Evaluation of the time to desensitization of the larynx of cats following topical lidocaine application

Abstract

Objectives The objective of this study was to evaluate the time to decreased reactivity of the arytenoid cartilages in cats after application of topical lidocaine. Methods One hundred and ten mixed-breed cats were randomly assigned to one of five groups based on the time between application of lidocaine and stimulation of the larynx: 5 (T5), 15 (T15), 30 (T30), 45 (T45) or 60 (T60) s. Cats were premedicated with dexmedetomidine, ketamine and buprenorphine. Anesthesia was induced with propofol to effect. Lidocaine 2% (2 mg/kg) was applied topically to the vocal cords using a catheter attached to a syringe under direct laryngoscopy. After lidocaine application, the designated time elapsed and the vocal cords were stimulated with the patient end of an endotracheal tube. Severity of reaction was reported as none, mild, moderate or severe. All cats were intubated after the reactivity score was recorded. Anesthesia was maintained with isoflurane and 100% oxygen while cats were spayed or neutered. Cats were monitored in recovery for signs of respiratory complications and pain. Results There was a significant difference in overall reactivity score between T5 and T45 ( P = 0.0038). Also, there was a significant difference in the number of cats with no reaction compared with cats with any reaction between T5 and T30 ( P = 0.03), as well as between T5 and T45 ( P = 0.0028). No cat had a severe reactivity score at T45 or T60. All cats were successfully intubated. There were no complications during intubation, maintenance of anesthesia or recovery. Conclusions and relevance As the lowest overall reactivity score occurred at T45, it is recommended to wait at least 45 s after application of topical lidocaine before attempting tracheal intubation.

Clinical effects and pharmacokinetics of nebulized lidocaine in healthy horses

“…As flow rate and volume of flow should be symmetrical throughout the proximal airways, the increased time between nebulization and stimulation of these right-sided sites compared to the left is considered the most likely justification for a unilateral decrease in sensitivity. Lidocaine takes <1 min to exert local anesthetic effects on the larynx when sprayed topically ( 31 , 32 ). Even though lidocaine has such a rapid onset of action, the lower local concentrations achieved via nebulization vs. a topical spray makes it likely that an extended contact time is required for the drug to exert its full effect.…”