TECHNIQUE

Medetomidine-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 Note: medetomidine doses are mainly given in microgrammes per kilogram bodyweight, indicated in the text below as "g/kg". Other drug doses are usually given in milligrams per kilogram bodyweight (mg/kg).

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, the bear should be moved to a safe, well-controlled situation to allow a quiet induction and recovery away from physical hazards and other animals. (B407.w18)
  • 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:

  • Medetomidine-ketamine is given by intramuscular injection with the two drugs mixed in the same syringe.
  • Usually administered by remote injection (darting) or if the bear is in a confined space, by pole syringe.

Suggested doses:

  • Medetomidine 30-50 g/kg plus Ketamine 1-2.5 mg/kg. (B407.w18)
  • CAUTION: if too low a dose of ketamine is given, sudden recoveries may occur: one captive female Ursus arctos - Brown bear, having not responded to blood sampling, suddenly stood when its screaming cub was carried past. A wild adult male, anaesthetised with 48 g/kg medetomidine, 1.0 mg/kg ketamine, plus an additional 1.0 mg/kg ketamine, suddenly attacked its handlers 78 minutes after darting, without any previous signs indicating arousal. (J2.21.w3)
  • In Ursus arctos - Brown bear:
    • In captive Ursus arctos - Brown bear, medetomidine 20-30 g/kg + ketamine 0.5-1.0 mg/kg gave an induction time averaging six minutes. (P7.1.w10)
    • In captive Ursus arctos - Brown bear (12 adults, 11 subadults or juveniles) 25-35 g/kg medetomidine plus 0.7 - 1.5 mg/kg ketamine was sufficient for translocation, tattooing and castration. However, in wild brown bears shot from a helicopter, higher doses were needed. (J2.21.w3)
    • In eight Ursus arctos - Brown bear, medetomidine 30-40 g/kg + ketamine 1.0-1.5 mg/kg produced adequate immobilisation. (P1.1990.w6)
    • In wild Ursus arctos - Brown bear darted from a helicopter, medetomidine 60-80 g/kg + ketamine 1.0-1.6 mg/kg was required. (P7.1.w10)
      • Supplementation with ketamine, 1.0 mg/kg intravenously was required to enable an incisor to be extracted without the bear showing a pain reaction. (P7.1.w10)
    • In captive European brown bears used for physiology studies: (J200.34.w1)
      • In bears < 1 year of age, medetomidine 45 - 106 g/kg plus ketamine 1.4 - 2.8 mg/kg.
      • In bears 1 year to 1 year 11 months, medetomidine 73 - 131 g/kg plus ketamine 2.0 - 4.0 mg/kg.
      • In bears 2 years old, medetomidine 70 - 128 k plus ketamine 2.0 - 3.9 mg/kg.
      • In bears three years plus, medetomidine 89 - 158 g/kg plus ketamine 2.0 - 4.0 mg/kg.
    • In captive European brown bears in Finland: (J400.109.w1)
      • Medetomidine 70-119 g/kg plus ketamine 2.0 - 3.4 mg/kg, for immobilization. Total doses, including top-ups, for sampling or surgical transmitter operations of more than one hour, 120-145 g/kg plus ketamine 4.0 - 4.5 mg/kg. (J400.109.w1)
  • In Ursus maritimus - Polar bear
    • doses used varied from medetomidine 77-352 g/kg and ketamine from 1.92-8.81 mg/kg. Variation was due to incorrect body mass estimation and in some cases (four of 12 bears) multiple injections required. (J2.30.w5)
    • In nine captive Ursus maritimus - Polar bear, medetomidine 30 g/kg + ketamine 1.0-1.5 mg/kg produced adequate immobilisation. (P1.1990.w6)
    • In five Ursus maritimus - Polar bear, 159 +/- 34 g/kg medetomidine and 4.0 +/- 0.8 mg/kg ketamine. (P1.1996.w5)
    • In captive Ursus maritimus - Polar bear (two adult females and three subadults), medetomidine 20-33 ug/kg plus ketamine 1-3 mg/kg (mean 1.5 mg/kg) was sufficient to enable translocation and skin biopsies. (J2.21.w3)
  • In Ursus thibetanus - Asiatic black bear (Himalayan bear): 
    • medetomidine 30-40 g/kg + ketamine 1.0-1.5 mg/kg produced adequate immobilisation. (P1.1990.w6)
  • In Ursus americanus - American black bear
    • Medetomidine 0.04 mg/kg, plus ketamine 1.5 mg/kg. (B345.6.w6)
    • medetomidine 30-40 g/kg + ketamine 1.0-1.5 mg/kg produced adequate immobilisation. (P1.1990.w6)
  • In Helarctos malayanus - Sun bear:
    • Medetomidine 0.07 mg/kg, plus ketamine 3 mg/kg. (B345.6.w6)
      • Ketamine 2.0 mg/kg can be given as a supplemental drug if required. (B345.6.w6)

