The effects of xylazine or detomidine when used as a pre-anesthetic sedative on recovery quality and duration in horses undergoing elective equine castration

The purpose of this prospective, blinded, randomized clinical trial was to compare the effects of low dose detomidine to xylazine on recovery quality and duration in a castration procedure. Horses were administered either detomidine [0.015 mg/kg body weight (BW)] or xylazine (1.1 mg/kg BW) intravenously (IV) before IV induction with ketamine (2.2 mg/kg BW) and diazepam (0.05 mg/kg BW). Two anesthesiologists who were unaware of treatment allocation scored the recoveries using a simple descriptive scale (with a low number representing the most desirable recovery) and recoveries were timed. Horses in the detomidine group (n = 16) had a median recovery score of 16 (range: 11 to 26), whereas horses in the xylazine group (n = 12) had a median recovery score of 12 (range: 10 to 16) (P = 0.001). There was no difference in surgery time (P = 0.52), time from the end of surgery to standing (P = 0.45), or time from induction to standing (P = 0.48) between the groups.

Role of alloplastic reconstruction of the temporomandibular joint in the juvenile idiopathic arthritis population

We present outcomes following total joint replacement of the temporomandibular joint (TMJ) in adolescent and young adult patients with juvenile idiopathic arthritis (JIA), and discuss a multidisciplinary treatment model. A retrospective review was performed of patients presenting to the University of North Carolina Oral and Maxillofacial Surgery Service (Chapel Hill, NC) from 2016- 2018 who underwent unilateral or bilateral total replacement of the TMJ for a diagnosis of end-stage joint disease secondary to JIA. Inclusion criteria included diagnosis by a rheumatologist, presentation to our department in adolescence (under 18 years of age), surgical intervention in adolescence or young adulthood (under 25 years of age), and documentation of preoperative and postoperative pain, maximum incisal opening (MIO), and quality of life measures. A database was created and data were then analysed both qualitatively and quantitatively. Five patients met the inclusion criteria. All achieved MIO of more than 35mm with a mean improvement of 24mm, and were able to tolerate a regular diet. All preoperative pain had essentially been eliminated. All patients reported a considerable improvement in quality of life. To our knowledge, this is the first report to document a series of paediatric and young adult patients with JIA who required total replacement of the joint for end-stage joint disease. To our knowledge, it is also the first to describe the use of a collaborative clinic of oral and maxillofacial surgeons, neuroradiologists, dental radiologists, orofacial pain specialists, paediatric rheumatologists, and paediatric nurse practitioners, to care for these patients.

Ultrasound versus magnetic resonance imaging of the temporomandibular joint in juvenile idiopathic arthritis: a systematic review

A systematic review of published articles on ultrasound (US) and magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) in juvenile idiopathic arthritis (JIA) was performed to answer the question "What is the sensitivity and specificity of US as compared to MRI in diagnosing acute and chronic joint changes in patients with JIA?" The most recent evidence was sought in published articles via a search of the PubMed, Ovid, and Embase databases. Article appraisal was performed by two reviewers. Nineteen articles reporting prospective or ambispective studies comparing US to MRI in TMJ imaging were found. Six of these articles were specific to JIA patients. The heterogeneity of these articles made comparison difficult. Of the acute and chronic changes assessed (disk displacement, joint effusion, bony deformity), only joint effusion was appropriately assessed by multiple authors, with US having a sensitivity of 0-72% and specificity of 70-83% as compared to MRI. There was a paucity of studies specific to JIA, with many studying adult, non-rheumatic patients. This systematic review found that dynamic imaging with high-resolution US improves sensitivity and specificity compared to static, low-resolution US. Additionally, there is evidence to suggest that US imaging following a baseline MRI can increase US sensitivity and specificity and may have a future role in disease surveillance.

Effect of ketamine hydrochloride on the analgesic effects of tramadol hydrochloride in horses with signs of chronic laminitis-associated pain

OBJECTIVE

To investigate the effects of ketamine hydrochloride on the analgesic effects of tramadol hydrochloride in horses with signs of pain associated with naturally occurring chronic laminitis.

ANIMALS

15 client-owned adult horses with chronic laminitis.

PROCEDURES

Each horse received tramadol alone or tramadol and ketamine in a randomized, crossover study (≥ 2 months between treatments). Tramadol (5 mg/kg) was administered orally every 12 hours for 1 week. When appropriate, ketamine (0.6 mg/kg/h) was administered IV for 6 hours on each of the first 3 days of tramadol administration. Noninvasive systemic blood pressure values, heart and respiratory rates, intestinal sounds, forelimb load and off-loading frequency (determined via force plate system), and plasma tumor necrosis factor-α and thromboxane B(2) concentrations were assessed before (baseline) during (7 days) and after (3 days) each treatment.

RESULTS

Compared with baseline data, arterial blood pressure decreased significantly both during and after tramadol-ketamine treatment but not with tramadol alone. Forelimb off-loading frequency significantly decreased during the first 3 days of treatment with tramadol only, returning to baseline frequency thereafter. The addition of ketamine to tramadol treatment reduced off-loading frequency both during and after treatment. Forelimb load did not change with tramadol alone but increased with tramadol-ketamine treatment. Plasma concentrations of tumor necrosis factor-α and thromboxane B(2) were significantly reduced with tramadol-ketamine treatment but not with tramadol alone.

CONCLUSIONS AND CLINICAL RELEVANCE

In horses with chronic laminitis, tramadol administration induced limited analgesia, but this effect was significantly enhanced by administration of subanesthetic doses of ketamine.

Comparative pharmacokinetics of meloxicam in clinically normal horses and donkeys

OBJECTIVE

To determine the disposition of a bolus of meloxicam (administered IV) in horses and donkeys (Equus asinus) and compare the relative pharmacokinetic variables between the species.

ANIMALS

5 clinically normal horses and 5 clinically normal donkeys.

PROCEDURES

Blood samples were collected before and after IV administration of a bolus of meloxicam (0.6 mg/kg). Serum meloxicam concentrations were determined in triplicate via high-performance liquid chromatography. The serum concentration-time curve for each horse and donkey was analyzed separately to estimate standard noncompartmental pharmacokinetic variables.

RESULTS

In horses and donkeys, mean +/- SD area under the curve was 18.8 +/- 7.31 microg/mL/h and 4.6 +/- 2.55 microg/mL/h, respectively; mean residence time (MRT) was 9.6 +/- 9.24 hours and 0.6 +/- 0.36 hours, respectively. Total body clearance (CL(T)) was 34.7 +/- 9.21 mL/kg/h in horses and 187.9 +/- 147.26 mL/kg/h in donkeys. Volume of distribution at steady state (VD(SS)) was 270 +/- 160.5 mL/kg in horses and 93.2 +/- 33.74 mL/kg in donkeys. All values, except VD(SS), were significantly different between donkeys and horses.

