Sedation with dexmedetomidine-butorphanol or xylazine-butorphanol continuous intravenous infusions during unilateral ovariectomy in standing donkeys.

BACKGROUND: Intravenous infusions of alpha-2 adrenoceptor sedatives and opioids can potentially facilitate surgery in donkeys while standing. Literature on this subject matter is scant. OBJECTIVES: Evaluation of efficacy of sedation from α2 -adrenoceptors (dexmedetomidine or xylazine) and butorphanol during ovariectomy in standing donkeys. STUDY DESIGN: Randomised, masked in vivo experiment. METHODS: Thirteen female donkeys were sedated with butorphanol (0.05 mg/kg bwt followed by 0.05 mg/kg bwt/h) IV. Concomitantly, 6 of the 13 jennies were sedated with dexmedetomidine 2.5 mcg/kg bwt followed by 2.5 mcg/kg bwt/h (Dex-B group), while seven jennies were sedated with xylazine 0.5 mg/kg bwt followed by 0.5 mg/kg bwt/h (Xyl-B group). A line block of the left flank and an infiltration block around uterine ligament were performed with lidocaine. While the jennies underwent ovariectomies standing, sedation scores and head height above ground were assessed at 2 and 10 min after sedative boluses and every 10 min thereafter. If sedation was too light or too deep, the dose of dexmedetomidine or xylazine was increased or decreased by 25% of the original infusion rate, while butorphanol infusion rate was constant. Physiological parameters were measured. Normally distributed data were compared using the two-sample t test while repeatedly measured data were tested for differences between and within groups using repeated measures analysis of variance (ANOVA) by ranks followed by a Wilcoxon test with Tukey Honest Significant Difference for multiple testing. Statistical significance was set at p < 0.05. RESULTS: Both Dex-B and Xyl-B caused moderate to marked sedation adequate for ovariectomy in donkeys. Evident sedation was absent by 60 min of termination of infusions. No adverse physiological effects were observed. MAIN LIMITATIONS: Study on ovariectomy cases only, no pharmacokinetic profiling. CONCLUSIONS: Dexmedetomidine or xylazine and butorphanol sedation is feasible for ovariectomy in standing donkeys.

Morphine in donkeys: Antinociceptive effect and preliminary pharmacokinetics.

BACKGROUND: Morphine is the prototypical µ-opioid receptor agonist used to provide analgesia in veterinary species. Its effects are well-described in horses but not donkeys. OBJECTIVES: To determine the antinociceptive effects of two doses of morphine in donkeys. To describe preliminary pharmacokinetic parameters of morphine in donkeys. STUDY DESIGN: In vivo experiment. METHODS: Eight adult castrated male donkeys were given intravenous (IV) 0.9% saline, morphine 0.1 mg/kg bwt (LDM), or morphine 0.5 mg/kg bwt (HDM) in a randomised order with a minimum 1-week washout period. Mechanical nociceptive thresholds (MNTs) were determined by a blinded investigator pre-injection and 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min post-injection. Venous blood samples were collected pre-injection and 2, 5, 10, 15, 30, 45, 60, 90, and 120 min post-injection. Data were analysed using Friedman's test with Dunn's post hoc test for multiple comparisons. Pharmacokinetic parameters were calculated for the HDM treatment. RESULTS: Baseline MNT was [median (interquartile range)] 8.9 (7.1-10.3) N and did not differ between treatments. Peak MNTs occurred at 60 min for both LDM (16.2 N) and HDM (25.0 N) treatments. MNTs after HDM treatment were higher than saline (p < 0.04) at 15, 60, 90, 120, 150, 180, 240, and 300 min post-injection. MNTs after LDM treatment were higher than baseline (p < 0.05) at 45 and 60 min post-injection. Terminal half-life for HDM was (mean ± SD) 51.0 ± 10.7 min, the volume of distribution at steady-state 2.07 ± 0.33 L/min and clearance 49.2 ± 4.16 ml * min/kg using noncompartmental analysis. The concentration of morphine-3-glucuronide (M3G) was higher than morphine-6-glucuronide (M6G) at all sampled time points. MAIN LIMITATIONS: Short duration of plasma sampling for pharmacokinetic analysis; lack of objective measure of gastrointestinal function. CONCLUSIONS: The HDM treatment provided mechanical antinociception in donkeys with no significant adverse effects.

