Objective: To compare effects of isoflurane and sevoflurane on intracranial pressure and cardiovascular variables at 1.0, 1.5, and 2.0 times the minimum alveolar concentration (MAC) in mechanically ventilated normocapnic dogs. Animals: 6 healthy male Beagles. Procedures: The individual MAC was determined for each agent with an electrical stimulus. After a minimum of 1 week, anesthetic induction by use of a mask with one of the inhalation anesthetics selected randomly was followed by mechanical ventilation and instrumentation for measurement of intracranial pressure and cardiovascular variables. Heart rate; systolic, mean, and diastolic arterial blood pressures; central venous pressure; mean pulmonary arterial pressure; pulmonary artery occlusion pressure; cardiac output; intracranial pressure (ICP); core body temperature; end-tidal inhalation anesthetic and carbon dioxide concentration; and arterial blood gas values were measured after attaining equilibrium at 1.0, 1.5, and 2.0 MAC of each inhalation anesthetic. Cardiac index, systemic vascular resistance, pulmonary vascular resistance, and cerebral perfusion pressure (CPP) were calculated. Results: Mean ICP did not differ within and between anesthetics at any MAC. Compared with equipotent concentrations of isoflurane, the CPP and mean values for systolic, mean, and diastolic arterial blood pressures were increased at 2.0 MAC for sevoflurane, whereas mean values for mean and diastolic arterial blood pressures and systemic vascular resistance were increased at 1.5 MAC for sevoflurane. Conclusions and Clinical Relevance: Although ICP was similar in healthy normocapnic dogs, CPP was better maintained during 2.0 MAC for sevoflurane, compared with isoflurane.

The aim of this study was to determine the viability and cardiorespiratory effects of the association of epidural alpha-2 adrenergic agonists and lidocaine for ovariohysterectomy (OH) in bitches. Forty-two bitches were spayed under epidural anesthesia with 2.5 mg/kg body weight (BW) of 1% lidocaine with adrenaline (CON) or in association with 0.25 mg/kg BW of xylazine (XYL), 10 μg/kg BW of romifidine (ROM), 30 μg/kg BW of detomidine (DET), 2 μg/kg BW of dexmedetomidine (DEX), or 5 μg/kg BW of clonidine (CLO). Heart rate (HR), respiratory rate (fR) and arterial pressures were monitored immediately before and every 10 min after the epidural procedure. Blood gas and pH analysis were done before, and at 30 and 60 min after the epidural procedure. Animals were submitted to isoflurane anesthesia if they presented a slightest sign of discomfort during the procedure. Time of sensory epidural block and postoperative analgesia were evaluated. All animals in CON and DEX, 5 animals in ROM and CLO, 4 animals in XYL, and 3 in DET required supplementary isoflurane. All groups, except CLO, showed a decrease in HR. There was an increase in arterial pressures in all groups. Postoperative analgesia lasted the longest in XYL. None of the protocols were totally efficient to perform the complete procedure of OH; however, xylazine provided longer postoperative analgesia than the others.

Objective: To evaluate the use of midazolam, ketamine, and xylazine for total IV anesthesia (TIVA) in horses. Animals: 6 healthy Thoroughbred mares. Procedures: Horses were sedated with xylazine (1.0 mg/kg, IV). Anesthesia was induced with midazolam (0.1 mg/kg, IV) followed by ketamine (2.2 mg/kg, IV) and was maintained with an IV infusion of midazolam (0.002 mg/kg/min), ketamine (0.03 mg/kg/min), and xylazine (0.016 mg/kg/min). Horses underwent surgical manipulation and injection of the palmar digital nerves; duration of the infusion was 60 minutes. Additional ketamine (0.2 to 0.4 mg/kg, IV) was administered if a horse moved its head or limbs during procedures. Cardiopulmonary and arterial blood variables were measured prior to anesthesia; at 10, 20, 30, 45, and 60 minutes during infusion; and 10 minutes after horses stood during recovery. Recovery quality was assessed by use of a numeric (1 to 10) scale with 1 as an optimal score. Results: Anesthesia was produced for 70 minutes after induction; supplemental ketamine administration was required in 4 horses. Heart rate, respiratory rate, arterial blood pressures, and cardiac output remained similar to preanesthetic values throughout TIVA. Arterial partial pressure of oxygen and oxygen saturation of arterial hemoglobin were significantly decreased from preanesthetic values throughout anesthesia; oxygen delivery was significantly decreased at 10- to 30-minute time points. Each horse stood on its first attempt, and median recovery score was 2. Conclusions and Clinical Relevance: Midazolam, ketamine, and xylazine in combination produced TIVA in horses. Further studies to investigate various dosages for midazolam and ketamine or the substitution of other α2-adrenoceptor for xylazine are warranted.

