Anaesthesia Flashcards
a) Phases of general anaesthesia (4)
b) Commonly used medication at each phase, and how administered
a) 1. Premedication, sedation
2. Induction
3. Maintenance
4. Recovery
b) Premedication: Acepromazine, α2 - agonists, opioids, benzodiazepines → tranquilisation / IV catheterisation
Induction: Propofol, alfaxalone → patent airways must be established
Maintenance: Isoflurane, sevoflurane → maintain patent airways, ventilatory support, monitor vitals
Recovery: α2 - agonists, opioids, NSAIDs → highest risk, vitals must be monitored until normalised
Main components of anaesthesia (4), where is affected with each component, and other features
- Unconsciousness: Reticular formation, Locus Caeruleus, frontal and prefrontal cortex → transient loss of memory
- Myorelaxation: Skeletal muscles, neuromuscular junction → loss of protective reflexes
- Immobility: Motor area of cerebral cortex → respiratory and cardiovascular depression
- Analgesia: Peripheral nociceptors, spinal cord, somatosensory cortex → impaired thermoregulation
Related risks of peri-anaesthetic complications (4)
- Species related
- Patient related
- Clinical status related (ASA-risk)
- Procedure related
Patient-related anaesthetic risks (3)
- Small/young animals - hypothermia
- Patient with liver dysfunction - bleeding, hypoglycaemic, delayed recovery
- Barchycephalic breeds - respiratory dysfunction / upper airway obstruction, high parasympathetic tone
ASA risk classification categories
ASA 1: normal healthy patient - minimal risk (eg castrate)
ASA 2: patient with mild systemic disease - slight risk (eg neonate, geriatric, controlled diabetic)
ASA 3: patient with obvious systemic disease - moderate risk (eg anaemic, liver disease, not well-controlled hyperthyroidism)
ASA 4: patient with severe systemic disease that is a constant threat to life - high risk (eg shock, uncontrolled diabetes, uncompensated heart disease)
ASA 5: patient not expected to survive without the operation - extreme risk (eg severe trauma, advanced heart disease)
ASA 6: patient declared brain dead, organs being used for donation
Premedication (sedation)
Overview of drug classes and licensing (5 types, 4 species types)
Premedication (sedation)
Phenothiazines: Acepromazine
a) Who is it suitable for
b) Pros (4) and cons (5)
a) Suitable for young healthy patients, risks in old geriatric patients
b) Pros: reliable in dogs, long-acting for smooth recovery, anti-arrhythmic properties, cheap and licensed
Cons: Unreliable in cats, long-lasting side effects, vasodilation causes hypotension, no analgesia, poor choice for aggressive animals
Premedication (sedation)
Phenothiazines: Acepromazine
mechanism of action
Premedication (sedation)
Butyrophenones (Azaperone)
Essential info
- Similar mechanism to acepromazine and can also produce hypotensive effects
- It is the only sedative licensed in pigs, and is only licensed for pigs
Premedication (sedation)
α2 agonists
a) Examples
b) Who suitable for/not suitable for
c) Pros and cons
a) Medetomidine, Dexmedetomidine (dogs and cats), Xylazine(dogs and cats, horses, cows), Romifidine (horses)
b) Suitable for young healthy patients, aggressive patients (IM) and non-conventional species. Not suitable for diabetic patients, >ASA 3 patients, cardiac disease patients
c) Pros: Good spinal analgesia, reliable in cats, dogs and equine, short acting, it’s an antagonisable sedative (Atipamezole an α2-antagonist can reverse effects)
Cons: Arrhythmogenic, hypertension/hypotension, cardiac and respiratory depression, moderately expensive
Premedication (sedation)
α2-agonists
a) Mechanism of action
b) Order of selectivity (α2 < α1)
b) Highest selectivity: Dexmedetomidine → Medetomidine → Romifidine → Detomidine → Xylazine :Lowest selectivity
(Dirty Minded Rabbits Don’t (need) X-rays)
Premedication (sedation)
Benzodiazepines
a) Examples
b) Who is it suitable for/not suitable for
c) Pros and Cons
a) Midazolam, Diazepam, Zolazepam
b) Suitable for seizure patients, fractious patients, old geriatric patients, cardiac disease patients, neonatal patients. Not suitable for young healthy patients, hepatic encephalopathy patients
c) Pros: Minimal cardio/respiratory effects, myorelaxation, can be used in neonates and geriatrics, anticonvulsant
Cons: Unreliable in small animals, behavioural excitability, antagonists are expensive, myorelaxation can lead to respiratory dysfunction
Premedication (sedation)
Opiods
a) Examples
b) Who suitable for
c) Pros and cons
d) What are they used synergistically with
a) Methadone, Buprenorphine, Fentanyl (cats and dogs), Butorphanol(cats and dogs, horses)
b) Suitable for invasive surgical patients, painful patients, cardiac disease patients. Risks in respiratory patients, asthmatic/allergic patients
c) Pros: Powerful analgesia, sedative effects, safe to use in cardiac patients, antagonisable sedative - NARCAN
d) Acepromazine, α2 agonists, benzodiazepines
Premedication (sedation)
Benzodiazepines mechanism of action
Premedication (sedation)
a) How do dosages change of acepromazine and α2 agonists when used in combination
b) Sedatives that must be administered IV
a) Decreased
b) Diazepam (benzodiazepine) and Fentanyl (opiod)
Premedication (sedative)
Opiod mechanism of action
Induction of anaesthesia
Stages of anaesthesia
Induction of anaesthesia
a) Steps of anaesthetic induction (6)
b) Advantages vs disadvantages of IV anaesthetic administration
a) 1. IM premedication 2. IV catheter placement 3. Pre-oxygenation 4. Anaesthetic agent administration 5. Endotracheal intubation 6. Connection to breathing system
Induction of anaesthesia
a) IV only drugs
b) IM and IV drugs
c) What is pre-oxygenation
a) Propofol, Ketamine, Thiopental
b) Zolazepam, Ketamine, Alfaxalone
c) 100% oxygen for 3 to 5 minutes
Induction of anaesthesia
Propofol mechanism of action + side effects
- Most common induction agent for dogs and cats
- Rapidly metabolised in liver and lungs (short duration)
- 2-6 mg/kg administered slowly, over 30-40s
Induction of anaesthesia
Alfaxalone mechanism of action + side effects
- Rapid hepatic metabolism
- 1-2 mg/kg IV over 45-60s
- Baroreceptor reflex better preserved than with propofol
Induction of anaesthesia
Ketamine mechanism of action + side effects
- More commonly used for large animals, used at sub-anaesthetic doses in dogs and cats as a complementary analgesic
- Poor myorelaxation, so often co-administered with benzodiazepines
Induction of anaesthesia
Etomidate mechanism of action + side effects
- Used particularly in animals with severe cardiovascular compromise as few effects on arterial blood pressure and cardiac rhythm
Induction of anaesthesia
a) Use of Tiletamine/zolazepam
b) Inhalation anaesthetics
a) Fixed 1:1 combination. Tiletamine produces similar analgesia to ketamine, zolazepam gives muscle relaxation.
IM dose: 10-20 mg/kg, 2-5 min onset
IV dose: 5-10 mg/kg, 30-60s onset
b) When IV access not possible, but this technique often causes distress to the animal.
Sevoflurane in oxygen is preferred as is less irritating on airways than isoflurane.
Breath holding is a problem