Effects of two continuous infusion doses of lidocaine on isoflurane minimum anesthetic concentration in chickens.

OBJECTIVE: To assess the effect of two intravenous (IV) doses of lidocaine on the minimum anesthetic concentration (MAC) of isoflurane in chickens. STUDY DESIGN: Blinded, prospective, randomized, experimental crossover study. ANIMALS: A total of six adult female chickens weighing 1.90 ± 0.15 kg. METHODS: Chickens were anesthetized with isoflurane and mechanically ventilated. Isoflurane MAC values were determined (T0) in duplicate using an electrical noxious stimulus and the bracketing method. After MAC determination, a low dose (LD; 3 mg kg-1 followed by 3 mg kg-1 hour-1) or high dose (HD; 6 mg kg-1 followed by 6 mg kg-1 hour-1) of lidocaine was administered IV. MAC determination was repeated at 1.5 (T1.5) and 3 (T3) hours of lidocaine administration and blood was collected for analysis of plasma lidocaine and monoethylglycinexylidide (MEGX) concentrations. Pulse rate, peripheral hemoglobin oxygen saturation, noninvasive systolic arterial pressure and cloacal temperature were recorded at T0, T1.5 and T3. Treatments were separated by 1 week. Data were analyzed using mixed-effects model for repeated measures. RESULTS: MAC of isoflurane (mean ± standard deviation) at T0 was 1.47 ± 0.18%. MAC at T1.5 and T3 was 1.32 ± 0.27% and 1.26 ± 0.09% (treatment LD); and 1.28 ± 0.06% and 1.30 ± 0.06% (treatment HD). There were no significant differences between treatments or times. Maximum plasma lidocaine concentrations at T3 were 496 ± 98 and 1200 ± 286 ng mL-1 for treatments LD and HD, respectively, and were not significantly different from T1.5. With treatment HD, plasma concentration of MEGX was significantly higher at T3 than at T1.5. Physiological variables were not significantly different among times with either treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of lidocaine did not significantly change isoflurane MAC in chickens. Within treatments, plasma lidocaine concentrations were not significantly different at 1.5 and 3 hours.

Determination of the minimum alveolar concentration of isoflurane in donkeys.

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of isoflurane in donkeys and characterize recovery from anesthesia. ANIMALS: 7 healthy castrated male adult donkeys. PROCEDURES: Anesthesia was induced with propofol and maintained under mechanical ventilation with 1.3% isoflurane end-tidal concentration (ETiso). The MAC of isoflurane was determined after a 60-minute propofol washout period using the bracketing method. A continuous noxious electrical stimulation was applied to the oral mucosa for 1 minute or until the donkey moved. The ETiso was increased or decreased by 10% depending on the response, and MAC was defined as the average of 2 ETiso values allowing and preventing movement in response to stimulation. Arterial blood gases were measured during anesthesia and the recovery period. Unassisted recovery was timed, and a quality score was assigned from 1 (very poor) to 5 (excellent). RESULTS: The mean dose of propofol required for induction was 3.0 ± 0.6 mg/kg. The MAC of isoflurane was 1.44 ± 0.13%. One donkey was excluded from the study because it was still responsive when stimulated at ETiso of 2.8%. Immediately after extubation, the median (range) partial pressure of oxygen in the arterial blood was 63 (minimum to maximum, 46 to 72) mm Hg and 3 donkeys were hypoxemic (partial pressure of arterial oxygen < 60 mm Hg). The median time to standing was 13 (7 to 38) minutes, while the recovery score was 3 (2 to 5). CLINICAL RELEVANCE: The MAC of isoflurane in donkeys is similar to that reported in other species. Oxygen support should be provided to donkeys during recovery from isoflurane anesthesia to prevent hypoxemia.

