Romifidine, medetomidine or xylazine before propofol-halothane-N2O anesthesia in dogs.

The objective of this paper was to evaluate romifidine as a premedicant in dogs prior to propofol-halothane-N2O anesthesia, and to compare it with the other alpha2-agonists (medetomidine and xylazine). For this, ten healthy dogs were anesthetized. Each dog received 3 preanesthetic protocols: atropine (10 microg/kg BW, IM), and as a sedative, romifidine (ROM; 40 microg/kg BW, IM), xylazine (XYL; 1 microg/kg, IM), or medetomidine (MED; 20 microg/kg BW, IM). Induction of anesthesia was delivered with propofol 15 min later and maintained with halothane and N2O for one hour in all cases. The following variables were registered before preanesthesia, 10 min after the administration of preanesthesia, and at 5-minute intervals during maintenance: PR, RR, rectal temperature (RT), MAP, SAP, and DAP. During maintenance, arterial oxygen saturation (SpO2), end-tidal CO2 (EtCO2) and percentage of halothane necessary for maintaining anesthesia (%HAL) were also recorded. Induction dose of propofol (DOSE), time to extubation (TE), time to sternal recumbency (TSR) and time to standing (TS) were also registered. The statistical analysis was carried out during the anesthetic period. ANOVA for repeat measures revealed no differences between the 3 groups for PR and RR; however, MAP, SAP and DAP were higher in the MED group; SpO2 was lower in MED and EtCO2 was lower in ROM; %HAL was higher in XYL. No statistical differences were observed in DOSE, TE, TSR or TS. Percentage of halothane was lower in romifidine and medetomidine than in xylazine premedicated dogs also anesthetized with propofol. All the cardiorespiratory variables measured were within normal limits. The studied combination of romifidine, atropine, propofol, halothane and N2O appears to be a safe and effective drug combination for inducing and maintaining general anesthesia in healthy dogs.     

Clearance of nasal mucus in nonanesthetized and anesthetized dogs

Clearance rates for nasal mucus in the maxillary turbinate region were measured in 8 Beagle dogs. 99mTc Macroaggregated albumin (10 microliters) was instilled in the nasal maxillary region of dogs under general anesthesia. A gamma camera was used to detect movement of the 99mTc macroaggregated albumin in the nose for 1 hour after it was instilled. Velocity of mucus was measured in the 8 dogs each under 3 conditions of anesthesia: anesthesia with pentobarbital given IV (20 mg/kg of body weight), anesthesia with halothane gas, and no anesthesia. Mean velocities (+/- SD) were 3.7 +/- 1.4 mm/min in dogs anesthetized with pentobarbital, 4.3 +/- 2.5 mm/min in dogs anesthetized with halothane, and 3.4 +/- 1.7 mm/min in awake dogs. The differences between the 3 anesthetic conditions were not significant at the P less than 0.05 level. Use of anesthesia at a light surgical plane provides a controlled method for measurement of clearance of nasal mucus with minimal alterations from the nonanesthetized state.     

Effects of carprofen on renal function during medetomidine-propofol-isoflurane anesthesia in dogs

OBJECTIVE: To investigate effects of carprofen on indices of renal function and results of serum bio-chemical analyses and effects on cardiovascular variables during medetomidine-propofol-isoflurane anesthesia in dogs. ANIMALS: 8 healthy male Beagles. PROCEDURES: A randomized crossover study was conducted with treatments including saline (0.9% NaCl) solution (0.08 mL/kg) and carprofen (4 mg/kg) administered IV. Saline solution or carprofen was administered 30 minutes before induction of anesthesia and immediately before administration of medetomidine (20 microg/kg, IM). Anesthesia was induced with propofol and maintained with inspired isoflurane in oxygen. Blood gas concentrations and ventilation were measured. Cardiovascular variables were continuously monitored via pulse contour cardiac output (CO) measurement. Renal function was assessed via glomerular filtration rate (GFR), renal blood flow (RBF), scintigraphy, serum biochemical analyses, urinalysis, and continuous CO measurements. Hematologic analysis was performed. RESULTS: Values did not differ significantly between the carprofen and saline solution groups. For both treatments, sedation and anesthesia caused changes in results of serum biochemical and hematologic analyses; a transient, significant increase in urine alkaline phosphatase activity; and blood flow diversion to the kidneys. The GFR increased significantly in both groups despite decreased CO, mean arterial pressure, and absolute RBF variables during anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Carprofen administered IV before anesthesia did not cause detectable, significant adverse effects on renal function during medetomidine-propofol-isoflurane anesthesia in healthy Beagles.     

