TECHNIQUE

Oral Carfentanil Anaesthesia of Bears  (Disease Investigation & Management - Treatment and Care)

Summary Information
Type of technique Health & Management / Disease Investigation & Management / Techniques:
Synonyms and Keywords
  • Oral carfentanil anaesthesia of bears
  • Orally delivered, transmucosally absorbed (OCTA) carfentanil citrate

See also:

Description An anaesthetic agent (carfentanil) is given orally in such a way that it is absorbed transmucosally. This can be used to allow safe handling, blood sampling etc or to make the bear indifferent to darting. It is given in honey or syrup, slowly, to maximise absorption, by allowing the bear to lick the mixture from a spoon or mixing container. If the bear simply swallows the mixture, without time for absorption across the oral mucous membranes, the bear is sedated only slightly or not at all. (B336.51.w51, J1.31.w11)

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:

  • Mix the required dose of carfentanil with honey or syrup, e.g. 5-20 mL. (B336.51.w51, J1.31.w11, J2.32.w2) 
  • Offer the mixture to the bear on a spoon or from a small container so that it is licked off over a period of about two minutes. (J1.31.w11, J2.32.w2)
    • NOTE: It is important to limit the access of the bear to the drug/honey mixture, so that transmucosal absorption of the drug occurs, rather than absorption post ingestion. (B336.51.w51, J1.31.w11, J2.32.w2)
  • In Ursus arctos - Brown bear, sternal recumbency occurred within 4-11 minutes and safe handling was possible after 8-40 minutes. (Ursus arctos - Brown bear)
  • Following a smooth induction, sternal recumbency occurred in 7-12 minutes (7.7 +/- 2.3 minutes) and first safe human contact at 11-26 minutes (19.7 +/- 5.6 minutes). (J1.31.w11)
    • Diazepam 10-25 mg/kg was given to all bears once they were safe to handle. (J1.31.w11)
    • Additional ketamine 1.9 mg/kg intravenously was given to one bear to enable safe examination; this bear had been excited and had been given the lowest dose rate (6.8 g/kg). (J1.31.w11)
  • Mean induction from 80-90% ingestion of carfentanil to sternal recumbency was 6-10 minutes (mean 8 minutes) for three Ursus maritimus - Polar bears over four immobilizations (one immobilised twice). (P36.1994.w7)
  • If the plane of anaesthesia is insufficient, supplementary ketamine can be administered (1.1 mg/kg intramuscularly). (J2.32.w2)
  • If muscle rigidity is problematic, give diazepam (0.05 mg/kg intravenously). (J2.32.w2)
  • Insufflate with oxygen once it is safe to handle the bear. (J1.31.w11, J2.32.w2, P2.1999.w2, P36.1994.w7)

Reversal:

  • When the procedure for which the anaesthesia has been undertaken is completed, reverse using naltrexone at a naltrexone: carfentanil ratio of 100:1, giving 25% intravenously or intramuscularly and 75% subcutaneously. Recovery to standing occurs within 4-9 minutes. (J1.31.w11, J2.32.w2)

OR 

  • ODTA carfentanil can be used as an initial sedative to make the bear indifferent to darting, with reversal using naltrexone after about 20 minutes, given by dart simultaneously with other anaesthetic agents (dissociative plus an alpha-2 agonist). (P2.1999.w2)
  • OR
  • ODTA carfentanil can be used as an initial sedative prior to hand-injection with further anaesthetic drugs.
    • In 590 kg 22-year-old castrated male, carfentanil 8 g/kg was given in 10 ml honey, licked off a spoon. After the bear became partially recumbent (7-10 minutes) a mouth gag was placed; gag reflex and head movements prevented endotracheal intubation, therefore tiletamine-zolazepam was administered (3 mg/kg) together with atropine (0.2 mg/kg) and the bears was insufflated with oxygen at 10 L/minute. Intubation with a 22 mm endotracheal tube was carried out 20 minutes after the tiletamine-zolazepam was given and anaesthesia was maintained using isofluorane (1.25 % gradually decreasing to 0.6%) in 4 L/min oxygen, for 2.25 hours, using a large animal anaesthetic breathing circle and an out-of-circuit vapouriser. (J4.217.w3)
Appropriate Use (?)
  • For anaesthesia, allowing handling, blood sampling etc. as an alternative to darting with anaesthetic drugs.(J1.31.w11)
    • Or as an initial sedative to allow darting without stress and excitation. (P2.1999.w2)
  • Advantages include removal of risks of physical injuries from dart impact, and the problems associated with incorrect dart placement.
  • Also removes the apprehension and excitement associated with the animal being darted, which can stress the animal, cause hyperthermia, and may affect the onset and duration of action of the anaesthetic drug.

