Risk of anesthesia-related complications in draft horses: a retrospective, single-center analysis.

OBJECTIVE: To report anesthetic-related complications and determine risks associated with anesthesia in draft horses. STUDY DESIGN: Retrospective study. ANIMALS: A total of 401 anesthetic records for draft horse breeds that underwent general anesthesia from January 2010 through December 2020 were reviewed; horses euthanized during general anesthesia were excluded. METHODS: Demographics, perioperative drugs used, procedure type and duration, time to extubation, number of attempts to stand, use of sling in recovery and perioperative morbidity and mortality were investigated. Morbidity and mortality statistical evaluation included univariable logistic regression analysis and ordinal regression analysis. RESULTS: American Society of Anesthesiologists (ASA) status I-II, ASA III-V and total mortality rate for all cases was 0.69% (2/288), 6.19% (7/113) and 2.24% (9/401), respectively, with Belgian horses being overrepresented (6/9). Cardiac arrest occurred in six out of nine horses that died without euthanasia, and five out of six of these horses underwent colic surgery. Factors associated with increased mortality risk included ASA status of III-V, increased body weight, emergency status and horses presenting for colic. Hypotension, hypercarbia and hypoxemia occurred in 56% (224/401), 46% (186/401) and 14% (58/401) of horses, respectively. During recovery from anesthesia, lighter horses and horses undergoing shorter anesthetic procedures were more likely to be successful on the first or second attempt to stand and were less likely to require a sling in recovery. CONCLUSIONS AND CLINICAL RELEVANCE: Draft horses undergoing general anesthesia had a higher mortality rate than previously reported for all types and breeds of horses.

Evaluation of intramuscular anesthetic protocols in healthy domestic horses.

OBJECTIVE: To assess anesthetic induction, recovery quality and cardiopulmonary variables after intramuscular (IM) injection of three drug combinations for immobilization of horses. STUDY DESIGN: Randomized, blinded, three-way crossover prospective design. ANIMALS: A total of eight healthy adult horses weighing 470-575 kg. METHODS: Horses were administered three treatments IM separated by ≥1 week. Combinations were tiletamine-zolazepam (1.2 mg kg-1), ketamine (1 mg kg-1) and detomidine (0.04 mg kg-1) (treatment TKD); ketamine (3 mg kg-1) and detomidine (0.04 mg kg-1) (treatment KD); and tiletamine-zolazepam (2.4 mg kg-1) and detomidine (0.04 mg kg-1) (treatment TD). Parametric data were analyzed using mixed model linear regression. Nonparametric data were compared using Skillings-Mack test. A p value <0.05 was considered statistically significant. RESULTS: All horses in treatment TD became recumbent. In treatments KD and TKD, one horse remained standing. PaO2 15 minutes after recumbency was significantly lower in treatments TD (p < 0.0005) and TKD (p = 0.001) than in treatment KD. Times to first movement (25 ± 15 minutes) and sternal recumbency (55 ± 11 minutes) in treatment KD were faster than in treatments TD (57 ± 17 and 76 ± 19 minutes; p < 0.0005, p = 0.001) and TKD (45 ± 18 and 73 ± 31 minutes; p = 0.005, p = 0.021). There were no differences in induction quality, muscle relaxation score, number of attempts to stand or recovery quality. CONCLUSIONS AND CLINICAL RELEVANCE: In domestic horses, IM injections of tiletamine-zolazepam-detomidine resulted in more reliable recumbency with a longer duration when compared with ketamine-detomidine and tiletamine-zolazepam-ketamine-detomidine. Recoveries were comparable among protocols.

Evaluation of perfusion index as a noninvasive tool to determine epidural anesthesia effectiveness in dogs.

OBJECTIVE: To evaluate perfusion index (PI) as a noninvasive tool to determine effectiveness and onset of epidural anesthesia in dogs. STUDY DESIGN: Prospective clinical trial. ANIMALS: A total of 21 adult dogs, aged 6.5 ± 3 years and weighing 34.9 ± 6.4 kg, undergoing a tibial plateau leveling osteotomy. METHODS: Dogs were premedicated intramuscularly with acepromazine (0.03 mg kg-1) and hydromorphone (0.1 mg kg-1) and anesthetized with intravenous propofol (to effect) and isoflurane in oxygen. A surface transflectance probe was secured to the tail base to monitor PI and a dorsal pedal artery catheter was placed for invasive blood pressure monitoring. A lumbosacral epidural was performed with the dog in sternal recumbency. Dogs were randomly assigned for inclusion of epidural morphine (0.1 mg kg-1) or morphine (0.1 mg kg-1) and lidocaine (4 mg kg-1). PI was recorded following instrumentation of each dog just prior to the epidural (baseline), at 10 minute intervals for 30 minutes, before and after the surgical skin incision and before and after completion of the osteotomy. Physiological variables and end-tidal isoflurane were recorded at the same time points. RESULTS: There was no significant difference in PI between the groups at any time point. There was a significant change in end-tidal isoflurane before and after the skin incision in the epidural morphine and epidural morphine-lidocaine groups (p = 0.04, p = 0.05, respectively) and before and after the osteotomy in each group for heart rate (p = 0.001, p = 0.04), diastolic (p = 0.01, p = 0.01) and mean arterial blood pressure (p = 0.03, p = 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: PI did not provide an objective means for determining the onset or effectiveness of epidural anesthesia in anesthetized dogs and alternate methods of noninvasive assessment should be investigated.

