Objective-To evaluate the effects of subarachnoidally administered hyperbaric morphine, buprenorphine, and methadone on avoidance threshold to noxious electrical stimulation of the perineal, sacral, lumbar, and thoracic regions in horses. Animals-6 healthy adult horses. Procedures-Horses were assigned to receive subarachnoid administration of hyperbaric morphine (0.01 mg/kg), buprenorphine (0.001 mg/kg), methadone (0.01mg/kg), or 10% dextrose solution in equal volumes (5 mL). Electrical stimulation was applied every 10 minutes for 60 minutes and every 30 minutes for 120 minutes after subarachnoid injection over the dermatomes of the perineal, sacral, lumbar, and thoracic regions, and the avoidance threshold voltage was recorded. Heart and respiratory rate, blood gas tensions, serum electrolyte concentrations, and sedative effects were also evaluated. Results-Administration of 10% dextrose solution did not change the avoidance threshold. Morphine and methadone significantly increased the avoidance threshold by 10 minutes after injection, which lasted until 120 minutes after subarachnoid administration in the perineal, sacral, lumbar, and thoracic regions. Profound analgesia (avoidance threshold > 40 V) was achieved in all regions. Buprenorphine also significantly increased the avoidance threshold by 10 minutes (36 V) after injection, which lasted 60 minutes and was considered moderate. Heart rate, blood pressure, respiratory rate, and blood gas tensions stayed within reference range. No ataxia, signs of sedation, or CNS excitement were observed. Conclusions and Clinical Relevance-Subarachnoid administration of hyperbaric morphine or methadone produces intense analgesia for 120 minutes over the dermatomes of the perineal, sacral, lumbar, and thoracic areas without cardiorespiratory depression, ataxia, or CNS excitement in horses.

Objective-To quantitate dose- and time-related magnitudes of interactive effects of morphine (MOR) and isoflurane (ISO) in horses and to characterize pharmacokinetics of MOR in plasma and the ventilatory response to MOR during administration of ISO. Animals-6 adult horses. Procedure-Horses were anesthetized 3 times to determine the minimum alveolar concentration (MAC) of ISO in O2 and then to characterize the change in anesthetic requirement as defined by the alteration in ISO MAC following IV administration of saline (0.9% NaCl) solution and 2 doses of MOR (low dose, 0.25 mg/kg; high dose, 2.0 mg/kg). Arterial blood samples were obtained before and after MOR and analyzed. Results-Mean +/- SD baseline ISO MAC was 1.43 +/- 0.06%. The ISO MAC did not change with time after administration of saline solution. Effects of MOR on ISO MAC varied. Maximal change in MAC ranged from –20.2 to +28.3% and -18.9 to +56.2% after low and high doses of MOR, respectively. Typical half-life of MOR in plasma was 40 to 60 minutes and related to dose. Mean PaCO2 increased from 70 mm Hg before MOR to 88 to 102 mm Hg for 30 to 240 minutes after the high dose of MOR. Recovery from anesthesia after administration of the high dose of MOR was considered undesirable and dangerous. Conclusions and Clinical Relevance-Our results do not support routine clinical use of MOR administered IV at dosages of 0.25 or 2.0 mg/kg as an adjuvant to anesthesia in horses administered ISO.

Objective-To evaluate effects of sedation on stability of resistance of the respiratory system (RRS) and measures of resting energy expenditure (REE) by use of open-flow indirect calorimetry (IC) and treatment with aerosolized albuterol on REE in horses with recurrent airway obstruction (RAO). Animals-9 clinically normal horses and 8 horses with RAO. Procedure-In phase 1, RRS was measured by using forced oscillometry (FOT) in 5 clinically normal horses before and after sedation with xylazine. In phase 2, REE was measured in 4 clinically normal horses between 20 and 25 minutes and again 35 to 40 minutes after sedation with xylazine. In phase 3, IC was performed between 20 and 25 minutes and FOT was performed between 30 and 35 minutes after xylazine administration in 8 horses with RAO; after administration of 450 µg of albuterol, IC and FOT were repeated. Results-In phase 1, RRS values were significantly lower 5 and 10 minutes after sedation. In phase 2, diminishing sedation did not significantly affect REE. In phase 3, there was a significant decrease in mean RRS (1.15 +/- 0.25 vs 0.84 +/- 0.14 cm H20/L/s) and REE (30.68 +/- 17.89 vs 27.46 +/- 16.54 kcal/kg/d) after albuterol administration. Conclusions and Clinical Relevance-FOT and IC are useful in obtaining repeatable measurements of RRS and REE, respectively, in sedated horses. Concurrent bronchodilation and decreased REE after albuterol administration suggest that increased work of breathing as a result of airway obstruction may contribute to increased energy demands in horses with RAO.

