Comparison of the clinical utility of medetomidine/ketamine and xylazine/ketamine combinations for the ovariectomy of cats

A controlled trial was conducted to assess suitability of combinations of medetomidine and ketamine for the ovariectomy of cats, to investigate the possible side effects, and to compare medetomidine/ketamine with a combination of xylazine and ketamine. Three hundred and thirty-seven cats were submitted to surgery; 100 were anaesthetised with 80 micrograms/kg medetomidine and 5 mg/kg ketamine, 137 with 80 micrograms/kg medetomidine and 7.5 mg/kg ketamine, and 100 were anaesthetised with 1 mg/kg xylazine and 10 mg/kg ketamine. The combinations were injected intramuscularly in the same syringe. The anaesthesia provided by the medetomidine/ketamine combinations was characterised by good muscle relaxation, good analgesia and minimal side effects. The only difference between the two doses of ketamine was the length of the period of anaesthesia. The advantages of the medetomidine/ketamine combination in comparison with xylazine/ketamine were the need for a lower dose of ketamine, a longer duration of action and better analgesia. Similar side effects were observed with both medetomidine/ketamine and xylazine/ketamine combinations.     

A comparative study of medetomidine/ketamine and xylazine/ketamine anaesthesia in dogs

The anaesthetic and physiological effects of a combination of 40 micrograms medetomidine with 2.5 ketamine, 5.0 or 7.5 mg/kg administered intramuscularly were compared with the effects of a combination of 1 mg/kg xylazine and 15 mg/kg ketamine. All the combinations rapidly induced an anaesthetic state that permitted endotracheal intubation, with the absence of the pedal reflex and with good muscle relaxation, and induced bradycardia that was less pronounced as the dose of ketamine was increased. All the combinations produced a decrease in respiratory rate. Increasing the dose of ketamine combined with medetomidine resulted in a very significant prolongation of the duration of anaesthesia, the duration of muscle relaxation and the arousal time. The duration of the anaesthetic effects of 40 micrograms/kg medetomidine with 5 mg/kg ketamine was comparable to that provided by the recommended xylazine/ketamine combination but the period of muscle relaxation was significantly longer. The recovery from medetomidine/ketamine took longer than recovery from xylazine/ketamine but there were fewer side effects.     

Anesthesia induced by administration of xylazine hydrochloride alone or in combination with ketamine hydrochloride and reversal by administration of yohimbine hydrochloride in captive Axis deer (Axis axis)

OBJECTIVE: To determine the anesthetic dose and cardiopulmonary effects of xylazine hydrochloride when used alone or in combination with ketamine hydrochloride and evaluate the efficacy of yohimbine hydrochloride to reverse anesthetic effects in captive Axis deer. ANIMALS: 35 adult (10 males and 25 females) Axis deer (Axis axis). PROCEDURES: All deer were anesthetized by IM administration of xylazine (3.5 mg/kg; experiment 1), a combination of ketamine and xylazine (1.25 and 1.5 mg/kg, respectively; experiment 2), or another combination of ketamine and xylazine (2.5 and 0.5 mg/kg, respectively; experiment 3). In addition, female deer were also anesthetized by IM administration of a third combination of ketamine and xylazine (1.5 and 1 mg/kg, respectively; experiment 4). Ten to 40 minutes after induction, anesthesia was reversed by IV administration of yohimbine (5, 8, or 10 mg). RESULTS: In male deer, experiment 3 yielded the most rapid induction of anesthesia. In females, experiment 4 yielded the best induction of anesthesia without adverse effects. All doses of yohimbine reversed anesthesia. Duration of anesthesia before administration of yohimbine had no effect on recovery time. CONCLUSIONS AND CLINICAL RELEVANCE: A combination of ketamine and xylazine can be used to induce anesthesia in Axis deer. Furthermore, anesthetic effects can be reversed by administration of yohimbine.     