Objective: To identify ventilatory protocols that yielded good image quality for thoracic CT and hemodynamic stability in cats. Animals: 7 healthy cats. Procedures: Cats were anesthetized and ventilated via 4 randomized protocols (hyperventilation, 20 seconds [protocol 1]; single deep inspiration, positive inspiratory pressure of 15 cm H2O [protocol 2]; recruitment maneuver [protocol 3]; and hyperventilation, 20 seconds with a positive end-expiratory pressure of 5 cm H2O [protocol 4]). Thoracic CT was performed for each protocol; images were acquired during apnea for protocols 1 and 3 and during positive airway pressure for protocols 2 and 4. Heart rate; systolic, mean, and diastolic arterial blood pressures; blood gas values; end-tidal isoflurane concentration; rectal temperature; and measures of atelectasis, total lung volume (TLV), and lung density were determined before and after each protocol. Results: None of the protocols eliminated atelectasis; the number of lung lobes with atelectasis was significantly greater during protocol 1 than during the other protocols. Lung density and TLV differed significantly among protocols, except between protocols 1 and 3. Protocol 2 TLV exceeded reference values. Arterial blood pressure after each protocol was lower than before the protocols. Mean and diastolic arterial blood pressure were higher after protocol 3 and diastolic arterial blood pressure was higher after protocol 4 than after protocol 2. Conclusions and Clinical Relevance: Standardization of ventilatory protocols may minimize effects on thoracic CT images and hemodynamic variables. Although atelectasis was still present, ventilatory protocols 3 and 4 provided the best compromise between image quality and hemodynamic stability.

Objective: To noninvasively evaluate physiologic postprandial adaptations of the heart in snakes. Animals: 6 juvenile Paraguay anacondas (Eunectes notaeus). Procedures: The heart of each anaconda was echocardiographically evaluated after food was withheld for 28 days as well as 3 and 10 days after feeding. Physical measurements included body length, weight, and circumference at the level of the heart. Echocardiographic measurements included heart rate and 2-D total and internal ventricular area. From these measurements, total ventricular volume as well as the myocardial area as a surrogate of myocardial mass was calculated. Results: No significant changes in body length, weight, and circumference were found. Significant increases in heart rate (from 45 to 58 beats/min), total ventricular volume (from 4.63 to 5.54 mL), and myocardial area (from 0.7 to 0.81 cm2) were detected 10 days after feeding, compared with results obtained prior to feeding after food had been withheld for 28 days. No pericardial effusion was detected at any time point. Conclusions and Clinical Relevance: Echocardiographic evaluation of the heart of anacondas was performed, and feeding resulted in concentric cardiac hypertrophy. Physiologic fluctuation of cardiac dimensions should be considered when cardiac imaging is performed in snakes.

Objective—To compare the toxic effects of a Delphinium occidentale chemotype containing -(methylsuccinimido) anthranoyllycoctonine (MSAL)—type alkaloids and a D occidentale chemotype lacking MSAL-type alkaloids in mice and cattle. Animals—225 male Swiss Webster mice and 11 Black Angus steers. Procedures—4 collections of larkspur containing MSAL-type alkaloids and 4 collections of larkspur lacking MSAL-type alkaloids were used. From each collection, total alkaloid extracts (0.05 to 0.20 mL) were administered via tail-vein injection in 27 to 29 mice. Dried, finely ground plant material from 1 collection with and 1 collection without MSAL-type alkaloids (doses equivalent to 37.6 mg of total alkaloids/kg) were each administered to 8 cattle via oral gavage in a crossover experiment; 3 cattle received a single dose equivalent to 150.4 mg of total alkaloids/kg (no MSAL-type alkaloids). In mice, clinical effects were monitored; in cattle, heart rate was monitored before (baseline) and 24 hours after treatment. At the 24-hour time point, cattle were exercised as a measure of muscle weakness. Results—In mice, mean LD50 associated with alkaloid extracts prepared from plants that did or did not contain MSAL-type alkaloids was 2.3 and 54.2 mg/kg, respectively. In cattle at 24 hours after treatment, plant material containing MSAL-type alkaloids significantly increased heart rate from baseline and was associated with exercise-induced collapse; plant material lacking MSAL-type alkaloids had no similar effects. Conclusions and Clinical Relevance—Taxonomic classification of D occidentale alone was not a good indicator of the toxic risk to grazing cattle.

Objective—To determine selected cardiopulmonary values and baroreceptor response in conscious green iguanas (Iguana iguana) and to evaluate the use of blood gas analysis and pulse oximetry in this species. Animals—15 healthy juvenile green iguanas. Procedures—Baseline cardiopulmonary values were determined in 15 conscious iguanas breathing room air. Effects of 100% O2 inspiration were also measured (n = 6), and the baroreceptor reflex was characterized by exponential sigmoidal curve fitting analysis. Results—Conscious iguanas had a mean ± SD resting heart rate of 52 ± 8 beats/min, respiratory rate of 28 ± 6 breaths/min, and systolic, mean, and diastolic arterial blood pressures of 69 ± 10 mm Hg, 62 ± 12 mm Hg, and 56 ± 13 mm Hg, respectively. Mean arterial pH at 37°C was 7.29 ± 0.11, Pao2 was 81 ± 10 mm Hg, and Paco2 was 42 ± 9 mm Hg; corrected for a body temperature of 30°C, mean arterial pH at 37°C was 7.382 ±0.12, Pao2 was 54 ± 15 mm Hg, and Paco2 was 32 ± 7 mm Hg. Inspiration of 100% O2 did not change heart and respiratory rates but increased Pao2 to 486 ± 105 mm Hg (corrected value, 437 ± 96 mm Hg). A baroreceptor reflex was evident, with mean heart rates ranging from 30 ± 3 beats/min to 63 ± 5 beats/min and mean arterial blood pressures ranging from 42 ± 3 mm Hg to 58 ± 3 mm Hg. Conclusions and Clinical Relevance—This study provided needed information on cardiopulmonary values in healthy green iguanas, the application and limitation of arterial and venous blood gas analysis, and the accuracy of pulse oximetry.