(J1.31.w11, P1.1996.w4, P2.1999.w2, P36.1994.w7)

Notes
  • Separate the bear to be immobilised from other bears. 
  • The dose required can vary depending on the physiological state of the bear. In a trial in Ursus arctos - Brown bear, it was found that, although the bears were not hibernating, the dose required in winter was lower than that required in summer: 7.6 +/- 0.4 g/kg body weight in winter, and 12.7 +/- 0.5 g/kg in summer. (J2.32.w2)
  • Provides a smooth induction and gradual loss of consciousness. (J1.31.w11, J2.32.w2)
  • Recovery is smooth following reversal. (J1.31.w11)
  • Heart rates were low during the immobilization. (J2.32.w2)
  • Ordinary honey, not containing any drug, can be offered to the bear in a similar manner in the days prior to immobilisation. (J2.32.w2)
  • Re-narcotization was not observed. (J1.31.w11)
  • Oxygen insufflation is recommended during immobilisation once it is safe to handle the bear (6 L/minute by unilateral nasal intubation). (P1.1996.w4)
Complications/ Limitations / Risk
  • Cannot be used if the bear will not consume the drug in its carrier.
    • In a trial, one brown bear appeared able to detect carfentanil in honey and refused to eat honey which contained carfentanil. (J2.32.w2)
  • It is important to ensure proper oral transmucosal absorption; too rapid ingestion of the drug/honey mixture may give increased induction times. (J1.31.w11, J2.32.w2)
    • If the bear simply swallows the mixture, without time for absorption across the oral mucous membranes, the bear may be sedated only slightly or not at all. (B336.51.w51, J1.31.w11)
  • Drug absorption (rate and percentage) is variable.
  • Hypoventilation and respiratory acidosis occur with oral carfentanil anaesthesia; administration of oxygen is recommended as soon as it is safe to do so. (J1.31.w11, J2.32.w2) 
    • Respiratory rate was below 8 per minute in eight Ursus americanus - American black bear and dropped below two per minute in two bears; these were given doxapram 40 mg/kg, intravenously or into the muscle of the tongue. (J1.31.w11)
    • If the respiratory rate drops below five breaths per minute, give doxapram HCl (0.01-0.10 mg/kg intravenously). Note this did not appear to be effective in stimulating respiration. (J2.32.w2)
    • Mild to severe haemoglobin desaturation (<70% - 89%) was evident when first measured. Following oxygen insufflation, haemoglobin saturation increased to a satisfactory level (SaO2 > 90%) after five minutes of oxygen insufflation in eight bears; in the other two it reached 86% and 89%. (J1.31.w11)
  • Bradycardia may occur:
  • Bradycardia (20 and 24 bpm) occurred in two of ten Ursus americanus - American black bear; the other eight bears has heart rates of 40-88 bpm. (J1.31.w11)
  • If the heart rate is too low, atropine sulphate can be given (0.03-0.04 mg/kg intramuscularly). This was used in 10 of 14 immobilizations and resulted in doubling of heart rate within 5-10 minutes. (J2.32.w2) However, it may act as a respiratory depressant.
    • Heart rates (normal 60-90 bpm) dropped to 30-44 bpm, but more than doubled following administration of atropine. (J2.32.w2)
  • Side effects during recovery have included panting and vomiting.
  • In one trial with five Ursus arctos - Brown bear, one female always panted during recovery while another female always vomited. (J2.32.w2)
  • The time to effect is variable. (J2.32.w2)
  • Muscle rigidity was noted in all 10 black bears; generalised muscle fasciculations were seen in three bears. (J1.31.w11)
  • Vomiting may occur following reversal. (J1.31.w11) With , five bears which had been given a food treat for separation prior to immobilisation vomited after thy recovered to full mobility. (J1.31.w11)
Equipment / Chemicals required and Suppliers
  • Carfentanil.

  • Honey or a similar substance. 

    • This must be an edible substance liked by bears, into which the anaesthetic drug can be mixed, and which will stay in contact with oral mucous membranes for sufficiently long to allow the drug to be absorbed.

Expertise level / Ease of Use
  • Bears are large, powerful carnivores. Anaesthesia of bears should be carried out by experienced personnel. (V.w6)
Cost/ Availability
  • Carfentanil is a powerful opiate and its accessibility may be restricted, depending on the country, to e.g. licensed veterinarians.
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).
  • 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)
  • Carfentanil is highly dangerous in humans. (B407.w18)
  • IMPORTANT: Very small doses of carfentanil 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. 
Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I. Boardman BVMS MRCVS (V.w6)
References B284.5.w5, J1.31.w11, J2.32.w2, V.w6

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