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Which anesthetics influence laryngeal motion during laryngoscopy in dogs?
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Various anesthetics are currently used in dogs undergoing laryngoscopy. Less is known about possible effects on laryngeal motion which could easiliy lead to misdiagnoses. In this experimental study, various drugs and drug combinations conventionally used for anesthesia on arytenoid cartilage motion during laryngoscopy in normal dogs are evaluated: intravenous thiopental given to effect is the best choice
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Six large breed healthy dogs with no previous history of respiratory dysfunction were included. Each dog was randomly assigned to a different injectable anesthetic protocol once weekly for 6 weeks, then in the 7th week all dogs were anesthetized with isoflurane.
Videolaryngoscopy was performed and recorded starting immediately after induction until dogs could no longer be safely restrained for endoscopy. Video was digitized and 3 still images of maximal inspiration and expiration from the first 15 seconds (induction) and the last 15 seconds (recovery) were captured and imported into an image analysis software program. The height andarea of the laryngeal ostium were measured in pixels. Normalization of the glottal gap areawasperformed using the formula (normalized glottal gap area (NGGA)=area in pixels/height2). ANOVA was performed on the NGGA of images collected at inspiration and expiration during induction and recovery. Fischer`s exact test was performed when significance (P<.05) wasfound.
Within each protocol, laryngeal motion (defined as change in NGGA) at induction was not significantly different from laryngeal motion measured at recovery. Additionally, no significant differences were found in arytenoid motion immediately after induction when anesthetic protocols were compared.
Arytenoid motion before recovery was significantly greater with thiopental when compared with propofol (P=.046), ketamine+diazepam (P=.0098), acepromazine+thiopental (P=.0021), and acepromazine+propofol (P=.0065).
No significant difference in arytenoid motion was seen immediately after induction or before recovery when acepromazine+butorphanol+ isoflurane and thiopental were compared.
The authors concluded that intravenous thiopental given to effect is the best choice for assessing laryngeal function in dogs. Dogs premedicated with acepromazine with or without opioids that require further anesthetic restraint for laryngoscopy should be anesthetized with isoflurane administered by mask.
Misdiagnosis of laryngeal paralysis during laryngoscopy can be avoided by selecting the anesthetic regimens with the least effect on arytenoid motion.
Source: Jackson, Aaron M., Tobias, Karen, Long, Cassie, Bartges, Joseph & Harvey, Ralph (2004): Effects of Various Anesthetic Agents on Laryngeal Motion During Laryngoscopy in Normal Dogs. In:
Veterinary Surgery 33 (2), 102-106.
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