Effect of oral trazodone on the minimum alveolar concentration of isoflurane in dogs.

OBJECTIVE: To determine the effect of oral trazodone on the minimum alveolar concentration (MAC) of isoflurane in dogs. STUDY DESIGN: Prospective blinded, single-observer, randomized crossover experimental study. ANIMALS: Six adult (age 6.8 ± 1.6 months) healthy dogs (three males and three females), weighing 24.8 ± 3.4 kg (mean ± standard deviation). METHODS: Each dog was anesthetized twice with a minimum of 7 days between anesthetic episodes. Dogs were randomly assigned to be administered two treatments in a crossover design: premedication with trazodone (8 mg kg-1; TRAZ-ISO) orally 2 hours prior to an anesthetic episode or no (ISO). Dogs were anesthetized with intravenous propofol (6 mg kg-1) and isoflurane in >95% oxygen. Isoflurane MAC was determined using an iterative bracketing technique with electrodes placed in the buccal mucosa. Hemodynamic variables were compared at the lowest end-tidal isoflurane concentration at which each dog did not respond. A paired t test was used to assess the effect of treatment on outcome variables with significance set to a value of p < 0.05. RESULTS: The MAC concentration (mean ± standard deviation) in dogs administered TRAZ-ISO was 0.85 ± 0.17% compared with 1.02 ± 0.11% in those administered ISO (p = 0.01, 95% confidence interval -0.25 to -0.05), resulting in a mean MAC reduction of 17 ± 12%. There were no differences in hemodynamic variables between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Premedication of dogs with oral trazodone (8 mg kg-1) 2 hours prior to anesthetic induction has a significant isoflurane MAC sparing effect with no significant observed hemodynamic benefit.

Total intravenous anesthesia using a midazolam-ketamine-xylazine infusion in horses: 46 cases (2011-2014).

This study evaluated use of midazolam, ketamine, and xylazine (MKX) for total intravenous (IV) anesthesia (TIVA) in horses. Medical records of 46 horses undergoing a clinical procedure using MKX for TIVA were reviewed. Age, breed, procedure, heart rate (HR), respiratory rate (RR), pre-anesthetic drugs, induction drugs, and total volume of MKX were recorded. Duration of anesthesia, time to standing, number of attempts to stand, and recovery score were also recorded. All horses were premedicated with an alpha-2 adrenoceptor agonist and anesthesia was induced with ketamine and midazolam. Duration of MKX infusion was 33 ± 14 min. Heart rate and RR decreased during the infusion of MKX. Time to endotracheal extubation was 19 ± 12 min. Horses stood at 33 ± 13 min. Median number of attempts to stand was 1. Maintenance of anesthesia of horses with MKX was useful for a variety of procedures and recovery from anesthesia was good.

Anesthésie intraveineuse totale à l'aide d'une infusion de midazolam-kétamine-xylazine chez les chevaux : 46 cas (2011­2014). Cette étude a évalué l'usage du midazolam, de la kétamine et de la xylazine (MKX) pour l'anesthésie intraveineuse (IV) totale (AITT) chez les chevaux. Les dossiers médicaux de 46 chevaux subissant une intervention clinique à l'aide de MKX pour l'AITT ont été évalués. L'âge, la race, l'intervention, la fréquence cardiaque, la fréquence respiratoire, les médicaments pré-anesthésiques, les médicaments d'induction et le volume total de MKX ont été consignés. La durée de l'anesthésie, le délai pour se tenir debout, le nombre de tentatives pour se tenir debout et la note de rétablissement ont aussi été consignés. Tous les chevaux ont reçu une prémédication avec un agoniste alpha-2 adrénocepteur et l'anesthésie a été induite avec de la kétamine et du midazolam. La durée de l'infusion de MKX a été de 33 ± 14 min. La fréquence cardiaque et la fréquence respiratoire ont diminué durant l'infusion de MKX. Le délai jusqu'à l'extubation endotrachéale a été de 19 ± 12 min. Les chevaux se sont tenus debout à 33 ± 13 min. Le nombre médian de tentatives pour se tenir debout était de 1. Le maintien de l'anesthésie chez les chevaux avec MKX était utile pour une diversité d'interventions et le rétablissement de l'anesthésie a été bon.(Traduit par Isabelle Vallières).

