Anaesthesia & analgesia of laboratory animals

1. Anaesthesia & analgesia of laboratory animals Timo Nevalainen University of Eastern Finland

2. Terminology • Anaesthesia = without sensation • an = without, aestos = sensation • Analgesia = without pain • an = without, algios = pain • Euthanasia = good death • eu = good, thanatos = death

3. How anaesthesia is chosen ? • Tradition • look articles of your discipline • Ask colleagues • end up to tradition • Rational way ?

4. Anaesthesia, how ? • Choice of anaesthetic • minimal interference of study • immobilisation and no/less pain • nature of the procedure • duration of the procedure • Humane handling of animals and safety of personnel are important

5. Problems with laboratory animals • Group anaesthesia • Large species, strain etc. differences • Follow-up difficulties • Anaesthesia poorly known • Clinical and research anaesthesia are not used properly • Postoperative care does not work

6. Pros no pain no muscle reflexes no muscle tension Clinical anaesthesia Cons changes in the body physiological status different responses may be different Research anaesthesia Pros and cons of anaesthesia

7. Depresses least depresses most alphachloralose thiobarbiturate + N2O cyclopropane barbiturates ether halothane chloroform Anaesthesia vs. CNS-mediated reflexes

8. Inspection before anaesthesia • Check animals before starting • Do not anaesthetise sick animals, they are unsuitable for experiments anyway • Pay attention to symptoms of infections

9. How to fast before anaesthesia ? • Take away food - not water • the smaller species, the faster metabolism, the shorter fasting • no fasting for mouse • abdominal procedures in rat, fast for 6 h • guinea-pig 6 h • rabbit 6 h

10. Dangers of vomiting • Horse vomits = rupture of stomach • ruminants can drop ruminating balls • carnivores vomit easily • among rodents guinea-pig vomits easily • can drain into trachea and cause aspiration pneumonia

11. Pre-anaesthetic hydration • Give animal balanced electrolyte fluid to drink couple of days before • yields better water balance • continue a few days after anaesthesia (and procedure)

12. Pre-medication atropine • No saliva, no vagal reflexes, less gut motility • Dose: rodents 0.05 mg/kg, rabbit 1-3 mg/kg about 30 min before • if autonomic nervous system is involved, atropine may be contraindicated

13. Sedative pre-medication • Decrease dose of anaesthetic by 20-50 % • better handling may be needed eg for iv injection • if procedure is not painful, but immobilisation is needed • some compounds dilate vessels - easier to see them

14. Ensuring oxygenation • Respiratory passages open • posture, atropine • additional oxygen • tubing directly into mouth • less dead space • intubation

15. ECG-recording

16. Pulse oxymeter

17. Maintaining normal temp

18. Control of anaesthesia • Inhalation is well controlled • iv-bolus anaesthesia - you give half of calculated dose, the rest to effect • infusion anaesthesia also well controlled • im, ip ja sc administration: you give calculated bolus - response may be variable

19. Inhalation - open mask

20. Intubation • Mouse - tracheostomy • rat - tube outer diameter = 1-1.5 mm, length 2 cm attached snugly inside wider tube • rat placed on back, fixed by maxilla incisors, tongue pulled out • larynx visible, becomes easier with high intensity light directed to neck

21. Intubation • Rabbit intubation difficult • laryngospasm unless not deep enough • small place, otoscope / pediatric laryngoscope • tube outer diameter = 3 - 3.5 mm, no cuff • Rabbit: guided or blind intubation

22. Mouse intubation video

23. Air movement ?

24. Wet - loosing heat

25. Skin disinfection

26. Assessment of anaesthetic depth • Mouse • respiratory rate, cornea • tail pinch and pedal reflex • pedal best • Rat • respiratory rate, tail pinch • pedal reflex and ear pinch • ear pinch best

27. Tail pinch

28. Pedal reflex

29. Anaesthetic depth • Rabbit • light surgical - pedal reflex • medium depth - palpebral reflex & ear pinch • corneal reflex - dangerously deep

30. Ear pinch

31. Hypnorm & midazolam • clinical anaesthesia, reasonable safety margin • NOT to be given ip, liver metabolism weakens effect • contains fentanyl = controlled substance • recovery is speeded by nalorphin • Rat: Combination 0.15 - 0.2 ml / 100 g sc • Mouse: Combination 0.10 - 0.15 ml / 20 g sc

32. Hypnorm – Midazolam • Combination • One part HypnormR (fentanyl-fluanisone) + one part midazolam (DormicumR, 5 mg/ml) + two parts sterile water • Mix both drugs first with water and then combine. Do not keep in refrigerator. • Duration of anesthesia: Mouse 30-60 min, rat 20-90 min • Reversal: Nalorphine 1 mg / kg iv, im, ip

33. Medetomidine & ketamine • Rat • Medetomidine 0.4 mg / kg + ketamine 60 mg / kg ip, sc. • Mouse • Medetomidine 1 mg / kg + ketamine 75 mg / kg. Mixed and diluted to yield 0.1 - 0.2 ml / mouse • Antagonist • Atipamezole 1 mg /kg (rat) im, ip, scor • 0.5 mg / kg (mouse) ip, sc.

37. Chloralhydrate • Used to be common in neuropharmacology • if too concentrated, fatal paralytic ileus, abdomen dilated, do badly and die • correct concentration is 36 mg/ml or less

38. Permanent iv-access

39. Barbiturate anaesthesia • Safety margin in rabbits narrow • may lead to 20-40 % mortality • if used - only for terminal procedures • Mouse - the same situation • can combine with e.g. ethanol • there are better combinations

40. Complete inhalation set

41. Induction chamber

42. THE UNIVENTOR 400 ANAESTHESIA UNIT designed to control the mixture of anesthetic and air with the precision required to successfully operate on animals weighing from 20-500 grams www.agnthos.se

43. Inhalation • halothane • common inhalation compound • does not evaporate concentrations with mortality at room temperature • liver necrosis • cheapest of proper inhalation compounds • good clinical anaesthesia with guidance

44. Isoflurane • Combines reasonable research anaesthesia and good guidance • more expensive than halothane • requires own vaporizer • no mortal concentrations at room temperature

47. No ether, neither chloroform • Evaporate to mortal concentrations at room temperature • ether explodes, and carcasses in cooler of freezer smell a long time • chloroform is liver toxic and suspected carcinogen

48. CO2 • Controversial • 1-2 min procedures, no longer • for rats and mice • incubation box with animals, tube CO2 in at a rate 0.6 x box volume l/min • righting reflex disappears, move to mouth cone with 50 % CO2 and 50 % O2

49. Postoperative care • temperature • infrared light bulb • insulation • fluid • ip or sc as boluses • air humidification • additional oxygen • carbogen flow to chamber

50. Insulated, recovering rat