Prepare and monitor anaesthesia in animals

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Prepare and monitor anaesthesia in animals

• PRE-ANAESTHETIC MEDICATIONS

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Premeds
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Why premed?

• What are the benefits of premeds?

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Why pre-meds?

• Pre-anaesthetic medication is frequently
  administrated prior to induction of general
  anaesthesia for a number of reasons.
• To calm control the patient
• To provide analgesia throughout surgery
• To reduce the amount of anaesthetic induction
  maintenance agent required
• To produce a smooth induction of anaesthetic
• To reduce some of the unwanted side-effects of
  some anaesthetic agents
• To ensure a smoother recovery from anaesthesia

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Why premed

• Reduce anaesthetic dose
• Analgesia
• Reduce stress of restraint
• Patient
• Staff
• Decrease saliva respiratory secretions
• Prevent bradycardia
• Muscle relaxation/paralysis
• Smoother induction and recovery
• Prevent vomiting

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Examples of premeds which

• Reduce Dose of anaesthetic
• Give Analgesia
• Give Sedation
• Give muscle relaxation
• Reduce salivation
• Increase heart rate (prevent bradycardia)

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Common premeds

• Anticholinergics
• Atropine
• Glycopyrrolate ( a long-acting atropine)
• Sedatives tranquillisers
• ACP, diazepam, midazolam, xylazine, medetomidine
• Dissociatives
• Ketamine, tiletamine
• Opioids
• Morphine, methadone, butorphanol, buprenorphine

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Choosing Premeds

• Depends on
• The species
• The anaesthetic agent to be used
• Personal preference of the vet practice
• The condition of the animal
• The availability

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Premeds Activity

• Read IVS, Mims, leaflets with the drugs.
• Select 3 premedicants and research uses,
  contraindications and modes of administration

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Tranquillisation Sedation

• Tranquillisers
• Reduce anxiety
• Sedatives
• Reduce anxiety depress CNS
• Thus also cause mental/physical depression
  ataxia etc
• Most veterinary premeds are Sedatives

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Common Sedatives

• Phenothiazines (e.g. acepromazine)
• Benzodiazepines (e.g. diazepam)
• Alpha-2 Agonists (e.g. xylazine)
• NMDA (Dissociatives (e.g. ketamine)

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Alpha-2 Agonists

• Xylazine (Xyalzil, Rompun)
• Reversed by yohimbine (Reversine)
• Medetomidine (Domitor)
• Reversed by atipemazole (Antisedan)

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Alpha-2 Agonists

• Reduce cardiac output
• Potent sedative rapid if given IV
• Some muscle relaxant properties
• Analgesic properties
• Effects largely reversible with a reversing drug
• Potent emetic in cats (v)
• Usually used in combination with ketamine to
  produce surgical anaesthesia
• Advised only to be used in young healthy patients
  
• Greatly reduce the required dose of injectable GA

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Xylazine

• Disadvantages
• Can cause profound cardiovascular pulmonary
  depression and arrhythmias due to increased
  vagal tone
• Respiratory depression if barbiturates or Saffan
  used as the anaesthetic agent
• Analgesic effect unpredictable
• Intense vasoconstriction (alpha-2 effect gt Pale
  /- Cyanotic MM
• Causes gt initial hyper-tension gt then severe
  bradycardia, hypo-tension, hypoventilation
  second degree heart block when given IV

YUCKY MM CRT !
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Medetomidine

• Domitor
• Duration 1.5 hrs
• Minimal respiratory depression
• Produces no effect on liver enzyme level, BUN or
  creatinine levels
• Disadvantages
• Produces vomiting in about 8 of dogs
• Profound bradycardia and decreased cardiac output
• Profound vasoconstriction

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Benzodiazepines

• Diazepam (Valium) and Midazolam (Hypnovel)
• Anticonvulsive
• Less sedative in animals than people
• Usually used in combination with other drugs such
  as ketamine and opiates
• Very safe drug
• Least respiratory depressant
• Fine for aged animals
• Can be used in animals with cardiovascular or
  respiratory disease
• Potentates the effects of most anaesthetic and
  narcotic analgesics
• Muscle relaxant