Effects of yohimbine on combined xylazine-ketamine-induced sedation and immobilization in juvenile African elephants

Twenty-two juvenile African elephants were given a combination of xylazine (mean +/- SD = 0.14 +/- 0.03 mg/kg of body weight) and ketamine (1.14 +/- 0.21 mg/kg) as a single IM injection; one elephant was immobilized twice, 77 days apart. After injection, 14 elephants were immobilized, 4 were sedated deeply, 2 were sedated moderately, and 2 were sedated minimally. Immobilized elephants had a mean immobilization time of 11.6 +/- 6.9 minutes. At the conclusion of a variety of clinical procedures, 12 of the 14 elephants immobilized with a single dose combination of xylazine and ketamine were given yohimbine (0.13 +/- 0.03 mg/kg) IV, and the remaining 2 elephants were allowed to recover spontaneously; the elephants given yohimbine had a mean standing time of 2.4 +/- 1.1 minutes. Of the 8 sedated elephants, 5 were given an additional dose of combined xylazine (0.08 +/- 0.03 mg/kg), and ketamine (0.61 +/- 0.19 mg/kg) IM, and 1 elephant was given ketamine (0.47 mg/kg) IV. After injection, 4 of the 8 elephants were recumbent laterally within 17 minutes and 2 remained standing, under deep sedation. Seven of the 8 elephants were given yohimbine (0.13 +/- 0.03 mg/kg) IV; all were ambulatory in 2 minutes. Results indicated that yohimbine may be useful in controlling duration of xylazine-ketamine sedation and immobilization in juvenile African elephants.     

Clinicophysiological Effects of Spinally Administered Ketamine and Its Combination with Xylazine and Medetomidine in Healthy Goats

The study was conducted in 9 healthy adult goats of either sex, weighing 15–20 kg, to evaluate and compare the clinicophysiological effects of spinally administered ketamine alone and in combination with xylazine and medetomidine. Nine trials each of the three treatments were conducted randomly by injecting ketamine (2.5 mg/kg) (n = 9), ketamine and xylazine (2.5 mg/kg and 0.05 mg/kg) (n = 9) and ketamine and medetomidine (2.5 mg/kg and 10 μg/kg) (n = 9). The drugs were administered at the lumbosacral subarachnoid space under strict aseptic conditions. The treatments were evaluated on the basis of clinicophysiological, haematological, biochemical and haemodynamic observations. Ketamine produced mild to moderate analgesia of the hindquarters. Its combination with either xylazine or medetomidine produced complete analgesia of the hindquarters for 45–60 min. Ataxia was moderate in the ketamine group, whereas animals attained sternal recumbency in the combination groups. A moderate degree of sedation was recorded in the combination groups. Heart rate and respiratory rate depression in the combination groups and heart rate and respiratory rate stimulation in ketamine group were recorded. Haematological parameters decreased in all the groups. Increase in serum glucose, creatinine and urea nitrogen was recorded in all the groups. Serum electrolytes did not show any significant change. The results showed that the combination of ketamine with xylazine or medetomidine at these dose rates produced a comparable degrees of analgesia of hindquarters with transient and minimal cardiopulmonary side effects.     

Effect of yohimbine on xylazine-ketamine anesthesia in cats

Xylazine and ketamine are an anesthetic combination used in feline practice for routine surgical procedures. In a controlled study, we evaluated the effects of yohimbine, an antagonist of xylazine, on the anesthesia induced by this anesthetic combination in cats. Two intramuscular doses of xylazine and ketamine (2.2 mg of xylazine/kg plus 6.6 mg of ketamine/kg and 4.4 mg of xylazine/kg plus 6.6 mg of ketamine/kg) caused approximately 60 and 100 minutes of anesthesia, respectively, in control cats. When yohimbine (0.1 mg/kg) was given intravenously 45 minutes after ketamine administration, the cats regained consciousness within 3 minutes. They were ambulatory 1 to 2 minutes after regaining consciousness. Yohimbine also reversed the bradycardia and respiratory depression elicited by xylazine-ketamine. The results indicated that yohimbine may be useful for controlling the duration of xylazine-ketamine anesthesia in cats.     