Evaluation of the Effects of Doxapram in Combination with Xylazine on Recovery of Horses Isoflurane-Anesthetized.

This randomized double-blinded study evaluated the recovery from isoflurane anesthesia in horses receiving doxapram and xylazine. 6 horses were anesthetized 4 times (minimum of 2-week washout period). Anesthesia was performed with xylazine (0.6 mg/kg), ketamine (2.2 mg/kg), midazolam (0.1 mg/kg), and maintained with isoflurane for 90 minutes. At recovery, horses received one of the following randomized treatments: RX: xylazine (0.2 mg/kg), RXD1: xylazine (0.2 mg/kg) and doxapram (0.1 mg/kg), RXD2: xylazine (0.2 mg/kg) and doxapram (0.2 mg/kg), or RS: saline. Recoveries were rope-assisted and evaluated with a descriptive qualitative scale. Heart rate, respiratory frequency (fR), and blood gas analysis were evaluated at 5 minutes intervals while the horse allowed. Data were analyzed with ANOVA or Friedman test (P < .05). Times to sternal (minutes) were RX: 40.5 ± 12.3, RXD1: 25.8 ± 11.5, RXD2: 31.4 ± 7.0, and RS: 33.4 ± 5.3, and were not different. Times to standing (minutes) were RX: 41.0 ± 9.9, RXD1: 33.5 ± 6.2, RXD2: 40.0 ± 11.3, and RS: 36.3 ± 9.9, and were not different. Heart rate decrease over time within RXD1 and RXD2 (T0 = 47 ± 15 and 47 ± 15, T5 = 38 ± 8 and 38 ± 8, T10 = 39 ± 4 and 36 ± 6, respectively), but was not different among groups. There was no difference in fR among groups or over time. There was no difference in recovery scores among groups. In conclusion, administration of doxapram to isoflurane-anesthetized horses did not change recovery time or quality.

Backyard Poultry and Waterfowl Sedation and Anesthesia.

The popularity of backyard poultry (chickens, turkey, guinea fowl) and waterfowl (ducks and geese) is increasing in the United States, and these animals frequently present for veterinary care. Like other birds, these species have unique anatomy that should be clinically considered before anesthesia. A balanced approach to an injectable, inhalational, or combination anesthesia protocol must be taken to ensure a safe outcome for the patient and to achieve the procedural needs. A well-informed clinician may use both sedation and general anesthesia to care for backyard bird patients in practice.

Safety and efficacy of intravesical instillation of resiniferatoxin in healthy cats: A preliminary study.

Objectives: To evaluate the safety of intravesical application of resiniferatoxin (RTX) in healthy cats and its effects on calcitonin gene-related peptide (CGRP) and substance P (SP) produced by C-fibers. Methods: Seven adult female cats received either 25 mL of saline (control; n = 1), or intravesical RTX at 5, 25, or 50 µg in 25 mL of saline to a final concentration of 0.2 µg/mL (318 nM), 1 µg/mL (1,591 nM), and 2 µg/mL (3,181 nM) (n = 2 per group). The treatment was instilled into the urinary bladder for 20 min. Plasma concentrations of RTX were measured at 0, 0.5, 1, and 4 h. Physical exam, complete blood count, and serum biochemical analysis were performed on day 0, 7, and 14. After 14 days, the sacral dorsal root ganglia (DRG) and the urinary bladder were harvested for histological and immunofluorescence analysis. Results: Intravesical RTX was well tolerated and plasma concentrations were below the quantifiable limits except for one cat receiving 1 µg/mL. Mild to moderate histopathological changes, including epithelial changes, edema, and blood vessel proliferation, were observed at lower doses (0.2 and 1 µg/mL), and were more severe at the higher dose (2 µg/mL). C-fiber ablation was observed in the urinary bladder tissue at all doses, as shown by an apparent reduction of both CGRP and SP immunoreactive axons. Conclusion: A dose of 25 µg (1 µg/mL) of RTX instilled in the urinary bladder of healthy cats appeared to decrease the density of SP and CGRP nerve axons innervating bladder and induced moderate changes in the bladder tissue.

ISOFLURANE RESPIRATORY ANESTHETIC INDEX IN CHICKENS (GALLUS GALLUS DOMESTICUS).

Respiratory depression from isoflurane seems to be greater in birds than in mammals. Isoflurane respiratory anesthetic index (AI) has only been evaluated in ducks (Anas platyrhynchos), which indeed showed a lower AI compared to mammals, but the isoflurane AI for other avian species is not known. The aim of this study was to evaluate the isoflurane AI in chickens (Gallus gallus domesticus). Six adult hens were anesthetized with isoflurane for determination of the minimum anesthetic concentration (MAC) using the bracketing method. During a second anesthetic event, the isoflurane AI was determined by progressively increasing the expired fraction of isoflurane by 0.5 times MAC until apnea was achieved (ETiso-apnea). The isoflurane AI was considered the ratio between the ETiso-apnea and the MAC. Heart rate, systolic arterial pressure, respiratory rate, and end-tidal carbon dioxide were continuously monitored throughout both anesthetic events. Data were analyzed using a mixed-effect model with Greenhouse-Geisser correction, followed by Tukey's test. The MAC for isoflurane was 1.18% ± 0.09% (mean ± SD). The ETiso-apnea was 3.31% ± 0.34% and the isoflurane AI was 2.80 ± 0.26. In chickens, isoflurane AI is similar to that measured in mammals, which is in contrast with published data in other avian species.

Pharmacokinetics and pharmacodynamics of methadone administered intravenously and intramuscularly to isoflurane-anesthetized chickens.

OBJECTIVE: To determine the pharmacokinetics and pharmacodynamics of methadone after IV or IM administration to isoflurane-anesthetized chickens. ANIMALS: 6 healthy adult Hy-Line hens. PROCEDURES: In a randomized crossover-design study, methadone (6 mg/kg) was administered IV and IM to isoflurane-anesthetized chickens with a 1-week washout period between experiments. Blood samples were collected immediately before and at predetermined time points up to 480 minutes after methadone administration. Plasma concentrations were determined by liquid chromatography-mass spectrometry, and appropriate compartmental models were fit to the plasma concentration-versus-time data. Cardiorespiratory variables were compared between treatments and over time with mixed-effect repeated-measures analysis. RESULTS: A 3-compartment model best described the changes in plasma methadone concentration after IV or IM administration. Estimated typical values for volumes of distribution were 692 mL/kg for the central compartment and 2,439 and 2,293 mL/kg for the first and second peripheral compartments, respectively, with metabolic clearance of 23.3 mL/kg/min and first and second distributional clearances of 556.4 and 51.8 mL/kg/min, respectively. Typical bioavailability after IM administration was 79%. Elimination half-life was 177 minutes, and maximum plasma concentration after IM administration was 950 ng/mL. Heart rate was mildly decreased at most time points beginning 5 minutes after IV or IM drug administration. CONCLUSIONS AND CLINICAL RELEVANCE: Disposition of methadone in isoflurane-anesthetized chickens was characterized by a large volume of distribution and moderate clearance, with high bioavailability after IM administration. Additional studies are warranted to assess pharmacokinetics and pharmacodynamics of methadone in awake chickens.

Topical and intradermal delivery of PpIX precursors for photodynamic therapy with intense pulsed light on porcine skin model.

In order to purposely decrease the time of the photodynamic therapy (PDT) sessions, this study evaluated the effects of PDT using topical and intradermal delivery of two protoporphyrin (PpIX) precursors with intense pulsed light (IPL) as irradiation source. This study was performed on porcine skin model, using an IPL commercial device (Intense Pulse Light, HKS801). IPL effect on different administration methods of two PpIX precursors (ALA and MAL) was investigated: a topical cream application and an intradermal application using a needle-free, high-pressure injection system. Fluorescence investigation showed that PpIX distribution by needle-free injection was more homogeneous than that by cream, suggesting that a shorter drug-light interval in PDT protocols is possible. The damage induced by IPL-PDT assessed by histological analysis mostly shows modifications in collagens fibers and inflammation signals, both expected for PDT. This study suggested an alternative protocol for the PDT treatment, possibility half of the incubation time and with just 3 min of irradiation, making the IPL-PDT, even more, promising for the clinical treatment.