Effect of pre-warming on perioperative hypothermia and anesthetic recovery in small breed dogs undergoing ovariohysterectomy.

This study compared perianesthetic body temperatures and times to recovery from general anesthesia in small dogs that were either warmed for 20 minutes prior to anesthesia or not warmed. Twenty-eight client-owned dogs that were presented for ovariohysterectomy were included in the study. Small (<10 kg body weight) dogs with normal circulatory status were randomly assigned to receive pre-warming for 20 minutes or no treatment. Body temperature was measured during the procedure using a calibrated rectal probe. Duration of anesthesia and surgery, time to rescue warming, time to extubation, presence and duration of shivering, and time to return to normal temperature were recorded. Temperature at the end of surgery was significantly higher in the control group than the pre-warmed group. There was no difference in time to extubation or duration of postoperative shivering between groups. Pre-warming did not result in improved temperature or recovery from anesthesia.

Effet du préchauffement sur l'hypothermie périopératoire et le réveil après l'anesthésie chez des chiennes de petites races subissant une ovario-hystérectomie. Cette étude a comparé les températures corporelles périanesthésiques et la durée du réveil après l'anesthésie générale chez des petites chiennes qui étaient soit réchauffées pendant 20 minutes avant l'anesthésie ou non réchauffées. Vingt-huit chiennes appartenant à des clients qui ont été présentées pour l'ovario-hystérectomie étaient incluses dans l'étude. Les petites chiennes (< 10 kg de poids corporel) avec un état circulatoire normal ont été assignées au hasard pour recevoir le préchauffement de 20 minutes ou aucun traitement. La température corporelle a été mesurée durant l'intervention à l'aide d'une sonde rectale calibrée. La durée de l'anesthésie et de la chirurgie, le temps jusqu'au réchauffement de secours, le temps jusqu'à l'extubation, la présence et la durée des frissons et le temps jusqu'au retour à la normale ont été consignés. La température à la fin de la chirurgie était significativement supérieure dans le groupe témoin comparativement au groupe préchauffé. Il n'y avait aucune différence au niveau du temps jusqu'à l'extubation ni de la durée des frissons postopératoires entre les groupes. Le préchauffement n'a pas amélioré la température ni le réveil après l'anesthésie.(Traduit par Isabelle Vallières).

Comparison of cardiorespiratory variables in dorsally recumbent horses anesthetized with guaifenesin-ketamine-xylazine spontaneously breathing 50% or maximal oxygen concentrations.

This study compared cardiorespiratory variables in dorsally recumbent horses anesthetized with guaifenesin-ketamine-xylazine and spontaneously breathing 50% or maximal (> 90%) oxygen (O2) concentrations. Twelve healthy mares were randomly assigned to breathe 50% or maximal O2 concentrations. Horses were sedated with xylazine, induced to recumbency with ketamine-diazepam, and anesthesia was maintained with guaifenesin-ketamine-xylazine to effect. Heart rate, arterial blood pressures, respiratory rate, lithium dilution cardiac output (CO), inspired and expired O2 and carbon dioxide partial pressures, and tidal volume were measured. Arterial and mixed-venous blood samples were collected prior to sedation (baseline), during 30 minutes of anesthesia, 10 minutes after disconnection from O2, and 30 minutes after standing. Shunt fraction, O2 delivery, and alveolar-arterial O2 partial pressures difference [P(A-a)O2] were calculated. Recovery times were recorded. There were no significant differences between groups in cardiorespiratory parameters or in P(A-a)O2 at baseline or 30 minutes after standing. Oxygen partial pressure difference in the 50% group was significantly less than in the maximal O2 group during anesthesia.

