prepare and monitor anaesthesia in animals
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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 - PowerPoint PPT PresentationTRANSCRIPT
PREANAESTHETIC EVALUATION
Prepare and monitor anaesthesia in animals
PRE-ANAESTHETIC EVALUATION
PREANAESTHETIC EVALUATION
PREANAESTHETIC 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
PREANAESTHETIC EVALUATION
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?
PREANAESTHETIC EVALUATION
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)
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
Monitoring forme.g. ‘AAS’ FORM
‘Physical Status’ 1-5
PREANAESTHETIC EVALUATION
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
Pre-Oxygenation
• Consider– Face mask (if tolerated)– Tube flow past nose– O2 chamber
PREANAESTHETIC EVALUATION
Pre-Oxygenation
PREANAESTHETIC EVALUATION
Class Activity 1
• What parameters will usually be performed in a physical examination?
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
• 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
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
Blood or Plasma?
• If PCV < 20% (normal 35-45%) give whole blood
• If TP (TPP) < 35g/L (normal 65-70g/L) give plasma
PREANAESTHETIC EVALUATION
Advisable
• Fluid administration sets– Patient > 8-10kg
• Regular 10-20 drops/mL set– Patient < 8-10 kg
• Mini drip (paediatric) 60 drops/mL set
PREANAESTHETIC EVALUATION
Question
• What tests make up an anaesthetic screen? ( pre-GA pathology tests)
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
Other tests for selected cases
• Radiographs• Ultrasound• Electrolytes• Specific examinations such as a
neurological exam• Blood pressure• Other serum chemistries such as clotting
tests
PREANAESTHETIC EVALUATION
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
PREANAESTHETIC EVALUATION
The End