Continuous Rate Infusion of Ketamine Hydrochloride And

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Continuous Rate Infusion of Ketamine Hydrochloride and Dexmedetomidine for Maintenance of Anesthesia during Laryngotracheal Surgery in New Zealand White Rabbits (Oryctolagus cuniculus)

Lea J Sayce,1,2,*,† Maria E Powell,2,† Emily E Kimball,3 Patty Chen,4 Gary J Gartling,1 and Bernard Rousseau1,2

New Zealand white rabbits (Oryctolagus cuniculus) are an established in vivo model for the study of structural and functional consequences of vocal-fold vibration. Research design requires invasive laryngotracheal procedures, and the presence of laryngospasms or pain responses (or both) hinder phonation-related data collection. Published anesthesia regimens report respiratory depression and muscle tone changes and have been unsuccessful in mitigating autonomic laryngeal responses in our protocol. Infusion of ketamine hydrochloride and dexmedetomidine hydrochloride in pediatric medicine provides effective analgesia and sedation for laryngotracheal procedures including intubation and bronchoscopy; however, data evaluating the use of ketamine–dexmedetomidine infusion in rabbits are unavailable. This study reports a new infusion regimen, which was used in 58 male New Zealand white rabbits that underwent a nonsurvival laryngotracheal procedure to induce phonotraumatic vocal-fold injury. Animals were sedated by using ketamine hydrochloride (20 mg/kg IM) and dexmedetomidine (0.125 mg/kg IM). Maintenance anesthesia was provided by using continuous rate intravenous infusion of ketamine hydrochloride (343 µg/kg/min) and dexmedetomidine (1.60 µg/kg/min). A stable plane of anesthesia with no autonomic laryngeal response (laryngospasm) was achieved in 32 of the 58 rabbits (55%). Laryngospasms occurred in 25 of 58 animals (43%) and were controlled in 20 cases (80%) by providing 0.33 mL 2% topical lidocaine, incremental increase in infusion rate, or both. Continuous rate infusion of ketamine hydrochloride–dexmedetomidine with prophylactic topical lidocaine provides a predictable and adjustable surgical plane of anesthesia, with minimal confounding respiratory and autonomic laryngeal responses, during extended-duration laryngotracheal surgery in rabbits. This regimen should be considered as an alternative to injection maintenance for prolonged, invasive procedures.

Abbreviations: CRI, continuous rate infusion; KD, ketamine hydrochloride + dexmedetomidine hydrochloride; MAP, mean arterial blood pressure

DOI: 10.30802/AALAS-JAALAS-19-000076

New Zealand white rabbits (Oryctolagus cuniculus) have Our lab has developed and validated experimental pro- become a popular model for the investigation of structural, mo- cedures to surgically induce vocal fold phonation that can be lecular, and functional consequences of hoarseness (dysphonia). visualized endoscopically.21 This methodology allows for the Phonotrauma is the leading cause of hoarseness, responsible for concurrent investigation of both the structural, molecular, and 43% of short-term disability claims for voice disorders.12 Dys- functional consequences of phonotraumatic behavior. Rabbits phonia affects an estimated 20 to 23 million adults in the United have become an important model for this line of investigation States each year, with an economic burden of approximately because of their histologic similarity in vocal fold structure $13 billion dollars,12 thus representing a significant public health to humans56 and their lower cost in comparison to larger ani- concern. Phonotrauma involves excessive or abusive vocal mal models. Rabbits typically do not vocalize unless they are behaviors that lead to damage to the vocal folds. As such, threatened or in pain (that is, nonhabitual vocalizers); therefore, the molecular, structural, and functional changes resulting from this model has the notable benefit of allowing investigators to phonotrauma have been the focus of ongoing investigation. surgically control for both dose magnitude and duration of vocalization experimentally. Phonotrauma-induced changes and vocal-fold wound Received: 19 May 2019. Revision requested: 17 Jun 2019. Accepted: 23 Aug 2019. 39,40,58 1Department of Communication Science and Disorders, School of Health and Reha- healing have been investigated in the rabbit model, and bilitation Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania; Departments of experimental findings align with those described in human 2Otolaryngology and 3Hearing and Speech Sciences, Vanderbilt University, Nashville, phonotrauma literature.8,70,71 Studies using the rabbit phona- 4 Tennessee; and Animal Care and Use Review Office, US Army Medical Research and tion model have characterized mRNA changes in response to Development, Frederick, Maryland 29,39 *Corresponding author. Email: [email protected] phonotraumatic behaviors, described changes elicited in †These authors contributed equally to this work epithelial barrier function,39 and elucidated timelines for the

