TECHNIQUE

Xylazine-Ketamine Anaesthesia in Bears  (Disease Investigation & Management - Treatment and Care)

Summary Information
Type of technique Health & Management / Disease Investigation & Management / Techniques:
Synonyms and Keywords See also:
Description N.B. Information given in this page is to be used in conjunction with the relevant section on Bears in Treatment and Care - Anaesthesia and Chemical Restraint

Preparation for anaesthesia:

  • Whenever possible (with captive bears), the bear should be moved to a safe, quiet, well-controlled situation away from other bears. (B407.w18, D247.7.w7)
  • Avoid anaesthetising immediately after the bear has eaten, to reduce the risks associated with vomiting and regurgitation during induction, anaesthesia or recovery. (D156.w2)
    • Preferably starve for 24 hours before anaesthesia. (B407.w18)
    • Withhold water for eight hours and food for 24 hours before immobilization. (D247.7.w7)

Administration:

  • Give Xylazine plus Ketamine by intramuscular injection, mixed together in one syringe, by hand syringe in physically restrained bears (e.g. cubs), by pole syringe, or by remote injection. (J1.25.w11, J1.25.w6)
  • Injection into the shoulder/neck region rather than the rump is suggested to ensure injection into muscle rather than fat. (J1.17.w12, J1.21.w7)
  • Blowpipes can be used for intramuscular injection of bears restrained in foot-hold snares or in trapps (barrel or culvert traps). (J46.271.w1, J345.13.w6)
  • Hand-injection can be used for additional doses in recumbent individuals. (J1.21.w8)
  • See: Intramuscular Injection of Bears

Suggested doses:

  • Usually a 1:2 Xylazine:Ketamine or a 1:1 ratio. (B10.48.w43) 
  • Xylazine 3-9 mg/kg + Ketamine 3-9 mg/kg OR xylazine 2-4.5 mg/kg + ketamine 5-9 mg/kg. (B10.48.w43)
  • Xylazine 2 mg/kg plus Ketamine 4-10 mg/kg. (B16.9.w9)
  • Xylazine 1-2 mg/kg plus Ketamine 5 mg/kg immobilises most bear species. (J213.4.w3)
  • Xylazine 2 mg/kg plus ketamine 5-8 mg/kg. (B407.w18)
  • Ursus americanus - American black bear: 
    • Xylazine 2 mg/kg plus ketamine 4.4 mg/kg. (B345.6.w6)
      • Ketamine 2.2 mg/kg as a supplemental dose if required. (B345.6.w6)
    • Xylazine 2 mg/kg + ketamine 4 mg/kg. (D156.w2)
    • Approximately 2:1 ketamine:xylazine ratio (1.5-17.1 mg ketamine + 0.9-10.0 mg/kg xylazine). (J1.15.w11)
    • Range 4 mg/kg ketamine plus 2 mg/kg xylazine to 16 mg/kg ketamine plus 8 mg/kg xylazine, mean 8 mg/kg ketamine plus 4 mg/kg xylazine, in wild bears. (J59.24.w1)
    • Initial intended dose 2.2 mg/kg xylazine plus 4.4 mg/kg ketamine in wild bears. (J1.25.w6)
  • Ursus arctos - Brown bear:
    • In captive bears, xylazine 1.0 mg/kg plus ketamine 10 mg/kg to produce immobilization for handling. (J27.53.w1)
    • In wild, barrel-trapped Ursus arctos yesoensis in Hokkaido, doses used were xylazine 1.0 +/- 0.3 mg/kg (mean +/- SD; range 0.4 - 1.4 mg/kg) plus ketamine 15.4 +/- 7.1 mg/kg (range 6.8 - 33.3 mg/kg). (J27.53.w1)
      • Atropine was given as premedication, at 0.028 +/- 0.09 mg/kg (mean +/- SD; range 0.012-0.040 mg/kg). (J27.53.w1)
    • Wild bears, caught in snares, 11 mg/kg ketamine plus 6 mg/kg xylazine. (J1.41.w5)
    • Xylazine 11 mg/kg + Ketamine 11 mg/kg. (B345.6.w6)
      • Note: Xylazine plus ketamine is not currently recommended for anaesthesia of adult brown bears [2002]. (D156.w2)
  • Ursus maritimus - Polar bear: 
    • For cubs-of-the-year, 3 mg/kg xylazine plus 3 mg/kg ketamine. (B345.6.w6)
    • For cubs of the year, effective doses were 1.6 - 5.0 mg  (mean 2.8 mg/kg) each drug, with first effect after 1.0-3.0 minutes (mean 1.6 minutes) and immobilisation by 1.0-4.0 minutes (mean 1.3 minutes). (J1.17.w12)
    • For older bears, 7 mg/kg xylazine plus 7 mg/kg ketamine. (B345.6.w6)
    • For older bears, effective doses were 3.3 - 10.6 mg/kg (mean 6.8 mg/kg) each drug, with first effect after 1.0-10.0 minutes (mean 4.6 minutes) and induction by 4.0-30.0 minutes (mean 13.2 minutes). (J1.17.w12)
    • Bears were tractable (handleable) for a period of at least 30 minutes. (J1.17.w12)
    • In bears of at least one year old, doses of 4.1 - 30.8 mg/kg, median 11.0 mg/kg in one year, and 10.7 mg/kg in a second year. (J1.21.w7)
  • Melursus ursinus - Sloth bear:
    • 2 mg/kg xylazine plus 7.5 mg/kg ketamine. (B345.6.w6)
    • Xylazine 1.4 - 2.44 mg/kg plus ketamine 5.80 - 9.75 mg/kg. (J4.189.w11)
  • Ursus thibetanus - Asiatic black bear:
    • Xylazine 2 mg/kg estimated body mass plus ketamine 4 - 5 mg/kg estimated body bass for wild bears following capture in traps. The drugs were administered intramuscularly using a blowpipe. (J46.271.w1)
    • Xylazine 1 mg/kg plus ketamine 15 mg/kg in culvert-trapped bears, for handling and attaching radio-collars. The drugs were administered intramuscularly using a blowpipe. (J345.13.w6)
  • Tremarctos ornatus - Spectacled bear
    • Xylazine 0.6 - 3.0 mg/kg plus ketamine 4.0 - 14.0 mg/kg. (P77.1.w19)