Comparaison des variables cardiorespiratoires chez les chevaux en décubitus dorsal anesthésiés à l'aide de la guaifénésine-kétamine-xylazine respirant spontanément des concentrations de 50 % ou des concentrations maximales d'oxygène. Cette étude a comparé les variables cardiorespiratoires chez les chevaux en décubitus dorsal anesthésiés à l'aide de guaifénésine-kétamine-xylazine et respirant spontanément des concentrations de 50 % ou des concentrations maximales (> 90 %) d'oxygène (O2). Douze juments en santé ont été assignées au hasard à la respiration de concentrations 50 % ou de concentrations maximales d' O2. Les chevaux ont été mis sous sédation avec de la xylazine, induits au décubitus à l'aide de kétamine-diazépam et l'anesthésie a été maintenue à l'aide de guaifénésine-kétamine-xylazine jusqu'à l'effet. Le rythme cardiaque, la pression artérielle, la fréquence respiratoire, le débit cardiaque par dilution au lithium, l' O2 à l'inspiration et à l'expiration ainsi que les pressions partielles de gaz carbonique et le volume courant ont été mesurés. Des échantillons sanguins artériels et veineux mixtes ont été prélevés avant la sédation (données de référence), durant 30 minutes d'anesthésie, 10 minutes après le débranchement de l'oxygène et 30 minutes après s'être mis debout. La fraction du shunt, l'alimentation en O2 et la différence des pressions partielles d' O2 alvéolaire-artérielle [P(A-a)O2] ont été calculées. Les temps de réveil ont été consignés. Il n'y avait pas de différences significatives entre les groupes dans les paramètres cardiorespiratoires ou dans P(A-a)O2 aux données de référence ou 30 minutes après s'être mis debout. La différence entre la pression partielle de l' O2 dans le groupe 50 % était significativement inférieure à celle du groupe avec des concentrations maximales d' O2 durant l'anesthésie.(Traduit par Isabelle Vallières).

Comparison of invasive and oscillometric blood pressure measurement techniques in anesthetized sheep, goats, and cattle.

OBJECTIVE: To determine the level of agreement between an oscillometric (O-NIBP) and an invasive method (IBP) of monitoring arterial blood pressure (ABP) in anesthetized sheep, goats, and cattle. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty sheep and goats, 20 cattle weighing < 150 kg body weight, and 20 cattle weighing 150 kg body weight. METHODS: Animals were anesthetized and systolic ABP (SABP), mean ABP (MABP), and diastolic ABP (DABP) were measured using IBP and O-NIBP. Differences between IBP and O-NIBP, and 95% limits of agreement (LOA) between SABP, MABP, and DABP values were assessed by the Bland-Altman method. RESULTS: Mean difference ± standard deviation (range) between SABP, DABP, and MABP measurements in sheep and goats was 0 ± 16 (-57 to 38) mmHg, 13 ± 16 (-37 to 70) mmHg, and 8 ± 13 (-34 to 54) mmHg, respectively. Mean difference between SABP, DABP, and MABP measurements in small cattle was 0 ± 19 (-37 to 37) mmHg, 6 ± 18 (-77 to 48) mmHg, and 4 ± 16 (-73 to 48) mmHg, respectively. Mean difference between SABP, DABP, and MABP measurements in large cattle was -18 ± 32 (-107 to 71) mmHg, 7 ± 29 (-112 to 63) mmHg, and -5 ± 28 (-110 to 60) mmHg, respectively. The 95% LOAs for SABP, DABP, and MABP were -31 to +31, -19 to +44, and -19 to +34 mmHg, respectively in sheep and goats; were -37 to +37, -19 to +44, and -19 to +34 mmHg, respectively in small cattle; and were -81 to +45, -50 to +63, and -59 to +50 mmHg, respectively in large cattle. CONCLUSIONS: Agreement was poor between O-NIBP and IBP monitoring techniques. CLINICAL RELEVANCE: Arterial BP should be monitored in anesthetized sheep, goats, and cattle using IBP.

Prevalence and risk factors for canine post-anesthetic aspiration pneumonia (1999-2009): a multicenter study.

OBJECTIVE: To determine the incidence of canine post-anesthetic aspiration pneumonia (AP) and to identify anesthetic agents, procedures and management factors associated with the development of AP. STUDY DESIGN: Multicenter, randomized, case-controlled retrospective study. ANIMALS: Two hundred and forty dogs affected with AP and 488 unaffected control dogs. METHODS: Electronic medical record databases at six Veterinary colleges were searched for dogs, coded for anesthesia or sedation and pneumonia from January 1999 to December 2009. The resultant 2158 records were hand-searched to determine eligibility for inclusion. Diagnosis of AP was made radiographically. Two unaffected control dogs were randomly selected for each affected dog, from a list of dogs that underwent sedation or anesthesia in the same time period and did not develop aspiration pneumonia. Fifty-seven factors were then evaluated for association with aspiration pneumonia. Data analysis was performed using univariate Chi-square or student t-tests, then multivariate logistic regression. RESULTS: Incidence of post-anesthetic AP was 0.17%, from 140,711 cases anesthetized or sedated over the 10 year period. Two anesthesia-related events were significantly associated with development of AP: regurgitation and administration of hydromorphone at induction. Administration of anticholinergics was not associated with AP. Procedures associated with increased odds of aspiration pneumonia included laparotomy, upper airway surgery, neurosurgery, thoracotomy and endoscopy. Orthopedic surgery, ophthalmologic surgery, dental procedures, MRI, CT, bronchoscopy, cystoscopy, tracheoscopy and neutering were not associated with development of AP. Three patient factors were associated with the development of AP: megaesophagus, and a history of pre-existing respiratory or neurologic disease. Sixty-nine% of dogs with two or more of the above independent predictive variables developed AP. CONCLUSION AND CLINICAL RELEVANCE: Most anesthetic agents and procedures were not associated with the development of AP. We need to devise and evaluate strategies to protect at risk patients.