176 Intravenous ketamine and dexmedetomidine for rabbit anesthesia

recovery of the vocal-fold epithelium after phonotrauma.48 variety of produce and other food enrichments, with municipal Increased understanding of the molecular and cellular response water provided through a drinking valve. The rabbits were ac- to phonotrauma will contribute to evidence-based medicine and climated prior to experimental procedures. therapy practices for this condition. Selection of route of administration. Standard anesthetic Currently, our group uses a rabbit surgical model to character- approaches for rabbits call for the administration of nebulized ize the safety and efficacy of glucocorticoid steroid use for the inhalational anesthesia agents (for example, isoflurane) through treatment of phonotraumatic vocal-fold damage. In these ex- either oral mask or laryngeal mask airway with spontane- periments, rabbits are anesthetized and surgically phonated by ous respiration6,33 or placement of an endotracheal tube with using cricothyroid electrical stimulation and forced, humidified mechanical ventilation.15,51 However, the complexity of our airflow through the glottis for 120 min.21 Autonomic laryn- surgical methods and the future need for animal recovery after geal response (for example, laryngospasm) to upper airway the procedure prevented the use of these standard anesthetic stimulation during general anesthesia is widely reported,20,42,59 regimens and necessitated careful consideration of alternative particularly in the presence of upper airway manipulation.42,59 routes of administration. To surgically induce phonation, con- These autonomic laryngeal responses posed a significant trolled airflow must be forced through the glottis as the vocal concern during the development of our surgical protocols, folds are adducted through electrical stimulation. To introduce due to the considerable negative effect they could have on airflow through the glottis, the trachea is transected, and the functional vocal-fold vibration and related downstream biologic cranial segment is redirected to receive positive airflow from an processes. Therefore, we needed an anesthetic regimen that external air supply (Figure 1). This diverted airway precludes would provide depth of anesthesia sufficient both to prevent oral administration of inhaled anesthesia, because the result- surgical pain responses (for example, movement, increased ing airway (caudal aspect of the trachea) bypasses the larynx, heart rate in response to surgical manipulation) and to mitigate nasopharynx, and oral cavity. The nebulized anesthesia agent break-through, local, autonomic laryngeal responses during delivered by tracheostomy with mechanical ventilation is a sustained phonation. standard alternative to oral administration, but this approach While multiple studies have reported continuous rate infu- requires a cuffed endotracheal tube to seal the caudal airway. sion (CRI) of ketamine hydrochloride plus dexmedetomidine Lumen pressure created by an inflated cuff can induce tissue hydrochloride for procedural sedation and analgesia in pediatric degradation over the course of these long procedures, thus po- populations,11,24,46,50,69 there is an absence of data regarding this tentially introducing complications during tracheal anastomosis route of administration in rabbits. In this report, we describe in survival procedures.38 Because a cuffed endotracheal tube the development of a ketamine–dexmedetomidine (KD) CRI is required in the cranial tracheal segment to create the sealed anesthetic regimen with topical lidocaine for use in New Zealand subglottis necessary for vocal-fold vibration, we prioritized white rabbits undergoing extended-duration procedures that finding an alternative to isoflurane with mechanical ventilation. require extensive manipulation of the trachea and larynx. To address the complex anesthesia needs of this protocol, we Within-procedure anesthetic doses and animal vital signs during chose to investigate intravenous CRI for multiple reasons: (1) this regimen are reported in comparison to normative values CRI would not interfere with the surgical site, (2) once achieved, for this species. Parameters reported include intraoperative steady-state anesthesia is readily maintained through CRI, respiratory rate, heart rate, mean arterial blood pressure (MAP), and (3) CRI results in predictable effects, because it avoids the and SpO2; we also describe the incidence and management of absorption-related variability associated with intramuscular clinically salient changes in vital signs and autonomic laryngeal maintenance. Furthermore, if negative anesthesia-associated responses (laryngospasms). consequences occur, CRI dosing can be quickly and easily adjusted, although the effects of these changes may lag somewhat, Materials and Methods depending on the pharmacokinetic properties of the drugs used. Research design. Data presented were obtained from animal Selection of anesthetic agents. Drug selection for this protocol records of surgical procedures that occurred during the devel- was informed through the clinical expertise of our research opment of the KD anesthetic regimen in our laboratory. These veterinarian and relevant literature review. Pentobarbital is data reflect the development and refinement of our anesthetic widely used for intravenous anesthesia in rabbits, but we regimen for our induced phonation procedures. excluded this drug due to its known respiratory and cardio- Animals. Animal records from 58 male adolescent New Zealand vascular depression32,74 and described immunosuppression,19 white rabbits (Oryctolagus cuniculus; age, 4 to 6 mo; weight, which was likely to affect experimental outcomes during the 3.21 ± 0.20 kg) were reviewed for this study. All procedures for evaluation of vocal-fold injury and subsequent glucocorticoid original studies were approved by the Vanderbilt University steroid treatment. Similarly, propofol was not considered for Medical Center Animal Care and Use Program, a Public Health this experiment in light of reported bradycardia and bradypnea Service–assured and AAALAC–accredited facility in compliance associated with higher doses and subtherapeutic anesthesia at with the Guide for the Care and Use of Laboratory Animals34 and lower doses.62 Thiopental was excluded due to its tendency to the Animal Welfare Act.2 Rabbits were purchased from Charles increase heart rate in rabbits,49 as well as its minimal analgesic River Laboratory (Senneville, Quebec, Canada), where they action, which indicated that the drug was unlikely to prevent were bred in an environment free from Encephalitozoon cuniculi, autonomic laryngeal responses and surgical pain for the dura- rabbit hemorrhagic disease virus, Pasteurella multiocida, Salmo- tion of the procedure. nella spp., Treponema spp., and Clostridium piliforme. Rabbits Ketamine hydrochloride is a N-methyl-D-aspartate recep- were ear-tattooed for identification and maintained in a closed tor antagonist with combined sedative and dose-dependent colony. The rabbits were single-housed in caging (Allentown, analgesic properties and provides fast-acting and long-lasting Allentown, NJ) in temperatures ranging from 62 to 70° F (16.7 to anesthesia. Ketamine was selected for CRI because (1) its dis- 21.1 °C) and in a humidity-controlled (35% to 75%) environment tribution half-life is only 10 min, (2) it does not significantly on a 12:12-h on:off light cycle. The daily diet consisted of chow decrease functional, residual, respiratory capacity, and (3) it does (Laboratory Rabbit Diet HF 5326, Purina, St Louis, MO) and a not increase pain sensitivity after dissipation of its analgesic ef-

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receptors.4,63,72 In addition, multiple reports describe laryngospasm during ketamine anesthesia;5,9,13 however, the causal relationship between ketamine and laryngospasm is not well defined.72 The unwanted side effects associated with high doses of ketamine have precipitated a need to identify drug combina- tions that result in potent anesthesia at lower doses.25,41 Dexmedetomidine hydrochloride is a selective α2 adrenergic receptor agonist and was chosen as a promising complement to ketamine in this study. Dexmedetomidine has a rapid onset of action (less than 5 min), with a peak effect within 15 min.37 Several reports demonstrate that the KD drug combination provided safe and effective analgesia, with reduced incidence of the tachycardia, hypertension, and salivation associated with the administration of ketamine only and absence of the bradycardia and hypotension observed with high doses of dexmedetomidine alone.22,26,37,67 Advantageous to our study addressing the effectiveness of glucocorticoid administration on recovery from phonotraumatic injury, single-dose intramuscular injection of KD in a rabbit resulted in stable serum glucocorticoid levels over a 24-h period, whereas the use of ketamine–buprenorphine, with or without dexmedetomidine, resulted in a decrease in cortisol.23 Because an autonomic response to laryngeal stimulation (for example, laryngospasm) is a commonly observed occurrence in procedures involving manipulation of the upper airway,20,42,59 management of these autonomic responses was a driving factor in modifying our anesthetic protocol. Initial procedures using KD alone revealed that additional local anesthetic agents were necessary to mitigate these responses. Lidocaine hydrochloride is the most common topical anesthetic used in the airway.55 Lidocaine’s initial anesthetic effect onsets at 1 min, with a therapeutic effect lasting as long as 45 min.57 When administered to the upper airway, lidocaine has been found to prevent airway protective reflexes (for example, laryngospasm).47 Therefore, topical administration of 2% lidocaine solution was added to our protocol, initially to be administered as a therapeutic agent in response to laryngospasm and ultimately as prophylactic agent to prevent laryngospasm. Sedation. On the day of the surgery, rabbits were weighed and transferred from the housing room to the operating room by using a covered pet carrier. Rabbits were immobilized in a sternal recumbent position, supplied with blow-by-nose oxygen, and sedated by injecting ketamine (20 mg/kg IM; Vedco, St Joseph, MO) and dexmedetomidine (0.125 mg/kg IM; Zoetis, Parsippany, NJ) into either the longissimus or illicostalis muscle. Sedation was determined by the following indicators: absence of pedal withdrawal reflex in response to toe pinch, stable reduced frequency of respiration (reduced from more than 150 breaths per minute to 30 to 60 evenly paced breaths per minute), reduction of smooth muscle tone, and loss of righting reflex when Figure 1. Procedural setup for an induced-phonation procedure. (A) A close view of the incision site, demonstrating endotracheal tube and placed in a lateral recumbent position. electrode placement. (B) Anesthetized rabbits are placed in a supine Maintenance anesthesia. Once sedation was confirmed, rabbits position on a circulating-water heat mat, and a surgical incision is were transferred to a supine position on a circulating water heat made to expose the larynx and trachea. Oxygen is supplied directly pad coupled to a heat therapy pump (model HTP-1500, Adroit to the airway through an uncuffed endotracheal tube in the caudal Medical Systems, Loudon, TN) to maintain body tempera- tracheal segment, while humidified air is directed through the cranial tracheal segment via a cuffed endotracheal tube. Custom stainless- ture, and the forelimbs were gently lateralized and restrained. steel electrodes are placed in the cricothyroid membrane and muscle Monitoring devices were attached after sedation but prior to the to deliver trains of electrical stimulation. A pediatric laryngoscope is initiation of maintenance CRI anesthesia; indirect blood pressure used to elevate the glottis such that vocal folds can be visualized, and was measured by using a Cardell multiparameter monitor (Mid- a cushion is used to support the rabbit’s neck and head. mark, Dayton, OH), with a size 2 cuff secured around the right hindleg; a probe was placed on a digit of a hindleg for monitoring fect.28,36 However, high doses of ketamine can have unwanted SpO2, heart rate was assessed by using a digital system (V5 Vet effects, including tachycardia, ventricular arrhythmia,44 respira- View, Scil Veterinary Excellence, Gurnee, IL), temperature was tory depression,35,63 increased muscle tone,35,54 suppression of measured by using a rectal thermometer, and respiratory rate 54 proinflammatory cytokines, and antagonistic action at opioid was determined visually. Heart rate and SpO2 were monitored 178 Intravenous ketamine and dexmedetomidine for rabbit anesthesia