Evaluation of total intravenous anesthesia with propofol or ketamine-medetomidine-propofol combination in horses

Objective-To compare the anesthetic and cardiorespiratory effects of total IV anesthesia with propofol (P-TIVA) or a ketamine-medetomidine-propofol combination (KMP-TIVA) in horses. Design-Randomized experimental trial. Animals-12 horses. Procedure-Horses received medetomidine (0.005 mg/kg [0.002 mg/lb], IV). Anesthesia was induced with midazolam (0.04 mg/kg [0.018 mg/lb], IV) and ketamine (2.5 mg/kg [1.14 mg/lb], IV). All horses received a loading dose of propofol (0.5 mg/kg [0.23 mg/lb], IV), and 6 horses underwent P-TIVA (propofol infusion). Six horses underwent KMP-TIVA (ketamine [1 mg/kg/h {0.45 mg/lb/h}] and medetomidine [0.00125 mg/kg/h {0.0006 mg/lb/h}] infusion; the rate of propofol infusion was adjusted to maintain anesthesia). Arterial blood pressure and heart rate were monitored. Qualities of anesthetic induction, transition to TIVA, and maintenance of and recovery from anesthesia were evaluated. Results-Administration of KMP IV provided satisfactory anesthesia in horses. Compared with the P-TIVA group, the propofol infusion rate was significantly less in horses undergoing KMP-TIVA (0.14 +/- 0.02 mg/kg/min [0.064 +/- 0.009 mg/lb/min] vs 0.22 +/- 0.03 mg/kg/min [0.1 +/- 0.014 mg/lb/min]). In the KMP-TIVA and P-TIVA groups, anesthesia time was 115 +/- 17 minutes and 112 +/- 11 minutes, respectively, and heart rate and arterial blood pressure were maintained within acceptable limits. There was no significant difference in time to standing after cessation of anesthesia between groups. Recovery from KMP-TIVA and P-TIVA was considered good and satisfactory, respectively. Conclusions and Clinical Relevance-In horses, KMP-TIVA and P-TIVA provided clinically useful anesthesia; the ketamine-medetomidine infusion provided a sparing effect on propofol requirement for maintaining anesthesia.     

Influence of nifedipine on xylazine-induced acute pressor response in halothane-anesthetized dogs

Effects and interaction of nifedipine (Ca channel blocker) and xylazine (mixed alpha agonist) during halothane anesthesia were examined in 6 dogs. After achievement of steady-state halothane (1.35%) anesthesia, blood pressure (BP) and heart rate (HR) were recorded in these dogs during 3-minute saline or nifedipine (20 micrograms/kg) infusion periods. Seven minutes after the end of saline or nifedipine infusion, xylazine (1.1 mg/kg of body weight) was infused over a 2-minute period. After saline pretreatment, xylazine administration increased diastolic BP (33.67 +/- 3.91 mm of Hg) and decreased HR. Nifedipine infusion induced a transient reduction in BP, accompanied by a more persistent increase in HR. Compared with saline pretreatment, nifedipine pretreatment significantly decreased the acute increase in diastolic BP (33.67 +/- 3.91 vs 14.00 +/- 2.94 mm of Hg) which occurred during xylazine injection. After saline and nifedipine infusions, xylazine administration decreased HR 30 +/- 15.02 and 36.5 +/- 10.36 beats/min, respectively. A pronounced sinus arrhythmia and/or 2nd-degree atrioventricular block developed in all dogs during xylazine injection after saline infusion. Arrhythmias were not observed in the dogs after nifedipine infusion. Nifedipine's Ca blocking action depressed xylazine-induced acute vasoconstriction and concomitant increase in diastolic BP. Because alpha 2-, but not alpha 1-adrenoceptor-mediated vasoconstriction is Ca-dependent, these results indicate that a portion of the acute pressor response induced by IV xylazine in halothane-anesthetized dogs may be alpha 2-mediated. Seemingly, nifedipine-induced hypotension and damping of xylazine-induced increases in BP attenuated xylazine's actions on cardiac rate and rhythm.     