Anesthesia in the Richardson's ground squirrel: comparison of ketamine, ketamine and xylazine, droperidol and fentanyl, and sodium pentobarbital

A combination of ketamine and xylazine (88.9 mg of ketamine/ml and 11.1 mg of xylazine/ml) given IM (85.5 +/- 3.4 mg of ketamine/kg of body weight and 10.6 +/- 0.5 mg of xylazine/kg) or subcutaneously (85.6 +/- 4.0 mg of ketamine/kg and 10.7 +/- 0.7 mg of xylazine/kg) induced effective surgical anesthesia for 20 to 30 minutes in Richardson's ground squirrels. Use of ketamine alone (86 +/- 7 mg/kg, IM), a droperidol and fentanyl combination (2.6 +/- 0.4 mg of droperidol/kg and 52 +/- 8 micrograms of fentanyl/kg, IM), or sodium pentobarbital (50 +/- 2 mg/kg, intraperitoneally) did not induce surgical anesthesia, but did induce depressed respiratory rates in the squirrels.     

Cardiopulmonary effects of romifidine/ketamine or xylazine/ketamine when used for short duration anesthesia in the horse

The cardiovascular changes associated with anesthesia induced and maintained with romifidine/ketamine versus xylazine/ ketamine were compared using 6 horses in a cross over design. Anesthesia was induced and maintained with romifidine (100 microg/kg, IV)/ketamine (2.0 mg/kg, IV) and ketamine (0.1 mg/kg/min, IV), respectively, in horses assigned to the romifidine/ ketamine group. Horses assigned to the xylazine/ketamine group had anesthesia induced and maintained with xylazine (1.0 mg/kg, IV)/ketamine (2.0 mg/kg, IV) and a combination of xylazine (0.05 mg/kg/min, IV) and ketamine (0.1 mg/kg/min, IV), respectively. Cardiopulmonary variables were measured at intervals up to 40 min after induction. All horses showed effective sedation following intravenous romifidine or xylazine and achieved recumbency after ketamine administration. There were no significant differences between groups in heart rate, arterial oxygen partial pressures, arterial carbon dioxide partial pressures, cardiac index, stroke index, oxygen delivery, oxygen utilization, systemic vascular resistance, left ventricular work, or any of the measured systemic arterial blood pressures. Cardiac index and left ventricular work fell significantly from baseline while systemic vascular resistance increased from baseline in both groups. The oxygen utilization ratio was higher in the xylazine group at 5 and 15 min after induction. In conclusion, the combination of romifidine/ketamine results in similar cardiopulmonary alterations as a xylazine/ketamine regime, and is a suitable alternative for clinical anesthesia of the horse from a cardiopulmonary viewpoint.     

Xylazine and ketamine anaesthesia in the dromedary camel under field conditions

The effects of either xylazine (0.25 mg/kg) intramuscularly, ketamine (5.5 mg/kg) intramuscularly, or a mixture of xylazine (0.15 mg/kg) and ketamine (2.5 mg/kg) intramuscularly on sedation, analgesia, cardiac and respiratory rates, body temperature and muscle relaxation were studied in the domesticated dromedary camel. Either drug used separately was suitable for sedation and analgesia in the camel. However, the mixture of xylazine and ketamine was superior to either drug used alone. Camels which received the combination of xylazine and ketamine had fewer effects on cardiac and respiratory rates and better analgesia. In addition, they showed better muscle relaxation, less central nervous system irritability and shorter recovery times than camels sedated with ketamine alone.     

Antagonism of some cyclohexamine-based drug combinations used for chemical restraint of southern elephant seals (Mirounga leonina)