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Diazepam

• Disadvantages
• Can increase pain perception in humans so it is
  possible that this also occurs in animals.
  Therefore should be given with an analgesic
• Some preparations given IM are painful and
  irritate the local tissue
• If mixed with atropine in the same syringe
  precipitation occurs
• No anti-emetic effect
• Can cause excitement in some animals

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Midazolam

• Versed
• Similar to Valium
• Water soluble
• Excellent sedation muscle relaxation in birds

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Phenothiazines

• Examples
• Acetylpromazine
• Chlorpromazine
• Promazine
• Act as tranquillizers in some species and
  sedatives in others
• Dose dependant effects- dose varies according to
  route, age, species and whether used alone or
  together with an opiate
• Given IV or SC

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Acepromazine

• Sedation usually
• Potentates the action of anaesthetic agents and
  therefore reduces the dosage of the agent
• Can extend the duration of the anaesthetic agent
• Promotes smooth recovery
• Inhibits vomiting ( use for car sickness)
• Protects the heart from arrhythmias associated
  with barbiturate GA catecholamine release
• Do not produce addiction
• Usually used in combinations such as opiates,
  atropine

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Acepromazine

• Disadvantages
• Respiratory depression
• Hypotension
• Hypothermia
• Involuntary muscle twitching
• Ataxia
• Nictitating membrane prolapse
• May precipitate convulsions may be aggression
• Non reversible
• No analgesia
• Has been associated with decreased platelet
  aggregation

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Acepromazine

• Not in Boxer dogs
• Bradycardia, hypotension
• Apparently not dependent on dose given
• DO NOT use where
• Risk of seizures
• Clotting deficits
• Caesarean section
• Crosses the placental barrier gt depresses pups
• Hypotension/dehydration/shock

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Opioids

• Pethidine - synthetic
• Morphine - natural
• Oxymorphone
• Butorphanol semi -synthetic
• Buprenorphine semi synthetic
• Methadone

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Opioids

• There is multiple receptor types that exist each
  causing different responses and different opioids
  stimulate (agonists) and/ or antagonize
  (antagonists) them
• Ones that are both agonists and antagonists can
  reverse the effects of the pure mu agonists such
  as morphine
• Receptor types are
• Mu
• Kappa
• Sigma

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Agonist Antagonist

• Agonist activates a receptor
• Full agonist
• Partial agonist
• Antagonist inactivates a receptor

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Mu

• Supraspinal analgesia
• Respiratory depression
• Euphoria
• Bradycardia
• Hypothermia
• Dependence
• Tolerance

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Kappa

• Spinal analgesia
• Sedation

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Sigma

• Dysphoria
• Hallucinations

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3 Opiates
Duration(hrs) Receptor Notes
Morphine 4 Mu ag Sedation, respiratory depression, bradycardia, nausea, hypothermia, hyperthermia in cats, dysphoria in cats without pain or excessive dose
Butorphanol 1-3 (dog)4 (cat) Mu antag Mild or no sedation, mild ventilatory depression
Buprenorphine 6-8 Mu partial ag Prolonged sleep times, vomiting, respiratory depression, difficult to antagonise
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Opioids

• Agonists
• Morphine, pethidine, oxymorphone, fentanyl
  (Sublimaze), carfentanil
• Agonist antagonists
• Pentazocine, butorphanol (torbugesic),
  nalbuphine, buprenorphine (temgesic)
• Antagonists
• naloxone

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Opioids

• Advantages
• Potent analgesics
• Sedation
• Reduces amount of anaesthetic agent required
• Reversible using for example Naloxone
• They may be safer in some cases of heart failure
  or pulmonary oedema than some sedatives because
  it increases the capacitance of great veins so
  lowers BP