continuously and reported every 15 min. Temperature, blood pain response, autonomic laryngeal response (laryngospasm), pressure, and respiratory rate were monitored and recorded at reduced respiratory rate (fewer than 30 breaths per minute),3 15-min intervals for the duration of the procedure. Saline-flushed and bradycardia (below 130 bpm).3 When autonomic laryngeal 24-gauge catheters (Surflash IV, Terumo, Tokyo, Japan) were response occurred, the larynx first was treated with 0.33 mL of 2% inserted into the marginal vein of each ear. One catheter was topical lidocaine. If symptoms did not abate within 2 min, CRI used to provide warmed 0.9% sodium chloride through a 70-in. maintenance anesthesia doses were increased in a step-wise macrobore primary intravenous line (Zoetis) at a rate of 30 drops fashion (increases of 50 µg/kg/min for ketamine and 0.5 µg/ per minute (30 mL/h). The second catheter was used to supply kg/min for dexmeditomidine) at 5-min intervals, with obser- maintenance intravenous KD anesthesia by CRI (ketamine, 200 vation for symptom abatement. When monitored parameters to 1000 µg/kg/min; dexmedetomidine, 0.65 to 3.0 µg/kg/min). increased, CRI maintenance anesthesia doses were increased Separate syringe infusion pumps (model AS50m Baxter, Chicago, again as described, followed by the administration of lidocaine IL) were used for each drug for the fidelity of dose adjustment. as needed. Conversely, when anesthesia side effects such as A surgical plane of anesthesia was determined by absence of a bradycardia or significantly reduced respiratory rate with corneal or laryngeal response under maintenance of independent a concomitant drop in SpO2 occurred, the CRI maintenance diaphragmatic breathing. anesthesia dose was decreased in a step-wise fashion until Surgical procedures. The nonsurvival phonation surgical pro- symptom abatement. cedure has previously been described.21 After confirmation of Statistical analysis Procedural durations are reported as mean a surgical plane of anesthesia, the chest and neck were clipped ± 1 SD. All vital signs data are reported as median ± interquar- to expose the skin from the sternal notch to the mandible. Lido- tile range and compared with published normative physiologic caine hydrochloride 2% (Hospira, Lake Forest, IL) was injected values for New Zealand white rabbits.3,10,18,27,45 Statistics were subcutaneously along the midline, to provide local anesthesia. calculated by using Prism version 8.2.0 (GraphPad Software, San A surgical incision was made from sternum to submentum, and Diego, CA). Baseline and final vital signs were compared by using the fascia and muscle were dissected away to expose the larynx the Wilcoxon matched-pair signed-rank test, with Spearman cor- and trachea. To maintain a constant supply of oxygen for spon- relation to calculate effect size. Initial and final doses of CRI were taneous respiration, the trachea was transected approximately compared by using the Wilcoxon matched-pair signed-rank test. 4 cm below the larynx, and oxygen was supplied directly to the The effect of transitioning from sedation to maintenance anesthe- caudal segment of the trachea by using an uncuffed endotra- sia was assessed; vital signs before and after the introduction of cheal tube. A cuffed endotracheal tube was placed in the upper intravenous anesthesia were compared by using the Wilcoxon tracheal segment, approximately 1cm below the larynx, and the matched-pair signed-rank test, with Spearman correlation to cuff was inflated to seal the upper airway (Figure 1 A). calculate effect size. The χ2 test of independence was used to To induce vocal-fold vibration, the vocal folds must be partial- evaluate the relationship between prophylactic administration of ly or completely adducted in the presence of transglottal airflow. lidocaine and the presence of laryngospasms. Significance was A ConchaTherm Neptune system (Hudson RCI, Temecula, CA) defined as a P value less than 0.05. was used to deliver humidified air to the upper airway, forcing air through the glottis at a controlled rate. The vocal folds were Results medialized into the airstream by using electrical stimulation Sedation was of sufficient depth, with no autonomic laryngeal of intrinsic laryngeal muscles. Custom, stainless-steel, hooked responses or surgical pain responses observed at the time of electrodes were inserted into the cricothyroid membrane and catheterization or surgical incision. Time from sedation to the the belly of the cricothyroid muscle bilaterally to produce ad- start of intravenous maintenance anesthesia start was 34 ± 10 duction of the vocal folds (Figure 1 A). Electrical stimulation min (mean ± 1 SD). The transition between sedation and anesthe- of the larynx was achieved by using a Grass S88 stimulator (SA sia was smooth, with no observed pain responses or autonomic Instrumentation, Encinitas, CA) and constant current isolation laryngeal responses. Minimal changes in the following vital unit (model PSIU6, Grass Telefactor, West Warwick, RI). signs were observed between before and after the introduction For visual evaluation of the vibratory consequences of of intravenous anesthesia (Table 1): body temperature decreased prolonged phonation, a pediatric laryngoscope (Karl Storz from 40 ± 0.5 to 39.9 ± 0.5 °C (P = 0.0182), heart rate increased Endoscopy, El Segundo, CA) was used to suspend the larynx from 157 ± 30 to 158.5 ± 27 bpm (P = 0.0015), respiratory rate for vocal-fold visualization, and the neck was supported by decreased from 48 ± 22 to 42 ± 16 breaths per minute (P = 0.0199), using a Vac-Lock cushion (CIVCO, Coralville, IA). Images of and MAP decreased from 82 ± 16 to 82 ± 21 mm Hg (P = 0.0138). vocal-fold vibration were captured by using a 0 , 4.0-mm rigid ° A large effect size was identified for all 4 of these variables (rs endoscope (KayPENTAX, Montvale, NJ) coupled to a mono- = 0.9282, 0.8439, 0.6026, and 0.6141, respectively; P < 0.0001 for chrome high-speed (8000 frames per second) camera (FASTCAM all 4 variables), indicating a strong positive linear relationship MC 2.1, KayPENTAX) and 300-W continuous xenon light source between vital signs before and after transition to intravenous (Karl Storz Endoscopy; Figure 1 B). After 120 min of surgically anesthesia. No significant difference between before and after induced phonation, rabbits were euthanized by intravenous transition to intravenous anesthesia introduction was found injection of 780 mg sodium pentobarbital–phenytoin (Virbac, for SpO2 (P = 0.2701). Carros, France), and the larynges were harvested for assessment The average procedure duration from sedation to termination of structural and molecular changes resulting from prolonged was 221 ± 80 min. Mean vital signs at 15-min intervals for the phonation. duration of the procedure are shown in Figure 2, and summary Maintenance anesthesia doses were initiated toward vital signs are reported in Table 2. Heart rate increased from an the low end of the range (mean initiation dose: ketamine, average of 146 bpm at baseline to 163 bpm at surgery termina- 331.3 ± 21.5 µg/kg/min; dexmeditomidine, 1.54 ± 0.38 µg/ tion (P < 0.0001), with a procedural average of 164 bpm and kg/min; Table 1) and were modified as required to provide a moderate pairwise correlation (rs = 0.3198). SpO2 increased from stable plane of anesthesia with minimal autonomic reflexes. 97% to 99% over the duration of sedation and anesthesia (P < Anticipated adverse events in this procedure included surgical 0.0001), with a procedural average of 98% and a small pairwise