Clinical comparison of xylazine and medetomidine for premedication of horses

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

Alteration in the arrhythmogenic dose of epinephrine (ADE) following xylazine administration to halothane-anesthetized dogs

The arrhythmogenic dose of epinephrine (ADE) was determined in six dogs during halothane (1.35%) anesthesia before and after xylazine administration (1.1 mg/kg, i.v. bolus; 1.1 mg/kg/hr, i.v. infusion). The arrhythmogenic dose was determined by constant infusion of freshly mixed epinephrine (100 microgram/ml). The ADE was defined as the total dose of epinephrine which produced four or more intermittent or continuous premature ventricular contractions within a 15-sec period. Total dose was calculated as a function of infusion rate and time to arrhythmia. Following xylazine administration, ADE significantly decreased from 6.28 +/- 0.522 to 4.17 +/- 0.679 micrograms/kg. At the end of i.v. xylazine bolus administration, heart rate significantly decreased (115 +/- 4 to 99 +/- 4.9 b.p.m.), and mean arterial pressure significantly increased (83 +/- 4.0 to 122 +/- 3.4 mm Hg). Heart rate measured immediately prior to epinephrine-induced arrhythmia formation was significantly increased following xylazine administration (177 +/- 8 vs 78 +/- 3 b.p.m.). Mean arterial blood pressure was unchanged. Apparently, xylazine, a mixed alpha agonist, potentiated halothane-induced myocardial sensitization to ventricular arrhythmogenesis and was associated with a significant increase in heart rate, but not blood pressure, during subsequent epinephrine infusions.     

Evaluation of Three Midazolam-Xylazine Mixtures Preliminary Trials in Dogs

The depressant effects of midazolam and xylazine on the central nervous system (CNS) were evaluated in 12 dogs. Xylazine was administered to six dogs (1.1 mg/kg intravenously [IV]) followed in 5 minutes by midazolam (1.0 mg/kg intramuscularly [IM]). In a second group of six dogs, xylazine (2.2 mg/kg IM) was followed in 5 minutes by midazolam (1.0 mg/kg IV). Both drug regimens induced rapid and profound sedation or anesthesia. Duration of action varied with the doses and routes of administration. Dogs given the high dose of xylazine IM had an arousal time of 95.4 +/- 8.9 minutes and a walking time of 155.4 +/- 8.8 minutes. These values exceeded the IV xylazine values threefold. Partial reversal of CNS depression was accomplished with either a benzodiazepine antagonist (flumazenil) or an alpha-2 antagonist (yohimbine). In a separate trial, a mixture of xylazine (0.55 mg/kg), midazolam (1.0 mg/kg), and butorphanol (0.1 mg/kg) with and without glycopyrrolate was evaluated in eight dogs. As with the xylazine-midazolam combinations, the CNS depressant effect of this mixture was clinically indistinguishable from anesthesia achieved with other rapid-acting injectable agents. Clinical signs of CNS depression were readily and completely antagonized by the simultaneous injection of flumazenil and yohimbine.     

The effect of general anesthesia and abdominal surgery upon plasma thromboxane B concentrations in horses