EFFECTS OF TRAMADOL ON THE MINIMUM ANESTHETIC CONCENTRATION OF ISOFLURANE IN WHITE-EYED PARAKEETS (PSITTACARA LEUCOPHTHALMUS).

The aim of this study was to determine the minimum anesthetic concentration (MAC) of isoflurane, and to investigate if tramadol changes the isoflurane MAC in white-eyed parakeets (Psittacara leucophthalmus). Ten adult birds weighing 157 ± 9 g were anesthetized with isoflurane in oxygen under mechanical ventilation. Isoflurane concentration for the first bird was adjusted to 2.2%, and after 15 min an electrical stimulus was applied in the thigh area to observe the response (movement or nonmovement). Isoflurane concentration for the subsequent bird was increased by 10% if the previous bird moved, or decreased by 10% if the previous bird did not move. This procedure was performed serially until at least four sequential crossover events were detected. A crossover event was defined as a sequence of two birds with different responses (positive or negative) to the electrical stimulus. Isoflurane MAC was calculated as the mean isoflurane concentration value at the crossover events. After 1 wk, the same birds were reanesthetized with isoflurane and MAC was determined at 15 and 30 min after intramuscular administration of 10 mg/kg of tramadol using the same method. A paired t-test (P < 0.05%) was used to detect significant differences for MAC between treatments. Isoflurane MAC in this population of white-eyed parakeets was 2.47 ± 0.09%. Isoflurane MAC values 15 and 30 min after tramadol administration were indistinguishable from each other (pooled value was 2.50 ± 0.18%); they were also indistinguishable from isoflurane MAC without tramadol. The isoflurane MAC value in white-eyed parakeets is higher than reported for other bird species. Tramadol (10 mg/kg, i.m.) does not change isoflurane MAC in these birds.

Effects of a single intravenous bolus of fentanyl on the minimum anesthetic concentration of isoflurane in chickens (Gallus gallus domesticus).

OBJECTIVE: To assess the temporal effects of a single fentanyl intravenous (IV) bolus on the minimum anesthetic concentration (MAC) of isoflurane in chickens and to evaluate the effects of this combination on heart rate (HR) and rhythm, systemic arterial pressures (sAP) and ventilation. STUDY DESIGN: Prospective experimental trial. ANIMALS: Seventeen adult chickens weighing 1.8±0.2 kg. METHODS: Individual isoflurane MAC for 17 chickens was previously determined using the bracketing method. Chickens were anesthetized with isoflurane to evaluate the effects of a single IV fentanyl bolus (10 or 30 µg kg-1) on isoflurane MAC over time using the up-and-down method. Ventilation was controlled. The isoflurane MAC reduction was estimated by logistic regression at 5 and 15 minutes after fentanyl administration. In the second phase, seven chickens were anesthetized with isoflurane, and fentanyl was administered (30 µg kg-1) IV over 1 minute during spontaneous ventilation and HR and rhythm, sAP and ventilation variables were measured. RESULTS: At 5 minutes after IV administration of fentanyl (10 or 30 µg kg-1), isoflurane MAC was significantly reduced by 17.6% (6.1-29.1%) [logistic regression estimate (95% Wald confidence interval)] and 42.6% (13.3-71.9%), respectively. Isoflurane MAC reduction at 15 minutes after IV administration of fentanyl (10 or 30 µg kg-1) was 6.2% (-0.6 to 12.9%) and 13.2% (-0.9 to 27.3%), respectively; however, this reduction was not significant. No clinically significant cardiopulmonary changes or arrhythmias were detected after the administration of fentanyl (30 µg kg-1). CONCLUSIONS AND CLINICAL RELEVANCE: Administration of a single fentanyl bolus induced a dose-dependent and short-lasting reduction in isoflurane MAC. The higher dose induced no significant cardiopulmonary depression in isoflurane-anesthetized chickens during spontaneous ventilation. In chickens anesthetized with isoflurane, the clinical usefulness of a single fentanyl bolus is limited by its short duration of effect.

