title: Suppression of spinal cord motoneuron excitability correlates with surgical immobility during isoflurane anesthesia.
abstract: BACKGROUND
  Recent evidence suggests that the spinal cord is an important site of anesthetic action that produces surgical immobility. Inhalation anesthetics depress the Hoffmann's reflex (H reflex) and F wave, indicating spinal motoneuron suppression. The aim of this study was to assess the correlation between isoflurane-induced immobility and H- and F-wave suppression.
  
  
  METHODS
  The baseline H reflex and F wave were measured before anesthesia in 15 adult patients. After induction, 1% end-tidal isoflurane was maintained for 20 min before the H and F waves were reelicited. Using an electric stimulus applied to the forearm and grading the response as movement or no movement, the authors increased or decreased the isoflurane concentration in 0.1% steps, depending on the movement responses. The H and F waves were recorded 20 min after each change of isoflurane concentration. The correlation between H- and F-wave suppression and surgical immobility was analyzed using a paired t test with Bonferroni correction.
  
  
  RESULTS
  H-reflex amplitude (2.74 +/- 1.63 mV) and F-wave persistence (70.69 +/- 26.19%) at the highest isoflurane concentration that allowed movement response to a stimulus are different (P < 0.01) from these (1.97 +/- 1.46 mV; 43.16 +/- 22.91%) at the lowest isoflurane concentration that suppressed response. At 0.8% isoflurane, the H-reflex amplitude was 3.69 +/- 1.83 mV with movement and 1.01 +/- 1.14 mV without movement (P < 0.01); F-wave amplitude was 0.29 +/- 0.15 mV with movement and 0.11 +/- 0.06 mV without movement (P < 0.01); F-wave persistence was 80 +/- 22.36% with movement and 34.9 +/- 25.75% without movement (P < 0.01).
  
  
  CONCLUSIONS
  The degree of H- and F-wave amplitude and F-wave persistence suppression correlates with movement response, suggesting that isoflurane-suppressive action in the spinal cord plays a significant role in producing surgical immobility.
authors.affiliation: Department of Anesthesiology, New York University Medical Center, New York 10016, USA. hzhou@mcan00.med.nyu.edu
authors.forename: H H
authors.initials: HH
authors.lastname: Zhou
authors.forename: T T
authors.initials: TT
authors.lastname: Jin
authors.forename: B
authors.initials: B
authors.lastname: Qin
authors.forename: H
authors.initials: H
authors.lastname: Turndorf
mesh_terms: D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D006181:H-Reflex / Q000187:drug effects*; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects*; D013514:Surgical Procedures, Operative
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane