Prepare and monitor anaesthesia in animals

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Prepare and monitor anaesthesia in animals

• ANAESTHESIA SCENARIOS

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Scenarios

• Urgency Emergency Scenarios
• See Anaesthesia emergencies
• Physiological Scenarios
• Pathological Scenarios

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Physiological Scenarios

• Young animals (Paediatric)
• Old animals (Geriatric)
• Obesity
• Caesarians
• Brachycephalic breeds
• Sighthound breeds
• Small breeds

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Young animals
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Young animals
Problem Solution
Greater oxygen demand, ventilation less efficient and prone to lung consolidation if anaesthetised for long periods. Monitor oxygenation Careful selection of ET tube - not too long. Ventilatory support if needed.
Liver and kidney function immature. Use lower than adult dose rates. Use drugs that are rapidly metabolised. Avoid fluid overload.
Prone to hypoglycaemia. Monitor blood glucose. Maybe add glucose to IV fluids.
Prone to hypothermia. Monitor temperature. Keep warm.
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Young animals

• Pups kittens
• Neonate lt 4 weeks
• Pediatric 4-6 weeks
• Immature 16-52 weeks

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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

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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 lt 8wks old
• Maintain PCV gt 20 and serum protein gt 35gm/l

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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

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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 gt 20 serum protein gt35 g/L

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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

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Geriatric animals

• Dogs gt 7 years

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Geriatric animals
Problem Solution
May have heart problems, poorer circulation. Anaesthetics may take longer to work, give it time rather than increasing dose. Avoid fluid overload.
Require less anaesthetic Reduce dose premed and GA
Reduced lung elasticity, may have respiratory disease. Monitor oxygen carefully. Supplement oxygen prior to induction and during recovery. Carefully monitor ventilation, assist if required.
Reduced renal function. May be PU/PD IV Fluids. Increase fluid rate prior to induction, make sure patient not dehydrated.
Reduced hepatic function Use drugs that are rapidly metabolised
May have other underlying diseases Do pre-anaesthetic blood tests
May be on medication Get good history from owner
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Geriatric animals - Physiology

• Cardiovascular system function
• Respiratory function
• CNS
• Hepatic function
• Renal function

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Geriatric animals - maintenance

• Inhalation best Isoflurane

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Geriatric animals - monitoring

• See section above
• Vital signs
• Mechanical devices
• Advise fluids for example hartmans solution

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Obesity

• Irregular gaseous anaesthesia?
• Restrictive pressures on URT

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Caesarian
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Caesarian Section

• G/A for small animals
• Local anesthesia for large animals usually

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Caesarian Section
Problem Solution
Increased oxygen consumption due to foetuses. Use at least 50 oxygen. Pre-oxygenate patient.
Risk of vomiting due to reduced gastric emptying time Can pre-med with metoclopramide. Be prepared for possibility of vomiting and aspiration during anaesthesia and recovery. Rapid induction - use IV agent, intubate quickly.
Patient may be exhausted and dehydrated. IV fluids ASAP
Distended abdomen puts pressure on diaphragm Minimise time animal is on its back. Ventilate if needed.
Foetuses can be affected by the drugs used. Keep induction to delivery time to min. Use lowest effective dose of drugs. Use short acting, rapidly metabolised drugs. Pre-clip
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Caesarian Physiology

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

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Caesarian Physiology

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

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Caesarian considerations

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

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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

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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.

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Caesarian Maintenance

• Isoflurane
• /- nitrous oxide

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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

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Check for deformities
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/- Weigh
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Brachycephalic Breeds
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Brachycephalic Syndrome

• Narrow nostrils (stenotic nares)
• Relatively long soft palate
• Narrow trachea (tracheal hypoplasia)
• Everted laryngeal saccules
• Laryngeal collapse

Normal gt Partial collapse gt Full collapse
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Brachycephalic Breeds
Problem Solution
Animal may be very stressed Use low-dose sedative.
May have trouble breathing spontaneously when extubated Avoid respiratory depressants, use only low-dose and short acting opiods. Use propofol- rapid induction, allows for top-up, rapid recovery. Use lignocaine gel on ET tubes and leave in as long as possible during recovery. Pre-oxygenate patient. Examine throat for mucous or other obstruction.
May have tracheal hypoplasia Use smaller ET tube than you would usually use for a patient of this size.
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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

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Brachycephalic Breeds

• Pre-oxygenate
• Rapid induction agent with rapid intubation
• On recovery leave ET tube in as long as possible
• virtually want them to cough it out!

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Sighthound Breeds

• Thin skin
• Initial rapid redistribution
• Altered hepatic metabolism of drugs
• Long recoveries
• Hypothermia

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Small/Toy Breeds

• Hypothermia
• Hypoglycemia
• Small veins
• Care with fluid administration (overhydration)
• Length of endotracheal tube
• Surgeons "resting" on patient

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Pathological Scenarios

• GDV
• Pyometra
• Pleural cavity
• Diaphragmatic hernia
• Pneumothroax/haemothorax
• Pulmonary
• Cardiac
• Kidney
• Liver

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GDV
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GDV

• Mainly large deep chested breeds
• Circulatory shock as high intra gastric pressure
  causes obstruction to gastric circulation, caudal
  vena cava and portal venous flow. Reduces venous
  return to heart and cardiac output
• Prolonged hypotension may lead to irreversible
  renal failure, acute liver failure
• Portal vein occlusion maybe initiates
  endotoxaemia from gut flora
• Enlarged stomach limits diaphragmatic
  movements- initially tidal volume lt and RR gt to
  maintain normal minute respiratory volume