Effects of IV and aerosol administration of 5-hydroxytryptamine (5-HT) on ventilation, pulmonary mechanics values, pulmonary arterial pressure, and heart rate were investigated in healthy unsedated Friesian calves. Minute volume increased significantly, mainly because of an increase in respiratory rate. Except for total pulmonary resistance after bolus injection, continuous administration of 5-HT given by either route caused significant alterations of lung dynamic compliance and total pulmonary resistance, the former decreasing to one-fifth of its baseline value and the latter increasing twofold. Pulmonary arterial pressure increased significantly, whatever the speed or route of administration. Administration of a bolus did not affect heart rate, whereas continuous iv administration of 5-HT as well by perfusion or by aerosol resulted in sustained tachycardia. It was concluded that 5-HT induces reversible bronchoconstriction and pulmonary vasoconstriction in healthy unsedated calves, 5-HT-induced functional alterations depend on the speed of administration, and excess of 5-HT production or depression in uptake by the lungs during bovine respiratory tract diseases could contribute to pulmonary dysfunction.

Pulmonary function tests were performed on seven adult dairy cows with an expanded tung field (ExLF) and the results were compared to the values from seven cows with normal lung fields. The cows with ExLF had an increased functional residual capacity (FRC) and end-tidal N2 concentration of the final breath of the multiple-breath N2 washout (FET(N2),fb), and an abnormal distribution of ventilation. The measurements of ventilation and gas exchange and pulmonary mechanics did not differ between the two groups. Postmortem examination of the lungs of five of the cows in each group indicated the cows with ExLF had a bronchiolitis with varying degrees of goblet cell hyperplasia, epithelial cell hyperplasia and metaplasia, smooth muscle hypertrophy, inflammatory cell infiltrate, vascular thickening, peribronchiolar fibrosis, and a mild overinflation of the lung. A histopathological score, based on the preceding indices and bronchus-associated lymphoid tissue, was correlated with FRC, FET(N2),fb, the lung clearance index and pulmonary resistance. There were no correlations between the histopathological score and any of the measures of ventilation and gas exchange.

Fourteen adult beavers (Castor canadensis) weighing 16.5 +/- 4.14 kg (mean +/- SD) were anesthetized for surgical implantation of radio telemetry devices. Beavers were anesthetized with diazepam (0.1 mg/kg) and ketamine (25 mg/kg) administered IM, which provided smooth anesthetic induction and facilitated tracheal intubation. Anesthesia was maintained with halothane in oxygen via a semiclosed circle anesthetic circuit. Values for heart rate, respiratory rate, esophageal temperature, direct arterial blood pressure, end-tidal halothane concentration, and end-tidal CO2 tension were recorded every 15 minutes during the surgical procedure. Arterial blood samples were collected every 30 minutes to determine pH, PaO2, and PaCO2. Values for plasma bicarbonate, total CO2, and base excess were calculated. Ventilation was spontaneous in 7 beavers and controlled to maintain normocapnia (PaCO2 approx 40 mm of Hg) in 7 others. Vaporizer settings were adjusted to maintain a light surgical plane of anesthesia. Throughout the surgical procedure, all beavers had mean arterial pressure < 60 mm of Hg and esophageal temperature < 35 C. Mean values for arterial pH, end-tidal CO2, PaO2, and PaCO2 were significantly (P < 0.05) different in spontaneously ventilating beavers, compared with those in which ventilation was controlled. Respiratory acidosis during halothane anesthesia was observed in spontaneously ventilating beavers, but not in beavers maintained with controlled ventilation. All beavers recovered unremarkably from anesthesia.

OBJECTIVE To compare the effects of a dexmedetomidine-ketamine-midazolam (DKM) anesthetic protocol versus isoflurane inhalation anesthesia on echocardiographic variables and plasma cardiac troponin 1 (cTnI) concentration in black-tailed prairie dogs (BTPDs; Cynomys ludovicianus). ANIMALS Nine 6-month-old sexually intact male captive BTPDs. PROCEDURES Each BTPD was randomly assigned to be anesthetized by IM administration of dexmedetomidine (0.25 mg/kg), ketamine (40 mg/kg), and midazolam (1.5 mg/kg) or via inhalation of isoflurane and oxygen. Three days later, each BTPD underwent the alternative anesthetic protocol. Echocardiographic data and a blood sample were collected within 5 minutes after initiation and just prior to cessation of each 45-minute-long anesthetic episode. RESULTS Time or anesthetic protocol had no significant effect on echocardiographic variables. For either protocol, plasma cTnI concentration did not differ with time. When administered as the first treatment, neither anesthetic protocol significantly affected plasma cTnI concentration. However, with regard to findings for the second treatments, plasma cTnI concentrations in isoflurane-treated BTPDs (n = 4; data for 1 animal were not analyzed because of procedural problems) were higher than values in DKM-treated BTPDs (4), which was suspected to be a carryover effect from prior DKM treatment. CONCLUSIONS AND CLINICAL RELEVANCE The DKM and isoflurane anesthetic protocols did not have any significant effect on echocardiographic measurements in the BTPDs. Increases in plasma cTnI concentration during the second anesthetic episode were evident when BTPDs underwent the DKM anesthetic protocol as the first of the 2 treatments, suggestive of potential myocardial injury associated with that anesthetic protocol. Clinicians should consider these findings, especially when evaluating BTPDs with known or suspected cardiac disease.