SUMMARY This study examined the use of 4 antagonists of chemical restraint in mature female southern elephant seals (Mirounga leonina) that were restrained with ketamine and diazepam, ketamine and xylazine, or tiletamine and zolazepam. The antagonists were: 4-aminopyridine, yohimbine, doxapram and sarmazenil. The effects of the antagonists on the animal's time to first movement forward and recovery, heart rate, respiratory rate and venous blood gas and pH values, and level of chemical restraint were recorded. Sarmazenil (1.0 mg/kg) and doxapram (5.0 mg/kg) partially antagonised 50:1 ketamine: diazepam (ketamine = 3.0 mg/kg, diazepam = 0.06 mg/kg) and tiletamine and zolazepam (tiletamine = 0.5 mg/kg, zolazepam = 0.5 mg/kg). However, the rapid recovery after low doses of anaesthetics means that antagonism is usually unnecessary, and it may increase the likelihood of shaking. Routine antagonism of ketamine and xylazine (ketamine = 3.0 mg/kg, xylazine = 0.5 mg/kg) is more useful given its usually delayed recovery time and potential for thermoregulatory problems. For this purpose yohimbine (0.06 mg/kg) offered advantages over doxapram in giving a smoother recovery with less aggression. 4-aminopyridine (0.2 mg/kg) prolonged chemical restraint by 100:1 ketamine: diazepam (ketamine = 3.0 mg/kg, diazepam = 0.03 mg/kg) and ketamine and xylazine, and should be contraindicated. Doxapram (5.0 mg/kg) was the most useful general antagonist for all groups of drugs but shaking was seen and a lower dose is recommended.     

Ketamine/xylazine anesthesia in the pregnant rat

Pregnant albino rats were anesthetized with a combination of ketamine and xylazine. A minimal effective dosage of 90 mg/kg for ketamine and 10 mg/kg for xylazine provided satisfactory anesthesia in 92% of the subjects, without adverse effects on gestation or the fetuses.     

Xylazine-ketamine-induced anesthesia in rats and its antagonism by yohimbine

A combination of xylazine and ketamine was used to anesthetize 60 male rats, and then yohimbine was given to evaluate its reversing effect on xylazine-ketamine-induced anesthesia. In experiment A, xylazine (21 mg/kg of body weight) and ketamine (45 mg/kg) were admixed and administered IM to 12 Sprague-Dawley rats. Anesthesia lasted approximately 70 minutes. The xylazine-ketamine combination also induced polyuria, bradycardia, and bradypnea. When yohimbine (2.1 mg/kg) was given intraperitoneally 20 minutes after the xylazine-ketamine injection, the rats regained consciousness and righting reflexes within approximately 10 minutes. Yohimbine also reversed the bradycardia and bradypnea and appeared to reduce the polyuria induced by the xylazine-ketamine combination. In experiment B, xylazine (15.4 mg/kg) and ketamine (33 mg/kg) were admixed and given IM to 48 Holtzman rats. The combination induced surgical anesthesia for at least 30 minutes, during which a surgical procedure involving grafting a section of the sciatic nerve into the hypothalamus was performed. In rats in which yohimbine (1 mg/kg) was given intraperitoneally 45 to 60 minutes after xylazine-ketamine administration (before natural recovery from the anesthesia), the righting reflex was apparent in less than 10 minutes.     

The parasympatholytic effects of atropine sulfate and glycopyrrolate in rats and rabbits.

Nine groups of rats (n = 5 per group) received an intramuscular (IM) injection of one of the following drugs or drug combinations: saline, atropine (0.05 mg/kg), glycopyrrolate (0.5 mg/kg), ketamine:xylazine (85:15 mg/kg), ketamine:detomidine (60:10 mg/kg), atropine:ketamine:xylazine (0.05: 85:15 mg/kg), glycopyrrolate: ketamine:xylazine (0.5:85:15 mg/kg), atropine:ketamine:detomidine (0.05: 60:10 mg/kg) or glycopyrrolate: ketamine:detomidine (0.5:60:10). Similarly six groups of rabbits (n = 5) received an IM injection of either saline, atropine (0.2 mg/kg), atropine (2 mg/kg), glycopyrrolate (0.1 mg/kg), ketamine:xylazine (35:10 mg/kg) or glycopyrrolate:ketamine:xylazine (0.1:35:10 mg/kg). In rats, atropine sulfate (0.05 mg/kg) and glycopyrrolate (0.5 mg/kg) produced an increase in heart rate for 30 and 240 min, respectively. In rabbits atropine sulfate at either 0.2 or 2.0 mg/kg did not induce a significant increase in heart rate, but glycopyrrolate (0.1 mg/kg) elevated the heart rate above saline treated animals for over 50 min. Both atropine and glycopyrrolate provided protection against a decrease in heart rate in rats anesthetized with ketamine: xylazine (85:15 mg/kg) or ketamine: detomidine (60:10 mg/kg); however, glycopyrrolate was significantly more effective in maintaining the heart rate within the normal range. Glycopprrolate also prevented a decrease in heart rate in rabbits anesthetized with ketamine:xylazine (35:5 mg/kg). Neither glycopyrrolate nor atropine influenced respiration rate, core body temperature or systolic blood pressure when used alone or when combined with the injectable anesthetic. Glycopyrrolate is an effective anticholinergic agent in rabbits and rodents and more useful as a preanesthetic agent than atropine sulfate in these animals.     