CONCLUSIONS AND CLINICAL RELEVANCE

The small VD(SS) of meloxicam in horses and donkeys (attributed to high protein binding) was similar to values determined for other nonsteroidal anti-inflammatory drugs. Compared with other species, horses had a much shorter MRT and greater CL(T) for meloxicam, indicating a rapid elimination of the drug from plasma; the even shorter MRT and greater CL(T) of meloxicam in donkeys, compared with horses, may make the use of the drug in this species impractical.

Effect of 1- and 10-day administration of tepoxalin on minimum alveolar concentration of isoflurane and sevoflurane in dogs

Analgesics given preoperatively have the potential to decrease the amount of inhalant anesthetics required intraoperatively (i.e., to decrease the minimum alveolar concentration, or MAC, for the inhalant). Tepoxalin is an NSAID approved for the treatment of arthritis in dogs in the United States and, hence, could be administered to patients undergoing anesthesia. In this study, administration of a single dose or a 10-day course of tepoxalin did not affect the MAC for isoflurane or sevoflurane.

Effect of preoperative administration of tepoxalin on induction dose of injectable anesthetics in dogs

Medications given preoperatively have the potential to affect the induction dose of injectable anesthetics, which could result in an anesthetic overdose. Tepoxalin is an NSAID approved for the treatment of arthritis in dogs in the United States and hence could be administered in patients requiring anesthesia. In this study, administration of a single dose or a 10-day course of tepoxalin did not affect the induction dose (dose that allowed intubation) of propofol, thiopental, or ketamine-diazepam and also did not affect the time required for dogs to recover from anesthesia.

Pharmacokinetics and clinical effects of a subanesthetic continuous rate infusion of ketamine in awake horses

OBJECTIVE

To determine the pharmacokinetics and clinical effects of a subanesthetic, continuous rate infusion of ketamine administered to healthy awake horses.

ANIMALS

8 adult horses.

PROCEDURES

Ketamine hydrochloride was administered to 2 horses, in a pilot study, at rates ranging from 0.4 to 1.6 mg/kg/h for 6 hours to determine an appropriate dose that did not cause adverse effects. Ketamine was then administered to 6 horses for a total of 12 hours (3 horses at 0.4 mg/kg/h for 6 hours followed by 0.8 mg/kg/h for 6 hours and 3 horses at 0.8 mg/kg/h for 6 hours followed by 0.4 mg/kg/h for 6 hours). Concentration of ketamine in plasma, heart rate, respiratory rate, blood pressure, physical activity, and analgesia were measured prior to, during, and following infusion. Analgesic testing was performed with a modified hoof tester applied at a measured force to the withers and radius.

RESULTS

No signs of excitement and no significant changes in the measured physiologic variables during infusion rates of 0.4 and 0.8 mg of ketamine/kg/h were found. At 6 hours following infusions, heart rate and mean arterial pressure were decreased, compared with preinfusion measurements. An analgesic effect could not be demonstrated during or after infusion. Pharmacokinetic variables for 0.4 and 0.8 mg/kg/h infusions were not significantly different.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketamine can be administered to awake horses at 0.4 or 0.8 mg/kg/h without adverse behavioral effects. The observed pharmacokinetic values are different than those reported for single-dose IV bolus administration of this drug.

Pharmacokinetics of R(-) and S(+) carprofen after administration of racemic carprofen in donkeys and horses

OBJECTIVE

To compare plasma disposition of the R(-) and S(+) enantiomers of carprofen after IV administration of a bolus dose to donkeys and horses.

ANIMALS

5 clinically normal donkeys and 3 clinically normal horses.

PROCEDURE

Blood samples were collected from all animals at time 0 (before) and at 10, 15, 20, 30, and 45 minutes and 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 24, 28, 32, and 48 hours after IV administration of a bolus of carprofen (0.7 mg/kg). Plasma was analyzed in triplicate via high-performance liquid chromatography to determine the concentrations of the carprofen enantiomers. A plasma concentrationtime curve for each donkey and horse was analyzed separately to estimate noncompartmental pharmacokinetic variables.

RESULTS

In donkeys and horses, the area under the plasma concentration versus time curve (AUC) was greater for the R(-) carprofen enantiomer than it was for the S(+) carprofen enantiomer. For the R(-) carprofen enantiomer, the AUC and mean residence time (MRT) were significantly less and total body clearance (CIT) was significantly greater in horses, compared with donkeys. For the S(+) carprofen enantiomer, AUC and MRT were significantly less and CIT and apparent volume of distribution at steady state were significantly greater in horses, compared with donkeys.

CONCLUSIONS AND CLINICAL RELEVANCE

Results have suggested that the dosing intervals for carprofen that are used in horses may not be appropriate for use in donkeys.

Repetitive Propofol Administration in Dogs and Cats

A bolus of propofol was administered to 10 dogs (6 mg/kg intravenously [IV]) and 10 cats (10 mg/kg IV) on three consecutive days. The occurrence of apnea, heart and respiratory rates, blood pressure, time to movement, and changes in a complete blood count and biochemical profile were recorded. Apnea was not seen in the dogs but was seen in three cats. Slight increases in the number of Heinz bodies were seen in six cats, but the increases were not considered clinically significant. No apparent cumulative adverse effects were seen from a bolus of bisulfite-containing propofol, administered on three consecutive days.

An evaluation of pulse oximeters in dogs, cats and horses

OBJECTIVE

Evaluation of five pulse oximeters in dogs, cats and horses with sensors placed at five sites and hemoglobin saturation at three plateaus.

STUDY DESIGN

Prospective randomized multispecies experimental trial.

ANIMALS

Five healthy dogs, cats and horses.

METHODS

Animals were anesthetized and instrumented with ECG leads and arterial catheters. Five pulse oximeters (Nellcor Puritan Bennett-395, NPB-190, NPB-290, NPB-40 and Surgi-Vet V3304) with sensors at five sites were studied in a 5 x 5 Latin square design. Ten readings (SpO2) were taken at each of three hemoglobin saturation plateaus (98, 85 and 72%) in each animal. Arterial samples were drawn concurrently and hemoglobin saturation was measured with a co-oximeter. Accuracy of saturation measurements was calculated as the root mean squared difference (RMSD), a composite of bias and precision, for each model tested in each species.