179 Vol 59, No 2 Journal of the American Association for Laboratory Animal Science March 2020

Table 1. Vital signs before and after and median change during transition from sedation to intravenous anesthesia maintenance Before After IV anesthesia IV anesthesia Sedation to anesthesia change Effect size

Median IQ Median IQ Median Range P rs P Body temperature (°C) 40.0 0.5 39.90 0.52 0 −0.60 to +0.40 0.0182 0.9282 <0.0001 HR (bpm) 157.0 30.3 158.5 27.0 4 −19.00 to +52.00 0.0015 0.8439 <0.0001 RR (breaths/min) 48 22 42 16 −4 −40.00 to +48.00 0.0199 0.6026 <0.0001

SpO2 (%) 98.5 1.0 99.0 1.0 0 −7.00 to +7.00 0.1998 0.2701 0.0202 MAP (mm Hg) 82.33 16.00 82.17 21.25 3.67 −50.33 to +49.00 0.0138 0.6141 <0.0001 HR, heart rate; IQ, interquartile range; MAP, mean arterial pressure; RR, respiratory rate Significant P values (that is, P < 0.05) are bolded.

Hg at baseline to 67 mm Hg at procedure termination, with a

procedural average of 70 mm Hg and a moderate effect size (rs = 0.4916). Baseline, final, and procedural averages for heart rate, respiratory rate, and temperature were within published normal limits for New Zealand white rabbits.3,10,18,27,45 The duration of CRI anesthesia was 187 ± 81 min (Table 3). Ketamine was initiated at an average starting dose of 331 µg/ kg/min and increased to a final dose of 372 µg/kg/min (P < 0.0001), with a procedural average of 343 µg/kg/min. Dex- medetomidine was initiated at an average starting dose of 1.5 µg/kg/min and increased to a final dose of 1.8 µg/kg/min (P < 0.0001), with an average procedural dose of 1.6 µg/kg/ min. Eight rabbits demonstrated acute changes in heart rate within a 15-min interval (mean increase, 52 bpm). One animal demonstrated an acute increase in respiratory rate, from 60 to 80 breaths per minute. These animals were all managed by increases in CRI, with heart rates stabilizing and respiratory rate returning to a physiologic level within 15 min. Laryngospasm events and their management are summarized in Figure 3. To minimize the occurrence of autonomic laryngeal responses, lidocaine was administered prophylactically in 31 of the 58 subjects (53%); 22 of these 31 animals (70%) experienced no laryngospasm, and the use of prophylactic lidocaine significantly (P = 0.009) reduced the likelihood of adverse events. Of the 9 animals that experienced adverse events despite prophylactic lidocaine, 8 had autonomic laryngeal responses, and one underwent cardiac arrest, which later was determined to be due to a congenital heart defect. Autonomic laryngeal response was successfully treated with lidocaine alone in 1 of 8 cases (12.5%) and with lidocaine plus CRI dosage increase in 5 of the 8 cases (62.5%). Among the 27 rabbits that did not receive prophylactic lidocaine, 17 (63%) experienced laryngospasm; these laryngospasms were managed successfully with lidocaine alone in 6 cases (35%), with increased CRI dosage alone in 1 case (6%), and with lidocaine plus CRI dosage increase in 7 cases (41%). In 5 subjects, autonomic laryngeal responses could not be resolved by using any of the management techniques described. Two of these 5 animals had received prophylactic lidocaine. The starting dosages of ketamine and dexmedetomidine did not Figure 2. Vital signs variables recorded from sedation (n = 58, time, have statistically significant or clinically salient effects on the 0 min) to termination of the surgical procedure. (A) Heart rate, SpO2, and respiratory rate. (B) Mean arterial blood pressure. (C) Rectal body manifestation of autonomic laryngeal responses (P = 0.199 and temperature. All values are reported as median ± interquartile range. P = 0.527, respectively).

correlation (rs = 0.2478). The respiratory rate decreased through- Discussion out the procedure, from 48 breaths per minute at baseline to 34 This study demonstrates that intramuscular injection of keta- breaths per minute at surgery termination (P < 0.0001), with a mine–dexmedetomidine for sedation followed by CRI infusion procedural average of 37 breaths per minute and moderate ef- of ketamine–dexmedetomidine for maintenance, combined with fect size (rs = 0.309). Body temperature was 39.6 °C at baseline prophylactic topical lidocaine, provides sufficient anesthesia and decreased throughout the procedure, to 38.2 °C at surgery to manage autonomic laryngeal responses and surgical pain termination (P < 0.0001), with a procedural average of 38.1 °C responses during invasive laryngotracheal surgery in rabbits. and moderate effect size (rs = 0.3149). MAP fell from 80 mm All 58 animals in this study were sedated within 10 min of 180 Intravenous ketamine and dexmedetomidine for rabbit anesthesia

Table 2. Vital signs at procedure start and termination, procedural change, and normative reference values Median change over procedure Procedure (median [IQ]) duration Effect size

Mean Start End P rs Pairing effect P Normative value Body temperature (°C) 38.07 (1.33) 39.65 (0.50) 38.25 (1.00) −1.4 <0.0001 0.3149 0.008 38-403

HR (bpm) 163.5 (13.6) 146.0 (19.5) 162.5 (34.5) 15.5 <0.0001 0.3120 0.0072 130-3253

RR (breaths/min) 37.04 (5.06) 48 (20) 34 (10) −14 <0.0001 0.309 0.0091 30-603

18 SpO2 (%) 98.45 (0.66) 97.00 (4.25) 99 (1) 1 <0.0001 0.2478 0.0304 >97

MAP (mm Hg) 69.69 (12.02) 80.33 (19.50) 66.83 (24.00) −12.83 <0.0001 0.4916 <0.0001 60-9710,27,45 HR, heart rate; IQ, interquartile range; MAP, mean arterial pressure; RR, respiratory rate Significant P values (that is, P < 0.05) are bolded.

