COMBINED SPINAL-EPIDURAL ANESTHESIA FOR OUTPATIENT SURGERY - DOSE-RESPONSE CHARACTERISTICS OF INTRATHECAL ISOBARIC LIDOCAINE USING A 27-GAUGE WHITACRE SPINAL NEEDLE

Background: Combined spinal-epidural anesthesia (CSE) may offer theore tic advantages for outpatient surgery, because it produces the rapid o nset of spinal anesthesia, with the option to extend the blockade with an epidural catheter. In this study, the authors attempted to determi ne an appropriate initial dose of a short-acting local anesthetic, 2% lidocaine, to administer for outpatient knee arthroscopy using CSE. Me thods: Data were collected from 90 patients undergoing outpatient knee arthroscopy, Using a double-blinded, prospective study design, patien ts were randomly assigned to receive CSE with an initial dose of intra thecal 2% lidocaine of 40, 60, or 80 mg. A 27-G 4(11)/(16)-inch Whitac re needle was placed through a 17-G Weiss needle. Onset and regression of sensory anesthesia and motor blockade were measured by a blinded o bserver at frequent intervals. Results: All 90 patients had adequate a nesthesia. Durations of thoracic and lumbar sensory and lower limb mot or blockade were significantly shorter in the 40-mg group compared wit h the 60- or 80-mg groups (P < 0.0002 Mantel-Cox, Survivorship Analysi s). Indices of neural blockade resolved 30-40 min more rapidly in the 40-mg group than in either the 60-or 80-mg group. Times to urinate, si t upright in a chair, take oral fluids, and be discharged were all sig nificantly shorter (between 30 and 60 min) in the 40-mg group compared with the 60- and 80-mg groups (P < 0.01). Seven patients required int raoperative epidural supplementation: three in the 40-mg group, three in the 60-mg group, and one in the 80-mg group. Conclusions:: Combined spinal-epidural anesthesia with a 40-mg initial intrathecal dose of l idocaine provided reliable anesthesia for knee arthroscopy. Duration o f spinal anesthesia with lidocaine was dose related.