OBJECTIVE: To compare the effect of anesthesia alone with anesthesia and abdominal surgery on plasma thromboxane B(2) concentrations in horses. STUDY DESIGN: Non-randomized experimental study. ANIMALS: Six male mixed-bred horses (5-12 years, 350 +/- 18 kg). METHODS: All horses were anesthetized for 2.5 hours using halothane, and a month later abdominal surgery was performed using the same anesthetic technique with a similar duration. The schedule of anesthesia included pre-medication with diazepam (0.1 mg kg(-1) IM), followed by xylazine (2.2 mg kg(-1) IV), and 10 minutes later anesthesia was induced with ketamine hydrochloride (2.2 mg kg(-1) IV). After orotracheal intubation, anesthesia was maintained with halothane. Blood samples for the determination of thromboxane B(2) (TXB(2)) were obtained before, at induction, at 60 minutes after halothane was first inspired, and at recovery from anesthesia as well as at the corresponding stages of the experimental abdominal surgery (before induction, prior to laparotomy, enterectomy, enteroanastomosis, abdominal wall closure). RESULTS: Baseline value for the anesthesia group was 76 +/- 12 pg mL(-1) and increased (p < 0.001) after 1 hour of anesthesia to 265 +/- 40 pg mL(-1). With surgery, the corresponding value was 285 +/- 21 pg mL(-1) (hour 1, p < 0.001) and 210 +/- 28 pg mL(-1) (hour 2, p < 0.001), respectively. These were not different from anesthesia alone. CONCLUSION: The increased concentrations of thromboxane B(2) between 1 and 2.5 hours of halothane anesthesia and during the corresponding stages of the surgical intervention suggested that the anesthetic technique caused a significant increase in thromboxane B(2) and that surgery did not appear to contribute to this response.     

Total intravenous anesthesia in greyhounds: pharmacokinetics of propofol and fentanyl--a preliminary study

OBJECTIVE: To evaluate concomitant propofol and fentanyl infusions as an anesthetic regime, in Greyhounds. ANIMALS: Eight clinically normal Greyhounds (four male, four female) weighing 25.58 +/- 3.38 kg. DESIGN: Prospective experimental study. METHODS: Dogs were premedicated with acepromazine (0.05 mg/kg) by intramuscular (i.m.) injection. Forty five minutes later anesthesia was induced with a bolus of propofol (4 mg/kg) by intravenous (i.v.) injection and a propofol infusion was begun (time = 0). Five minutes after induction of anesthesia, fentanyl (2 microg/kg) and atropine (40 microg/kg) were administered i.v. and a fentanyl infusion begun. Propofol infusion (0.2 to 0.4 mg/kg/min) lasted for 90 minutes and fentanyl infusion (0.1 to 0.5 microg/kg/min) for 70 minutes. Heart rate, blood pressure, respiratory rate, end-tidal carbon dioxide, body temperature, and depth of anesthesia were recorded. The quality of anesthesia, times to return of spontaneous ventilation, extubation, head lift, and standing were also recorded. Blood samples were collected for propofol and fentanyl analysis at varying times before, during and after anesthesia. RESULTS: Mean heart rate of all dogs varied from 52 to 140 beats/min during the infusion. During the same time period, mean blood pressure ranged from 69 to 100 mm Hg. On clinical assessment, all dogs appeared to be in light surgical anesthesia. Mean times (+/- SEM), after termination of the propofol infusion, to return of spontaneous ventilation, extubation, head lift and standing for all dogs were 26 +/- 7, 30 +/- 7, 59 +/- 12, and 105 +/- 13 minutes, respectively. Five out of eight dogs either whined or paddled their forelimbs in recovery. Whole blood concentration of propofol for all eight dogs ranged from 1.21 to 6.77 microg/mL during the infusion period. Mean residence time (MRTinf) for propofol was 104.7 +/- 6.0 minutes, mean body clearance (Clb) was 53.35 +/- 0.005 mL/kg/min, and volume of distribution at steady state (Vdss) was 3.27 +/- 0.49 L/kg. Plasma concentration of fentanyl for seven dogs during the infusion varied from 1.22 to 4.54 ng/mL. Spontaneous ventilation returned when plasma fentanyl levels were >0.77 and <1.17 ng/mL. MRTinf for fentanyl was 111.3 +/- 5.7 minutes. Mean body clearance was 29.1 +/- 2.2 mL/kg/min and Vdss was 2.21 +/- 0.19 L/kg. CONCLUSION AND CLINICAL RELEVANCE: In Greyhounds which were not undergoing any surgical stimulation, total intravenous anesthesia maintained with propofol and fentanyl infusions induced satisfactory anesthesia, provided atropine was given to counteract bradycardia. Despite some unsatisfactory recoveries the technique is worth investigating further for clinical cases, in this breed and in mixed breed dogs.     

Evaluation of the arrhythmogenicity of a low dose of acepromazine: comparison with xylazine.