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Opioids

• Disadvantages
• Considerable species variation
• Cats horses may get psychotic episodes of
  excitement
• Can depress the respiration and BP may be severe
• Decrease HR and cardiac output
• Require special storage dispensing conditions
• Not always predictable
• Hyper-responsive to sound
• Some may lead to post operative vomiting or
  constipation such as morphine , fentanyl
  butorphanol
• Crosses the placental barrier
• Predispose to hyperthermia

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Opioids

• Disadvantages (contd)
• Morphine causes contraction of the sphincter of
  Oddi and therefore is contraindicated with
  biliary stasis
• Morphine give IV can cause release of histamine
  causing CV collapse, therefore not advisable to
  administer IV to conscious dogs and cats. May
  happen with S/C or IM administration
• If this happens give supportive treatment with
  steroids and fluids
• Morphine is painful on injection

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Neurolept-analgesia

• Term for Major Tranquilliser Opioid
• Very good combination of sedation, restraint
  analgesia
• E.g.
• ACP Methadone
• ACP Buprenorphine
• Diazepam Fentanyl

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Dissociative Anaesthetics

• Ketamine and Tiletamine (Zoletil)
• can also be used for sedation at lower doses

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Atropine

• Is an anticholinergic
• Decreases activity of neurotransmitter
  acetylcholine in parasympathetic nervous system
• Routine use declining
• Onset of action slow 10-15 minutes
• ? HR 30 min
• What does this mean for long anaesthetics?
• ? salivation several hours
• ? pupil dilation many hours

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Atropine

• Indications
• Bradycardia
• Vago-vagal reflex (eye laryngeal surgery)
• Salivation
• OP poisoning
• Contra-indications
• Marked tachycardia
• Hyperthermia
• Animals with hyperthyroidism, paralytic ileus,
  glaucoma
• Not advised to use in horses (increases chance of
  colic)
• Endoscopic examinations of duodenum as causes
  spasm of pyloric sphincter

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Atropine

• ? bronchial salivary secretions
• Protects heart from vagal reflex at intubation
  and during surgery, esp eye surgery (vasovagal
  reflex)
• Pupillary dilation
• Hence its scientificname Atropa belladonna
• Mild GIT spasm-relieving agent
• Given by many routes SC, IM, IV, IP
• Usual doses dog/cat 0.04 mg/kg SC, 0.02 mg/kg IV
  rabbit 1 mg/kg SC usual formulation 0.6 mg/mL

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Atropine Blocks Acetylcholine

• Amanita muscaria, the "fly agaric" taken on
  Devil's Thumb Trail near Boulder Colorado. This
  is the source of muscarine, the agonist for the
  metabotropic Acetylcholine receptor ("muscarinic
  receptor").

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Special considerations

• Atropine
• Rabbits rapidly metabolize atropine (need more
  top ups)
• Guinea pigs always need atropine to prevent
  bronchial secretions blocking their narrow airways

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Glycopyrrolate

• Used mainly in ruminants
• Twice as potent as atropine
• Lasts twice as long up to 4 hours
• Less likely to cause a tachycardia
• Others are Scopolamine Methylatropine nitrate

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Dose Calculations (mL needed)

• Atropine
• Bottle Concentration 0.65 mg/mL
• Required dose rate 0.05 mg/kg
• 13 kg dog
• Morphine
• Bottle concentration 10 mg/mL
• Dose rate 0.5 mg/kg
• 26 kg dog

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Suggest premedication for?

