Drug Summaries:
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Drug
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Features
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Adverse effects
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Premedication
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Xylazine
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- Alpha-2 agonist
- Sedative
- Analgesic
- Muscle relaxant
- Reversible
- Sedative effects last longer than analgesic effect
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- Bradycardia
- Emesis
- Salivation
- Vasoconstriction followed by hypotension
- Hypoventilation
- Thermoregulation – matches env. Temp
- Bradydysrhythmias or ventricular arrhythmias – potentially fatal
- Catastrophic if cardiac dz is present
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Induction
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Ketamine
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- Dissociative anesthetic
- Wide safety margin
- Wide dose range
- Safe agent – minimal CV and respiratory effects
- 1-2 minute of onset
- Preserves cranial and airway reflexes
- Must be combined with a muscle relaxant
- Lubricate eyes to avoid dry cornea
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- Does not provide good relief from visceral pain
- Muscle rigidity and involuntary movement
- Convulsions
- Prolonged recovery (especially if topping off)
- Ataxia
- Excitement/bizarre behavior, vocalization
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Diazepam
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- Benzodiazepines
- Mild sedatives
- Centrally mediated muscle relaxation
- Anticonvulsant
- Synergistic effects with other drugs
- No respiratory or CV effects at clinical doses
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- Can cause excitement if used on its own
- Long ½ life = 21-37 hours
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If something worries you = ASK FOR HELP
- Don’t panic…
- Xylazine – heart rate can easily drop to 30
- Individual variability in metabolic rate / drug metabolism
- Ask the surgeons to stop what they are doing
- Reassess the patient without surgical stimulation
- Check equipment – eg absent heart beat may be due to esophageal stethoscope moving cranially
- Decide to administer more anesthetic drugs
- Better to give lower top up and repeat if needed
- Wait for drugs to take effect – at least 2 minutes
- Consider Other drugs – eg Atropine
- Emergency Situations
- 1st step – is it actually an emergency?
- Airway, Breathing, Circulation
- Emergencies that you are most likely to see
- Cardiac arrest – most likely (esp with Xylazine)
- Respiratory arrest
- Emergency action
- Can you ventilate patient?
- ET tube + manual ventilation with AMBU bag (avoid hyper/over inflation)
- Is the heart beating?
- Cardiac massage – 80-100bpm
- Can you feel a pulse?
- Carotid, femoral
- Drugs: Epinephrine, atropine, lidocaine
- IV Fluid bolus = 90ml/kg over 15 minutes (dog)
Additional clinical notes:
- If monitor every 5-10 minutes – will be able to spot any changes and will be able to intervene before a dog moves
- BE CONSISTENT If you want to detect changes
- Expect reaction when traction on ovarian pedicle (tachycardia, patient movement)
- If on light plane, will wake up when start pulling ovarian and require top-ups
- “Topping Up”
- Ketamine: Give fractions of induction does (eg Ketamine at 2mg/kg)
- Repeated top-up doses can cause prolonged recovery
- Max dose for anesthesia = 20-30mg/kg → We’re only using 5mg/kg
- Xylazine: Give 1/10 the initial dose
- May supply 10-15 minutes additional relaxation and analgesia
- Be aware of cardiovascular effects – BRADYCARDIA (reflex vagal response to vasoconstriction and hypertension and decreased sympathetic outflow from CNS)
- Recovery will be prolonged à esp with lots of top ups
- Ketamine may cause hallucinations, ataxia
- Can use ace for dysphoria, but not in geriatric patients due to risk of hypotension
- Likely problems to be encountered
- Dogs with pre-existing conditions: cardiac abnormalities, renal insufficiency, respiratory disease, emaciation, parasites
- These should be assessed during our THOROUGH PHYSICAL EXAMS
- Lightening of anesthetic plane → patient moving on surgery table
- Regurgitation/vomit – why we intubate
- May need to flush esophagus
- Bradycardia – likely due to Xylazine
- After 2 hours, bradycardia not likely related to xylazine anymore – probably OK to treat with Atropine
- Poor quality recovery