RESULTS

Accuracy varied widely. In dogs, the RMSD for the NPB-395, NPB-190, NPB-290, NPB-40 and V3304 were 2.7, 2.2, 2.4, 1.7 and 2.7% respectively. Failure to produce readings for the NPB-395, NPB-190, NPB-290, NPB-40 and V3304 were 0, 0, 0.7, 0, and 20%, respectively. The Pearson correlation coefficients for the tongue, toe, ear, lip and prepuce or vulva were 0.95, 0.97, 0.69, 0.87 and 0.95, respectively. In horses, the RMSD for the NPB-395, NPB-190, NPB-290, NPB-40 and V3304 were 3.1, 3.0, 4.7, 3.3 and 2.1%, respectively while rates of failure to produce readings were 10, 21, 0, 17 and 60%, respectively. The Pearson correlation coefficients for the tongue, nostril, ear, lip and prepuce or vulva were 0.98, 0.94, 0.88, 0.93 and 0.94, respectively. In cats, the RMSD for all data for the NPB-395, NPB-190, NPB-290, NPB-40 and V3304 were 5.9, 5.6, 7.9, 7.9 and 10.7%, respectively while failure rates were 0, 0.7, 0, 20 and 32%, respectively. The correlation coefficients for the tongue, rear paw, ear, lip and front paw were 0.54, 0.79,.0.64, 0.49 and 0.57, respectively. For saturations above 90% in cats, the RMSD for the NPB-395, NPB-190, NPB-290, NPB-40 and V3304 were 2.6, 4.4, 4.0, 3.5 and 4.8%, respectively, while failure rates were 0, 1.7, 0, 25 and 43%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Accuracy and failure rates (failure to produce a reading) varied widely from model to model and from species to species. Generally, among the models tested in the clinically relevant range (90-100%) RMSD ranged from 2-5% while failure rates were highest in the V3304.

Preliminary assessment of skeletal stability after sagittal split mandibular advancement using a bioresorbable fixation system

We studied skeletal stability during the first year after mandibular advancement and fixation with bioresorbable self-reinforced poly-L-lactide (SR-PLLA) screws in 11 patients by cephalometric measurements. We compared these with a cohort of 11 patients, in whom titanium screws were used for fixation. We found no significant difference between the two groups in the median preoperative cephalometric values and the median changes after operation. There was also no significant difference between the two groups regarding the median extent of relapse 1-year after operation. We conclude that bioresorbable SR-PLLA screws are comparable to metallic screws for fixation of bone after sagittal split mandibular advancement.

Anesthetic considerations of the older equine

This article briefly reviews physiologic changes that may occur with aging in equine patients. It summarizes anesthetic protocols and problems encountered in a group of older horses (> 20 years old) anesthetized over the previous 10 years in the teaching hospital and makes recommendations for appropriate management of these patients.

Pharmacokinetics of sulfamethoxazole and trimethoprim in donkeys, mules, and horses

OBJECTIVE

To compare serum disposition of sulfamethoxazole and trimethoprim after IV administration to donkeys, mules, and horses.

ANIMALS

5 donkeys, 5 mules, and 3 horses.

PROCEDURE

Blood samples were collected before (time 0) and 5, 15, 30, and 45 minutes and 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 10, and 24 hours after IV administration of sulfamethoxazole (12.5 mg/kg) and trimethoprim (2.5 mg/kg). Serum was analyzed in triplicate with high-performance liquid chromatography for determination of sulfamethoxazole and trimethoprim concentrations. Serum concentration-time curve for each animal was analyzed separately to estimate noncompartmental pharmacokinetic variables.

RESULTS

Clearance of trimethoprim and sulfamethoxazole in donkeys was significantly faster than in mules or horses. In donkeys, mean residence time (MRT) of sulfamethoxazole (2.5 hours) was less than half the MRT in mules (6.2 hours); MRT of trimethoprim in donkeys (0.8 hours) was half that in horses (1.5 hours). Volume of distribution at steady state (Vdss) for sulfamethoxazole did not differ, but Vdss of trimethoprim was significantly greater in horses than mules or donkeys. Area under the curve for sulfamethoxazole and trimethoprim was higher in mules than in horses or donkeys.

CONCLUSIONS AND CLINICAL RELEVANCE

Dosing intervals for IV administration of trimethoprim-sulfamethoxazole in horses may not be appropriate for use in donkeys or mules. Donkeys eliminate the drugs rapidly, compared with horses. Ratios of trimethoprim and sulfamethoxazole optimum for antibacterial activity are maintained for only a short duration in horses, donkeys, and mules.

A multisite case report on the clinical use of sevoflurane in dogs

The purpose of this report was to evaluate the clinical safety and efficacy of sevoflurane as an inhalant anesthetic in dogs. Subjective and objective data from 196 clinical cases utilizing sevoflurane as the maintenance anesthetic was collected at three sites. After preanesthetic evaluation, the attending anesthesiologist assigned the dogs to one of the following six anesthetic protocols: protocol 1, oxymorphone premedication and thiopental induction; protocol 2, oxymorphone/acetylpromazine premedication and thiopental induction; protocol 3, xylazine/butorphanol premedication and thiopental induction; protocol 4, opioid premedication and propofol induction; protocol 5, optional premedication and mask induction with sevoflurane in oxygen; and protocol 6, optional premedication and optional induction. The average quality of induction, maintenance, and recovery was good to excellent in all protocols. The three most common side effects during maintenance and recovery were hypotension, tachypnea, and apnea. Sevoflurane produces anesthesia in dogs comparable to the other inhalation anesthetics currently used (i.e., halothane and isoflurane) for diagnostic or therapeutic procedures.

Pharmacokinetics of phenylbutazone and its metabolite oxyphenbutazone in miniature donkeys

OBJECTIVE

To describe the pharmacokinetics of phenylbutazone and oxyphenbutazone after IV administration in miniature donkeys.

ANIMALS

6 clinically normal miniature donkeys.

PROCEDURE

Blood samples were collected before and 5, 10, 20, 30, 45, 60, 90, 120, 180, 240, 300, 360, and 480 minutes after IV administration of phenylbutazone (4.4 mg/kg of body weight). Serum was analyzed in triplicate by use of high-performance liquid chromatography for determination of phenylbutazone and oxyphenbutazone concentrations. The serum concentration-time curve for each donkey was analyzed separately to estimate model-independent pharmacokinetic variables.

RESULTS

Serum concentrations decreased rapidly after IV administration of phenylbutazone, and they reached undetectable concentrations within 4 hours. Values for mean residence time ranged from 0.5 to 3.0 hours (median, 1.1 hour), whereas total body clearance ranged from 4.2 to 7.5 ml/kg/min (mean, 5.8 ml/kg/min). Oxyphenbutazone appeared rapidly in the serum; time to peak concentration ranged from 13 to 41 minutes (mean, 26.4 minutes), and peak concentration in serum ranged from 2.8 to 4.0 mg/ml (mean, 3.5 microg/ml).