Influence of the mode of ventilation on ketamine/xylazine requirements in rabbits

OBJECTIVE: To evaluate the effect of the mode of mechanical ventilation (MV) on the dose of intravenous anesthetic during 3 hours of ketamine/xylazine anesthesia. STUDY DESIGN: Prospective laboratory study. ANIMALS: Sixty-one adult male New Zealand White rabbits. METHODS: Rabbits were anesthetized (ketamine/xylazine 35 + 5 mg kg(-1), IM), the trachea was intubated and randomized to four groups - (1) CMV-1 (n = 14), ventilated with traditional conventional volume-cycled MV [V(T) = 12 mL kg(-1), RR = 20, positive end-expiratory pressure (PEEP) = 0 cmH(2)O]; (2) CMV-2 (n = 13), ventilated with a modern lung-protective regimen of volume-cycled MV (V(T) = 6 mL kg(-1), RR = 40, PEEP = 5 cmH(2)O); (3) HFPV (n = 17) ventilated with high-frequency percussive ventilation [high-frequency oscillations (450 minute(-1)) superimposed on 40 minute(-1) low-frequency respiratory cycles, I:E ratio = 1:1], oscillatory continuous positive airway pressure (CPAP) of 7-10 cmH(2)O, and demand CPAP of 8-10 cmH(2)O. (4) A fourth group, spontaneously ventilating (SV, n = 17), was anesthetized, intubated, but not ventilated mechanically. FiO(2) in all groups was 0.5. Anesthesia was maintained at a surgical plane by IV administration of a ketamine/xylazine mixture (10 + 2 mg kg(-1), as necessary) for 3 hours after intubation. Total dose of xylazine/ketamine administered and the need for yohimbine to facilitate recovery were quantitated. RESULTS: The total dose of xylazine/ketamine was significantly higher in the HFPV and SV groups compared with CMV-1 (p < 0.01). Fewer animals required yohimbine to reverse anesthesia in the HFPV than CMV-1 group (p < 0.05). CONCLUSIONS: The HFPV mode of MV led to higher doses of ketamine/xylazine being used than the other modes of MV. CLINICAL RELEVANCE: In rabbits, anesthetic dose for the maintenance of anesthesia varied with the mode of MV used. Investigators should be aware of the possibility that changing the mode of ventilation may lead to an alteration in the amount of drug required to maintain anesthesia.     

Effects of ketamine, xylazine, and a combination of ketamine and xylazine in Pekin ducks