Alteration in the arrhythmogenic dose of epinephrine (ADE) was determined in 6 healthy dogs under halothane anesthesia following the administration of xylazine at 1.1 mg/kg i.v. and acepromazine at 0.025 mg/kg i.v. The order of treatment was randomly assigned with each dog receiving both treatments and testing was carried out on 2 separate occasions with at least a 1 wk interval. The ADE determinations were made prior to drug administration during halothane anesthesia (CNTL) and then 20 min and 4 h following drug treatment. Epinephrine was infused for 3 min at increasing dose rates (2.5, 5.0, 10.0 micrograms/kg/min) until the arrhythmia criterion (4 or more intermittent or continuous premature ventricular contractions) was reached within the 3 min of infusion or the 1 min following cessation. The interinfusion interval was 20 min. There was a significant difference (P = 0.0001) in the ADE determined following acepromazine administration at 20 min (20.95 micrograms/kg +/- 2.28 SEM) compared to CNTL (6.64 micrograms/kg +/- 1.09), xylazine at 20 min (5.82 micrograms/kg +/- 0.95) and 4 h (6.13 micrograms/kg +/- 1.05), and acepromazine at 4 h (7.32 micrograms/kg +/- 0.34). No other significant differences existed (P < 0.05). In this study we were unable to show any sensitization to epinephrine following xylazine administration during halothane anesthesia, while a protective effect was shown with a low dose of acepromazine.     

Infusion of a combination of propofol and medetomidine for long-term anesthesia in ponies

OBJECTIVE: To determine the minimal infusion rate of propofol in combination with medetomidine for long-term anesthesia in ponies and the effects of atipamezole on recovery. ANIMALS: 12 ponies. PROCEDURE: Ponies were sedated with medetomidine (7 microg/kg of body weight, IV). Ten minutes later, anesthesia was induced with propofol (2 mg/kg, IV). Anesthesia was maintained for 4 hours, using an infusion of medetomidine (3.5 microg/kg per hour, IV) and propofol at a rate sufficient to prevent ponies from moving after electrical stimulation. Arterial blood pressures and blood gas analysis, heart rates, and respiratory rates were monitored. For recovery, 6 ponies were given atipamezole (60 microg/kg, IV). Induction and recovery were scored. RESULTS: Minimal propofol infusion rates ranged from 0.06 to 0.1 mg/kg per min. Mean arterial blood pressure was stable (range, 74 to 86 mm Hg), and heart rate (34 to 51 beats/min) had minimal variations. Variable breathing patterns were observed. Mean PaO2 (range, 116 to 146 mm Hg) and mean PaCO2 (range, 48 to 51 mm Hg) did not change significantly with time, but hypoxemia was evident in some ponies (minimal PaO2, 47 mm Hg). Recovery was fast and uneventful with and without atipamezole (completed in 20.2 and 20.9 minutes, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Infusion of a combination of medetomidine and propofol was suitable for prolonged anesthesia in ponies. Recovery was rapid and uneventful. A combination of propofol and medetomidine may prove suitable for long-term anesthesia in horses. Monitoring of blood gases is essential because of potential hypoxemia.     

Evaluation of propofol and medetomidine-ketamine for short-term immobilization of Gulf of Mexico sturgeon (Acipenser oxyrinchus de soti).

Parenteral anesthetic protocols for short-term immobilization were evaluated in twenty 4-yr-old Gulf of Mexico sturgeon (Acipenser oxyrinchus de soti). An initial dose-response trial determined the efficacy of either propofol (3.5-7.5 mg/kg. i.v.) or combinations of medetomidine (0.03-0.07 mg/kg, i.m.)-ketamine (3-7 mg/kg, i.m.). A subsequent study evaluated the physiologic effects of propofol (6.5 mg/kg, i.v.)-induced anesthesia and anesthesia induced with a medetomidine (0.06 mg/kg, i.m.)-ketamine (6 mg/kg i.m.) combination. The effects of medetomidine were reversed at 30 min with atipamezole (0.30 mg/kg, i.m.). Both drug protocols provided adequate short-term immobilization for minor diagnostic procedures. Sturgeon receiving propofol were in a light plane of anesthesia within 5 min after drug administration, whereas only 30% of the medetomidine-ketamine group reached a light plane of anesthesia in the same time period. Both propofol and medetomidine-ketamine resulted in mild bradycardia and apparent respiratory depression, with propofol producing more profound effects. At the dosages used in this study, both propofol and the medetomidine-ketamine combination effectively induced a light plane of anesthesia. Induction times were shorter in the propofol group.     

