TECHNIQUE

Carfentanil 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)

The following is based on description of the use of carfentanil for anaesthesia of free-ranging Ursus maritimus - Polar bears. This drug may be used for immobilisation of polar bears in the wild when rapid induction is required. (J1.19.w10)

Induction of anaesthesia:
  • Carfentanil, 20 g/kg, or 3 mg/bear for most Ursus maritimus - Polar bears, up to 5 mg/bear for large males. Only 0.1 mg/bear (mean 4.5 g/kg) for cubs of the year. (J1.19.w10)
  • Load the required dose into a dart and attach a needle of an appropriate length: 4.5 cm for adults, 3 cm for cubs of the year. (J1.19.w10)
  • Deliver intramuscularly by remote injection, from a helicopter for adults; use a blowpipe for injecting cubs of the year, from the ground. (J1.19.w10)
  • Recumbency should occur in 2-12 minutes (mean 5.0 +/- 2.4 minutes). (J1.19.w10)
    • The bear's gait slows, it becomes ataxic, then the head and neck droop so that the nose points straight down; the stride shortens and the feet are not picked up properly. Once the head is pointing down, the bear generally stands, swaying slightly for about 30 seconds, then collapses.
    • In a very short induction, the bear may simply appear to collapse suddenly into sternal recumbency.

    (J1.19.w10)

  • If the bear's nose is pressing straight down into snow, it may be necessary to disturb the bear ("buzz" it with the helicopter) to make it lift its head. If this is unsuccessful, it is necessary to approach and quickly but cautiously pull the bear's head out to one side, then retreat. (J1.19.w10)
  • Once the bear is recumbent and in a safe position, leave it for five minutes before approaching. (J1.19.w10)
  • If the bear does not become recumbent, a further dose of carfentanil is required. This is most likely to be needed if the injection side was not optimal. Bears continue walking "in a slow stumbling manner" or may become recumbent but get up when approached by the helicopter. (J1.19.w10)
  • General anaesthetic information for bears: if the initial anaesthetic dose fails to adequately immobilise the bear, a top-up dose is required. It is important not to underdose at this stage. It is suggested that if the bear is able to sit up or move substantially, a second dose should be equal to the first dose. If the bear is recumbent but reactive to stimuli a minimum 2/3 dose should be given. Generally bears can rouse extremely quickly from an apparently deep plane of anaesthesia and great care should be taken during induction and anaesthesia. (V.w6)

(J1.19.w10)

Reversal of anaesthesia:

  • Naltrexone or naloxone, 100 mg per 1 mg carfentanil given. (B345.6.w6)
    • Note: renarcotization can occur. Giving an additional dose of the reversal agent subcutaneously or intramuscularly (to prolong absorption) is recommended. (B345.6.w6)
  • Naloxone 60 mg intravenously, 40 mg intramuscularly and 20 mg subcutaneously. (J1.19.w10)
    • Bears were standing in mean 8.75 +/- 5.59 minutes. 
    • Tracks indicated some gait incoordination as late as the following day.

    (J1.19.w10)

  • Diprenorphine 2-3 mg subcutaneously plus naloxone 50 mg intravenously. (J1.19.w10)
    • Bears were standing within 5.59 +/- 2.06 minutes. 
    • Renarcotisation ("recycling") still occurred; one bear was found in a snow bank, partially drugged, 20 hours after release.

    (J1.19.w10)

  • Diprenorphine 2-3 mg subcutaneously plus naloxone 30-50 mg intravenously plus naloxone 30-40 mg/kg intramuscularly. (J1.19.w10)
    • No renarcotised bears were observed, but observation was limited due to bad weather.

    (J1.19.w10)

    Signs of reversal: (J1.19.w10)

    • Abrupt, marked increase in respiratory rate, often with panting,
    • Lifting of the head, followed quickly by
    • Standing and moving off.
    • Often incoordinated initially, usually only for 50-100 m. 

(J1.19.w10)

