Prepare and monitor anaesthesia in animals

1. Prepare and monitor anaesthesia in animals PRE-ANAESTHETIC EVALUATION

3. Findings of concern for GA • Central nervous System disease • Cardiovascular & Respiratory disease • Liver & Renal disease • Unstable blood glucose levels • Hypoalbuminaemia • Coagulation problems • Electrolyte & pH abnormalities • Hypovolaemia & dehydration • Anaemia & polycythaemia • Pyrexia • Current medications

4. Routine checks • Food withheld (fasted) for 12-24 hrs • +/- Water withheld 6 hrs • Consent forms filled • Does not, however, indemnify vet against any negligence • Toileted if possible • Bath & flea treatment?

5. More on Fasting times • Dog & Cat • Food: 12 hrs • Water: 8-10 hrs(??) • Neonate: No fasting • Colonic Surgery: 2 days(??) • Cattle • Food: 36-48 hrs • Water: 12-24 hrs • Sheep & Goats • Food: 18-24 hrs • Water: 8-10 hrs • Birds & Animals<2kg • Food: No fasting • Ferrets 2-4 hrs as high metabolic rate and short GI transit time • Rabbits • 30-60mins to ensure no food in mouth (have a strong lower oesophageal sphincter)

6. Why pre-GA evaluation? • To check for anyabnormalities • Anaesthesia risk • Surgical considerations • In case there is more to be done under the one GA

7. Pre-anaesthetic Assessment • Physical Exam • & distant exam/patient details – age, species, breed/history –medication, seizures, previous GA, last meal • Pathology • Blood & urine • ‘Pre-GA Profile’ • Diagnostic imaging

8. Pre-anaesthetic Gear • Drugs • Catheter, tape, fluids, syringes • ET tubes (cuffs checked), laryngoscope • Heating pads • Monitoring equipment (pulse ox, apnoea alert, oesophageal stethoscope) • Anaesthetic machine fitted and checked (bag, anaesthetic)

9. Anaesthetic Risk Classification(‘Risk Class’ , ‘Physical Status’) • Standardizes the pre-operative evaluation of a patients anaesthetic risk • A common classification system: • Class 1 (minimal risk) • Class 2 (minor risk) • Class 3 (moderate risk) • Class 4 (high risk) • Class 5 (grave risk) • E: adding ‘E’ to any of the above denotes emergency basis for anaesthetic and increases the risk in that class

10. Monitoring form ‘Physical Status’ 1-5 e.g. ‘AAS’ FORM

12. Class 1 • Normal animal admitted for elective surgery • A patient with no organic or physiological disease • Localized surgery • E.g. elective surgeries such as de-sexings, simple fractures, pin removal, some tumours

13. Class 2 • Animal which has slight to moderate systemic disturbance • Patient has mild systemic disturbance which may or may not be related to the surgery • May only mildly interfere with the patients normal activity • Clinical pathologic changes may not be seen • Examples are obesity, neonate or geriatric, compensated mitral insufficiency, mild dehydration

14. Class 3 • Animal with major systemic disturbance that limits activity but is not incapacitating • Patients have moderate systemic disturbances which interfere with the patients normal activity • Clinical pathologic changes are present • E.g. anaemia, uraemia, pneumonia, electrolyte imbalances, liver disease, renal disease, diaphragmatic hernia, severe fracture

15. Class 4 • Animal with very severe systemic disturbance that could lead to death if surgical or medical intervention is not applied • These patients present with life-threatening conditions • Surgical intervention may be necessary to preserve life • Systemic involvement and severe pathologic changes are present • E.g. equine colic, haemorrhage, pneumothorax, gastric dilatation & volvulus, ruptured bladder, frequent arrhythmias

16. Class 5 • Animal in a moribund state that will probably die despite surgical or medical intervention • These patients present in a moribund condition and have little chance of survival with or without surgical intervention • E.g. prolonged GDV/volvulus, cerebral trauma with intracranial haemorrhage, gastric rupture