Fluorescence evaluations for porphyrin formation during topical PDT using ALA and methyl-ALA mixtures in pig skin models.

BACKGROUND: Photodynamic Therapy (PDT) using Aminolevulinic acid (ALA) and derivative molecules as topical medication and as a precursor of protoporphyrin (PPIX), is limited due to low permeation through skin or efficiency in porphyrin production. This behavior affects the production and homogeneity of PPIX distribution on superficial skin and in the deeper skin layers. Many authors propose alternatives to solve this such as, modification in the ALA and derivativemolecules, modifying the chemical properties of emulsion external phase or incorporating a delivery system to the emulsion. The goal of this study is to discuss what proportion of ALA and Methyl aminolevulinate (MAL) on mixtures increase the amount and uniformity of PPIX formation at superficial skin by fluorescence evaluations. METHODS: The study was conducted in vivo using a pig skin model. PPIX production was monitored using fluorescence spectroscopy and widefield fluorescence imaging on skin surface. 20% of ALA and MAL cream were done mixing the following proportions: ALA, M2 (80% ALA-20% MAL), M3 (60% ALA-40% MAL), M4 (50% ALA-MAL), M5 (40% ALA-60% MAL), M6 (20% ALA-80% MAL) and MAL. RESULTS: Mixtures M3, M4, and M5 showed the most PPIX production on skin by widefield fluorescence imaging and fluorescence spectroscopy in 3h of incubation. These results suggest that 50% of ALA and MAL in the same mixture increase the PPIX production in amount, homogeneity and time production when compared to ALA and MAL. This has a positive impact on photodynamic damage optimizing the PDT treatment.

Effects of Methadone on the Minimum Anesthetic Concentration of Isoflurane, and Its Effects on Heart Rate, Blood Pressure and Ventilation during Isoflurane Anesthesia in Hens (Gallus gallus domesticus).

The aim of this study was to measure the temporal effects of intramuscular methadone administration on the minimum anesthetic concentration (MAC) of isoflurane in hens, and to evaluate the effects of the isoflurane-methadone combination on heart rate and rhythm, blood pressure and ventilation. Thirteen healthy adult hens weighing 1.7 ± 0.2 kg were used. The MAC of isoflurane was determined in each individual using the bracketing method. Subsequently, the reduction in isoflurane MAC produced by methadone (3 or 6 mg kg(-1), i.m.) was determined by the up-and-down method. Stimulation was applied at 15 and 30 minutes, and at 45 minutes if the bird had not moved at 30 minutes. Isoflurane MAC reduction was calculated at each time point using logistic regression. After a washout period, birds were anesthetized with isoflurane and methadone, 6 mg kg(-1) i.m. was administered. Heart rate and rhythm, respiratory rate, blood gas values and invasive blood pressure were measured at 1.0 and 0.7 isoflurane MAC, and during 45 minutes after administration of methadone once birds were anesthetized with 0.7 isoflurane MAC. Fifteen minutes after administration of 3 mg kg(-1) of methadone, isoflurane MAC was reduced by 2 (-9 to 13)% [logistic regression estimate (95% Wald confidence interval)]. Administration of 6 mg kg(-1) of methadone decreased isoflurane MAC by 29 (11 to 46)%, 27 (-3 to 56)% and 10 (-8 to 28)% after 15, 30 and 45 minutes, respectively. Methadone (6 mg kg(-1)) induced atrioventricular block in three animals and ventricular premature contractions in two. Methadone caused an increase in arterial blood pressure and arterial partial pressure of carbon dioxide, while heart rate and pH decreased. Methadone, 6 mg kg(-1) i.m. significantly reduced isoflurane MAC by 30% in hens 15 minutes after administration. At this dose, methadone caused mild respiratory acidosis and increase in systemic blood pressure.