Pharmacokinetics and pharmacodynamics of intramuscular dexmedetomidine in dogs.

OBJECTIVE: To determine the pharmacokinetics and pharmacodynamics of dexmedetomidine after IM administration in dogs. ANIMALS: 6 healthy adult purpose-bred dogs (3 males, 3 females) with a mean ± SD body weight of 25.2 ± 1.8 kg. PROCEDURES: Each dog received 10 µg/kg dexmedetomidine, IM. Heart rate and respiratory rate were counted via cardiac auscultation and visual assessment of chest excursions. Sedation was assessed utilizing 2 sedation scoring systems. Plasma concentrations were determined using ultra performance liquid chromatography-mass spectrometry. Plasma concentrations versus time data after IM dexmedetomidine were analyzed using noncompartmental analysis for extravascular administration. RESULTS: Over the first 2 hours following IM injection of dexmedetomidine, plasma concentrations fluctuated in each dog. The geometric mean (range) maximum plasma concentration was 109.2 (22.4 to 211.5) ng/mL occurring at 20.5 (5 to 75) minutes, and the mean half-life was 25.5 (11.5 to 41.5) minutes. Heart rate was significantly lower than baseline from 30 minutes to 2 hours postdexmedetomidine administration, and respiratory rate was significantly lower than baseline from 45 minutes to 1.75 hours. Dogs were significantly more sedated from 30 minutes to 1.5 hours postdexmedetomidine administration. Median time to onset of sedation was 7.5 minutes (range, 2 to 10 minutes), and median time to peak sedation was 30 minutes (range, 15 to 60 minutes). CLINICAL RELEVANCE: Variations in plasma concentrations occurred in all dogs for the 2 hours postinjection of dexmedetomidine at 10 µg/kg, IM. This was likely due to alterations in absorption due to dexmedetomidine-induced local vasoconstriction. Despite variable plasma concentrations, all dogs were sedated following IM dexmedetomidine administration.

Comparison of invasive and oscillometric blood pressure measurement techniques in anesthetized camelids.

This study assessed the accuracy of the oscillometric method for arterial blood pressure (ABP) monitoring in anesthetized camelids. Twenty camelids were anesthetized and systolic ABP (SABP), mean ABP (MABP), and diastolic ABP (DABP) were measured directly and using the oscillometric method. The mean difference between SABP measurements was -9.9 ± 21.9 mmHg with a range of -76 to 54 mmHg, and the 95% limits of agreement (LOA) were -33 to 53 mmHg. The difference between DABP measurements was -1.8 ± 15.6 mmHg with a range of -81 to 36 mmHg, and the 95% LOA were -32 to 29 mmHg. The difference between MABP measurements was -2.9 ± 17.0 mmHg with a range of -81 to 36 mmHg, and the 95% LOA were -30 to 36 mmHg. Accurate ABP monitoring in anesthetized camelids cannot be accomplished using the oscillometric method.

RésuméComparaison des techniques invasives et oscillométriques de mesure de la tension artérielle chez les camélidés anesthésiés. Cette étude évalue l'exactitude de la méthode oscillométrique pour la surveillance de la tension artérielle (TA) chez les camélidés anesthésiés. Vingt camélidés ont été anesthésiés et la TA systolique (TAS), la TA moyenne (TAM) et la TA diastolique (TAD) ont été mesurées directement et en utilisant la méthode oscillométrique. La différence moyenne entre les mesures TAS était de −9,9 ± 21,9 mmHg avec un écart de −76 à 54 mmHg et les limites de 95 % de concordance (LC) étaient de −33 à 53 mmHg. La différence entre les mesures TAD était de −1,8 ± 15,6 mmHg avec un écart de −81 à 36 mmHg et les LC de 95 % étaient de −32 à 29 mmHg. La différence entre les mesures de TAM était de −2,9 ± 17,0 mmHg avec un écart de −81 à 36 mmHg et la LC de 95 % étaient de −30 à 36 mmHg. Une surveillance exacte de la TA chez les camélidés ne peut pas être réalisée en utilisant la méthode oscillométrique.(Traduit par Isabelle Vallières).

Effect of 50% and maximal inspired oxygen concentrations on respiratory variables in isoflurane-anesthetized horses.