Table 3. CRI dosage at procedure start and termination and change in dosage Change over procedure Final CRI dosage duration Induction dose Initial CRI dosage (µg/kg/min) (µg/kg/min) (µg/kg/min) Effect size

(mg/kg) Mean 95% CI Range Mean 95% CI Range Mean P rs P K 20 331.25 321.00–342.80 200–350 372.41 346.3–398.5 250–1000 41.16 <0.0001 0.2374 0.0364 D 0.125 1.54 1.435–1.639 0.50–2.15 1.76 1.641–1.890 0.65–3.00 0.22 <0.0001 0.5345 <0.0001 D, dexmeditomidine; K, ketamine Significant P values (that is, P < 0.05) are bolded. administration of the intramuscular injection; we anecdotally change. Similarly, increases in heart rate and decreases in rectal observed this rate to be slower than in previous experiments temperature were observed over the course of the procedure but using sedation with ketamine–acepromazine–xylazine. Auto- remained within physiologically normal limits. Acute increases nomic laryngeal responses were successfully managed in all in heart rate (greater than 50 bpm in15 min) and respiratory rate but 5 cases, supporting the use of this anesthetic regimen for (more than 20 breaths per minute in 15 min) were ameliorated procedures like this one. through stepwise increases in CRI. In addition, MAP decreased KD sedation was successful and well tolerated in all ani- over study duration but remained within physiologically nor- mals. Although ketamine is known to elicit tachycardia and mal limits.10,27,45 These vital signs suggest that a KD anesthetic bradypnea, among other side effects, coadministration with the regimen provides similar respiratory rate, SpO2, heart rate, α2-adrenergic agonist dexmedetomidine has been demonstrated and rectal temperature but a more stable MAP compared with to minimize respiratory and cardiovascular effects, providing a 4-h intravenous ketamine–xylazine anesthetic regimen.73 a stable plane of anesthesia without affecting endogenous Furthermore, MAP averages were consistent with a combined steroid levels.23 The effects of dexmedetomidine, including protocol of inhaled isoflurane with intramuscular injection of increased sedation, dose-dependent bradycardia, bradypnea, either ketamine–xylazine–buprenorphine or ketamine–medeto- 75 66 16 and decreased SpO2, result from α2-adrenoreceptor agonism midine–buprenorphine. These findings indicate that a CRI and appear to negate the negative symptoms associated with KD anesthetic regimen with topical lidocaine produces vital ketamine; we noted these effects in the current regimen, given sign stability comparable with other intravenous, inhaled, or that all vital signs remained within normative limits for the combination anesthetic regimens. duration of anesthesia. Moreover, an antagonist (atipamezole) Consistent with previous studies evaluating ketamine and is available for dexmedetomidine, and dexmeditomidine has dexmedetomidine,46 coadministration of these agents appears a dose-sparing effect for many anesthesia drugs,7,64,65 reducing to minimize the cardiorespiratory effects associated with the the total volume of anesthetic agent administered during pro- independent use of each agent, and body temperature was cedures and likely improving recovery outcomes—important regulated within normative values over an extended-duration considerations for future survival procedures. surgical procedure.3,10,18,27,45 Of note, within the current anes- Significant changes in vital signs were observed from seda- thesia regimen, weak to moderate correlation was observed tion to procedure termination for all parameters measured between baseline and final vital signs, whereas the pairing effect in the study. Consistent with reports that dexmedetomidine was significant across all measured variables, suggesting that causes decreased respiratory rate in a nonlinear dose-dependent although individual animals had different physiologic baselines, manner,52 we noted a modest reduction in the respiratory rate animal-specific vital signs remained stable and within physi- between sedation and study termination; however, respiratory ologic norms for the duration of the procedure. rate remained within normal physiologic limits3 and, given that The findings of this study supporting the use of intravenous

SpO2 remained within expected levels for the study duration, CRI of KD with topical lidocaine are promising; however, the decreased respiratory rate was not indicative of pathologic limitations within the methodology of this study warrant

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Figure 3. Frequency of occurrence and applied interventions for periprocedural autonomic laryngeal responses. consideration. We chose to use only male rabbits in these experi- contribute to the presentation of these responses during this ments to control for known differences in laryngeal architecture stressful procedure. and functional vocal-fold vibration between sexes; however, this Autonomic laryngeal response was the leading complication methodology excluded analysis of sex as a biologic variable in in this study, affecting 25 of 58 animals. The presence of these this anesthesia regimen. Previous studies have identified sex- reflexes is not unexpected, given the extensive manipulation associated differences in ketamine anesthesia: female rabbits of of the larynx and proximal areas, and has occurred in previous a mixed breed backgrounds that received injection anesthesia studies from our group. Nevertheless, the current anesthesia ketamine and medetomidine required more frequent sup- regimen was successful in managing these reflexes in 80% (20 plementation with isoflurane than male rabbits,53 and studies of 25) of these animals. For other procedures that do not require have identified that females are more susceptible to the anti- such extensive upper airway manipulation, this anesthetic depressant effects of low-dose ketamine.61 The nonrandomized regimen likely would adequately maintain a surgical plane of approach to treatment with prophylactic topical lidocaine is a anesthesia in the vast majority of rabbits. shortcoming of this study. Although the introduction of prophy- Insufficient depth of anesthesia and superior laryngeal lactic lidocaine partway through the study reduced incidence of nerve activation are the most likely causes of intraoperative autonomic laryngeal response, consistent with findings in previ- laryngospasm.31 We were unable to elucidate why the regimen ous studies and meta-analyses,14 the lack of blinding prevented described was unsuccessful in controlling autonomic laryn- analysis of the risk factors for developing autonomic laryngeal geal responses in 5 cases, but it is possible that these animals responses. Furthermore, dose selection in our study was driven were particularly sensitive to stimulation from laryngoscope by the need to maintain sufficient anesthesia depth to minimize placement and endoscopy or that these animals were more laryngeal responses. Consequently, we did not seek to evalu- resistant to the effects of the anesthesia regimen. Deepening ate excessive anesthesia unless negative consequences (apnea, of anesthesia by using either propofol or midazolam has been decreased heart rate) occurred. As such, the implementation demonstrated as effective in overcoming intraoperative laryn- of this approach mainly resulted in unidirectional anesthesia gospasm;60 however, these methods were not pursued due to adjustment. Therefore, this study does not identify an effective concerns for bradycardia with propofol62 and airway obstruc- upper dosing limit or a mean effective dose. Finally, vital signs tion with midazolam.17 The application of positive pressure were recorded at relatively long intervals (15 min), which may was not pursued, given that supplemental oxygen bypassed result in masking of negative anesthesia effects in subjects that the larynx and was administered through an uncuffed tube to is experienced an unstable plane of anesthesia. the aboral portion of the trachea. We did not consider the use Given the continuous strain placed on the tissue during this of the Larson maneuver,43 applying pressure to the ‘laryngo- procedure, local autonomic responses such as laryngospasm spasm notch’ while performing a jaw thrust, because to our are common. With the regimen evaluated in this study, 55% of knowledge this technique has not been performed in rabbits animals did not exhibit autonomic laryngeal responses, and the and is contraindicated for our protocol because it would re- majority of these (21, 66%) had received prophylactic lidocaine quire removal of the laryngoscope. Other potential therapeutic to the larynx at 40-min intervals, consistent with the duration avenues, such as the administration of the muscle relaxant of lidocaine’s therapeutic effect.57 Although CRI starting dose succinylcholine,1,59 were not considered because moderate tone did not influence whether animals experienced involuntary of the thyroarytenoid and cricothyroid muscles is required for responses, the administration of topical prophylactic lidocaine normal phonation.30,68 did reduce the likelihood of autonomic reflexes. However, Overall, analgesia was most successful with the administra- prophylactic lidocaine did not eliminate autonomic laryngeal tion of prophylactic topical lidocaine with adjuvant CRI dosage responses, suggesting that interindividual differences may increase plus additional topical lidocaine as needed. In the single

