title: The effects of differing concentrations of bupivacaine on the epidural somatosensory evoked potential after posterior tibial nerve stimulation.
abstract: The somatosensory evoked potential (SEP) recorded from the cervical epidural space in response to stimulation of the posterior tibial nerve is often used to monitor spinal cord integrity during scoliosis surgery. Epidural analgesia may be used as part of the anesthetic technique for scoliosis surgery, but the effects of the local analgesic on the evoked potential must be determined to ensure that it does not interfere with the monitoring of spinal cord function. Therefore, we compared the effects of the administration of 10 mL of 0.25% (n = 8), 0.5% (n = 8), or 0.75% (n = 8) bupivacaine injected into the L3-4 epidural space on the somatosensory evoked potential to posterior tibial nerve stimulation in patients anesthetized with a propofol infusion, nitrous oxide and oxygen, immediately before scoliosis surgery. Compared with a control group (n = 8), a concentration-dependent effect of bupivacaine was found on overall amplitude of the evoked potentials and the amplitude of all peaks. There were no significant differences between 0.25% bupivacaine and the control group, but both 0.5% and 0.75% bupivacaine were associated with clinically and statistically significant decreases in overall amplitude (P < 0.002, 0.5% bupivacaine; P < 0.001, 0.75% bupivacaine). Latency increased similarly in all groups. We conclude that bupivacaine in concentrations greater than 0.25% is not suitable for scoliosis surgery, if spinal somatosensory evoked potentials (SSEP) are to be measured.
authors.affiliation: Department of Anaesthetics, Northwick Park Hospital, Middlesex, United Kingdom.
authors.forename: B A
authors.initials: BA
authors.lastname: Loughman
authors.forename: M E
authors.initials: ME
authors.lastname: Fennelly
authors.forename: M
authors.initials: M
authors.lastname: Henley
authors.forename: G M
authors.initials: GM
authors.lastname: Hall
mesh_terms: D000293:Adolescent; D015360:Analgesia, Epidural; D000769:Anesthesia, Inhalation; D000771:Anesthesia, Intravenous; D001794:Blood Pressure / Q000187:drug effects; D002045:Bupivacaine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D016343:Monitoring, Intraoperative; D009609:Nitrous Oxide; D015742:Propofol / Q000008:administration & dosage; D011930:Reaction Time / Q000187:drug effects; D012600:Scoliosis / Q000601:surgery; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013979:Tibial Nerve / Q000187:drug effects* / Q000502:physiology
chemical_list: D009609:Nitrous Oxide; D002045:Bupivacaine; D015742:Propofol