Analgesia

Every effort should be made to minimise any pain or distress that animals experience during scientific procedures. In addition to compromising animal welfare, pain is a source of stress that can cause undesirable effects on the outcome of research projects. Considerable progress has been made over the last decade in preventing or alleviating pain. In particular, there is now considerable opportunity to minimise or eliminate pain following surgical procedures. A wide range of analgesics are available, so it would seem a simple process to administer one of these agents to prevent or alleviate postoperative pain. Administering an analgesic is not sufficient, however, as it is important to:

  • Administer an appropriate analgesic that provides the required intensity of pain relief
  • Administer the analgesic at an appropriate dose
  • Continue its administration at appropriate time intervals
  • Stop administering the analgesic at an appropriate time after surgery

Provision of effective pain relief requires that all of these points are addressed, but this can only be done by assessing the degree of pain experienced by the animal involved. Animal pain assessment can be difficult and time consuming to implement effectively. Consequently it can be tempting to simply give all animals a "standard dose" of analgesic. In man, the use of such fixed dose regimens has been identified as one of the factors contributing to inadequate pain management, so this approach should be avoided when dealing with laboratory animals.

A further problem is that in man the analgesic dose rates that are used are based on clinical trials, using well established methods of assessing pain. In animals, it is not possible to assess the severity of many types of pain accurately. This means that the effects of different analgesics cannot be measured; for example when using them to alleviate post-operative pain. Often, all that is possible is to use dose rates that have been established to be safe and effective in some of the tests used in rodents during early drug development. Provided these limitations are appreciated, pain management strategies can be recommended that make best use of existing knowledge:

  • If methods of pain assessment have been developed for the species used, then these should be adapted to the requirements of the particular research procedure being undertaken.
  • If methods of pain assessment are not available, consideration should be given to devoting resources to developing some form of pain scoring system.
  • If pain scoring is not possible, determine the analgesic protocol based on clinical experience with other surgical procedures in that species.
  • If possible, use dose rates that have been established using studies that have employed pain scoring systems.
  • When data on pain scoring is not available, estimate doses from results of analgesiometric studies using tonic (longer lasting) nociceptive stimuli (e.g. late phase formalin test).
  • Use pre-emptive analgesia and consider using multimodal strategies.
  • Attempt to evaluate the efficacy of the analgesic regimen selected, if only by clinical assessment.

Similar problems have been recognised when dealing with pain in companion animals, farm animals, and zoo and wild animals, and this is an area in which rapid developments are underway. It is therefore important to regularly review pain management procedures to ensure they represent current best practice. Whichever method of pain control is employed, it must be integrated into an overall scheme of peri-operative care.

Pain assessment from NC3Rs on Vimeo.

Writhing, twitching and back-arching are behaviours that can be used to assess pain following abdominal surgery in rats. Writhing is a muscular contraction causing a concavity of the flank. Twitches are spasmodic movements of the fur, usually on the back of the rat. Back-arching is stretching of the fore- and hind legs causing the abdomen of the rat to be raised from the cage floor and the back to be arched. For more information, see the CD 'Pain Assessement in the Rat' at www.digires.co.uk

Related resources

A reference source for the recognition and alleviation of pain and distress in animals Animal Welfare Information Center (2005)
Digital Resources for Veterinary Trainer (DIGIRES)
Vets On Line Email (VOLE) - Email discussion list used by many Named Veterinary Surgeons (NVSs) under the Animals (Scientific Procedures) Act 1986. Contact: secretary@lava-vet.org

References

Information porvided by Paul Flecknell, Newcastle University
Last updated: June 2014

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