Anaesthesia of laboratory animals

1. Anaesthesia of laboratory animals Timo Nevalainen University of Eastern Finland www.uku.fi/~tnevalai/anaesthesia.ppt

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. Bedding Volatile Compounds / With Highest Sums concentration microg/g Vesel et al. 1966: Bedding volatile compounds induce liver microsomal enzymes

10. 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

11. 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

12. Handling vomiting dangers • Fasting decreases amount vomited, but reflex stays • if vomits, place head over table edge, drains away from mouth • once anaesthetised, intubate, closes passage to respiratory system

13. 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)

14. 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

15. 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

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

17. Pulse oxymeter

18. Sensor around leg

19. Maintaining normal temp

20. ECG-recording

21. 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

22. Inhalation - open mask

23. 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

24. Intubation • Guinea pig intubation - easier version of rat, tube outer diameter =2 - 2.5 mm • 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

25. Mouse intubation video

26. Using otoscope

27. Air movement ?

28. Rodent respirator

29. Wet - loosing heat

30. Skin disinfection

31. Assessment of anaesthetic depth (video) • Mouse • respiratory rate, cornea • tail pinch and pedal reflex • pedal best • Rat • respiratory rate, tail pinch • pedal reflex and ear pinch • ear pinch best

32. Tail pinch

33. Pedal reflex

34. Anaesthetic depth • Guinea-pig • palpebral reflex and ear pinch • ear pinch best • may move 1-2 times, is not lightening of anaesthesia • Rabbit • light surgical - pedal reflex • medium depth - palpebral reflex & ear pinch • corneal reflex - dangerously deep

35. Ear pinch

36. Dose memos • www.uku.fi/~tnevalai/ratmouseanes.html • Rabbit dose calculator • www.morfz.com/rx/drugcalc.html

37. 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

38. 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

39. Medetomidine & fentanyl • Works reasonably well in rats • animals pale and urine drips • major advantage: antagonist wakes them real fast

40. Chloralhydrate • Common in neuropharmacology • if too concentrated, fatal paralytic ileus, abdomen dilated, do badly and die • correct concentration is 36 mg/ml or less

41. Permanent iv-access

42. Infusion anaesthesia • Typical compound propofol • used in rats, single bolus 10 mg/kg produces anaesthesia of about 5 min • infusion anaesthesia can provide stable anaesthetic level without a vaporizer

43. 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

44. Complete inhalation set

45. Induction chamber

46. Nose cones with exhaust

47. 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

48. 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

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

50. 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