182 Intravenous ketamine and dexmedetomidine for rabbit anesthesia

animal that experienced cardiac arrest, postmortem necropsy namic response and dose sparing effect on opioid and anaesthetic revealed a congenital ventricular septal defect, which likely agents in patients undergoing laparoscopic cholecystectomy—a contributed to this outcome; however, other factors cannot be randomized study. J Clin Diagn Res 10:UC01–UC05. excluded. 8. Branski RC, Perera P, Verdolini K, Rosen CA, Hebda PA, Agar- wal S. 2007. Dynamic biomechanical strain inhibits IL-1β–induced In conclusion, we describe a regimen for CRI of ketamine– inflammation in vocal fold fibroblasts. J Voice 21:651–660. https:// dexmedetomidine, with topical lidocaine, that provides an doi.org/10.1016/j.jvoice.2006.06.005. adequate surgical plane of anesthesia for invasive laryngotra- 9. Burnett AM, Watters BJ, Barringer KW, Griffith KR, Frascone RJ. cheal procedures in New Zealand white rabbits. Furthermore, 2012. Laryngospasm and hypoxia after intramuscular administra- this regimen can easily be adjusted to manage involuntary tion of ketamine to a patient in excited delirium. Prehosp Emerg reflexes and mitigate complications of underdosing. Optimal Care 16:412–414. https://doi.org/10.3109/10903127.2011.640766. surgical outcomes were observed with induction through 10. van den Buuse M, Malpas SC. 1997. 24-hour recordings of blood 20 mg/kg IM ketamine hydrochloride and 0.125 mg/kg IM pressure, heart rate and behavioural activity in rabbits by radio- dexmedetomidine, followed by CRI intravenous maintenance telemetry: effects of feeding and hypertension. Physiol Behav 62: anesthesia of 300 to 350 µg/kg/min ketamine hydrochloride 83–89. https://doi.org/10.1016/S0031-9384(97)00145-5. 11. Chun EH, Han MJ, Baik HJ, Park HS, Chung RK, Han JI, Lee HJ, and 1.5 to 1.75 µg/kg/min dexmedetomidine, with prophy- Kim JH. 2016. Dexmedetomidine-ketamine versus Dexmedeto- lactic topical 2% lidocaine administered every 40 min. Adverse midine-midazolam-fentanyl for monitored anesthesia care during events were best managed with a combination of CRI dosage chemoport insertion: a Prospective Randomized Study. BMC increase paired with additional application of 2% topical Anesthesiol 16:1–9. https://doi.org/10.1186/s12871-016-0211-4. lidocaine. 12. Cohen SM, Kim J, Roy N, Asche C, Courey M. 2012. Direct health Circumventing known difficulties in the provision of rabbit care costs of laryngeal diseases and disorders. Laryngoscope anesthesia, such as challenges intubating for ventilated anesthe- 122:1582–1588. https://doi.org/10.1002/lary.23189. sia and variable anesthesia plane with anesthesia maintenance 13. Cohen VG, Krauss B. 2006. Recurrent episodes of intractable laryn- through intramuscular injection, this method represents an gospasm during dissociative sedation with intramuscular ketamine. Pediatr Emerg Care 22:247–249. https://doi.org/10.1097/01. easily implementable and reliable alternative to existing anes- pec.0000210174.63633.92. thesia techniques and facilitates superior animal welfare and 14. Collins S, Schedler P, Veasey B, Kristofy A, McDowell M. 2019. experimental rigor. In addition, this regimen has previously Prevention and treatment of laryngospasm in the pediatric patient : been demonstrated to have no effect on endogenous steroid lev- a literature review. AANA J 87:145–151. els,23 positioning this anesthesia protocol as a strong option for 15. DeValle JMS. 2009. Successful management of rabbit anesthesia studies investigating injury, repair, and inflammation pathways. through the use of nasotracheal intubation. J Am Assoc Lab Anim Further experiments are in progress to evaluate postprocedural Sci 48:166–170. recovery with this anesthesia regimen. 16. Difilippo SM, Norberg PJ, Suson UD, Savino AM, Reim DA. 2004. A comparison of xylazine and medetomidine in an anesthetic combination in New Zealand White Rabbits. Contemp Top Lab Acknowledgments Anim Sci 43:32–34. We thank Azure C Wilson for her assistance with data entry, the 17. Drummond GB. 1996. Comparison of sedation with midazolam veterinary pathologists at Vanderbilt Translational Pathology Shared and ketamine: effects on airway muscle activity. Br J Anaesth Resource, and the staff of the Department of Animal Care at Vanderbilt 76:663–667. https://doi.org/10.1093/bja/76.5.663. University, who provided welfare and husbandry support for the sub- 18. Eatwell K, Mancinelli E. [Internet]. 2013. Anesthesia guidelines jects in this study. This study was supported by research grants from for airway management in rabbits.[Cited 8 August 2019]. Available the National Institute on Deafness and Other Communication Disorders at: https://www.vettimes.co.uk/. of the National Institutes of Health (R01DC01545-05, PI: Rousseau; 19. Formeister JF, Locke D, Nash GS, Roberson BS. 1980. Alteration F32DC015726-03, PI: Powell). The content is solely the responsibility of lymphocyte function due to anesthesia: In vivo and in vitro of the authors and does not necessarily represent the official views of suppression of mitogen-induced blastogenesis by sodium pento- the NIH. barbital. Surgery 87:573–580. 20. Gavel G, Walker RW. 2014. Laryngospasm in anaesthesia. Con- References tinuing education in anaesthesia, critical care & pain 14:47–51. 1. Al-alami AA, Zestos MM, Baraka AS. 2009. Pediatric laryn- https://doi.org/10.1093/bjaceaccp/mkt031. gospasm: prevention and treatment. Curr Opin Anaesthesiol 21. Ge PJ, French LC, Ohno T, Zealear DL, Rousseau B. 2009. Model 22:388–395. https://doi.org/10.1097/ACO.0b013e32832972f3. of evoked rabbit phonation. Ann Otol Rhinol Laryngol 118:51–55. 2. Animal Welfare Act as Amended. 2008. 7 USC §2131–2156. https://doi.org/10.1177/000348940911800109. 3. Pritchett-Corning K, Girod A, Avellaneda G, Fritz P, Chou S, 22. González Gil A, Illera JC, Silván G, Illera M. 2001. Plasma Brown M. 2010. Handbook of clinical signs in rodents and rabbits. glucocorticoid concentrations after fentanyl-droperidol, ketamine- 1st ed. (France): Charles River xylazine and ketamine-diazepam anaesthesia in New Zealand 4. Baker AK, Hoffmann VLH, Meert TF. 2002. Dextromethorphan white rabbits. Vet Rec 148:784–786. https://doi.org/10.1136/ and ketamine potentiate the antinociceptive effects of µ- but vr.148.25.784. not δ- or k-opioid agonists in a mouse model of acute pain. 23. González-Gil A, Villa A, Millán P, Martínez-Fernández L, Illera Pharmacol Biochem Behav 74:73–86. https://doi.org/10.1016/ JC. 2015. Effects of dexmedetomidine and ketamine-dexmedetomi- S0091-3057(02)00961-9. dine with and without buprenorphine on corticoadrenal function 5. Barbi E, Marchetti F, Gerarduzzi T, Neri E, Gagliardo A, Sarti A, in rabbits. J Am Assoc Lab Anim Sci 54:299–303. Ventura A. 2003. Pretreatment with intravenous ketamine reduces 24. Goyal R, Singh S, Bangi A, Singh SK. 2013. Case series: Dex- propofol injection pain. Paediatr Anaesth 13:764–768. https://doi. medetomidine and ketamine for anesthesia in patients with org/10.1046/j.1460-9592.2003.01150.x. uncorrected congenital cyanotic heart disease presenting for 6. Bateman L, Ludders JW, Gleed RD, Erb HN. 2005. Comparison non-cardiac surgery. J Anaesthesiol Clin Pharmacol 29:543–546. between facemask and laryngeal mask airway in rabbits during https://doi.org/10.4103/0970-9185.119142. isoflurane anesthesia. Vet Anaesth Analg 32:280–288. https://doi. 25. Green CJ, Knight J, Precious S, Simpkin S. 1981. Ketamine org/10.1111/j.1467-2995.2005.00169.x. alone and combined with diazepam or xylazine in laboratory 7. Bhagat N, Yunus M, Karim HMR, Hajong R, Bhattacharyya P, animals: a 10 year experience. Lab Anim 15:163–170. https://doi. Singh M. 2016. Dexmedetomidine in attenuation of haemody- org/10.1258/002367781780959107.