Objective: To evaluate effects of racemic ketamine and S-ketamine in gazelles. Animals: 21 male gazelles (10 Rheem gazelles [Gazella subgutturosa marica] and 11 Subgutturosa gazelles [Gazella subgutturosa subgutturosa]), 6 to 67 months old and weighing (mean±SD) 19 ± 3 kg. Procedures: In a randomized, blinded crossover study, a combination of medetomidine (80 μg/kg) with racemic ketamine (5 mg/kg) or S-ketamine (3 mg/kg) was administered IM. Heart rate, blood pressure, respiratory rate, rectal temperature, and oxygen saturation (determined by means of pulse oximetry) were measured. An evaluator timed and scored induction of, maintenance of, and recovery from anesthesia. Medetomidine was reversed with atipamezole. The alternate combination was used after a 4-day interval. Comparisons between groups were performed with Wilcoxon signed rank and paired t tests. Results: Anesthesia induction was poor in 2 gazelles receiving S-ketamine, but other phases of anesthesia were uneventful. A dominant male required an additional dose of S-ketamine (0.75 mg/kg, IM). After administration of atipamezole, gazelles were uncoordinated for a significantly shorter period with S-ketamine than with racemic ketamine. Recovery quality was poor in 3 gazelles with racemic ketamine. No significant differences between treatments were found for any other variables. Time from drug administration to antagonism was similar between racemic ketamine (44.5 to 53.0 minutes) and S-ketamine (44.0 to 50.0 minutes). Conclusions and Clinical Relevance: Administration of S-ketamine at a dose 60% that of racemic ketamine resulted in poorer induction of anesthesia, an analogous degree of sedation, and better recovery from anesthesia in gazelles with unremarkable alterations in physiologic variables, compared with racemic ketamine.

This study investigated the sedative, cardiopulmonary, and gastrointestinal effects produced by buprenorphine and xylazine given in combination to horses. Six healthy adult horses underwent 4 randomized treatments, with an interval of 1 wk between treatments. A control group was given a saline solution intravenously (IV) and the experimental groups received buprenorphine [10 μg/kg bodyweight (BW)] in combination with 1 of 3 different doses of xylazine: 0.25 mg/kg BW (BX25), 0.50 mg/kg BW (BX50), or 0.75 mg/kg BW (BX75), all of them by IV. Cardiopulmonary parameters were evaluated for 120 min after the drugs were administered and intestinal motility was observed for 12 h after treatment. Sedation was found to be dose-dependent in all groups receiving buprenorphine and xylazine and it was observed that the heart rate decreased in the first 5 min and increased at the end of the sedation period. Arterial blood gas tension analyses showed minimal alterations during the experiment. Gastrointestinal hypomotility was observed for up to 8 h. The combination of buprenorphine and 0.50 mg/kg BW of xylazine (BX50) provided a 30-minute period of sedation without intense ataxia and maintained cardiopulmonary parameters within acceptable limits for the species.

Objective--To describe the simple elimination kinetics of methyllycaconitine (MLA) and deltaline and evaluate the heart rate response in cattle following oral administration of larkspur. Animals--5 healthy Angus steers that were habituated to metabolism crates. Procedures--Tall larkspur (Delphinium barbeyi) in the early flowering stage was collected, dried, and ground. Each steer received a single dose of larkspur that was equivalent to 10.4 mg of MLA/kg and 11.0 mg of deltaline/kg via oral administration. Steers were housed in metabolism crates during a 96-hour period following larkspur administration; heart rate was monitored continuously, and blood samples were collected periodically for analysis of serum MLA and deltaline concentrations as well as assessment of pharmacokinetic parameters. Results--No overt clinical signs of poisoning developed in any steer during the experiment. Mean ± SE heart rate reached a maximum of 79.0 ± 5.0 beats/min at 17 hours after larkspur administration. Serum MLA concentration was correlated directly with heart rate. Mean times to maximal serum concentration of MLA and deltaline were 8.8 ± 1.2 hours and 5.0 ± 0.6 hours, respectively. Mean elimination half-life values for MLA and deltaline were 20.5 ± 4.1 hours and 8.2 ± 0.6 hours, respectively. Conclusions and Clinical Relevance--Following larkspur administration in 5 healthy steers, maximum serum concentrations of MLA and deltaline were detected within 10 hours, and changes in serum MLA concentration and heart rate were correlated. Results indicated that cattle that have consumed larkspur will eliminate 99% of MLA and deltaline from serum within 144 hours.