Assessment of ALA-induced PpIX production in porcine skin pretreated with microneedles.

Photodynamic therapy (PDT) is used for skin treatments of premalignant and cancer lesions and recognized as a non-invasive technique that combines tissue photosensitization and subsequent exposure to light to induce cell death. However, it is limited to the treatment of superficial lesions, mainly due to the low cream penetration. Therefore, the improvement of transdermal distribution of aminolevulinic acid (ALA) is needed. In this study, the kinetics and homogeneity of production of ALA-induced PpIX after the skin pre-treatment with microneedles rollers of 0.5, 1.0 and 1.5 mm length were investigated. An improvement in homogeneity and production of PpIX was shown in a porcine model. Widefield fluorescence imaging three hours after the topical application of ALA-cream in the combined treatment with microeedles rollers.

Hyoscine-N-butylbromide premedication on cardiovascular variables of horses sedated with medetomidine.

OBJECTIVE: To evaluate the effects of intravenous (IV) or intramuscular (IM) hyoscine premedication on physiologic variables following IV administration of medetomidine in horses. STUDY DESIGN: Randomized, crossover experimental study. ANIMALS: Eight healthy crossbred horses weighing 330 ± 39 kg and aged 7 ± 4 years. METHODS: Baseline measurements of heart rate (HR), cardiac index (CI), respiratory rate, systemic vascular resistance (SVR), percentage of patients with second degree atrioventricular (2(o) AV) block, mean arterial pressure (MAP), pH, and arterial partial pressures of carbon dioxide (PaCO2 ) and oxygen (PaO2 ) were obtained 5 minutes before administration of IV hyoscine (0.14 mg kg(-1) ; group HIV), IM hyoscine (0.3 mg kg(-1) ; group HIM), or an equal volume of physiologic saline IV (group C). Five minutes later, medetomidine (7.5 µg kg(-1) ) was administered IV and measurements were recorded at various time points for 130 minutes. RESULTS: Medetomidine induced bradycardia, 2(o) AV blocks and increased SVR immediately after administration, without significant changes in CI or MAP in C. Hyoscine administration induced tachycardia and hypertension, and decreased the percentage of 2(o) AV blocks induced by medetomidine. Peak HR and MAP were higher in HIV than HIM at 88 ± 18 beats minute(-1) and 241 ± 37 mmHg versus 65 ± 16 beats minute(-1) and 192 ± 38 mmHg, respectively. CI was increased significantly in HIV (p ≤ 0.05). Respiratory rate decreased significantly in all groups during the recording period. pH, PaCO2 and PaO2 were not significantly changed by administration of medetomidine with or without hyoscine. CONCLUSION AND CLINICAL RELEVANCE: Hyoscine administered IV or IM before medetomidine in horses resulted in tachycardia and hypertension under the conditions of this study. The significance of these changes, and responses to other dose rates, requires further investigation.

Effects of hypercapnic hyperpnea on recovery from isoflurane or sevoflurane anesthesia in horses.

OBJECTIVE: To test the hypothesis that hypercapnic hyperpnea produced using endotracheal insufflation with 5-10% CO(2) in oxygen could be used to shorten anesthetic recovery time in horses, and that recovery from sevoflurane would be faster than from isoflurane. STUDY DESIGN: Randomized crossover study design. ANIMALS: Eight healthy adult horses. METHODS: After 2 hours' administration of constant 1.2 times MAC isoflurane or sevoflurane, horses were disconnected from the anesthetic circuit and administered 0, 5, or 10% CO(2) in balance O(2) via endotracheal tube insufflation. End-tidal gas samples were collected to measure anesthetic washout kinetics, and arterial and venous blood samples were collected to measure respiratory gas partial pressures. Horses recovered in padded stalls without assistance, and each recovery was videotaped and evaluated by reviewers who were blinded to the anesthetic agent and insufflation treatment used. RESULTS: Compared to isoflurane, sevoflurane caused greater hypoventilation and was associated with longer times until standing recovery. CO(2) insufflation significantly decreased anesthetic recovery time compared to insufflation with O(2) alone without significantly increasing PaCO(2) . Pharmacokinetic parameters during recovery from isoflurane with CO(2) insufflation were statistically indistinguishable from sevoflurane recovery without CO(2). Neither anesthetic agent nor insufflation treatment affected recovery quality from anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Hypercapnic hyperpnea decreases time to standing without influencing anesthetic recovery quality. Although the lower blood gas solubility of sevoflurane should favor a shorter recovery time compared to isoflurane, this advantage is negated by the greater respiratory depression from sevoflurane in horses.