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26. Gündüz M, Sakalli S, Güneş Y, Kesiktaş E, Ozcengiz D, Işik G. 45. Lim K, Burke SL, Armitage JA, Head GA. 2012. Comparison of 2011. Comparison of effects of ketamine, ketamine-dexmedeto- blood pressure and sympathetic activity of rabbits in their home midine and ketamine-midazolam on dressing changes of burn cage and the laboratory environment. Exp Physiol 97:1263–1271. patients. J Anaesthesiol Clin Pharmacol 27:220–224. https://doi. https://doi.org/10.1113/expphysiol.2012.064972. org/10.4103/0970-9185.81823. 46. Luscri N, Tobias JD. 2006. Monitored anesthesia care with a 27. Guo GB, Thames MD, Abboud FM. 1983. Arterial baroreflexes combination of ketamine and dexmedetomidine during mag- in renal hypertensive rabbits. Selectivity and redundancy of netic resonance imaging in three children with trisomy 21 and baroreceptor influence on heart rate, vascular resistance, and obstructive sleep apnea. Paediatr Anaesth 16:782–786. https:// lumbar sympathetic nerve activity. Circ Res 53:223–234. https:// doi.org/10.1111/j.1460-9592.2006.01857.x. doi.org/10.1161/01.RES.53.2.223. 47. McCulloch TM, Flint PW, Richardson MA, Bishop MJ. 1992. 28. Haas DA, Harper DG. 1992. Ketamine: a review of its pharmaco- Lidocaine effects on the laryngeal chemoreflex, mechanoreflex, logic properties and use in ambulatory anesthesia. Anesth Prog and afferent electrical stimulation reflex. Ann Otol Rhinol Laryngol 39:61–68. 101:583–589. https://doi.org/10.1177/000348949210100707. 29. Hall JE, Suehiro A, Branski RC, Garrett CG, Rousseau 48. Mizuta M, Kurita T, Kimball EE, Rousseau B. 2017. Structurally B. 2012. Modulation of inflammatory and profibrotic and functionally characterized in vitro model of rabbit vocal fold signaling in a rabbit model of acute phonotrauma using triam- epithelium. Tissue Cell 49:427–434. https://doi.org/10.1016/j. cinolone. Otolaryngol Head Neck Surg 147:302–307. https://doi. tice.2017.03.006. org/10.1177/0194599812440419. 49. Mohammed A, Abdelnabi M, Sayed M. 2001. A new protocol of 30. Havas T, Lowinger D, Priestley J. 1999. Unilateral vocal fold pa- anesthesia using thiopental, diazepam and xylazine in White New ralysis: causes, options and outcomes. Aust N Z J Surg 69:509–513. Zealand rabbits. Aust J Basic Appl Sci 5:1296–1300. https://doi.org/10.1046/j.1440-1622.1999.01613.x. 50. Munro HM, Felix DE, Nykanen DG. 2009. Dexmedetomidine/ 31. Hernández-Cortez E. 2018. Update on the management of laryn- ketamine for diagnostic cardiac catheterization in a child with gospasm. J Anesth Crit Care 8:1–6. idiopathic pulmonary hypertension. J Clin Anesth 21:435–438. 32. Hurlé MA, Mediavilla A, Flórez J. 1982. Morphine, pentobarbital https://doi.org/10.1016/j.jclinane.2008.10.013. and naloxone in the ventral medullary chemosensitive areas: dif- 51. Nicol ME, Dritsopoulou A, Wang C, Holdcroft A, Chakrabarti ferential respiratory and cardiovascular effects. J Pharmacol Exp MK, Whitwam JG. 1994. Ventilation techniques to minimize circu- Ther 220:642–647. latory depression in rabbits with surfactant deficient lungs. Pediatr 33. Inglis S, Strunk A. 2009. Rabbit anesthesia. Lab Anim (NY) Pulmonol 18:317–322. https://doi.org/10.1002/ppul.1950180509. 38:84–85. https://doi.org/10.1038/laban0309-84. 52. Nishida T, Nishimura M, Kagawa K, Hayashi Y, Mashimo T. 34. Institute for Laboratory Animal Research Council. 2011. Guide 2002. The effects of dexmedetomidine on the ventilatory response to hypercapnia in rabbits. Intensive Care Med 28:969–975. https:// for the care and use of laboratory animals, 8th ed. Washington doi.org/10.1007/s00134-002-1338-y. (DC): National Academies Press. 53. Orr HE, Roughan JV, Flecknell PA. 2005. Assessment of ketamine 35. Jaber SM, Hankenson FC, Heng K, McKinstry-Wu A, Kelz MB, and medetomidine anaesthesia in the domestic rabbit. Vet Anaesth Marx JO. 2014. Dose regimens, variability, and complications associ- Analg 32:271–279. https://doi.org/10.1111/j.1467-2995.2005.00211.x. ated with using repeat-bolus dosing to extend a surgical plane of 54. Pai A, Heining M. 2007. Ketamine. Contin Educ Anaesth Crit Care anesthesia in laboratory mice. J Am Assoc Lab Anim Sci 53:684–691. Pain 7:59–63. https://doi.org/10.1093/bjaceaccp/mkm008. 36. Julien RM. 2001. Barbiturates, general anesthetics, and antiepileptic 55. Pani N, Kumar Rath S. 2009. Regional and topical anaesthesia of drugs, p 82–99. In: Julien RM, editor. A primer of drug action: a concise, upper airways. Indian J Anaesth 53:641–648. nontechnical guide to the actions, uses, and side effects of psychoac- 56. Perazzo PS, Duprat A de C, Lancelotti C, Donati F. 2007. A study tive drugs. 9th ed. New York (NY): WH Freeman and Company. of the histological behavior of a rabbit vocal fold after a hyaluronic 37. Kaur M, Singh PM. 2011. Current role of dexmedetomidine in acid injection. Braz J Otorinolaryngol 73:171–178. https://doi. clinical anesthesia and intensive care. Anesth Essays Res 5:128–133. org/10.1590/S0034-72992007000200006. https://doi.org/10.4103/0259-1162.94750. 57. Ritchie J, Green N. 1990. Local anesthetics, p 311. In: Goodman 38. Klainer AS, Turndorf H, Wu WH, Maewal H, Allender P. 1975. and Gilman’s the pharmacological basis of therapeutics, 8th ed. Surface alterations due to endotracheal intubation. Am J Med New York (NY): Pergamon Press. 58:674–683. https://doi.org/10.1016/0002-9343(75)90504-5. 58. Rousseau B, Suehiro A, Echemendia N, Sivasankar M. 2011. 39. Kojima T, Valenzuela CV, Novaleski CK, Van Deusen M, Mitch- Raised intensity phonation compromises vocal fold epithelial bar- ell JR, Garrett CG, Sivasankar MP, Rousseau B. 2014. Effects rier integrity. Laryngoscope 121:346–351. https://doi.org/10.1002/ of phonation time and magnitude dose on vocal fold epithelial lary.21364. genes, barrier integrity, and function. Laryngoscope 124:2770–2778. 59. Roy WL, Lerman J. 1988. Laryngospasm in paediatric anaesthesia. https://doi.org/10.1002/lary.24827. Can J Anaesth 35:93–98. https://doi.org/10.1007/BF03010554. 40. Kojima T, Van Deusen M, Jerome WG, Garrett CG, Sivasankar 60. Salah D, Azzazi H. 2014. Comparative study between propofol MP, Novaleski CK, Rousseau B. 2014. Quantification of acute and midazolam in treatment of postextubation laryngospasm. vocal fold epithelial surface damage with increasing time and Ains Shams Journal of Anesthesiology 7:148–150. https://doi. magnitude doses of vibration exposure. PLoS One 9:1–9. https:// org/10.4103/1687-7934.133357. doi.org/10.1371/journal.pone.0091615. 61. Saland SK, Duclot F, Kabbaj M. 2017. Integrative analysis of 41. Kurdi MS, Theerth KA, Deva RS. 2014. Ketamine: Current ap- sex differences in the rapid antidepressant effects of ketamine in plications in anesthesia, pain, and critical care. Anesth Essays Res preclinical models for individualized clinical outcomes. Curr Opin 8:283–290. https://doi.org/10.4103/0259-1162.143110. Behav Sci 14:19–26. https://doi.org/10.1016/j.cobeha.2016.11.002. 42. Landsman IS. 1997. Mechanisms and treatment of laryngospasm. 62. Santos M, Viñuela A, Vela AA, Tendillo FJ. 2016. Single-syringe Int Anesthesiol Clin 35:67–73. https://doi.org/10.1097/00004311- ketamine-propofol for induction of anaesthesia in rabbits. Vet 199703530-00008. Anaesth Analg 43:561–565. https://doi.org/10.1111/vaa.12345. 43. Larson PC Jr. 1998. Laryngospasm—the best treatment. 63. Sarton E, Teppema LJ, Olievier C, Nieuwenhuijs D, Matthes Anesthesiology 89:1293–1294. https://doi.org/10.1097/00000542- HWD, Kieffer BL, Dahan A. 2001. The involvement of the 199811000-00056. µ-opioid receptor in ketamine—induced respiratory depression 44. Li Y, Shi J, Yang BF, Liu L, Han CL, Li WM, Dong DL, Pan ZW, and antinociception. Anesth Analg 93:1495–1500. https://doi. Liu GZ, Geng JQ, Sheng L, Tan XY, Sun DH, Gong ZH, Gong org/10.1097/00000539-200112000-00031. YT. 2012. Ketamine-induced ventricular structural, sympathetic 64. Scheinin H, Aantaa R, Anttila M, Hakola P, Helminen A, and electrophysiological remodelling: pathological consequences Karhuvaara S. 1998. Reversal of the sedative and sympatho- and protective effects of metoprolol. Br J Pharmacol 165:1748–1756. lytic effects of dexmedetomidine with a specificα 2–adrenoceptor https://doi.org/10.1111/j.1476-5381.2011.01635.x. antagonist atipamezole: a pharmacodynamic and kinetic study