CONCLUSION AND CLINICAL RELEVANCE

Clearance of phenylbutazone in miniature donkeys after injection of a single dose (4.4 mg/kg, IV) is rapid. Compared with horses, miniature donkeys may require more frequent administration of phenylbutazone to achieve therapeutic efficacy.

The use of halothane gas to identify turkeys prone to developing pale, exudative meat when transported before slaughter

Halothane screening has been used in the swine industry to identify animals susceptible to stress and prone to developing pale, soft, exudative (PSE) meat. This study evaluated the ability of halothane to identify stress-susceptible turkeys prone to developing PSE meat when reared to market age and transported before slaughter. Male Nicholas turkeys (n = 1,286) were exposed to 3% halothane for 5 min at 4 wk of age in two trials. Birds were classified as halothane sensitive (HAL+) or halothane nonresponder (HAL-), in which HAL+ birds showed signs of muscle rigidity in the legs upon removal from halothane gas, and HAL- birds showed no stiffness response. Approximately 3.5% (45) of the turkeys were HAL+. All HAL+ birds and an equal number of HAL- birds were grown until 20 wk of age. Immediately prior to slaughter, all birds were transported in coops on a flatbed trailer for 2 h and then immediately slaughtered upon arrival at the processing plant. Breast muscle pH (0, 1.5, and 24 h postmortem) and L* value (1.5 h and 24 h postmortem) were measured on the fillets. Drip loss and cook loss were also determined on marinated and nonmarinated breast fillets from each carcass. There were no significant mean differences in any parameter measured between the HAL+ and HAL- turkeys. However, the HAL+ turkeys had a greater percentage of fillets with L* values >51 compared with the HAL- turkeys. These results suggest that either halothane response is only a limited predictor of PSE meat in turkeys or that transportation is not an appropriate stressor to induce the PSE condition.

The development of pale, exudative meat in two genetic lines of turkeys subjected to heat stress and its prediction by halothane screening

Previous research has indicated that seasonal-type heat stress (HS) can contribute to the development of pale, soft, exudative (PSE) meat in fast-growing turkeys and that halothane exposure may identify stress-susceptible animals. This study evaluated the ability of halothane screening to identify stress-susceptible birds prone to developing pale, exudative meat when reared to market age. Two lines of turkeys (n = 292), one selected for rapid overall growth (BODY) and the other for large breast muscle yield (BREAST), were exposed to 3% halothane for 5 min at 2 to 4 wk of age and were raised together until 16 wk of age. Approximately 10% of both BODY and BREAST birds were sensitive to halothane. Between 16 and 20 wk, all of the halothane sensitive (HAL+) and half of the halothane nonresponders (HAL-) were exposed to an HS environment of 30 to 36 C (night/day), whereas the other half of the HAL- birds were kept at an ambient temperature of 13 to 21 C (night/day). All birds were slaughtered at 20 wk of age, and samples were collected for pH, L* value, drip loss, cooking loss, and shear value. The BREAST strain had 5% greater breast percentage than the BODY strain, and there were no differences in ready-to-cook yields between any treatments. The HAL+ HS birds had significantly lower muscle pH (0 h) and significantly higher L* values at 2 h postmortem compared with HAL- HS birds in the BREAST strain; however, there was no difference in L* value at 24 h postmortem. The HAL- HS birds had significantly lower muscle pH (0 h and 2 h) and significantly higher L* values at 2 h postmortem compared with HAL- controls in the BODY strain. The HAL- HS BREAST birds had significantly higher drip loss than HAL- controls. No differences in shear value were found among any treatments. The incidence of PSE (2-h L* values >52) was significantly higher in HAL+ HS birds (34.7%) compared with HAL- HS birds (13.4%). These results suggest that halothane sensitivity early in life is associated with HS susceptibility and the development of pale meat when birds are slaughtered at market age. These results also suggest that halothane screening may be better at predicting the development of PSE meat during HS in the strain selected for large breast yield rather than rapid overall growth.

A halothane test to detect turkeys prone to developing pale, soft, and exudative meat

The turkey industry suffers from pale, soft, and exudative meat (PSE) that is unsuitable for further processing because of excessive color variation, poor meat binding, and depressed water holding ability. This condition is caused by accelerated postmortem muscle metabolism and is thought to be related to a similarly inherited condition in swine. A quick, nondestructive method of screening animals is needed to avoid further propagation of PSE in breeding flocks. In this study, a halothane test used with swine was evaluated as a possible detection method for PSE-susceptible turkeys. In Experiment 1, a commercial strain of 4-wk-old male turkeys (n = 116) was exposed to 3% halothane gas for 3 min (6 L/min) and examined for leg muscle rigidity. Experiment 2 followed similar testing measures, using two strains of growth-selected turkeys (n = 504). Measurements of pH, R-value (ratio of inosine:adenosine), color, and expressible moisture content were made from each bird's breast fillet to determine whether the muscles of the responding birds would develop PSE characteristics. Five percent of tested birds in the first experiment and 2% in the second experiment exhibited rigid legs, indicating some of the discriminating power of this test. However, the data indicated that the characteristics of muscles from these birds did not differ from those of the nonresponding birds (P < 0.05). Possibly, the birds may need to be screened or slaughtered at a different age or using different methods.

Pharmacokinetics of flunixin meglumine in donkeys, mules, and horses

OBJECTIVE

To compare serum disposition of flunixin meglumine after i.v. administration of a bolus to horses, donkeys, and mules.

ANIMALS

3 clinically normal horses, 5 clinically normal donkeys, and 5 clinically normal mules.

PROCEDURE

Blood samples were collected at time zero (before) and 5, 10, 15, 30, and 45 minutes, and at 1, 1.25, 1.5, 1.75, 2, 2.5, 2.75, 3, 3.5, 4, 4.5, 5, 5.5, 6, and 8 hours after i.v. administration of a bolus of flunixin meglumine (1.1 mg/kg of body weight). Serum was analyzed in duplicate by the use of high-performance liquid chromatography for determination of flunixin meglumine concentrations. The serum concentration-time curve for each horse, donkey, and mule were analyzed separately to estimate noncompartmental pharmacokinetic variables

RESULTS

Mean (+/-SD) area under the curve for donkeys (646 +/- 148 minute x microg/ml) was significantly less than for horses (976 +/- 168 minute x microg/ml) or for mules (860 +/- 343 minute x microg/ml). Mean residence time for donkeys (54.6 +/- 7 minutes) was significantly less than for horses (110 +/- 24 minutes) or for mules (93 +/- 30 minutes). Mean total body clearance for donkeys (1.78 +/- 0.5 ml/kg/h) was significantly different from that for horses (1.14 +/- 0.18 ml/kg/h) but not from that for mules (1.4 +/- 0.5 ml/kg/h). Significant differences were not found between horses and mules for any pharmacokinetic variable.