During induction:

  • Ataxia occurs within 5-8 minutes and recumbency in 15 minutes. (B16.9.w9)
  • Described in detail for Ursus americanus - American black bear:
    • Relaxation of the hind legs causing staggering or sitting generally occurs within 1-3 minutes. (J1.15.w11)
    • The forelegs lose coordination and the bear's head droops. (J1.15.w11)
    • The bear usually assumes sternal recumbency then lateral recumbency. (J1.15.w11)
    • The neck and head muscles relax; the external ear still responds to sharp sounds prior to full development of anaesthesia.
    • Occasionally, bears groan late in the induction phase. (J1.15.w11)
    • Vomiting may occur during induction in recently-fed bears. (J1.15.w11)
  • The eyes do not close. (J1.15.w11, J1.17.w12, J1.21.w7)
  • Incompletely sedated bears are able to focus on movement and react to loud, sharp sounds. (J1.17.w12)
  • Undersedated bears show "persistent slow walking with some staggering" and often fall then continue walking (J1.17.w12)
  • In wild Ursus americanus - American black bear, induction took mean 17.7 minutes; a second injection of xylazine plus ketamine was required to make the bear tractable in 15 bears (44% of immobilisations). (J59.24.w1)
  • In wild, barrel-caught Ursus arctos - Brown bear, smooth induction was noted. Induction ranged from 4 - 82 minutes (mean 24 min.). (J27.53.w1)
  • In Melursus ursinus - Sloth bear with xylazine 1.4 - 2.44 mg/kg plus ketamine 5.80 - 9.75 mg/kg:
    • Induction (to sternal recumbency) took 2-25 minutes; ataxia and disorientation were noted prior to development of sternal recumbency. Immobilisation (lateral recumbency) occurred after 4-30 minutes. (J4.189.w11)
    • All bears showed moderate salivation; two vomited white, frothy liquid (food and water had been withheld for 24 hours prior to immobilisation). (J4.189.w11)