OBJECTIVE To evaluate the diagnostic usefulness of focused cardiac ultrasonography and selected echocardiographic variables for predicting fluid responsiveness in conscious, spontaneously breathing dogs with various clinical conditions. ANIMALS 26 dogs (15 males and 11 females) with a median age of 84 months (range, 12 to 360 months) and median body weight of 8 kg (range, 2 to 35 kg) referred for various clinical conditions. PROCEDURES Left ventricular end-diastolic internal diameter normalized to body weight (LVIDDn), left ventricular volume score (LVVS), left ventricular end-diastolic volume index (EDVI), aortic velocity time integral (VTIAo), and aortic peak flow velocity (VmaxAo) were echocardiographically measured before and after IV administration of a bolus of lactated Ringer solution (4 mL/kg) over a 1-minute period. Dogs were classified on the basis of the observed change in aortic stroke volume following fluid administration as responders (≥ 15%) or nonresponders (< 15%) to fluid administration. Receiver operating characteristic curves were generated for the ability of LVVS, LVIDDn, EDVI, VTIAo, and VmaxAo to predict responder status. RESULTS 13 dogs were classified as responders and 13 as nonresponders. Areas under the receiver operating characteristic curves (95% confidence intervals) for predicting fluid responsiveness were as follows: VTIAo, 0.91 (0.74 to 0.99); LVIDDn, 0.85 (0.66 to 0.96); EDVI, 0.85 (0.65 to 0.96); LVVS, 0.85 (0.65 to 0.96); and VmaxAo, 0.75 (0.54 to 0.90). CONCLUSIONS AND CLINICAL RELEVANCE The evaluated echocardiographic variables were useful for noninvasive prediction of fluid responsiveness in conscious dogs and could be valuable for informing clinical decisions regarding fluid therapy.

The aim of this study was to compare nasopharyngeal and esophageal temperature measurements in anesthetized sheep with a range of fresh gas flows (1 to 6 L/min) through the breathing system. Data were compared using a Bland-Altman plot and correlation coefficients, and error measures were calculated. One hundred and ninety-five sets of data were collected from 20 sheep weighing 41 kg (31 to 51.5 kg). The bias (95% limit of agreement), correlation coefficient, and absolute error for nasopharyngeal compared to esophageal temperature were 0.04°C (-0.77°C to 0.85°C), 0.92, and 0.29°C ± 0.29°C, respectively. The percentage of nasopharyngeal readings within 0.5°C of the esophageal temperature was 77.44%. The error did not significantly increase with increasing fresh gas flow. Nasopharyngeal temperature measurement is suitable for estimation of esophageal temperature during general anesthesia of sheep when the fresh gas flow through the breathing system is between 1 and 6 L/min.

OBJECTIVE To determine the effects of acepromazine maleate premedication on cardiovascular function before and after infusion of dobutamine hydrochloride for 30 minutes in isoflurane-anesthetized horses. ANIMALS 6 healthy adult horses. PROCEDURES Each horse was anesthetized once following premedication with acepromazine (0.02 mg/kg, IV) administered 30 minutes prior to anesthetic induction (ACP+ treatment) and once without premedication (ACP– treatment). Anesthesia was induced with IV administration of xylazine hydrochloride (0.8 mg/kg), ketamine hydrochloride (2.2 mg/kg), and diazepam (0.08 mg/kg). Horses were positioned in right lateral recumbency, and anesthesia was maintained via inhalation of isoflurane delivered in oxygen. End-tidal isoflurane concentration was adjusted to achieve a target mean arterial blood pressure of 60 mm Hg (interquartile range [25th to 75th percentile], 57 to 63 mm Hg) for at least 15 minutes. Cardiac index, oxygen delivery index, and femoral arterial blood flow indices were determined 60 minutes after anesthetic induction (baseline). Dobutamine was then infused to achieve a target mean arterial blood pressure of 80 mm Hg (interquartile range, 76 to 80 mm Hg). Data collection was repeated 30 minutes after the start of dobutamine infusion for comparison with baseline values. RESULTS Complete data sets were available from 5 of the 6 horses. Dobutamine administration resulted in significant increases in oxygen delivery and femoral arterial blood flow indices but no significant change in cardiac index for each treatment. However, at baseline or 30 minutes after the start of dobutamine infusion, findings for the ACP+ and ACP– treatments did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized horses, dobutamine administration increased oxygen delivery and femoral arterial blood flow indices, but these changes were unaffected by premedication with acepromazine.