184 Intravenous ketamine and dexmedetomidine for rabbit anesthesia

in healthy volunteers. Anesthesiology 89:574–584. https://doi. laryngeal secretions following phonotrauma: a preliminary org/10.1097/00000542-199809000-00005. study. Ann Otol Rhinol Laryngol 112:1021–1025. https://doi. 65. Sharma P, Gombar S, Ahuja V, Jain A, Dalal U. 2017. Sevoflu- org/10.1177/000348940311201205. rane sparing effect of dexmedetomidine in patients undergoing 72. Williams NR, Heifets BD, Blasey C, Sudheimer K, Pannu J, laparoscopic cholecystectomy: a randomized controlled trial. J Pankow H, Hawkins J, Birnbaum J, Lyons DM, Rodriguez Anaesthesiol Clin Pharmacol 33:496–502. CI, Schatzberg AF. 2018. Attenuation of antidepressant

66. Sinclair MD. 2003. A review of the physiological effects of α2–ago- effects of ketamine by opioid receptor antagonism. Am J nists related to the clinical use of medetomidine in small animal Psychiatry 175:1205–1215. https://doi.org/10.1176/appi. practice. Can Vet J 44:885–897. ajp.2018.18020138. 67. Sinha SK, Joshiraj B, Chaudhary L, Hayaran N, Kaur M, Jain A. 73. Wyatt JD, Scott RA, Richardson ME. 1989. The effects of prolonged 2014. A comparison of dexmedetomidine plus ketamine combination ketamine-xylazine intravenous infusion on arterial blood pH, with dexmedetomidine alone for awake fiberoptic nasotracheal blood gases, mean arterial blood pressure, heart and respiratory intubation: a randomized controlled study. J Anaesthesiol Clin rates, rectal temperature and reflexes in the rabbit. Lab Anim Sci Pharmacol 30:514–519. https://doi.org/10.4103/0970-9185.142846. 39:411–416. 68. Titze IR, Luschei ES, Hirano M. 1989. Role of the thyroarytenoid 74. Yamada KA, Moerschbaecher JM, Gillis RA. 1983. Pentobarbital muscle in regulation of fundamental frequency. J Voice 3:213–224. causes cardiorespiratory depression by interacting with a gabaergic https://doi.org/10.1016/S0892-1997(89)80003-7. system at the ventral surface of the medulla. J Pharmacol Exp Ther 69. Tobias JD. 2012. Dexmedetomidine and ketamine. Pediatr Crit Care 226:349–355. Med 13:423–427. https://doi.org/10.1097/PCC.0b013e318238b81c. 75. Zornow MH. 1991. Ventilatory, hemodynamic and

70. Verdolini Abbott K, Li NYK, Branski RC, Rosen CA, Grillo E, sedative effects of the α2 adrenergic agonist, dexmedeto- Steinhauer K, Hebda PA. 2012. Vocal exercise may attenuate acute midine. Neuropharmacology 30:1065–1071. https://doi. vocal fold inflammation. J Voice 26:814.e1–814.e13. https://doi. org/10.1016/0028-3908(91)90135-X. org/10.1016/j.jvoice.2012.03.008. 71. Verdolini K, Branski RC, Rosen CA, Hebda PA. 2003. Shifts in biochemical markers associated with wound healing in

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