Sedative and cardiopulmonary effects of medetomidine hydrochloride and xylazine hydrochloride and their reversal with atipamezole hydrochloride in calves

OBJECTIVE: To assess the sedative and cardiopulmonary effects of medetomidine and xylazine and their reversal with atipamezole in calves. ANIMALS: 25 calves. PROCEDURES: A 2-phase (7-day interval) study was performed. Sedative characteristics (phase I) and cardiopulmonary effects (phase II) of medetomidine hydrochloride and xylazine hydrochloride administration followed by atipamezole hydrochloride administration were evaluated. In both phases, calves were randomly allocated to receive 1 of 4 treatments IV: medetomidine (0.03 mg/kg) followed by atipamezole (0.1 mg/kg; n = 6), xylazine (0.3 mg/kg) followed by atipamezole (0.04 mg/kg; 7), medetomidine (0.03 mg/kg) followed by saline (0.9% NaCl; 6) solution (10 mL), and xylazine (0.3 mg/kg) followed by saline solution (10 mL; 6). Atipamezole or saline solution was administered 20 minutes after the first injection. Cardiopulmonary variables were recorded at intervals for 35 minutes after medetomidine or xylazine administration. RESULTS: At the doses evaluated, xylazine and medetomidine induced a similar degree of sedation in calves; however, the duration of medetomidine-associated sedation was longer. Compared with pretreatment values, heart rate, cardiac index, and PaO(2) decreased, whereas central venous pressure, PaCO(2), and pulmonary artery pressures increased with medetomidine or xylazine. Systemic arterial blood pressures and vascular resistance increased with medetomidine and decreased with xylazine. Atipamezole reversed the sedative and most of the cardiopulmonary effects of both drugs. CONCLUSIONS AND CLINICAL RELEVANCE: At these doses, xylazine and medetomidine induced similar degrees of sedation and cardiopulmonary depression in calves, although medetomidine administration resulted in increases in systemic arterial blood pressures. Atipamezole effectively reversed medetomidine- and xylazine-associated sedative and cardiopulmonary effects in calves.     

Alterations in epinephrine-induced arrhythmogenesis after xylazine and subsequent yohimbine administration in isoflurane-anesthetized dogs

Effects of xylazine (1.1 mg/kg of body weight, IV bolus, plus 1.1 mg/kg/h infusion) and subsequent yohimbine (0.125 mg/kg, IV bolus) administration on the arrhythmogenic dose of epinephrine (ADE) in isoflurane (1.8% end-tidal)-anesthetized dogs were evaluated. The ADE was defined as the total dose of epinephrine that induced greater than or equal to 4 premature ventricular contractions within 15 seconds during a 3-minute infusion period or within 1 minute after the end of infusion. Total ADE values during isoflurane anesthesia, after xylazine administration, and after yohimbine injection were 36.6 +/- 8.45 micrograms/kg, 24.1 +/- 6.10 micrograms/kg, and 45.7 +/- 6.19 micrograms/kg, respectively. Intravenous xylazine administration significantly (P less than 0.05) increased blood pressure and decreased heart rate, whereas yohimbine administration induced a significant (P less than 0.05) decrease in blood pressure. induced a significant (P less than 0.05) decrease in blood pressure. After yohimbine administration, the ADE significantly (P less than 0.05) increased above that after isoflurane plus xylazine administration. After yohimbine administration, blood pressure measured immediately before epinephrine-induced arrhythmia was significantly (P less than 0.05) less than the value recorded during isoflurane plus xylazine anesthesia. Heart rate was unchanged among treatments immediately before epinephrine-induced arrhythmia. Seemingly, yohimbine possessed a protective action against catecholamine-induced arrhythmias in dogs anesthetized with isoflurane and xylazine.     