• Geriatric poodle with mild cardiac disease for a
  dental including extractions
• A young Labrador for routine desexing
• A Samoyed for orthopaedic surgery
• An aggressive 4 year old male German Shepherd for
  desexing
• A 6 month old cat for desexing
• A 12 week old puppy for hernia repair
• A young boxer dog for lumpectomy
• A young Cocker spaniel with a history of
  epilepsy for an ear clean and haematoma drainage

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Appendices
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Premed dose rates
Drug Dose rate (mg/kg) Concentration (mg/ml) Route
Acepromazine 0.02 0.05 2 IM / SC
Morphine 0.3 0.5 10 or 30 IM / SC
Methadone 0.3 0.5 10 IM / SC
Buprenorphine 0.01 0.03 0.3 IM / SC
Butorphanol 0.1 0.4 10 IM / SC
Diazepam 0.2 0.5 5 IM / SC / IV
Midazolam 0.2 0.3 5 IM / SC / IV
Atropine 0.02 0.04 0.6 IM / SC / IV
Zoletil 3 100 IM / SC
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Acepromazine

• Phenothiazine
• Mechanism of action
• Blocking excitatory dopamine receptors
• Effects
• Dose-related sedation
• Degree of sedation is variable and unpredictable
  (more reliable in dogs)
• Central anti-emetic action and extrapyramidal
  effect (high dose)
• Lower seizure threshold DO NOT use in animals
  with history of seizuring and in premedication
  prior to myelography
• Depresses hypothalamic thermoregulation Use
  heating devices
• Causes peripheral vasodilatation ? hypotension

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Acepromazine

• Metabolism
• Liver
• Excretion
• Renal
• Dose rate
• 0.01 0.05 mg/kg
• Route of administration
• IM
• SC
• IV
• Note
• DO NOT use in boxers prone to hypotension,
• bradycardia and syncope, effect is not dose
  related

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Acepromazine

• Concentration
• 2 mg/ml
• Duration of action
• 2 6 hrs
• Onset of effect
• 20 40 min after IM / SC
• Colour
• yellow

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Morphine

• Pure agonist at all opioid receptor sites
• Dose dependent sedation and analgesia
• Effective premedicant (esp. combination with
  tranquillizer)
• Potent analgesic
• Vomiting and defaecation are very common
• Poor lipid solubility, crosses BBB slowly
• Elimination half life
• 1 2 hrs
• Metabolism
• Liver
• Duration of action
• 2 4 hrs (depends on
• dose and route of
• administration)
• Note
• When given rapidly IV, may cause histamine
  release ? marked hypotension
• IV doses are only about 0.1 0.2 mg / kg, do not
  exceed 0.2 mg / kg
• Causes urinary retention
• 1ml glass vials

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Methadone

• Synthetic opioid
• Equipotent to morphine
• Less incidence of vomiting
• High lipid solubility, more rapid onset of action
  than morphine
• Causes less constipation
• May cause panting
• Very long terminal half life
• 35 hrs
• Duration of a single dose
• 4 - 6 hrs
• Colour
• Clear
• Dose rate
• 0.1 1.0 mg/kg
• Concentration
• 10 mg/ml
• Route of administration
• IM
• SC

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Buprenorphine

• Partial µ agonist
• Mechanism of action
• Binds to and dissociates from the µ receptor very
  slowly
• Very difficult to reverse with naloxone
• Limited analgesic effectiveness
• Slow onset of action (even with IV
  administration)
• Up to 30 min
• Prolonged duration of action
• Up to 12 hrs
• Route of administration
• IM
• SC
• IV
• Colour
• Clear
• Dose rate
• 0.01 0.03 mg/kg
• Concentration
• 0.3 mg/ml

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Butorphanol

• µ antagonist and ? agonist
• Respiratory depressant effects are not as marked
• Potent anti-tussive
• Effective against mild to moderate pain
• Can be used to reverse some of the respiratory
  depressant effects of pure µ agonist
• Plasma half life
• 3 4 hrs
• Clinical effects
• About 2 hrs
• Dose rate
• 0.1 0.4 mg/kg
• Concentration
• 10 mg/ml
• Colour
• clear
• Route of administration
• IV
• IM
• SC