During anaesthesia:

  • Approach with care, particularly if the bear took a relatively long time to become recumbent or if several darts were required. (P84.1.w1)
  • Bears anaesthetised with this drug combination may arouse suddenly. (D156.w2)
  • Note: Incompletely sedated bears are able to focus on movement and may react to loud, sharp sounds. (J1.17.w12)
  • Protect the eyes with a bland ophthalmic ointment and a blindfold. (J1.15.w11, J1.17.w12, J1.21.w7)
  • Respiration is regular, but the rate of respiration may reduce during anaesthesia. (J1.15.w11)
  • Atropine (0.02 mg/kg) may be required to control salivation. (B407.w18)
  • Diazepam, 0.05-0.1 mg/kg can be used in case of muscular spasm. (B407.w18)
  • Artificial respiration may be required in bears which have been overdosed. (J1.25.w11)
  • In wild Ursus americanus - American black bear, heart rate was 88.8 +/- 4.3 bpm (mean +/- SE), range 80-100 bpm, respiratory rate was 32.0 +/- 7.3 breaths per minute (range 7-60) and was not correlated with body temperature (mean 39.7 +/- 0.42 C, range 37.2-41.9 C). (J59.24.w1)
  • In wild, barrel-caught Ursus arctos - Brown bear, good myorelaxation with slight quivering, and a high safety margin were noted. heart rates in three bears were 64, 66 and 76 bpm. (J27.53.w1)
  • Monitor rectal temperature. 
    • Hyperthermia may occur particularly in bears which have been chased by helicopter to enable darting. (J1.17.w12)
    • The depressed respiratory rate increases the risk of hyperthermia, particularly in high ambient temperatures. (J1.21.w7)
    • Cooling is required if bears develop rectal temperatures above 40 C; alternatively/additionally the anaesthetic needs to be reversed quickly. (J59.24.w1)
    • In wild Ursus americanus - American black bear, mean rectal temperatures varied with season and between males and females. Panting was observed in bears with rectal temperatures of 42.0 C or greater. (J1.25.w6)
      • Male bears were more likely to become hyperthermic than were female bears, Larger bears were more likely to become hyperthermic than were smaller bears. (J1.25.w6)
      • Mean +/- SE rectal temperatures of male bears were: spring 40.1 +/- 0. C3, early summer 39.5 +/- 0.2 C, late summer 40.1 +/- 0.4 C, early fall 40.1 +/- 0.3 C, late fall 38.5 +/- 0.6 C. (J1.25.w6)
      • Mean +/- SE rectal temperatures of female bears were: spring 39.2 +/- 0.7 C, early summer 39.6 +/- 0.3 C, late summer 39.6 +/- 0.4 C, early fall 39.7 +/- 0.3 C. late fall 37.8 +/- 0.7 C. during denning, 37.4 +/- 0.7 C. (J1.25.w6)
    • In wild, barrel-caught Ursus arctos - Brown bear, rectal temperatures in 12 bears were 37.5 to 41.3 C.. (J27.53.w1)

Duration of anaesthesia:

  • If this combination is used without reversal, recovery is slow. (J1.21.w7)
  • The period of restraint lasts about 40-60 minutes. (B16.9.w9)
  • Full recovery usually takes 2-3 hours for bears not given a reversal agent. (B16.9.w9)

Reversal with an alpha-2 antagonist:

