a catheter, can represent a potential risk of damage to the spinal cord. Furthermore, the use of t he maneuver previously described and performed in the 4 cases of diffi cult threading can not be recommended because one adds the risk of cat heter shearing.