BACKGROUND: The purpose of this study was to compare the effects of 0.5 fraction of inspired oxygen (FiO2) and >0.95 FiO2 on pulmonary gas exchange, shunt fraction and oxygen delivery (DO2) in dorsally recumbent horses during inhalant anesthesia. The use of 0.5 FiO2 has the potential to reduce absorption atelectasis (compared to maximal FiO2) and augment alveolar oxygen (O2) tensions (compared to ambient air) thereby improving gas exchange and DO2. Our hypothesis was that 0.5 FiO2 would reduce ventilation-perfusion mismatching and increase the fraction of pulmonary blood flow that is oxygenated, thus improving arterial oxygen content and DO2. RESULTS: Arterial partial pressures of O2 were significantly higher than preanesthetic levels at all times during anesthesia in the >0.95 FiO2 group. Arterial partial pressures of O2 did not change from preanesthetic levels in the 0.5 FiO2 group but were significantly lower than in the >0.95 FiO2 group from 15 to 90 min of anesthesia. Alveolar to arterial O2 tension difference was increased significantly in both groups during anesthesia compared to preanesthetic values. The alveolar to arterial O2 tension difference was significantly higher at all times in the >0.95 FiO2 group compared to the 0.5 FiO2 group. Oxygen delivery did not change from preanesthetic values in either group during anesthesia but was significantly lower than preanesthetic values 10 min after anesthesia in the 0.5 FiO2 group. Shunt fraction increased in both groups during anesthesia attaining statistical significance at varying times. Shunt fraction was significantly increased in both groups 10 min after anesthesia but was not different between groups. Alveolar dead space ventilation increased after 3 hr of anesthesia in both groups. CONCLUSIONS: Reducing FiO2 did not change alveolar dead space ventilation or shunt fraction in dorsally recumbent, mechanically ventilated horses during 3 hr of isoflurane anesthesia. Reducing FiO2 in dorsally recumbent isoflurane anesthetized horses does not improve oxygenation or oxygen delivery.

AAHA anesthesia guidelines for dogs and cats.

Safe and effective anesthesia of dogs and cats rely on preanesthetic patient assessment and preparation. Patients should be premedicated with drugs that provide sedation and analgesia prior to anesthetic induction with drugs that allow endotracheal intubation. Maintenance is typically with a volatile anesthetic such as isoflurane or sevoflurane delivered via an endotracheal tube. In addition, local anesthetic nerve blocks; epidural administration of opioids; and constant rate infusions of lidocaine, ketamine, and opioids are useful to enhance analgesia. Cardiovascular, respiratory, and central nervous system functions are continuously monitored so that anesthetic depth can be modified as needed. Emergency drugs and equipment, as well as an action plan for their use, should be available throughout the perianesthetic period. Additionally, intravenous access and crystalloid or colloids are administered to maintain circulating blood volume. Someone trained in the detection of recovery abnormalities should monitor patients throughout recovery. Postoperatively attention is given to body temperature, level of sedation, and appropriate analgesia.

Sedative and cardiorespiratory effects of intramuscular administration of alfaxalone and butorphanol combined with acepromazine, midazolam, or dexmedetomidine in dogs.

OBJECTIVE: To evaluate the sedative and cardiorespiratory effects of IM administration of alfaxalone and butorphanol combined with acepromazine, midazolam, or dexmedetomidine in dogs. ANIMALS: 6 young healthy mixed-breed hounds. PROCEDURES: Dogs received each of 3 treatments (alfaxalone [2 mg/kg] and butorphanol [0.4 mg/kg] combined with acepromazine [0.02 mg/kg; AB-ace], midazolam [0.2 mg/kg; AB-mid], or dexmedetomidine [0.005 mg/kg; AB-dex], IM) in a blinded, randomized crossover-design study with a 1-week washout period between treatments. Sedation scores and cardiorespiratory variables were recorded at predetermined time points. Data were analyzed by use of mixed-model ANOVA and linear generalized estimating equations with post hoc adjustments. RESULTS: All treatments resulted in moderate to deep sedation (median score, ≥ 15/21) ≤ 5 minutes after injection. Sedation scores did not differ among treatments until the 40-minute time point, when the score was higher for AB-dex than for other treatments. Administration of AB-dex resulted in median scores reflecting deep sedation until 130 minutes, versus 80 and 60 minutes for AB-ace and AB-mid, respectively, after injection. Heart rate, cardiac output, and oxygen delivery decreased significantly after AB-dex, but not AB-ace or AB-mid administration. Respiratory variables remained within clinically acceptable ranges after all treatments. Undesirable recovery characteristics were observed in 4 dogs after AB-mid treatment. Four dogs required atipamezole administration 180 minutes after AB-dex injection. CONCLUSIONS AND CLINICAL RELEVANCE: All protocols produced reliable sedation. The results indicated that in young, healthy dogs, AB-mid may produce undesirable recovery characteristics; AB-dex treatment caused cardiovascular depression and should be used with caution.

