Choice of anaesthetic can determine post-operative pain in animals

“By trying different anaesthetics and different doses of various analgesic, I can see how the signs of pain change, and then work out the best pain relief method,” says Patricia Hedenqvist, postgraduate student at the Department of Physiology and Pharmacology.

It was when comparing different anaesthetics (gas and injected) on rats and examining their experience of pain after surgery that she found that the animals sedated with gas exhibited less pain behaviour and recovered more quickly than those given an injection. This was a welcome find, since gas anaesthesia has many other advantages; for example, it has less of an adverse effect on liver function, and thus on the metabolism of other substances that have been introduced into the body for research purposes.

Rabbits, on the other hand, do not react well to the inhalation of gas anaesthetics. They are much more sensitive than mice and rats and respond by struggling or holding their breath. One objective was therefore to find a substance that rabbits can tolerate, and the one she found caused least problems for them was the gas desflurane. However, she also examined injected anaesthetics on rabbits and by comparing different injection methods found that subcutaneous injection, which can be the easiest on the animal and the least painful, was just as effective as intramuscular injection.

Small animals like mice, rats and rabbits have to recover quickly after anaesthetic since they have a higher metabolism than larger animals and humans, and must therefore eat more often. Patricia Hedenqvist therefore also examined a type of injected anaesthetic, the effects of which can be reversed by the injection of an antidote. The method worked well on rats, which recovered quickly after the injection of the antidote, although it also caused hypoxia and the rats needed to be given supplementary oxygen. She also tried giving a morphine-like analgesic before sedation, this time using a different type of injection anaesthetic, but, although having proved effective on other animals, it did not work so well for rats.

“Discovering pain in rodents can be difficult because being the prey of other animals, they mask their pain, so if they display any weakness, they will make much easier quarry for the predator,” says Patricia Hedenqvist. “However, if you look closely enough, signs of pain in rats are possible to identify, such as after abdominal surgery. The rat arches its back, its abdominal muscles contract or the skin on its back twitches.”

Research into animal pain has grown since the early 1990s, but has concentrated mostly on house pets and domesticated farm animals. Pain therapy has also become more common, but is still relatively rare, internationally speaking, for laboratory animals. Sweden is ahead of many other countries in this respect owing to its strict animal protection laws.

Thesis: Anaesthesia and analgesia for surgery in rabbits and rats: A comparison of the effects of different compounds, Patricia Hedenqvist, Karolinska Institutet, Department of Physiology and Pharmacology. Her public defence is due to take place on 30 May 2008.

Download: http://diss.kib.ki.se/2008/978-91-7357-578-2/

Press photo: ki.se/pressbilder

A seminar is being arranged to coincide with the thesis defence on how to detect, measure and relieve pain in animals, particularly rodents.

When: Thursday 29 May, 1.00 pm
Where: Department of Physiology and Pharmacology lecture hall, Nanna Svarz väg 2, Karolinska Institutet, Solna.
Registration: sabina.bossi@ki.se