Laryngeal mask airway insertion requires less propofol than endotracheal intubation in dogs

OBJECTIVE: To compare the doses of propofol required for insertion of the laryngeal mask airway (LMA) with those for endotracheal intubation in sedated dogs. STUDY DESIGN: Randomized prospective clinical study. Animals Sixty healthy dogs aged 0.33-8.5 (3.0 +/- 2.3, mean +/- SD) years, weighing 2.2-59.0 (23.4 +/- 13.6, mean +/- SD) kg, presented for elective surgery requiring inhalation anaesthesia. METHODS: Animals were randomly assigned to receive either a LMA or an endotracheal tube. Pre-anaesthetic medication was intravenous (IV) glycopyrrolate (0.01 mg kg(-1)) medetomidine (10 microg kg(-1)) and butorphanol (0.2 mg kg(-1)). Repeated IV propofol injections (1 mg kg(-1) in 30 seconds) were given until LMA insertion or endotracheal intubation was achieved, when the presence or absence of laryngospasm, the respiratory rate (fr) and the total dose of propofol used were recorded. RESULTS: The total propofol dose (mean +/- SD) required for LMA insertion (0.53 +/- 0.51 mg kg(-1)) was significantly lower than for endotracheal intubation (1.43 +/- 0.57 mg kg(-1)). The LMA could be inserted without propofol in 47% of dogs; the remainder needed a single 1 mg kg(-1) bolus (n = 30). Endotracheal intubation was possible without propofol in 3.3% of the dogs, 47% needed one bolus and 50% required two injections (n = 30). The f(r) (mean +/- SD) was 18 +/- 6 and 15 +/- 7 minute(-1) after LMA insertion and intubation, respectively. CONCLUSION AND CLINICAL RELEVANCE: Laryngeal mask airway insertion requires less propofol than endotracheal intubation in sedated dogs therefore propofol-induced cardiorespiratory depression is likely to be less severe. The LMA is well tolerated and offers a less invasive means of securing the upper airway.     

Results of cystometry and urethral pressure profilometry in dogs sedated with medetomidine or xylazine

OBJECTIVE: To compare effects of medetomidine and xylazine hydrochloride on results of cystometry and micturition reflexes in healthy dogs and results of urethral pressure profilometry (UPP) in sedated and conscious dogs. ANIMALS: 20 dogs. PROCEDURES: Urodynamic testing was performed 6 times in each dog (3 times after administration of xylazine [1 mg/kg of body weight, IV] and 3 times after administration of medetomidine (30 microg/kg, IM). Before each episode of sedation, UPP was performed. Heart and respiratory rates and indirect blood pressures were recorded prior to and 5, 10, 20, and 30 minutes after injection of sedative. Cystometry measurements included threshold volume, threshold pressure, and tonus limb. The UPP measurements included maximal urethral closure pressure (MUCP), functional profile length, and, in male dogs, plateau pressure. RESULTS: Mean MUCP was decreased markedly in xylazine- and medetomidine-sedated dogs. Xylazine and medetomidine also decreased plateau pressure in male dogs. The MUCP measurements were consistent among days for conscious and xylazine-sedated dogs but were inconsistent for medetomidine-sedated female dogs. The proportion of valid cystometry measurements was greater for xylazine (39 of 60) than for medetomidine (27 of 60). Cystometry was considered invalid when bladder pressure reached 30 cm H2O without initiation of a micturition reflex. CONCLUSIONS AND CLINICAL RELEVANCE: Medetomidine and xylazine have similar effects on measurement of UPP and cystometry. Medetomidine was less consistent among days for UPP in female dogs and produced fewer valid cystometry tests, compared with xylazine. For urodynamic evaluations, medetomidine administered IM cannot be substituted for xylazine administered IV.     

Comparison of high (5%) and low (1%) concentrations of micellar microemulsion propofol formulations with a standard (1%) lipid emulsion in horses