CONCLUSION AND CLINICAL RELEVANCE

Significant differences exist with regard to serum disposition of flunixin meglumine in donkeys, compared with that for horses and mules. Consequently, flunixin meglumine dosing regimens used in horses may be inappropriate for use in donkeys.

Detomidine-propofol anesthesia for abdominal surgery in horses

OBJECTIVE

To evaluate propofol for induction and maintenance of anesthesia, after detomidine premedication, in horses undergoing abdominal surgery for creation of an experimental intestinal adhesion model.

STUDY DESIGN

Prospective study.

ANIMALS

Twelve horses (424 +/- 81 kg) from 1 to 20 years of age (5 females, 7 males).

METHODS

Horses were premedicated with detomidine (0.015 mg/kg i.v.) 20 to 25 minutes before induction, and a propofol bolus (2 mg/kg i.v.) was administered for induction. Propofol infusion (0.2 mg/kg/min i.v.) was used to maintain anesthesia. The infusion rate was adjusted to maintain an acceptable anesthetic plane as determined by muscle relaxation, occular signs, response to surgery, and cardiopulmonary responses. Oxygen (15 L/min) was insufflated through an endotracheal tube as necessary to maintain the SpO2 greater than 90%. Systolic (SAP), mean (MAP), and diastolic (DAP) arterial pressures, heart rate (HR), electrocardiogram (ECG), respiratory rate (RR), SpO2 (via pulse oximetry), and nasal temperature were recorded at 15 minute intervals, before premedication and after induction of anesthesia. Arterial blood gas samples were collected at the same times. Objective data are reported as mean (+/-SD); subjective data are reported as medians (range).

RESULTS

Propofol (2.0 mg/kg i.v.) induced anesthesia (mean bolus time, 85 sec) within 24 sec (+/-22 sec) after the bolus was completed. Induction was good in 10 horses; 2 horses showed signs of excitement and these two inductions were not smooth. Propofol infusion (0.18 mg/kg/min +/- 0.04) was used to maintain anesthesia for 61 +/- 19 minutes with the horses in dorsal recumbency. Mean SAP, DAP, and MAP increased significantly over time from 131 to 148, 89 to 101, and 105 to 121 mm Hg, respectively. Mean HR varied over time from 43 to 45 beats/min, whereas mean RR increased significantly over anesthesia time from 4 to 6 breaths/min. Mean arterial pH decreased from a baseline of 7.41 +/- 0.07 to 7.30 +/- 0.05 at 15 minutes of anesthesia, then increased towards baseline values. Mean PaCO2 values increased during anesthesia, ranging from 47 to 61 mm Hg whereas PaO2 values decreased from baseline (97 +/- 20 mm Hg), ranging from 42 to 57 mm Hg. Muscle relaxation was good and no horses moved during surgery: Recovery was good in 9 horses and acceptable in 3; mean recovery time was 67 +/- 29 minutes with 2.4 +/- 2.4 attempts necessary for the horses to stand.

CONCLUSIONS

Detomidine-propofol anesthesia in horses in dorsal recumbency was associated with little cardiovascular depression, but hypoxemia and respiratory depression occurred and some excitement was seen on induction.

CLINICAL RELEVANCE

Detomidine-propofol anesthesia is not recommended for surgical procedures in horses if dorsal recumbency is necessary and supplemental oxygen is not available (eg, field anesthesia).

Drug interactions during anesthesia. General principles

Anesthesia for most procedures in small animal practice involves administration of more than one drug. In addition, many patients concurrently receive a number of other drugs related to their surgical condition or disease. The probability of a drug interaction increases exponentially with the number of drugs a patient receives; therefore, the potential for drug interactions may be greater in anesthesia than for any other area of medicine. This article describes potentially harmful drug interactions that may occur in the anesthetic setting.

Maintenance of anaesthesia with sevoflurane and oxygen in mechanically-ventilated horses subjected to exploratory laparotomy treated with intra- and post operative anaesthetic adjuncts

Eight healthy horses premedicated with xylazine and induced with ketamine were used to evaluate sevoflurane in oxygen for maintenance of anaesthesia during elective exploratory laparotomy. After orotracheal intubation, horses were hoisted, placed in dorsal recumbency on a padded surgery table, and received sevoflurane in oxygen for maintenance of anaesthesia. The horses were allowed to breathe spontaneously until instrumented; then, they were mechanically ventilated to maintain the PaCO2 between 35 and 45 mmHg. Systolic (SAP), diastolic (DAP), and mean (MAP) arterial blood pressures, heart rate (HR), ECG, respiratory rate, an estimation of the saturation of haemoglobin with oxygen in peripheral arterial blood (S(p)O2), nasal temperature, end-tidal CO2(ET(CO2)), end-tidal sevoflurane (ET(SEVO)), and vaporiser concentration were recorded every 5 min post induction; arterial blood samples were obtained soon after induction, at 30 min after induction, and every hour thereafter until surgery was completed. Recovery data including times from the sevoflurane vaporiser being turned off to first movement, to sternal recumbency, and to standing, number of attempts to stand, and recovery score (between 1 = safe, smooth and 6 = stormy, major injury to horse) were collected. Analysis of variance was performed using physiological data collected over 195 min of anaesthesia, the longest time period during which all 8 horses were instrumented. Time effects (P<0.05) for HR, SAP, DAP, MAP, and nasal temperature were identified. Heart rate peaked at 45 min and declined over the course of the procedure. Arterial blood pressure generally decreased over time. Body temperature decreased over time. From 15 to 195 min mean ET(SEVO)concentration ranged from 2.0 to 3.3%, while mean vaporiser settings ranged from 3.7 to 5.5%. Three horses received intra-operative ketamine; all horses received dobutamine infusions; and 2 horses received intra-operative calcium-dextrose. Total anaesthesia time was 222-316 min (mean+/-s.d.269+/-31 min). Time from turning the sevoflurane vaporiser off to first movement was mean +/-s.d.18+/-15 min; to sternal recumbency was 54+/-22 min; to standing was 65+/-27 min; and to returning the horse to the stall in the ward was 78+/-24 min. Six horses stood on the first attempt; 2 horses stood on the second attempt. The median recovery score was one (1-3). In conclusion, sevoflurane provided a stable, easily controllable anaesthetic plane during prolonged exploratory laparotomies; horses experienced smooth, safe recoveries after maintenance of anaesthesia with sevoflurane following routine anaesthetic induction and post operative xyalzine administration.

Recovery from sevoflurane anesthesia in horses: comparison to isoflurane and effect of postmedication with xylazine

OBJECTIVE

To compare recovery from sevoflurane or isoflurane anesthesia in horses.

STUDY DESIGN

Prospective, randomized cross-over design.