17. Precautions for high risk patients • Pre-stabilise • Treat underlying problem if possible– eg decompress GDV, drain thorax etc • IV fluids*** • Eg dehydration, shock, kidney/liver failure • But care with heart failure (easily overhydrated) • Pre-med, Induction & Maintenance drugs • Careful selection of types & doses (vet decides) • Pre-oxygenation*** • Eg resp problems (diaphragmatic hernia) • Pre-clipping/surgical prep*** • Eg caesarian

18. Pre-Oxygenation • Consider • Face mask (if tolerated) • Tube flow past nose • O2 chamber

19. Pre-Oxygenation

20. Class Activity 1 • What parameters will usually be performed in a physical examination?

21. Answers 1 • Temperature • PR and rhythm • RR and nature • MM colour • CRT • Skin fold return and hydration status • HR and rhythm • If any of these measurements are abnormal then there is the possibility of increased anaesthetic risk

22. Pre-existing cardiac murmurs • Murmurs are caused by turbulent blood flow • Most common is ‘mitral valve’ murmur • Left atrio-ventricular valve • Left systolic murmur • Not necessarily associated with physical signs of cardiac disease

23. Murmurs can be grouped as • Young animals – congenital problem, requires further investigation prior to GA • Old animals with no clinical signs or history of murmur – GA usually no significant risk • Older patients with evidence of cardiac disease • requires further investigation prior to GA • Re-evaluate requirement for GA procedure • Select GA for specific cardiac abnormality

24. IV fluids during anaesthesia • Replace losses • Maintain effective circulating volume to perfuse vital organs • Replace blood and /or fluid lost during surgery • Correct acid-base disorders

25. < 5% 5-6% 6-8% 10-12% 12-15% Not detectable Subtle loss of skin elasticity Marked loss of skin elasticity Slightly sunken eyes & prolonged CRT Dry MM Tented skin stands in place Prolonged CRT Dry MM % sunken eyes Early shock, moribund Clinical signs of Dehydration

26. Pure Water depletion Prolonged inappetence Diabetes insipidus Water unavailable Unconsciousness Fever or excessive panting Water + Electrolyte depletion Vomiting & diarrhoea Pyometra Wound drainage Third space losses Fluid abnormalities

27. Potassium depletion Reduced rate of K+ intake Prolonged inappetence Increased rate of K+ loss Prolonged diuretic therapy Prolonged diarrhoea Vomiting Potassium accumulation Reduced rate of K+ loss (in urine) Acute renal failure Ruptured bladder Urethral obstruction Addison's disease Potassium levels

28. Selecting Fluids • Balance electrolyte solutions preferred such as Hartmanns solution • Routine maintenance during anaesthesia/surgery is 10 mL/kg/hr • Can monitor particularly in small patients to prevent over hydration by doing PCV and TP periodically • Advised to warm fluids • To replace blood loss with crystalloid fluids. 2-3 x the volume lost must be administered. As this fluid redistributes also to the extracellular space which is about 3x as large as the intracellular space

29. Blood or Plasma? • If PCV < 20% (normal 35-45%) give whole blood • If TP (TPP) < 35g/L (normal 65-70g/L) give plasma

30. Advisable • Fluid administration sets • Patient > 8-10kg • Regular 10-20 drops/mL set • Patient < 8-10 kg • Mini drip (paediatric) 60 drops/mL set

31. Question • What tests make up an anaesthetic screen? ( pre-GA pathology tests)

32. Answer • Minimum data base for elective patients • PCV • TPP • Urine SG • Additional tests for non elective patients and those > 7 • Pre –anaesthetic profile: urea and/or creatinine • CBC

33. Other tests for selected cases • Radiographs • Ultrasound • Electrolytes • Specific examinations such as a neurological exam • Blood pressure • Other serum chemistries such as clotting tests

34. Consent forms for G/A • Provide legal consent for the administration of an anaesthetic? • Provide declaration that the owner is prepared to pay the appropriate fee • Acts as an indemnity form for the loss or liability associated with unintended consequence of the anaesthetic procedure • Usually incorporated with the surgery consent form

35. The End