Dose-dependent suppression of the electrically elicited stapedius reflex by general anesthetics in children undergoing cochlear implant surgery.
BACKGROUND
Cochlear implants stimulate the auditory nerve to enable hearing. Determining appropriate upper and lower limits of stimulation is essential for successful cochlear implantation. The intraoperative evoked stapedius reflex threshold (ESRT) and evoked compound action potential (ECAP) are commonly used to determine the limits of implant stimulation. In this study, we evaluated the dose-related effects of sevoflurane, desflurane, isoflurane, and propofol on the intraoperative ESRT and ECAP.


METHODS
Forty-four children aged 6 mo to 17 yr undergoing cochlear implantation were recruited. Each child was randomly assigned to receive sevoflurane, desflurane, isoflurane, or propofol. Evoked responses were measured by a blinded investigator at end-tidal anesthetic concentrations corresponding to 0, 0.75, and 1.5 age-adjusted minimum alveolar concentration administered in random sequence and at targeted blood concentrations of propofol of 0, 1.5, and 3.0 microg/mL. Data were analyzed using one-way repeated-measures analysis of variance. P < 0.05 was considered statistically significant.


RESULTS
The ESRT increased dose dependently with increasing volatile anesthetic concentration (P < 0.01). The stapedius reflex was completely abolished by volatile anesthesia in more than half of children. Propofol minimally affected the ESRT. In contrast, the ECAP was unaffected by anesthesia.


CONCLUSIONS
Volatile anesthetics suppress the stapedius reflex in a dose-dependent manner, suggesting that ESRT measurements acquired during volatile anesthesia will overestimate the maximum comfort level, which may cause discomfort postoperatively and adversely affect the child's adaptation to the implant. We advise against the use of volatile anesthetics for measurement of the stapedius reflex threshold during cochlear implant surgery.
Department of Anesthesia and Pain Medicine, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada. mark.crawford@sickkids.ca
Mark W
MW
Crawford
Michelle C
MC
White
Evan J
EJ
Propst
Christian
C
Zaarour
Sharon
S
Cushing
Carolyne
C
Pehora
Adrian L
AL
James
Karen A
KA
Gordon
Blake C
BC
Papsin
D000293:Adolescent; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000097:blood / Q000494:pharmacology*; D001309:Auditory Threshold / Q000187:drug effects; D002648:Child; D002675:Child, Preschool; D019929:Cochlear Implantation; D000077335:Desflurane; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects*; D006801:Humans; D007223:Infant; D007530:Isoflurane / Q000031:analogs & derivatives / Q000494:pharmacology; D008738:Methyl Ethers / Q000494:pharmacology; D016343:Monitoring, Intraoperative / Q000379:methods*; D015742:Propofol / Q000494:pharmacology; D011446:Prospective Studies; D012022:Reflex, Acoustic / Q000187:drug effects*; D000077149:Sevoflurane; D013198:Stapedius / Q000294:innervation*
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane; D015742:Propofol