Effect of intravenous administration of lactated Ringer's solution or hetastarch for the treatment of isoflurane-induced hypotension in dogs.

OBJECTIVE: To determine the effect of IV administration of crystalloid (lactated Ringer's solution [LRS]) or colloid (hetastarch) fluid on isoflurane-induced hypotension in dogs. ANIMALS: 6 healthy Beagles. PROCEDURES: On 3 occasions, each dog was anesthetized with propofol and isoflurane and instrumented with a thermodilution catheter (pulmonary artery). Following baseline assessments of hemodynamic variables, end-tidal isoflurane concentration was increased to achieve systolic arterial blood pressure (SABP) of 80 mm Hg. At that time (0 minutes), 1 of 3 IV treatments (no fluid, LRS [80 mL/kg/h], or hetastarch [80 mL/kg/h]) was initiated. Fluid administration continued until SABP was within 10% of baseline or to a maximum volume of 80 mL/kg (LRS) or 40 mL/kg (hetastarch). Hemodynamic variables were measured at intervals (0 through 120 minutes and additionally at 150 and 180 minutes in LRS- or hetastarch-treated dogs). Several clinicopathologic variables including total protein concentration, PCV, colloid osmotic pressure, and viscosity of blood were assessed at baseline and intervals thereafter (0 through 120 minutes). RESULTS: Administration of 80 mL of LRS/kg did not increase SABP in any dog, whereas administration of

Pharmacokinetics and pharmacodynamics of intranasal and intravenous naloxone hydrochloride administration in healthy dogs.

OBJECTIVE: To evaluate the pharmacokinetics and pharmacodynamics of naloxone hydrochloride in dogs following intranasal (IN) and IV administration. ANIMALS: 6 healthy adult mixed-breed dogs. PROCEDURES: In a blinded crossover design involving 2 experimental periods separated by a washout period (minimum of 7 days), dogs were randomly assigned to receive naloxone IN (4 mg via a commercially available fixed-dose naloxone atomizer; mean ± SD dose, 0.17 ± 0.02 mg/kg) or IV (0.04 mg/kg) in the first period and then the opposite treatment in the second period. Plasma naloxone concentrations, dog behavior, heart rate, and respiratory rate were evaluated for 24 hours/period. RESULTS: Naloxone administered IN was well absorbed after a short lag time (mean ± SD, 2.3 ± 1.4 minutes). Mean maximum plasma concentration following IN and IV administration was 9.3 ± 2.5 ng/mL and 18.8 ± 3.9 ng/mL, respectively. Mean time to maximum concentration following IN administration was 22.5 ± 8.2 minutes. Mean terminal half-life after IN and IV administration was 47.4 ± 6.7 minutes and 37.0 ± 6.7 minutes, respectively. Mean bioavailability of naloxone administered IN was 32 ± 13%. There were no notable changes in dog behavior, heart rate, or respiratory rate following naloxone administration by either route. CONCLUSIONS AND CLINICAL RELEVANCE: Use of a naloxone atomizer for IN naloxone administration in dogs may represent an effective alternative to IV administration in emergency situations involving opioid exposure. Future studies are needed to evaluate the efficacy of IN naloxone administration in dogs with opioid intoxication, including a determination of effective doses.

Pharmacokinetics and pharmacodynamic effects of oral transmucosal and intravenous administration of dexmedetomidine in dogs.

OBJECTIVE: To determine pharmacokinetic and pharmacodynamic properties of the injectable formulation of dexmedetomidine administered via the oral transmucosal (OTM) route to healthy dogs. ANIMALS: 6 healthy dogs. PROCEDURES: Injectable dexmedetomidine was administered IV (5 µg/kg) or via the OTM route (20 µg/kg) in a blinded, single-observer, randomized crossover study. Dogs received dexmedetomidine and a sham treatment at each administration. Serial blood samples were collected from a catheter in a saphenous vein. Heart rate, respiratory rate, and subjective sedation score were assessed for 24 hours after administration. Plasma samples were analyzed for dexmedetomidine concentrations by use of ultraperformance liquid chromatography-tandem mass spectrometry. RESULTS: For the OTM route, the mean ± SD maximum plasma concentration was 3.8 ± 1.3 ng/mL, which was detected 73 ± 33 minutes after administration. The mean maximum concentration for the IV dose, when extrapolated to the time of administration, was 18.6 ± 3.3 ng/mL. The mean terminal-phase half-life was 152 ± 146 minutes and 36 ± 6 minutes for OTM and IV administration, respectively. After IV administration, total clearance was 8.0 ± 1.6 mL/min/kg and volume of distribution at steady state was 371 ± 72 mL/kg. Bioavailability for OTM administration of dexmedetomidine was 11.2 ± 4.5%. Peak sedation scores did not differ significantly between routes of administration. Decreases in heart rate, respiratory rate, and peak sedation score were evident sooner after IV administration. CONCLUSIONS AND CLINICAL RELEVANCE: OTM administration of the injectable formulation of dexmedetomidine resulted in a similar degree of sedation and prolonged duration of action, compared with results for IV administration, despite relatively low bioavailability.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in dogs.