  • Xylazine can be antagonised with atipamezole (preferred), idazoxan, tolazoline or yohimbine. (B345.1.w1, B345.6.w6, D156.w2)
    • [Editor's note: most of the data below concern yohimbine, since this was used in the studies referred to, in the 1980s. Atipamezole is now normally used for reversing alpha-2 agonist drugs.]
  • Atipamezole, at 5:1 (i.e. five times the dose in mg/kg of atipamezole as the dose of xylazine that was given) can be used. (J213.4.w3)
  • The xylazine can be antagonised using yohimbine (0.1 mg/kg) or idazoxan (0.05 mg/kg) [for the initial drug combination of xylazine 2 mg/kg plus ketamine 5-8 mg/kg.]. (B407.w18)
  • Antagonising the xylazine with yohimbine (0.3 mg/kg, IV or IM) gives rapid reversal, to standing usually within less than 10 minutes. (J213.4.w3)
  • In Ursus americanus - American black bear, following immobilization with xylazine 2 mg/kg, ketamine 4.4 mg/kg, reversal with yohimbine at 0.15 mg/kg. (B345.6.w6)
  • In 11 Ursus americanus - American black bear reversed with 0.05 mg yohimbine given intramuscularly, only two bears (18%) recovered (to walking) in under 10 minutes, while in 35 bears given yohimbine intravenously, 31 (89%) recovered in less than 10 minutes (median five minutes). (J345.7.w1)
  • In Ursus maritimus - Polar bear, yohimbine was injected intravenously about 90 minutes after original dosing with xylazine and ketamine. Recovery occurred after a median of 10 minutes (mean 14.6 +/- 18.8 minutes), with some bears being on their feet within five minutes. (J1.21.w7)
  • Melursus ursinus - Sloth bear, given 2 mg/kg xylazine plus 7.5 mg/kg ketamine, reverse with 0.125 mg/kg yohimbine. (B345.6.w6)
  • In Melursus ursinus - Sloth bear, intravenous injection with yohimbine (0.125 mg/kg) reduced recovery times considerably: 2-20 minutes to arousal and 17-51 minutes to standing. (J4.189.w11)
  • In Ursus arctos - Brown bear, yohimbine 0.125 mg/kg. (B345.6.w6)
  • Avoid reversing the xylazine too soon - not until AT LEAST 30 minutes after the last injection of ketamine. (B345.1.w1)
    • Reversal of the xylazine with an alpha-2 antagonist can unmask the adverse effects of ketamine and may result in rigidity, hyperthermia and convulsions. (B345.1.w1, D156.w2)

During recovery:

