title: The effects of general anaesthesia on nerve-motor response characteristics (rheobase and chronaxie) to peripheral nerve stimulation.
abstract: Using a simple surface nerve stimulation system, I examined the effects of general anaesthesia on rheobase (the minimum current required to stimulate nerve activity) and chronaxie (the minimum time for a stimulus twice the rheobase to elicit nerve activity). Nerve stimulation was used to elicit a motor response from the ulnar nerve at varying pulse widths before and after induction of general anaesthesia. Mean (SD) rheobase before and after general anaesthesia was 0.91 (0.37) mA (95% CI 0.77-1.04 mA) and 1.11 (0.53) mA (95% CI 0.92-1.30 mA), respectively. Mean (SD) chronaxie measured before and after general anaesthesia was 0.32 (0.17) ms (95% CI 0.26-0.38 ms) and 0.29 (0.13) ms (95% CI 0.24-0.33 ms), respectively. Under anaesthesia, rheobase values increased by an average of 20% (p = 0.05), but chronaxie values did not change significantly (p = 0.39). These results suggest that threshold currents used for motor response from nerve stimulation under general anaesthesia might be higher than those used in awake patients.
authors.affiliation: Department of Anesthesia and Pain Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: B C
authors.initials: BC
authors.lastname: Tsui
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D004562:Electrocardiography; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology*; D004561:Transcutaneous Electric Nerve Stimulation / Q000295:instrumentation* / Q000379:methods
chemical_list: D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local