ANIMALS

Nine Arabian horses (3 mares, 3 geldings, and 3 stallions) weighing 318 to 409 kg, 4 to 20 years old.

METHODS

Horses were anesthetized on three occasions with xylazine (1.1 mg/kg), Diazepam (0.03 mg/kg intravenously [i.v.]), and ketamine (2.2 mg/kg i.v.). After intubation, they were maintained with isoflurane or sevoflurane for 90 minutes. On a third occasion, horses were maintained with sevoflurane and given xylazine (0.1 mg/kg i.v.) when the vaporizer was turned off. Horses were not assisted in recovery and all recoveries were videotaped. Time to extubation, first movement, sternal, and standing were recorded as was the number of attempts required to stand. Recoveries were scored on a 1 to 6 scoring system (1 = best, 6 = worst) by the investigators, and by three evaluators who were blinded to the treatments the horses received. These blinded evaluators assessed the degree of ataxia present at 10 minutes after each horse stood, and recorded the time at which they judged the horse to be ready to leave the recovery stall.

RESULTS

Mean times (+/- SD) to extubation, first movement, sternal, and standing were 4.1 (1.7), 6.7 (1.9), 12.6 (4.6), and 17.4 (7.2) minutes with isoflurane; 3.4 (0.8), 6.6 (3.1), 10.3 (3.1), and 13.9 (3.0) minutes with sevoflurane; and 4.0 (1.2), 9.1 (3.3), 13.8 (6.5), and 18.0 (7.1) with sevoflurane followed by xylazine. Horses required a mean number of 4 (2.3), 2 (0.9), and 2 ( 1.6) attempts to stand with isoflurane, sevoflurane, and sevoflurane followed by xylazine respectively. The mean recovery score (SD) for isoflurane was 2.9 (1.2) from investigators and 2.4 (1.1) from blinded evaluators. For sevoflurane, the mean recovery score was 1.7 (0.9) from investigators and 1.9 (1.1) from evaluators, whereas the recoveries from sevoflurane with xylazine treatment were scored as 1.7 (1.2) from investigators and 1.7 (1.0) from blinded evaluators.

CONCLUSIONS

Recoveries appeared to vary widely from horse to horse, but were significantly shorter with sevoflurane than isoflurane, although sevoflurane followed by xylazine was no different from isoflurane. Under the conditions of the study, recoveries from sevoflurane and sevoflurane followed by xylazine were of better quality than those from isoflurane.

CLINICAL RELEVANCE

Sevoflurane anesthesia in horses may contribute to a shorter, safer recovery from anesthesia.

Evaluation of analgesia provided by postoperative administration of butorphanol to cats undergoing onychectomy

OBJECTIVE

To evaluate adequacy of analgesia provided by postoperative administration of butorphanol to cats undergoing onychectomy.

DESIGN

Randomized controlled trial.

ANIMALS

63 cats undergoing elective onychectomy.

PROCEDURE

Cats were randomly assigned to a treatment (n = 42) or control group (21). Cats in the treatment group were given butorphanol parenterally immediately and 4 hours after surgery and orally for 2 days after surgery. Rectal temperature, heart rate, and respiratory rate were recorded and scores were assigned for temperament, recovery, sedation, analgesia, and lameness for the first 24 hours after surgery. Owners provided scores for appetite, personality, and lameness the first and second days after discharge from the hospital.

RESULTS

Heart rate, respiratory rate, rectal temperature, and temperament and sedation scores were not significantly different between groups at any evaluation time. Recovery scores were significantly better for butorphanol-treated than for control-group cats 10 minutes after extubation. Analgesia scores were significantly better for butorphanol-treated than for control-group cats between 5 and 24 hours after surgery. Fewer butorphanol-treated than control-group cats were lame at the time of discharge from the hospital. The first day after discharge, owners reported that percentages of butorphanol-treated cats that ate normally, acted normally, and had only mild or no lameness were significantly higher than percentages of control-group cats that did. Significant differences between groups were not detected the second day after discharge.

CLINICAL IMPLICATIONS

Results suggest that for cats undergoing onychectomy, administration of butorphanol the day of surgery and the first full day after surgery provides effective analgesia and improves recovery, appetite, and gait.

Detomidine-butorphanol-propofol for carotid artery translocation and castration or ovariectomy in goats

OBJECTIVE

To determine the safety and efficacy of propofol, after detomidine-butorphanol premedication, for induction and anesthetic maintenance for carotid artery translocation and castration or ovariectomy in goats.

STUDY DESIGN

Case series.

ANIMALS

Nine 4-month-old Spanish goats (17.1 +/- 2.6 kg) were used to evaluate propofol anesthesia for carotid artery translocation and castration or ovariectomy.

METHODS

Goats were premedicated with detomidine (10 micrograms/kg intramuscularly [i.m.]) and butorphanol (0.1 mg/kg i.m.) and induced with an initial bolus of propofol (3 to 4 mg/kg intravenously [i.v.]). If necessary for intubation, additional propofol was given in 5-mg (i.v.) increments. Propofol infusion (0.3 mg/kg/min i.v.) was used to maintain anesthesia, and oxygen was insufflated (5 L/min). The infusion rate was adjusted to maintain an acceptable anesthetic plane as determined by movement, muscle relaxation, ocular signs, response to surgery, and cardiopulmonary responses. Systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures, heart rate (HR), ECG, respiratory rate (RR), SpO2, and rectal temperature (T) were recorded every 5 minutes postinduction; arterial blood gas samples were collected every 15 minutes. Normally distributed data are represented as mean +/- SD; other data are medians (range).

RESULTS

Propofol (4.3 +/- 0.9 mg/kg/min i.v.) produced smooth, rapid (15.2 +/- 6 sec) sternal recumbency. Propofol infusion (0.52 +/- 0.11 mg/kg/min i.v.) maintained anesthesia. Mean anesthesia time was 83 +/- 15 minutes. Muscle relaxation was good; eye signs indicated surgical anesthesia; two goats moved before surgery began; one goat moved twice during laparotomy. Means are reported over the course of the data collection period. Means during the anesthesia for pHa (arterial PH), PaCO2, PaO2, HCO3-, and BE (base excess) ranged from 7.233 +/- 0.067 to 7.319 +/- 0.026, 54.1 +/- 4.6 to 65.3 +/- 12.0 mm Hg, 133.1 +/- 45.4 to 183.8 +/- 75.1 mm Hg, 26.9 +/- 2.6 to 28.2 +/- 2.1 mEq/L, and -0.8 +/- 2.9 to 1.4 +/- 2.2 mEq/L. Means over time for MAP were 53 +/- 12 to 85 +/- 21 mm Hg. Mean HR varied over time from 81 +/- 6 to 91 +/- 11 beats/minute; mean RR, from 9 +/- 8 to 15 +/- 5 breaths/minute; SpO2 from 97 +/- 3% to 98 +/- 3%; mean T, from 36.0 +/- 0.6 degrees C to 39.1 +/- 0.7 degrees C. Over time, SpO2 and SaO2 did not change significantly; HR, RR, T, and PaCO2 decreased significantly; SAP, DAP, MAP, pHa, PaO2, and BE increased significantly. HCO3- concentrations increased significantly, peaking at 45 minutes. Recoveries were smooth and rapid; the time from the end of propofol infusion to extubation was 7.3 +/- 3 minutes, to sternal was 9.2 +/- 5 minutes, and to standing was 17.7 +/- 4 minutes. Median number of attempts to stand was two (range of one to four). Postoperative pain was mild to moderate.