  • Coordination is regained in reverse order to that in which it is lost during induction. (J1.15.w11)
  • If bears are undisturbed, the recovery phase generally takes at least ten minutes, although it may take less than three minutes. (J1.15.w11)
  • If bears are disturbed (auditory, visual or tactile stimulation) during the recovery phase they return to standing faster than if they are undisturbed. (J1.15.w11)
  • Following administration of yohimbine, heart rate and respiratory rate increase (from five to 12 breaths per minute and 51 to 79 bpm) usually within one minute. (J1.21.w7)
Appropriate Use (?)
  • Ketamine 5 mg/kg plus xylazine 1-2 mg/kg immobilises most bear species. (J213.4.w3)
  • Xylazine-ketamine is safe for the bear, with a high therapeutic index and a low fatality rate. (B16.9.w9, J1.17.w12)
  • Xylazine-ketamine in most species produces good muscle relaxation, good analgesia and a calm recovery. (P1.1990.w6)
  • This drug combination may be suitable for use in small bears for short procedures. (D156.w2)
  • The xylazine can be antagonised with yohimbine or idazoxan. (B407.w18, D156.w2)
    • In Melursus ursinus - Sloth bear, intravenous injection with yohimbine (0.125 mg/kg) reduced recovery times considerably: 2-20 minutes to arousal and 17-51 minutes to standing. (J4.189.w11)
  • Unlike with ketamine alone, muscle rigidity and convulsions were not seen in 45 immobilisations of Ursus maritimus - Polar bear. Bears had relaxed muscles, slow, deep breathing, no excess salivation and no convulsions. (J1.17.w12)
  • In Ursus americanus - American black bears, the anaesthesia was characterised by a smooth induction, relaxed muscles and a smooth recovery. (J1.15.w11)
  • The combination of xylazine with ketamine reduces the ketamine dose (compared with ketamine used alone) and the hyperexitation and muscle spasm seen with ketamine when used alone. (B407.w18)
Notes
  • This was the preferred drug combination in bears prior to the availability of tiletamine-zolazepam. (D156.w2)
  • In Ursus americanus - American black bears, heart rates generally declined during the tractable phase, from mean 62 bpm early on to mean 41 bpm late in the tractable phase. The respiratory rate varied from 5-34 breaths per minute (plus one bear at 84 breaths/minute). Body temperature varied from 36.5 - 41.0 C, mean 38.3 C. (J1.15.w11)
  • In wild Ursus maritimus - Polar bear, cubs anaesthetised with this combination had respiratory rates of 9.0-13.0/min, heart rates of 63-102 bpm and rectal temperatures of 36.4-39.0 C; older bears had respiratory rates of 5.0-17.0/ minute, heart rates of 36-90 bpm and rectal temperature of 36.4-40.2 C. (J1.17.w12)
  • Incompletely sedated bears are able to focus on movement and react to loud, sharp sounds. (J1.17.w12)
  • Undersedated bears show "persistent slow walking with some staggering" and often fall then continue walking (J1.17.w12)
  • Undersedation may be due to underdosing or injection into fat rather than muscle. (J1.17.w12)
  • Note: Two bears immobilised with ketamine alone did not wake when given intravenous yohimbine, although their heart rates increased appreciably; this indicates that yohimbine does not antagonise the effects of ketamine. (J345.7.w1)
Complications/ Limitations / Risk
  • Bears anaesthetised with this drug combination may arouse suddenly. (D156.w2, B345.6.w6)
    • This is no longer the drug combination of choice for bear immobilisations, particularly not for larger, more aggressive bears. (D156.w2)
    • It has been necessary to shoot wild bears which suddenly woke and were dangerous to researchers. (P84.1.w1)
  • Avoid loud or sudden noises when this drug combination is used, and if possible prevent cubs from vocalising while their mother is immobilized. (B345.6.w6)
  • Depending on the concentrations of drugs available, large volumes may be required, so that two or three darts have to be fired in quick succession to inject an appropriate dose in large bears. (B16.9.w9)
  • There are sometimes considerable variations between individuals in the doses required for immobilization. (P84.1.w1)
  • In Tremarctos ornatus - Spectacled bears, although this combination has been used successfully in some captured wild bears, lack of effect has been observed in some wild and a stressed captive bear, presumably associated with the stress response [dose rates not stated]. (V.w99)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted. (P9.2004.w4, J40.32.w1, D249.w10)
  • The eyes generally do not close and should be protected with a bland ophthalmic ointment and a blindfold. (J1.15.w11, J1.17.w12, J1.21.w7)
  • Xylazine-ketamine commonly produces slight respiratory depression. (P1.1990.w6)
  • The depressed respiratory rate increases the risk of hyperthermia [Hyperthermia - Sunstroke - Heatstroke in Waterfowl, Elephants and Bears], particularly in high ambient temperatures. (J1.21.w7)
  • Side effects seen in some bears include convulsions and hyperthermia. (D156.w2, P84.1.w1)
  • Hyperthermia may occur in bears which have been chased by helicopter to enable darting. (J1.17.w12)
  • It is possible that convulsions may sometimes be due to hyperthermia. (P84.1.w1)
  • If this combination is used without reversal, recovery is slow. (J1.21.w7)
  • Recovery may take 2-3 hours if the xylazine is not antagonised. (J4.189.w11)
  • In Ursus americanus - American black bears, occasional vomiting was noted and the eyes did not close. (J1.15.w11)
  • Note: Reversal of the xylazine with yohimbine can unmask the adverse effects of ketamine - rigidity, hyperthermia and convulsions. (D156.w2)
    • In one juvenile Melursus ursinus - Sloth bear, following intravenous injection of yohimbine, a mild seizure developed four minutes later and lasted 45 seconds. (J4.189.w11)
    • In Ursus maritimus - Polar bears, out of 48 bears, 16 showed slight twitching of either the extremities or the whole body after yohimbine was given, and one 20-month-old cub developed seizures within four minutes, lasting for more than 10 minutes, and was found dead the following day. (J1.21.w7)
    • Seizures can be treated with diazepam, 0.01-0.4 mg/kg. (B10.48.w43)
  • SAFETY NOTE: reversal can be rapid following administration of yohimbine; personnel and equipment should be removed to safe locations before the reversal agent is administered to the bear. (J1.21.w7)
Equipment / Chemicals required and Suppliers
  • Xylazine