OBJECTIVE: To compare anesthesia-related events associated with IV administration of 2 novel micellar microemulsion preparations (1% and 5%) and a commercially available formulation (1%) of propofol in horses. Animals-9 healthy horses. PROCEDURES: On 3 occasions, each horse was anesthetized with 1 of the 3 propofol formulations (1% or 5% microemulsion or 1% commercial preparation). All horses received xylazine (1 mg/kg, IV), and anesthesia was induced with propofol (2 mg/kg, IV). Induction and recovery events were quantitatively and qualitatively assessed. Venous blood samples were obtained before and at intervals following anesthesia for quantification of clinicopathologic variables. RESULTS: Compared with the commercial formulation, the quality of anesthesia induction in horses was slightly better with the micellar microemulsion formulas. In contrast, recovery characteristics were qualitatively and quantitatively indistinguishable among treatment groups (eg, time to stand after anesthesia was 34.3 +/- 7.3 minutes, 34.1 +/- 8.8 minutes, and 39.0 +/- 7.6 minutes in horses treated with the commercial formulation, 1% microemulsion, and 5% microemulsion, respectively). During recovery from anesthesia, all horses stood on the first attempt and walked within 5 minutes of standing. No clinically relevant changes in hematologic and serum biochemical analytes were detected during a 3-day period following anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the micellar microemulsion preparation of propofol (1% or 5%) has similar anesthetic effects in horses, compared with the commercially available lipid propofol formulation. Additionally, the micellar microemulsion preparation is anticipated to have comparatively low production costs and can be manufactured in various concentrations.     

Effect of general anesthesia and minor surgical trauma on urine and serum measurements in horses

OBJECTIVE: To characterize the effect of general anesthesia and minor surgery on renal function in horses. ANIMALS: 9 mares with a mean (+/- SE) age and body weight of 9+/-2 years and 492+/-17 kg, respectively. PROCEDURE: The day before anesthesia, urine was collected (catheterization) for 3 hours to quantitate baseline values, and serum biochemical analysis was performed. The following day, xylazine (1.1 mg/kg, IV) was administered, and general anesthesia was induced 5 minutes later with diazepam (0.04 mg/kg, IV) and ketamine (2.2 mg/kg, IV). During 2 hours of anesthesia with isoflurane, Paco2 was maintained between 48 and 52 mm Hg, and mean arterial blood pressure was between 70 and 80 mm Hg. Blood and urine were collected at 30, 60, and 120 minutes during and at 1 hour after anesthesia. RESULTS: Baseline urine flow was 0.92+/-0.17 ml/kg/h and significantly increased at 30 and 60 minutes after xylazine administration (2.14+/-0.59 and 2.86+/-0.97 ml/kg/h respectively) but returned to baseline values by the end of anesthesia. Serum glucose concentration increased from 12+/-4 to 167+/-8 mg/dl at 30 minutes. Glucosuria was not observed. CONCLUSIONS AND CLINICAL RELEVANCE: Transient hyperglycemia and an increase in rine production accompanies a commonly used anesthetic technique for horses. The increase in urine flow is not trivial and should be considered in anesthetic management decisions. With the exception of serum glucose concentration and urine production, the effect of general anesthesia on indices of renal function in clinically normal horses is likely of little consequence in most horses admitted for elective surgical procedures.     

Sedative and analgesic effects of medetomidine in dogs

The sedative and analgesic effects of medetomidine were studied in 18 laboratory beagles in a randomized cross-over study which was carried out in a double-blind fashion. Xylazine was included as a positive control and placebo as a negative control. Medetomidine was used at doses of 10, 30, 90 and 180 micrograms/kg i.m. compared to a dose of 2.2 mg/kg xylazine i.m. Parameters closely related to sedation were used to measure the degree of sedation. These were a posture variable (including evaluation of the dog's posture without external disturbance and resistance when laid recumbent) and a relaxation variable (including relaxation of the jaws, upper eyelids and anal sphincter). The first signs of sedation were recorded 1.5-3.5 min after administration of both drugs. The dogs sat down at 0.6-2.6 min post-injection and became prone at 1.9-5.9 min. Medetomidine dose-dependently affected the posture of the dogs and the relaxation variable--the higher the dose, the stronger and longer lasting the effect recorded. The sedative effect of xylazine was comparable to a medetomidine dose of 30 micrograms/kg. The analgesic effect was assessed as changes in the response to superficial pain induced by electrical stimuli. The response threshold increased significantly with both drugs and the effect of medetomidine was dose-dependent. The effects of the doses of 30 micrograms/kg medetomidine and 2.2 mg/kg xylazine did not differ significantly. In summary, medetomidine possessed an excellent sedative effect associated with analgesia in dogs.