During induction:

  • Induction is rapid. (B407.w18)
  • In Ursus maritimus - Polar bear, induction took 4.0 +/- 0.7 minutes in bears requiring a single dose of anaesthetic. (J2.30.w5)
  • Ursus maritimus - Polar bear generally remained still during induction, slowly sinking to recumbency. (J2.30.w5)
    • Note: Two individuals, having become recumbent and appearing to be safely immobilised, rose to standing on approach 15 minutes after drug administration. (J2.30.w5)
  • In five Ursus maritimus - Polar bear, 159 +/- 34 g/kg medetomidine and 4.0 +/- 0.8 mg/kg ketamine, bears were immobilised in 3.9 +/- 2.4 minutes. (P1.1996.w5)

During anaesthesia:

  • Flaccid, no muscle rigidity. (J2.30.w5)
  • Eyes remain in a fixed stare. (J2.30.w5)
  • Expect bradycardia: heart rates may be 30-40 beats per minute. (D156.w2)
  • Usually remain unresponsive to noxious stimuli. (J2.30.w5)
    • In five Ursus maritimus - Polar bear given 159 +/- 34 g/kg medetomidine and 4.0 +/- 0.8 mg/kg ketamine, compression of the nail bed with haemostats did not affect heart rate or blood pressure, suggesting good analgesia. (P1.1996.w5)
  • In Ursus arctos - Brown bear, respiration was 4-8 beats per minutes and stable, heart rate was 60-70 bpm in five subadults but bradycardia (24-32 bpm) was noted in three adult females. (P7.1.w10)
  • In Ursus maritimus - Polar bears, respiration consisted of single deep breaths separated by intervals of 10-50 seconds. Pulse rate was about 60-70 bpm, but sometimes transient bradycardia (< 40 bpm) occurred early in the first 15 minutes. Mean rectal temperatures varied from about 38.2 C to 38.6 C. Moderate to marked hypoxaemia sometimes occurred, most commonly after top-up doses were administered. (J2.30.w5)
  • In five Ursus maritimus - Polar bear given 159 +/- 34 g/kg medetomidine and 4.0 +/- 0.8 mg/kg ketamine, at 30 minutes after administration, body temperature was 37.0 +/- 0.7 C, heart rate 39 +/- 9 bpm, respiratory rate 4 +/- 3 breaths per minute, mean arterial pressure 205 +/- 28 mm Hg, pH (arterial blood) 7.3 +/- 0.5, base excess -5.6 +/- 2, PaO2 70 +/- 16, PaCO2 40 +/- 9 and haemoglobin concentration 160 +/- 16 g/L. Compared with tiletamine-zolazepam anaesthesia, mean arterial pressure was significantly (p<0.05) higher, heart rate significantly lower and haemoglobin concentration significantly higher, while the PaO2, respiratory rate trend was lower and the PaCO2 trend was higher. Overall, ventilation and oxygenation were excellent. (P1.1996.w5)

Duration of anaesthesia:

Reversal of anaesthesia with Atipamezole (alpha-2 antagonist):