  • Ketamine

  • Alpha-2 antagonist, e.g. atipamezole (preferred), idazoxan, tolazoline or yohimbine, to enable reversal of the xylazine. (B345.1.w1, D156.w2)

  • Injection equipment, including 3 cm needles for cubs, 4.5 cm needles for older bears (longer needles may be required). (J1.15.w11)

Expertise level / Ease of Use
  • Bears are large, powerful carnivores. Anaesthesia of bears should be carried out by experienced personnel. (V.w6)
Cost/ Availability
  • Relatively inexpensive.
Legal and Ethical Considerations
  • In some countries there may be legislation restricting the use of this type of technique to licensed veterinarians. For example in the UK: "The Veterinary Surgeons Act 1966 (Section 19) provides, subject to a number of exceptions, that only registered members of the Royal College of Veterinary Surgeons may practice veterinary surgery." (see: LCofC1 - RCVS Guide to Professional Conduct 2000 - Treatment of Animals by Non-Veterinary Surgeons).).

Use of Drugs (Medication):

  • Many drugs are not registered for use in particular species and care should be taken in their use, with proper regard for possible toxic effects. Consideration should be give to relevant legislation regarding the use of drugs.
  • In any country, drugs are unlikely to be specifically licensed for use in bears. 
    • In Europe the prescription cascade must be followed, and the client's informed consent should be obtained, whenever a drug is used which is not licensed for use in a given species. (B284.5.w5)
    • In the UK, guidelines regarding the use of drugs are set out in the Royal College of Veterinary Surgeons Guide to Professional Conduct 2000: (see: LCofC1 - RCVS Guide to Professional Conduct 2000 - Choice of Medicinal Products).
    • In the USA, the Food and Drug Administration (FDA) regulates specific conditions for the use of drugs in animals and people. The Animal Medicinal Use Clarification Act of 1996 allows extra-label use of approved animal and human drugs under certain conditions, with extra-label use being allowed "in non-food-producing animals if the drug is approved by the FDA, is used by or on order of a licenced veterinarian, and there is a valid veterinarian/client/patient relationship." In food-producing animals (including game wildlife species), additional conditions for extra-label use include that there is no approved alternative drug for such use (or if there is, it is clinically ineffective), the veterinarian has established a substantially extended withdrawal period; the treated animal can be individually identified (e.g. with an ear tag or a collar) and assigned withdrawal times can be assured, ensuring no illegal residues. (B486.11.w11)
  • Additionally, many drugs used for immobilisation are controlled substances in many countries, and appropriate registration/licences, records etc. for the country in which the drugs are being obtained/used must be followed.

Use of remote injection systems

  • In some countries a firearms licence may be required for use of remote injection equipment.
    • e.g. in the UK, anyone possessing a blow-pipe, dart-gun etc. which can be used to discharge tranquillising drugs (i.e. for remote injection), must be authorised by a Firearms Certificate. This is issued by the police. (B284.5.w5)
Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I. Boardman BVMS MRCVS (V.w6)
References B16.9.w9, B284.5.w5, B345.1.w1, B345.6.w6, B486.11.w11, D156.w2, J1.15.w11, J1.17.w12, J1.21.w7, J1.21.w8, J1.25.w11, J1.41.w5, J4.189.w11, J46.271.w1, J345.13.w6, P1.1990.w6, P77.1.w19, P84.1.w1, V.w6, V.w99

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