Effects of butorphanol on the minimum anesthetic concentration for sevoflurane in guineafowl (Numida meleagris).

OBJECTIVE: To determine the minimum anesthetic concentration (MAC) for sevoflurane and measure the dose and temporal effects of butorphanol on the MAC for sevoflurane in guineafowl. ANIMALS: 10 healthy adult guineafowl (Numida meleagris). PROCEDURES: Each bird was anesthetized with sevoflurane, and a standard bracketing method was used to measure the MAC in response to a noxious electrical stimulus. Subsequently, conditions were adjusted so that each bird was anesthetized with sevoflurane at a fraction of its respective MAC (eg, 0.7 times the MAC for that bird). Butorphanol tartrate (2 mg/kg, IV) was administered, and a noxious stimulus was applied every 15 minutes until the bird moved in response. The reduction in MAC was estimated with logistic regression by use of a standard quantal method. After an interval of ≥ 1 week, the MAC reduction experiment was repeated with an increased butorphanol dosage (4 mg/kg). RESULTS: Individual mean ± SE MAC for sevoflurane was 2.9 ± 0.1%. At 15 minutes after administration of 2 mg of butorphanol/kg, estimated reduction in the MAC for sevoflurane was 9 ± 3%. At 15 and 30 minutes after administration of 4 mg of butorphanol/kg, estimated reduction in the MAC for sevoflurane was 21 ± 4% and 11 ± 8%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: In guineafowl, the MAC for sevoflurane was similar to values reported for other species. Increasing the butorphanol dosage decreased the MAC for sevoflurane, but the effect was small and of short duration for dosages up to 4 mg/kg.

Pharmacokinetics of dexmedetomidine administered intravenously in isoflurane-anesthetized cats.

OBJECTIVE: To determine the pharmacokinetics of dexmedetomidine administered as a short-duration IV infusion in isoflurane-anesthetized cats. ANIMALS: 6 healthy adult domestic female cats. PROCEDURES: Dexmedetomidine hydrochloride was injected IV (10 µg/kg over 5 minutes [rate, 2 µg/kg/min]) in isoflurane-anesthetized cats. Blood samples were obtained immediately prior to and at 1, 2, 5, 6, 7, 10, 15, 30, 60, 90, 120, 240, and 480 minutes following the start of the IV infusion. Collected blood samples were transferred to tubes containing EDTA, immediately placed on ice, and then centrifuged at 3,901 × g for 10 minutes at 4°C. The plasma was harvested and stored at -20°C until analyzed. Plasma dexmedetomidine concentrations were determined by means of liquid chromatography-mass spectrometry. Dexmedetomidine plasma concentration-time data were fitted to compartmental models. RESULTS: A 2-compartment model with input in and elimination from the central compartment best described the disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats. Weighted mean ± SEM apparent volume of distribution of the central compartment and apparent volume of distribution at steady-state were 402 ± 47 mL/kg and 1,701 ± 200 mL/kg, respectively; clearance and terminal half-life (harmonic mean ± jackknife pseudo-SD) were 6.3 ± 2.8 mL/min/kg and 198 ± 75 minutes, respectively. The area under the plasma concentration curve and maximal plasma concentration were 1,061 ± 292 min•ng/mL and 17.6 ± 1.8 ng/mL, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats was characterized by a moderate clearance and a long terminal half-life.