OBJECTIVE: To determine the effect of oral administration of gabapentin (20 mg/kg) on the minimum alveolar concentration (MAC) of isoflurane in dogs. ANIMALS: 6 healthy adult dogs (3 males and 3 females with a mean ± SD body weight of 24.8 ± 1.3 kg). PROCEDURES: Each dog was anesthetized twice. Dogs were initially assigned to 1 of 2 treatments (gabapentin [20 mg/kg, PO] followed 2 hours later by anesthesia maintained with isoflurane or anesthesia maintained with isoflurane alone). A minimum of 7 days later, dogs received the other treatment. The MAC of isoflurane was determined by use of an iterative bracketing technique with stimulating electrodes placed in the maxillary buccal mucosa. Hemodynamic variables and vital parameters were recorded at the lowest end-tidal isoflurane concentration at which dogs did not respond to the stimulus. Effect of treatment on outcome variables was analyzed by use of a paired t test. RESULTS: Mean ± SD MAC of isoflurane was significantly lower when dogs received gabapentin and isoflurane (0.71 ± 0.12%) than when dogs received isoflurane alone (0.91 ± 0.26%). Mean reduction in MAC of isoflurane was 20 ± 14%. Hemodynamic variables did not differ significantly between treatments. Mean time to extubation was significantly less when dogs received gabapentin and isoflurane (6 ± 4 minutes) than when dogs received isoflurane alone (23 ± 15 minutes). CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration of gabapentin 2 hours before anesthesia maintained with isoflurane had a MAC-sparing effect with no effect on hemodynamic variables or vital parameters of dogs.

Pharmacokinetics and pharmacodynamics of buprenorphine and sustained-release buprenorphine after administration to adult alpacas.

OBJECTIVE To determine pharmacokinetics and pharmacodynamics of buprenorphine after IV and SC administration and of sustained-release (SR) buprenorphine after SC administration to adult alpacas. ANIMALS 6 alpacas. PROCEDURES Buprenorphine (0.02 mg/kg, IV and SC) and SR buprenorphine (0.12 mg/kg, SC) were administered to each alpaca, with a 14-day washout period between administrations. Twenty-one venous blood samples were collected over 96 hours and used to determine plasma concentrations of buprenorphine. Pharmacokinetic parameters were calculated by use of noncompartmental analysis. Pharmacodynamic parameters were assessed via sedation, heart and respiratory rates, and thermal and mechanical antinociception indices. RESULTS Mean ± SD maximum concentration after IV and SC administration of buprenorphine were 11.60 ± 4.50 ng/mL and 1.95 ± 0.80 ng/mL, respectively. Mean clearance was 3.00 ± 0.33 L/h/kg, and steady-state volume of distribution after IV administration was 3.8 ± l.0 L/kg. Terminal elimination half-life was 1.0 ± 0.2 hours and 2.7 ± 2.8 hours after IV and SC administration, respectively. Mean residence time was 1.3 ± 0.3 hours and 3.6 ± 3.7 hours after IV and SC administration, respectively. Bioavailability was 64 ± 28%. Plasma concentrations after SC administration of SR buprenorphine were below the LLOQ in samples from 4 alpacas. There were no significant changes in pharmacodynamic parameters after buprenorphine administration. Alpacas exhibited mild behavioral changes after all treatments. CONCLUSIONS AND CLINICAL RELEVANCE Buprenorphine administration to healthy alpacas resulted in moderate bioavailability, rapid clearance, and a short half-life. Plasma concentrations were detectable in only 2 alpacas after SC administration of SR buprenorphine.

Clinical comparison of xylazine and medetomidine for premedication of horses.

OBJECTIVE: To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia. DESIGN: Randomized clinical trial. ANIMALS: 40 horses. PROCEDURE: Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at the time of anesthetic induction. After induction of anesthesia, sodium pentothal was administered as necessary to prevent limb movements. Hypotension was treated with dobutamine; hypoventilation and hypoxemia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored. RESULTS: Scores for the quality of the transition to inhalation anesthesia were significantly higher for horses premedicated with medetomidine than for horses premedicated with xylazine. However, other scores, recovery times, and numbers of attempts needed to achieve sternal recumbency and to stand were not significantly different between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that medetomidine is suitable for premedication of horses undergoing general anesthesia. Analgesic and cardiopulmonary effects of medetomidine were similar to those of xylazine, except that the transition to inhalation anesthesia was smoother when horses were premedicated with medetomidine, rather than xylazine.