CONCLUSIONS

Detomidine-butorphanol-propofol provided good anesthesia for carotid artery translocation and neutering in goats.

CLINICAL RELEVANCE

Detomidine-butorphanol-propofol anesthesia with oxygen insufflation may be safely used for surgical intervention in healthy goats.

Pharmacokinetics and cardiopulmonary effects of guaifenesin in donkeys

Five donkeys and three horses were given guaifenesin, intravenously, by gravity administration, until recumbency was produced. The time and dose required to produce recumbency, recovery time to sternal and standing were recorded. Blood samples were collected for guaifenesin assay at 10, 20, 30, 40, 50, 60 min, and 2, 3, 4 and 6 h after guaifenesin administration. Serum was analysed for guaifenesin using HPLC and pharmacokinetic values were calculated using a computer software package (RSTRIP). In donkeys, heart and respiratory rates and blood pressures were recorded before and at 5-min intervals during recumbency. Arterial blood samples were collected before and at 5 and 15 min intervals during recumbency for analysis of pH, CO2, and O2. ANOVA was used to evaluate dynamic data, while t-tests were used for kinetic values. Respiratory rate was decreased significantly during recumbency, but no other significant changes from baseline occurred. The mean (+/- SD) recumbency dose of guaifenesin was 131 mg/kg (27) for donkeys and 211 mg/kg (8) for horses. Recovery time to sternal (min) was 15 (SD, 11) for donkeys and 34 (SD, 1.4) for horses. Time to standing was 32 min for donkeys and 36 min for horses. Calculation of AUC (area under the concentration-time curve) microgram/mL) (dose-dependent variable) was 231 (SD, 33) for donkeys and 688 (SD, 110) for horses. The clearance (CL) (mL/h.kg) was 546 (SD, 73) for donkeys, which was significantly different from 313 (SD, 62) for horses. Mean residence time (MRT) (h) was 1.2 (SD, 0.1) for donkeys and 2.6 (SD, 0.5) for horses. Volume of distribution Vd(area) (mL/kg) was 678 (SD, 92) for donkeys and 794 (SD, 25) for horses. At the rate of administration used in this study, donkeys required less guaifenesin than horses to produce recumbency, but cleared it more rapidly.

Cardiovascular effects of buprenorphine in anesthetized dogs

OBJECTIVE

To determine the cardiovascular effects of buprenorphine in isoflurane- and halothane-anesthetized dogs.

ANIMALS

6 healthy adult hound-type dogs given buprenorphine (16 micrograms/kg of body weight, i.v.) or isovolumetric 5% dextrose solution during anesthesia with isoflurane or halothane.

PROCEDURE

Each dog was anesthetized 4 times, with a minimum of 10 days between episodes. Anesthesia was induced with isoflurane or halothane in O2 by mask, and was maintained with 1.9% isoflurane or 1.3% halothane (end-tidal concentration). The PaCO2 was maintained between 35 and 45 mm of Hg by use of mechanical ventilation, and the following variables were determined: systolic, diastolic, and mean arterial blood pressures; cardiac output; cardiac index; stroke volume; heart rate; systemic vascular resistance; mean pulmonary arterial pressure; and pulmonary vascular resistance. In addition, arterial blood samples for gas and acid-base analyses were collected at 30-minute intervals for 2.5 hours. After baseline values were recorded, dogs were randomly assigned to receive either buprenorphine (16 micrograms/kg, i.v.) or isovolumetric 5% dextrose solution. All variables were then recorded at 15-minute intervals for 2.5 hours.

RESULTS

During isoflurane anesthesia, buprenorphine administration caused significant (P < or = 0.05) reductions in diastolic arterial pressure, mean arterial pressure, systolic arterial pressure, cardiac index, and heart rate, whereas systemic vascular resistance increased significantly. During halothane anesthesia, buprenorphine administration caused significant decreases in heart rate, cardiac index, mean, systolic and diastolic arterial blood pressures, and stroke volume, whereas pulmonary arterial blood pressure and systemic vascular resistance increased significantly.

CONCLUSION

Although the changes seen were significant, they were not sufficiently large to be of clinical importance in healthy dogs.

Comparative pharmacokinetics of caffeine and three metabolites in clinically normal horses and donkeys

OBJECTIVE

To determine whether clearance of capacity-limited drugs in horses differs from that in donkeys by comparing the serum disposition of caffeine and its metabolites, theophylline, theobromine, and paraxanthine after i.v. administration of caffeine to horses and donkeys.

ANIMALS

4 healthy horses and 5 healthy donkeys.

PROCEDURE

Blood samples were collected from each animal at time 0 (before) and 5, 10, 15, 20, 30, and 45 minutes, and 1, 2, 3, 4, 6, 8, 12, 24, 30, 36, 48, 54, 60, 72, and 96 hours after IV administration of a bolus of caffeine. Serum was analyzed in triplicate by high-performance liquid chromatography to determine caffeine, theophylline, theobromine, and paraxanthine concentrations. The serum concentration-time curves for each animal were analyzed separately to estimate model-independent pharmacokinetic variables.

RESULTS

Mean pharmacokinetic values for caffeine, theophylline, and paraxanthine did not differ significantly in horses, compared with donkeys. Mean peak serum concentration of theobromine was significantly higher in donkeys, compared with horses.

CONCLUSION

Clearance of the capacity-limited drug caffeine does not appear to differ in horses, compared with donkeys.

CLINICAL RELEVANCE

For some drugs that undergo hepatic metabolism, the dose and dose interval used for horses may be appropriate for use in donkeys.

Magnetic resonance imaging of the brain of normal neonatal foals

Magnetic resonance imaging (MRI) was performed on the brain of 5 normal, anesthetized, neonatal (age 3-to-6 days) Quarter Horse foals. The objectives of the study were to develop a technique for imaging the brain of neonatal foals, and to ascertain their normal brain anatomy. Intravenous propofol was administered for induction and maintenance of general anesthesia. Using spin echo MR techniques, T1 weighted sagittal and transverse views, and spin density and T2 weighted transverse views were successfully made of each foal. MR images provided excellent visualization of many anatomic structures of the brain and head. MRI of the brain is feasible for selected neonatal equine patients.