Appropriate Use (?)
  • For immobilisation of polar bears in the wild when rapid induction is required. (J1.19.w10)
Notes
  • No excitation was seen during induction, even in animals with underdose/prolonged induction. (J1.19.w10)
  • Muscle relaxation was excellent. (J1.19.w10)
  • The bears' eyes remained closed and no urination, excessive salivation, tetany or convulsions were observed. (J1.19.w10)
  • Heart rates of 27-123 were recorded. (J1.19.w10)
  • Respiratory rates of 2-12 were recorded. Administration of azaperone may provide deeper, more regular and possibly slightly more frequent respiration. (J1.19.w10)
  • Rectal temperatures were elevated: 38.0 - 41.0 C, mean 39.4 C. This is probably related to reduced respiratory heat exchange due to the reduced respiratory rate. (J1.19.w10)
Complications/ Limitations / Risk
  • IMPORTANT: Very small doses can be fatal in humans. This drug should be handled with care. It should be used only when an appropriate reversal agent for humans is available and there are personnel present who know what to do in the event of an accident.
  • Severe respiratory depression can occur with this anaesthetic. (B345.6.w6)
  • Polar bears which are harassed (e.g. bothered by a helicopter) tend to head for open water. (J1.19.w10)
  • Polar bears forced to continuous physical exertion (e.g. by being chased by a helicopter) tend to get overheated. (J1.19.w10)
  • On becoming recumbent in snow, some bears collapse with their nose down in the snow and are in danger of suffocation. (J1.19.w10)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted. (P9.2004.w4, J40.32.w1, D249.w10)
  • Carfentanil may severely depress respiration. (B407.w18)
  • Carfentanil is a controlled drug in the UK. (B407.w18)
  • Carfentanil is highly dangerous in humans. (B407.w18)
  • Note: renarcotization can occur. Giving an additional dose of the reversal agent subcutaneously or intramuscularly (to prolong absorption) is recommended. (B345.6.w6)
  • General anaesthetic information for bears: if the initial anaesthetic dose fails to adequately immobilise the bear, a top-up dose is required. It is important not to underdose at this stage. It is suggested that if the bear is able to sit up or move substantially, a second dose should be equal to the first dose. If the bear is recumbent but reactive to stimuli a minimum 2/3 dose should be given. Generally bears can rouse extremely quickly from an apparently deep plane of anaesthesia and great care should be taken during induction and anaesthesia. (V.w6)

Equipment / Chemicals required and Suppliers
  • Carfentanil

  • Reversal agents: naloxone (Endo Labs Ltd., Baie d'Urfe, Quebec, Canada), diprenorphine

  • Azaperone (for improving respiration)

  • Needles and syringes for loading darts and injecting reversal agents.

  • Darting equipment:

    • Darts;

    • 4.5 cm needles (for adults); 3 cm needles (for cubs).

    • Darting rifle suitable for use from a helicopter.

    • Blowpipe (for injection of cubs from the ground).

  • Anaesthetic monitoring equipment: minimum rectal thermometer and stethescope.

Expertise level / Ease of Use
  • Bears are large, powerful carnivores. Anaesthesia of bears should be carried out by experienced personnel. (V.w6)
  • Carfentanil anaesthesia should be used only by personnel experienced with this drug and treatment following accidental human injection.
  • This procedure should only be carried out by an individual with appropriate clinical training and practical experience.
    • In some countries a firearms licence may be required for use of remote injection equipment. See section below: Legal and Ethical Considerations
  • Practice is required before administering intramuscular injections with a remote injection system (blowpipe, dart pistol or dart rifle). 
    • It is important also to be familiar with the individual dart gun being used. (D249.w10)
Cost/ Availability
  • Cost and availability of drugs required may vary between countries.
Legal and Ethical Considerations

Human safety considerations

  • IMPORTANT: Carfentanil is highly dangerous in humans (B407.w18) very small doses can be fatal in humans.  Always consider whether it is necessary to use this drug, or whether alternatives are available. This drug should be handled with care. It should be used only when an appropriate reversal agent for humans is available and there are personnel present who know what to do in the event of an accident.
  • There is an inherent risk of human injury when using potent animal capture drugs. It is important to use protocols which prevent such accidents. Additionally, protocols should be established to deal with what may be a potentially lethal exposure. (P1.2006.w3)
  • Accidental exposure to capture drugs should always be considered an emergency which needs a calm, prompt, organised response. (P1.2006.w3)
    • In the event of human exposure to an animal capture drug, the aim of treatment is to maintain life until professional medical care is available. (B70.A1.w3)
    • If this drug is to be used then telephone numbers for one or more local hospitals must be readily available.
  • Carfentanil should never be used when working alone. The specific antagonist for humans (naloxone) must always be available and someone must be present who (a) can give the antagonist in the case of accidental human injection and (b) can give artificial respiration if necessary in the case of accidental human injection. Particularly when carrying out immobilsations in remote locations, the capture team must be self-reliant for dealing with situations, possibly life-threatening, including cardio-respiratory arrest, respiratory depression, CNS depression and hypotension. (P1.2006.w3)
    • "As a minimum when working in the field the following precautions should be adhered to: use capture drugs only with a second, trained person present; respect the potency of the drugs and do not take chances by underestimating a potentially dangerous situation; never work with opioid drugs without having the human antidote and administration protocol in the emergency kit; and limit personnel present when working with the drugs." (P1.2006.w3) Both a thorough theoretical understanding and practical experience in cardiopulmonary resuscitation are essential. (P1.2006.w3) Several members of the capture/immobilisation team should be trained in cardiopulmonary resuscitation. (P1.2006.w3)
  • Note that the laws regarding administration of medical treatment to accident victims by personnel who may not be officially qualified vary between countries. (B70.A1.w3, P1.2006.w3)
  • Dirty needles and syringes must be disposed of properly (needles always into a properly marked sharps container). (D249.w10)
Use of remote injection systems
  • 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).).
  • 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)

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).
  • Carfentanil is a controlled drug in the UK. (B407.w18)
  • Carfentanil is labeled by the FDA for use in cervidae in the USA. Use in bears is extra-label. 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)
Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I. Boardman BVMS MRCVS (V.w6)
References

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