  • This reverses the medetomidine.
  • Atipamezole is given at five times the dose of medetomidine which was used for anaesthesia. (B345.1.w1, B407.w18)
    • i.e. 0.2 mg/kg atipamezole to antagonise medetomidine given at 0.04 mg/kg. (B345.6.w6)
  • In Helarctos malayanus - Sun bear: 0.35 mg/kg atipamezole, half intravenously, half intramuscularly (to reverse following medetomidine 0.07 mg/kg, plus ketamine 3 mg/kg). (B345.6.w6)
  • In Ursus maritimus - Polar bears, atipamezole was given at 166 +/- 88 g/kg after 205.6 +/- 6.4 minutes of handling. Bears recovered within 2.0 +/- 0.4 minutes if the whole dose was given intravenously, or 15.4 +/- 4.7 minutes if it was given half intramuscularly half intravenously. (J2.30.w5)
  • Atipamezole should be given at five times the dose of medetomidine used for induction. Give half of the reversal dose intramuscularly and the other half intravenously. (P1.1990.w6)
    • A lower dose may be used if the atipamezole is given more than one hour after administration of the medetomidine. (P1.1990.w6)

During recovery:

  • If the full reversal dose of atipamezole is given intravenously, the animal tends to be excited on recovery. (P1.1990.w6)
  • Ursus maritimus - Polar bears sometimes showed "heightened awareness and threatening behaviour" following reversal of the medetomidine. (J2.30.w5)
  • If half the dose of atipamezole is given intravenously and half intramuscularly, recovery tends to be rapid but calm. Animals usually stand within 10 minutes, with hind limb ataxia for about a further 5-10 minutes. (P1.1990.w6)
  • Recovery may take 20-30 minutes. (B407.w18)
  • Caution: recovery sometimes can be very rapid. (V.w6)
Appropriate Use (?)
  • Safe for "knock-down" of bears. (P1.1990.w6)
  • Gives a rapid knock-down. (B407.w18)
  • Useful for short procedures in smaller bears, with experienced personnel. (D156.w2)
  • The total volume is lower than with xylazine-ketamine, which is advantageous. (D156.w2, P7.1.w10)
  • Low volume (e.g. 3.0 mL is sufficient to knock down a polar bear). (B407.w18)
  • The dose of ketamine used is low, therefore reversal of the medetomidine with an alpha-2 antagonist does not result in side-effects of rigidity or convulsions from the ketamine. (D156.w2)
  • Medetomidine-ketamine can be used with a low dose of ketamine, has a low volume for injection (therefore small dart when given by remote injection), has a rapid onset of deep sedation, good muscle relaxation, and good reversal following administration of atipamezole, with shorter and lesser ataxia than seen with xylazine-ketamine. (P1.1990.w6)
  • Can be reversed, giving rapid recovery. (P7.1.w10)
Notes
  • Following induction of anaesthesia with medetomidine and ketamine, isoflurane at 2-2.5% or halothane at 1% or less is sufficient for anaesthetic maintenance; higher concentrations can be used if required for deeper anaesthesia. (P1.1990.w6)
  • Recovery following administration of atipamezole can take 20-30 minutes. (B407.w18)
Complications/ Limitations / Risk
  • Not recommended for larger bears; sudden recoveries have occurred in Ursus arctos - Brown bear and Ursus maritimus - Polar bear. (D156.w2, P1.1997.w9)
    • In one study, two of 12 Ursus maritimus - Polar bears, having become recumbent and appearing to be safely immobilised, rose to standing on approach 15 minutes after drug administration. (J2.30.w5)
  • If the full reversal dose of atipamezole is given intravenously, the animal tends to be excited on recovery. (P1.1990.w6)
  • Spontaneous recovery may occur. (B345.6.w6)
  • Avoid loud or sharp noises, and if possible prevent cubs vocalising while their mother is anaesthetised. (B345.6.w6)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted. (P9.2004.w4, J40.32.w1, D249.w10)
Equipment / Chemicals required and Suppliers
Expertise level / Ease of Use
Cost/ Availability
  • Cost and availability of drugs required may vary between countries.
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 B284.5.w5, B345.1.w1, B345.6.w6, B407.w18, B486.11.w11, D156.w2, J2.21.w3, J2.30.w5, J200.34.w1, J400.109.w1, P1.1990.w6, P1.1996.w5, P7.1.w10, V.w6

Return to Top of Page