prepare and monitor anaesthesia in animals

PREANAESTHETIC EVALUATION

Prepare and monitor anaesthesia in animals

PRE-ANAESTHETIC EVALUATION


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


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?


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)


Why pre-GA evaluation?

• To check for any abnormalities– Anaesthesia risk– Surgical considerations

• In case there is more to be done under the one GA


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


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)

PREANAESTHETIC EVALUATIONAnaesthetic 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


Monitoring forme.g. ‘AAS’ FORM

‘Physical Status’ 1-5


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


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


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


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


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


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


Pre-Oxygenation

• Consider– Face mask (if tolerated)– Tube flow past nose– O2 chamber


Pre-Oxygenation


Class Activity 1

• What parameters will usually be performed in a physical examination?


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


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


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


IV fluids during anaesthesia

1. Replace losses2. Maintain effective circulating volume to

perfuse vital organs3. Replace blood and /or fluid lost during

surgery4. Correct acid-base disorders


Clinical signs of Dehydration

• < 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


Fluid abnormalities

• 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


• 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


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


Blood or Plasma?

• If PCV < 20% (normal 35-45%) give whole blood

• If TP (TPP) < 35g/L (normal 65-70g/L) give plasma


Advisable

• Fluid administration sets– Patient > 8-10kg

• Regular 10-20 drops/mL set– Patient < 8-10 kg

• Mini drip (paediatric) 60 drops/mL set


Question

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


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


Other tests for selected cases

• Radiographs• Ultrasound• Electrolytes• Specific examinations such as a

neurological exam• Blood pressure• Other serum chemistries such as clotting

tests


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


The End

prepare and monitor anaesthesia in animals

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