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Benzodiazepines

• Diazepam Midazolam
• Mechanism of action
• Stimulates inhibitory gamma amino butyric acid
  (GABA) neurones in the CNS causing sedation and
  anticonvulsant effects
• Unreliable sedative effect in healthy animals
• No intrinsic analgesic properties
• Good muscle relaxant
• Usage
• In combination with ketamine for sedation and
  anaesthesia in cats
• Anticonvulsant
• Relieve post-operative restlessness in
  conjunction with opioid analgesics
• Appetite stimulants in cats
• Sedation of old and debilitated animals esp. with
  cardiovascular and respiratory disease
• Metabolism
• Primarily liver
• Note
• Little cardiovascular and respiratory depression
  on its own

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Diazepam

• Valium / Pamlin
• Active substance is dissolved in a propylene
  glycol base which
• is water insoluble and does not mix well with
  other drugs
• Can cause thrombophlebitis and pain on IV
  injection
• If injected rapidly IV, can cause haemolysis,
  hypotension and cardiac arrhythmia
• Effect after SC or IM injection is unpredictable
  because it is unreliably absorbed
• More fat soluble than midazolam
• Duration of action
• 15 20 min
• Dose rate
• 0.2 0.5 mg/kg
• Concentration
• 5 mg/ml
• Note
• Do not draw up and leave it in syringe as it
  adheres to plastic. Therefore, draw up
  immediately before use.
• Colour
• White / pale yellow
• Route of administration
• IV

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Midazolam

• Water soluble benzodiazepine
• Minimal local irritation on IM or IV injection
• Rapid absorption and onset of action after IM
  injection
• Duration of action
• Similar to diazepam (15 20 min)
• Dose rate
• 0.1 0.3 mg/kg
• Concentration
• 5 mg/ml
• Colour
• White / clear
• Route of administration
• IM
• SC
• IV

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Atropine

• Anticholinergic
• Tertiary ammonium alkaloid compound
• Indications
• Reduce salivary and bronchial secretions
• Prevent vagally mediated bradyarrhythmias
• Contraindications
• Tachycardia and/or ventricular dysrhythmia
• Hypertrophic cardiomyopathy
• Hyperthermia
• Hyperthyroidism
• Paralytic ileus
• Increased intraocular pressure e.g. perforating
  eye injury, glaucoma
• Effects
• Pupillary dilation and unopposed sympathetic
  dilator activity (mydriasis)
• Paralysis of ciliary muscle (cycloplegia)
• Increases intra-ocular pressure
• Toxic doses result in CNS excitement followed by
  depression
• Paralysis of bronchial glands
• Decreased volume

• Metabolism
• Mainly liver
• Elimination half life
• 2 5 hrs
• Duration of cardiac effect
• 30 40 min
• Anti-sialagogue effect
• Longer
• Dose rate
• 0.02 0.04 mg/kg
• Concentration
• 0.6 mg/ml
• Colour
• Clear
• Route of administration
• IM
• SC
• IV

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Zoletil

• Mechanism of action
• Interrupts ascending transmission from
  unconscious
• to conscious parts of the brain
  (thalamoneocortical
• and limbic systems)
• Longer acting dissociative agent (tiletamine) in
  combination with a benzodiazepine
• Cataleptic state
• Eyes remain open
• Muscle rigidity
• Nystagmus in some species
• Spontaneous limb movements
• May cause rough recoveries. Therefore, addition
  of 0.02 mg/kg Acepromazine will decrease the
  effect.
• Rapid onset of action
• Dose rate (cats)
• 3 mg/kg
• Concentration
• 100 mg/ml
• Route of administration
• IM
• IV

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Routes of Premed Administration

• Intramuscular (preferred)
• More reliable absorption of drugs, thus more
  reliable sedation
• Difficult to perform on agitated / excited
  animals
• More painful
• Sites
• Lumbar (preferred)
• Thigh quadriceps m. (cranial to femur)

• Subcutaneous
• Less reliable absorption of drugs, thus less
  reliable sedation
• Easier to perform on agitated / excited animals
• Less painful
• Sites
• Back of neck (preferred)
• Flank

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The End