Effects of ketamine, xylazine, and a combination of ketamine and xylazine were studied in 12 male Pekin ducks (7 to 12 weeks old; mean [+/- SD] body weight, 3.1 +/- 0.3 kg). After venous and arterial catheterization and fixation of a temperature probe in the cloaca, each awake duck was confined, but not restrained, in an open box in a dimly lit room. Blood pressure and lead-II ECG were recorded. Three arterial blood samples were collected every 15 minutes over a 45-minute period (control period) and were analyzed for pHa, PaCO2 and PaO2. After the control period, each duck was assigned at random to 1 of 3 drug groups: (1) ketamine (KET; 20 mg/kg of body weight, IV), (2) xylazine (XYL; 1 mg/kg, IV), and (3) KET + XYL (KET 20 mg/kg and XYL, 1 mg/kg; IV). Measurements were made at 1, 5, 10, 15, 30, 45, 60, and 90 minutes after drug administration. All ducks survived the drug study. Cloacal temperature was significantly (P less than or equal to 0.05) increased above control cloacal temperature at 90 minutes after the administration of ketamine, and from 10 through 90 minutes after administration of ketamine plus xylazine. In ducks of the KET group, pHa, PaCO2, and PaO2, remained unchanged after administration of the drug. In ducks of the XYL group, pHa and PaO2 decreased significantly (P less than or equal to 0.05) from control values for all time points up to and including 15 minutes after drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antinociceptive Effects of Oxymorphone-Butorphanol-Acepromazine Combination in Cats

Objective—To determine the antinociceptive effects of oxymorphone, butorphanol, and acepromazine individually and in combination to a noxious visceral stimulus in cats. Study Design—Randomized, blinded controlled study. Animals—Eight healthy mixed-breed cats (four male, four female) weighing 4.4 ± 1.2 kg and aged 1 to 2 years old. Methods—A silastic balloon catheter was inserted per rectum and inflated at various pressures. Physiological parameters (respiratory rate, pulse rate, and blood pressure) were also recorded. Subjects were administered individual and combined intravenous (IV) doses of 0.025, 0.05, 0.10, and 0.20 mg/kg oxymorphone and 0.025, 0.05, 0.10, and 0.20 mg/kg butorphanol. A further study of various ratios of butorphanol and oxymorphone (3:1, 2:1, 1:1, 1:2, and 1:3), at a combined equivalent dose of 0.1 mg/kg, was performed in four cats per dose combination. In a separate study, four cats were administered combined IV doses of 0.05 mg/kg each of oxymorphone and butorphanol or 0.05 mg/kg each of oxymorphone, butorphanol, and acepromazine. Results—Combined doses of 0.05 and 0.10 mg/kg of oxymorphone and butorphanol showed mainly additive with some synergistic antinociceptive interactions and the combined dose of 0.2 mg/kg of each agent demonstrated additional antinociceptive effects, P < .05. Additional studies showed that various ratios of the two agents at a total combined dose of 0.10 mg/kg IV did not produce levels of antinociception that were significantly different from each other, P > .05. Acepromazine (ACE) significantly increased the magnitude of antinociception at 15 minutes when administered in combination with oxymorphone and butorphanol, P < .05. Also, physiological variables were unaffected by these drug combinations. Conclusions—Low doses of oxymorphone and butorphanol in combination can produce greater levels of antinociception than when used individually. ACE, in conjunction with oxymorphone and butorphanol, produced even greater levels of antinociception than the two-opioid drug combination. Clinical Relevance—Oxymorphone, butorphanol, and ACE can be used in combination to produce additive or synergistic effects without adverse effects in cats. These data suggest that ACE and butorphanol at low doses given as preanesthetic medication followed by a mu opioid (eg, oxymorphone) after surgery at low doses may provide an effective method of pain management in the cat.     

Immobilization of goitred gazelles (Gazella subgutterosa) and Arabian mountain gazelles (Gazella gazella) with xylazine-ketamine.

Xylazine combined with ketamine successfully immobilized free-ranging and captive goitred gazelles (Gazella subgutterosa) and Arabian mountain gazelles (Gazella gazella). One hundred thirty immobilizations were performed on 58 individuals. When administered i.m. via dart to free-ranging gazelles, xylazine (125 mg/ml) combined with ketamine (100 mg/ml) produced smooth induction and recovery. Mountain gazelles required higher dosages (11.7-15.2 mg/kg xylazine and 9.3-12.2 mg/kg ketamine) than goitred gazelles (6.8-7.4 mg/kg xylazine and 5.4-5.9 mg/kg ketamine). For manually restrained captive gazelles of both species, i.v. xylazine (11 mg/ml) combined with i.v. ketamine (44 mg/ml) immobilized the gazelles at considerably lower doses (0.4-1.0 mg/kg xylazine and 1.4-3.9 mg/kg ketamine). These anesthetic combinations are useful alternatives to ultrapotent narcotics in these gazelle species.     