The effect of detomidine and its antagonism with tolazoline on stress-related hormones, metabolites, physiologic responses, and behavior in awake ponies

Six ponies were used to investigate the effect of tolazoline antagonism of detomidine on physiological responses, behavior, epinephrine, norepinephrine, cortisol, glucose, and free fatty acids in awake ponies. Each pony had a catheter inserted into a jugular vein 1 hour before beginning the study. Awake ponies were administered detomidine (0.04 mg/kg intravenously [i.v.]) followed 20 minutes later by either tolazoline (4.0 mg/kg i.v.) or saline. Blood samples were drawn from the catheter 5 minutes before detomidine administration (baseline), 5 minutes after detomidine administration, 20 minutes before detomidine administration which was immediately before the administration of tolazoline or saline (time [T] = 0), and at 5, 30, and 60 minutes after injections of tolazoline or saline (T = 5, 30, and 60 minutes, respectively). Compared with heart rate at T = 0, tolazoline antagonism increased heart rate 45% at 5 minutes. There was no difference in heart rate between treatments at 30 minutes. Blood pressure remained stable after tolazoline, while it decreased over time after saline. Compared with concentrations at T = 0, tolazoline antagonism of detomidine in awake ponies resulted in a 55% increase in cortisol at 30 minutes and a 52% increase in glucose at 5 minutes. The change in free fatty acids was different for tolazoline and saline over time. Free fatty acids decreased after detomidine administration. Free fatty acids did not change after saline administration. After tolazoline administration, free fatty acids increased transiently. Tolazoline tended to decrease sedation and analgesia at 15 and 60 minutes postantagonism. Antagonism of detomidine-induced physiological and behavioral effects with tolazoline in awake ponies that were not experiencing pain appears to precipitate a stress response as measured by cortisol, glucose, and free fatty acids. If antagonism of an alpha-agonist is contemplated, the potential effect on hormones and metabolites should be considered.

Comparative pharmacokinetics of phenylbutazone and its metabolite oxyphenbutazone in clinically normal horses and donkeys

OBJECTIVE

To compare plasma disposition of phenylbutazone and its metabolite oxyphenbutazone after i.v. administration of phenylbutazone in horses and donkeys.

ANIMALS

4 clinically normal horses and 6 clinically normal donkeys.

PROCEDURE

Blood samples were collected from each animal at time 0 (before) and 5, 10, 20, 30, 45, 60, 90, 120, 180, 240, 300, 360, and 480 minutes after i.v. administration of a bolus dose of phenylbutazone. Serum was analyzed in triplicate by use of high-performance liquid chromatography for determination of phenylbutazone and oxyphenbutazone concentrations. The serum concentration-time curve for each horse and donkey was analyzed separately to estimate model-independent pharmacokinetic variables.

RESULTS

Significant differences were found in several pharmacokinetic variables of phenylbutazone and oxyphenbutazone in horses, compared with donkeys. Mean total body clearance of phenylbutazone in horses was fivefold less than that in donkeys (29.3 and 170.3 ml/kg/h, respectively). Mean values for area under the curve and mean residence time in horses (118.3 micrograms/h/ml and 3.6 hours, respectively) were significantly greater than values in donkeys (28.3 micrograms/h/ml and 1.7 hours, respectively). Mean values for apparent volume of distribution at steady state were not significantly different between horses and donkeys. For oxyphenbutazone, mean time to peak concentration in donkeys was significantly less than that in horses (1.6 and 6.4 hours, respectively).

CONCLUSION

Phenylbutazone clearance in donkeys was higher than that in horses, and appearance of the metabolite oxyphenbutazone in serum was more rapid in donkeys than in horses, indicating that hepatic metabolism of phenylbutazone is more rapid in donkeys than in horses.

CLINICAL RELEVANCE

Because serum concentration of phenylbutazone after single i.v. bolus administration (4.4 mg/kg of body weight) decreases more rapidly in donkeys, compared with horses, phenylbutazone may require more frequent administration in donkeys to achieve therapeutic efficacy.

Evaluation of pulse oximetry in anaesthetised foals using multiple combinations of transducer type and transducer attachment site

A commercially available pulse oximeter was evaluated in anaesthetised foals to determine its accuracy for estimating arterial haemoglobin saturation (SaO2). Five different transducer/transducer attachment site (TTAS) combinations were evaluated; 1-3) a fingertip transmission transducer attached to the foal's ear, lip and tongue, 4) an adhesive transmission transducer positioned on the foal's ear and 5) a forehead reflectance transducer placed on the ventral aspect of the foal's tail-base. Eight normal, Quarter Horse foals (age 5-10 days) were studied while under general anaesthesia. Alterations in arterial carbon dioxide tension (PaCO2) were produced by changing the level of ventilation. At each level of ventilation, alterations of arterial haemoglobin saturation (SaO2) were produced by varying the inspired fraction of oxygen (FIO2). At each level of ventilation and each level of FIO2, arterial blood samples were obtained for blood gas analysis while pulse oximeter readings were recorded simultaneously for each TTAS combination. Arterial blood oxygen saturation (SaO2) was calculated from arterial blood gas values and the equine blood oxygen dissociation curve. Pulse oximeter readings from each TTAS combination were compared with SaO2 values with linear regression analyses. Bias and precision values were determined and the sensitivity and specificity of each TTAS combination for detecting desaturation (SaO2 < 90%) were determined. Linear regression analyses indicated significant (P < 0.05) linear correlation between oxygen saturation determined by pulse oximeter (SpO2) and SaO2 for each of the 5 TTAS combinations. The combinations TTAS-1, TTAS-3 and TTAS-4 tended slightly to underestimate SaO2 at high SaO2 ranges, but overestimated SaO2 at low ranges of SaO2. Combination TTAS-2 overestimated SaO2 over all ranges of SaO2. Combination TTAS-5 consistently underestimated SaO2 at all ranges of SaO2. In general, accuracy and precision of each TTAS combination decreased at lower SaO2 ranges. All TTAS combinations, except TTAS-2 and TTAS-4, had good sensitivity for detecting SaO2 less than 90%. All TTAS combinations except TTAS-5 demonstrated good specificity. We concluded that pulse oximetry appears to be a valuable method for assessing SaO2 and detecting desaturation in anaesthetised foals. Clinicians should be aware that the type of transducer used and the anatomical site to which it is attached can have marked effects on the accuracy of pulse oximetry; and that different TTAS combinations may behave differently over various ranges of SaO2.