Prepare and monitor anaesthesia in animals

1. Prepare and monitor anaesthesia in animals ANAESTHESIA SCENARIOS

2. Scenarios • Urgency & Emergency Scenarios • See Anaesthesia emergencies • Physiological Scenarios • Pathological Scenarios

3. Physiological Scenarios • Young animals (Paediatric) • Old animals (Geriatric) • Obesity • Caesarians* • Brachycephalic breeds • Sighthound breeds • Small breeds

4. Young animals

5. Young animals

6. Young animals • ‘Pups & kittens’ • Neonate: < 4 weeks • Pediatric: 4-6 weeks • Immature: 16-52 weeks

7. Young animals - Physiology • Cardiovascular function - can only increase Hr not increase the force of the heart contractions • Respiratory function – have a higher O2 requirement • Hepatic – renal function – liver enzymes at very low levels • Body composition • Large SA to body ratio therefore prone to hypothermia • Poor regulation of body fluids – cannot cope conserve or cope with overload

8. Young animals - Pre-op • Correct pre-existing deficits • Rapid induction and recovery • Prevent hypothermia, hypoglycemia and dehydration • Should be on fluids warmed 10mls/kg/hr such as hartmans +/- 5% dextrose added • Minimize use of metabolizable drugs, no barbiturates if < 8wks old • Maintain PCV > 20 % and serum protein > 35gm/l

9. Young animals - Anaesthetics • Atropine – to all • Sedation – may not be needed, low dose opioids • Induction – a.if parenteral ketamine/valium or propofol or Alfaxalone • inhalation probably best –mask, chamber, drug of choice is isoflurane, may cause stress and release of adrenalin causing cardiac arrhythmias • Maintenance – inhalation G/A , T-piece

10. Young animals - Support • Supplementary heat & prepare with war fluids and warm IV fluids etc • Fluids essential • Hartmanns (10mLs/kg/hr) • May require 5% glucose need to monitor • Maintain PCV > 20 % & serum protein >35 g/L

11. Young animals – cases • Discuss the following for a 10 week old 4kg puppy to under go an elective ovariohysterectomy • Physical status: 1 2 3 4 E • Pre-anaesthetic considerations • Premedicants and rationale • Induction technique, agents & rationale • Maintenance technique • Monitoring • Post operative support and analgesia

12. Geriatric animals • Dogs > 7 years

13. Geriatric animals

14. Geriatric animals - Physiology • Cardiovascular system function • Respiratory function • CNS • Hepatic function • Renal function

15. Geriatric animals - CV function • Decrease with age due to • a decline in cardiac response to sympathetic nervous system stimulation • A rise in peripheral vascular resistance due to thickening of the walls of large arteries • This results in • Increased blood pressure • Reduction in cardiac output • Reduction in vascular volume • Less tolerance to anaesthetic drug induced cardiovascular depression

16. Geriatric animals - resp function • There is loss of strength of the muscles of respiration • A decrease in elastic recoil of the chest • An increase in the resting volume of the thoracic cage • Pulmonary capillary blood volume decreases & alveolar surface area, resulting in a reduction in diffusion capacity • Therefore there is an increased resistance to chest expansion and a decrease in gas exchange efficiency with age

17. Geriatric animals - CNS function • Reduction in brain weight with age due to a loss of individual cells • Increased breakdown and decreased production of neurotransmitters • Therefore the anaesthetic requirement decreases with age

18. Geriatric animals - liver function • Age related increase in BSP retention partly due to a decrease in liver blood flow • Drugs dependant on liver metabolism & biliary excretion for their have a prolonged plasma half life in aged patients

19. Geriatric animals - renal function Function decreases with age due to • Reduction of cortical renal mass, reduction in glomeruli and tubular atrophy • Reduction in renal blood flow • Therefore there is a reduced renal reserve (so less tolerant of dehydration or fluid overload) & a prolonged drug elimination • More susceptible to renal failure

20. Geriatric animals - drugs • Albumin mass is reduced so plasma protein binding of drugs is reduced • Results in higher levels of unbound (active) drugs • Receptor numbers also decline with age

21. Geriatric animals - pre-op • Correct pre –existing problems –fluids, assess by pre – G/A bloods, history, PE • Premeds to reduce stress on induction • 5 minutes pre –oxygenation if cardiopulmonary dysfunction • Keep warm as decreased ability to shiver • Handle gently and provide padding

22. Geriatric animals - pre-med • Anti-cholinergic such as atropine may not be needed ( an increased HR could stress the heart) • Opioids good premeds • Diazepam + Opioids – minimal cardiac depression • ACP –use with caution at low doses or not at all because of its long duration of hypotension, in animals with dehydration or poor cardiac or renal function

23. Geriatric animals - inductions • Thiopentone • Propofol – use with care in dehydrated animals as it will cause vasodilatation and therefore hypotension, minimal hepatic metabolism and renal excretion • Ketamine /valium – except in patients with cardiac disease as it increases sympathetic tone (increases HR and BP) • Inhalation – as long as not stressful particularly with cardiopulmonary disease

24. Geriatric animals - maintenance • Inhalation – best Isoflurane

25. Geriatric animals - monitoring • See section above • Vital signs • Mechanical devices • Advise fluids for example hartmans solution

26. Obesity • Irregular gaseous anaesthesia? • Restrictive pressures on URT

27. Caesarian

28. Caesarian Section • G/A for small animals • Local anesthesia for large animals usually

29. Caesarian Section

30. Caesarian Physiology • Blood volume > ( cardiac output >) • But causes PCV < as RBCs not increased • Increase abdominal pressure causes diaphragm to shift cranially causing < functional residual capacity • Increased RR, increased O2 consumption – increases minute ventilation • Delayed gastric emptying increases risk of vomiting • Maternal anesthetic requirements reduced

31. Caesarian Physiology… • Cardiac reserve depleted • MAC lowered • Increased speed of inhalation induction • Inappropriate positioning < cardiac output and compromises ventilation • Respiratory depression - no O2 supplement will result in foetal hypoxaemia

32. Caesarian considerations • History and PE • Blood glucose, electrolytes an acid/base status assessed if available • Fluids

33. Caesarian Premedication • Fluids – maybe with glucose • Minimal doses • Opioids good • +/- anticholinergics • +/- Midazolam ( short acting benzodiazepine ) • DO NOT USE – phenothiazines ( ACP ), butyrophenones, alpha2 agonists • Clip and prepare prior to induction if possible

34. Caesarian Induction • Pre oxygenation for 5 minutes • Rapid induction advised +/- on surgical table • +/- anti emetic • Minimize dorsal recumbency prior to intubations • Artificial ventilation should commence after intubations particularly when placed in dorsal recumbency.

35. Caesarian Maintenance • Isoflurane • +/- nitrous oxide

37. Care of neonate • Clear oral and nasal passages • Vigorous rubbing • Doxapram on tongue if apnoea • Intubate and ventilate if required • O2 via mask if required • Dry and keep warm • Encourage sucking ASAP

42. Check for deformities

43. +/- Weigh

47. Brachycephalic Breeds

48. Brachycephalic Syndrome • Narrow nostrils (stenotic nares) • Relatively long soft palate • Narrow trachea (tracheal hypoplasia) • Everted laryngeal saccules • Laryngeal ‘collapse’ Normal > Partial collapse > Full collapse

49. Brachycephalic Breeds

50. Brachycephalic Breeds • Minimal, if any, sedation • Laryngoscope ready • Small ET tubes ready (down to 5.0mm!) • Pre-oxygenate (if not stressful) • Rapid induction agent with rapid intubation • On recovery leave ET tube in as long as possible