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GDV

• Ventricular cardiac dysrhythmias common 12 48
  hrs after the initial ischaemic episodes, maybe
  occur 4 days post op
• Cause unknown suspect myocardial ischaemic
  hypoxia
• Advise treat with lignocaine usually an infusion

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GDV

• Initial stabilisation needed
• A. decompress stomach
• B. correct hypovolaemic shock hartmans at
  60-90mls/kg max.
• Monitor PCV and TPP
• If TPP low may require colloids
• C. pain relief low dose opoids eg methadone or
  pethidine
• D. ECG - monitor

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GDV - Premeds

• Avoid drugs that cause vomiting
• Best methadone and pethidine

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GDV - Induction

• O2 prior to induction
• Small doses of thiopentone or propofol if no
  longer severely compromized
• If severe maybe intubate and put on gas

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GDV - maintenance

• Ovoid nitrous oxide as increases the volume and
  pressure of gas containing spaces
• Isoflurane agent of choice
• Maybe need IPPV

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Pyometra
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Pyometra

• Usually D/H as are PU/PD even if appears bright
• Usually have acidosis correct
• Hypotensive
• If closed will present with septic shock

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Pyometra

• Aggressive fluid therapy continue for at least
  24 hrs post op and monitor urine output
• Antiboitics
• Monitor blood glucose levels pre/op/post if
  sepsis is suspected and supplement if required

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Pyometra

• Benzodiazepines and opioids as premeds cause
  little C/V depression
• Induction mask best
• Maintain on isoflurane

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Cardiac patients

• 1. Reduced cardiac reserve avoid stress as this
  increases sympathetic tone and increases work
  load on the heart
• 2. If pulmonary edema present maybe require IPPV
• 3. may have or predispose to arrhythmias
• 4. Reduced myocardial contractility
• 5. reduced cardiac output favours brain perfusion
  so lt amounts of IV agents required even though
  induction may be slow

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Cardiac Disease drugs

• 1. opioids causes no significant reduction in
  myocardial contractility
• 2. Benzodiazepines minimal C/V effects
• 3. Phenothiazines only in VVV small doses,
  AVOID in cardiac tamponade
• 4. Barbituates/propofol slowly to effect, small
  doses
• 4. Isoflurane less arrythmiogenic effects
• 5. Anticholinergics

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Thoracotomy/Diaphragmatic hernia/Pneumothorax etc
Problem Solution
Cant breathe spontaneously once chest opened IPPV immediately after induction
May have stomach/intestines in chest cavity Dont use nitrous oxide.
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Diaphragmatic hernia
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Thoracic Surgery

• Pre Oxygenation is recommended
• Light sedation
• Quick induction and intubation
• Maintenance inhalational
• Pneumothorax avoid Nitrous oxide
• Take control of ventilation
• Neuromuscular blockers or
• Hyperventilation reduces PaCO2

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Thoracic Continued

• Mechanical ventilation
• Use of a ventilator or
• Anaesthetist squeezing rebreathing bag
• Post op
• Analgesics
• Local anaesthetics around the intercostal nerves

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Surgical fixes

• Widen nostrils

Remove everted laryngeal saccule
Trim soft palate
Permanent tracheostomy
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Lung disease
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Lung disease
Problem Solution
Prone to hypoxia Pre-oxygenate. Rapid induction - use 100 oxygen. May need to ventilate. Supplement oxygen post operatively. Avoid drugs causing i may be helpful to animals with pulmonary oedema.
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Kidney disease
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Kidney disease
Problem Solution
Kidney function reserve reduced Maintain renal perfusion - IV fluids essential. Avoid hypotension, dont use ACP.
May be azotaemic (high urea, creatinine) Avoid prolonged fluid restriction. Correct prior to GA.
May be dehydrated.
May be polyuric Need higher than maintenance rates for fluids
May have electrolyte disturbances, hypoalbuminaemia, anaemia Correct prior to GA.
Reduced renal clearance of drugs. Dont use ketamine. Ok to use propofol, thiopentone, opioids, benzodiazepines.
Reduced renal clearance of drugs.
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Kidney disease

• Correct if possible prior to induction
• May be dehydrated
• May have electrolyte abnormalities
• May be anaemic Why?
• Premedication may not be required
• Induction rapid
• Best inhalational techniques

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Liver disease
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Liver disease
Problem Solution
May have low plasma protein (esp. albumin) Use lower doses of protein bound drugs. Avoid fluid overload (prone to oedema)
May have reduced clotting time Evaluate before surgery
Prone to hypoglycaemia Supplement IV fluids with glucose. Monitor blood glucose.
Reduced ability to metabolise some drugs Avoid thiopentone, ACP, diazepam. Opiates and propofol are OK.
Maybe anaemic - reduced oxygen carrying capacity. Evaluate prior to GA 100 oxygen
May be jaundiced - bilirubin and endotoxins from gut affecting kidneys IV fluids
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Liver disease

• Considerations
• May have decreased plasma proteins (increases
  amount of free agents in blood)
• Clotting factors may be affected
• May have anaemia
• May have ascites or pleural effusions
• Premedication usually not desirable
• Induction ultra-short acting drugs or gas
• Maintenance best is Isoflurane

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The End