Effects of anesthetic agents on serum parathyroid hormone and calcium concentrations in mice

OBJECTIVE: To determine the effects of three anesthetic regimens on serum calcium and parathyroid hormone (PTH) in mice. STUDY DESIGN: Prospective experimental study. ANIMALS: Twenty-seven, 12-week-old, FVB mice. METHODS: Mice were anesthetized with either isoflurane, a combination of ketamine plus xylazine (100 and 10 mg kg(-1), respectively) or ketamine alone (100 mg kg(-1)). Blood was collected before and after the induction of anesthesia. Serum calcium and PTH concentrations were measured and compared. RESULTS: Isoflurane or ketamine did not significantly alter either serum calcium or serum PTH concentrations. A combination of ketamine plus xylazine significantly increased serum PTH, but not serum calcium concentrations. CONCLUSIONS: A combination of ketamine and xylazine should be avoided prior to collection of blood for measurement of serum PTH concentrations. Isoflurane is suitable for this purpose.     

Euthanasia of rabbits by intravenous administration of ketamine

Six New Zealand White rabbits (5 females and 1 male) were anesthetized with a combination of xylazine (4.3 mg/kg of body weight) and ketamine (29.1 mg/kg) administered IM. The rabbits were then attached to instruments that continuously monitored blood pressure and electrocardiographic and electroencephalographic values. Each rabbit was then administered a lethal dose of ketamine (600 mg, IV). Within 90 seconds after injection of the ketamine, brain death developed and the heart rate and blood pressure decreased greatly. Circulatory activity persisted for a maximum of 240 seconds. This method of euthanasia did not result in histopathologic changes in tissue specimens evaluated. Although death occurred rapidly, extensive muscle contractions made euthanasia of rabbits with ketamine aesthetically unacceptable. Therefore, this method would not be a suitable means of euthanasia for routine use in rabbits.     

Guaifenesin-Ketamine-Xylazine Infusions to Provide Anesthesia in Donkeys

The purpose of this study was to determine a satisfactory combination of guaifenesin, ketamine, and xylazine (GKX) that would produce safe and satisfactory total intravenous anesthesia in donkeys for use under field conditions. Donkeys require higher amounts of ketamine in GKX to achieve satisfactory anesthetic levels without producing excessive depression with guaifenesin. Five adult standard donkeys (average weight, 264 kg) were anesthetized with 1.5 mg/mL ketamine, 0.5 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-1); 2.0 mg/mL ketamine, 0.5 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-2); or 2.0 mg/mL ketamine, 0.75 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-3). For the first trial, two donkeys received GKX-1, two received GKX-2, and one received GKX-3. One donkey received GKX-1, one received GKX-2, and three received GKX-3 for the second trial. In the final trial, two received GKX-1, two received GKX-2, and one received GKX-3. Donkeys were sedated with xylazine (1.1 mg/kg body weight) intravenously, and anesthesia was induced using intravenous GKX-1, GKX-2, or GKX-3. Anesthesia was maintained for 45 minutes; temperature, respiration rate, heart rate, hemoglobin saturation, partial pressure of arterial oxygen (PaO₂), partial pressure of carbon dioxide in arterial gas (PaCO₂), and pH were measured. There was no significant difference between combinations for temperature, respiration rate, heart rate, hemoglobin saturation, PaCO₂, or pH. At 30 and 45 minutes, GKX-3 produced significantly (P < .05) lower PaO₂ values than GKX-1 and GKX-2. GKX-3 is not recommended for field use in donkeys because of respiratory depression (PaO₂= 48.7 [±5.84] and 46.0 ± 3.11 mmHg at 30 and 45 minutes, respectively), whereas more voluntary movement was apparent with GKX-1. GKX-2 produced satisfactory anesthesia without significant respiratory depression in donkeys and should produce safe and effective anesthesia in donkeys under field conditions.