Anaesthetics Overview Flashcards
What are the three stages of GA?
Induction
Maintenance
Emergence/reversal
What are the components of the anaesthetic triad?
Unconsciousness
Muscle relaxation
Analgesia
Which agent is most commonly used for induction of GA?
IV propofol
What is the onset and offset time for propofol?
Onset about 30 seconds
Offset 3-7 minutes
What are some of the physiological effects of propofol?
Hypnosis Myocardial depression Reduced SVR Respiratory depression Obtunds upper airway reflexes (good for putting in LMA)
Which allergy would be a contraindication for propofol?
Egg
Which factors might lead to a delay in induction of anaesthesia?
Slow arm to brain circulation time e.g. elderly, CVD
Patient anxiety
Recreational drug use
Extravasation (drug leaks out of vein)
Which other type of agent is used for induction?
Inhalation of volatile agent e.g. sevoflurane
In which situations is inhaled induction commonly used?
Paediatrics
Cases of difficult airway
Difficult IV access
Inhaled foreign body (maintaining spontaneous ventilation is preferable)
Why is rapid sequence induction (RSI) used?
To minimise risk of regurgitation + aspiration
Give some examples of when RSI might be used:
Bowel obstruction or intra-abdominal pathology
Un-fasted patient in an emergency or trauma situation
Obstetric emergency
Strong history of reflux
How does RSI work?
Pre-oxygenation with 100% O2
Cricoid pressure (compress oesophagus) –> prevents regurgitation of gastric contents
Pre-oxygenation plus rapid induction + paralysis removes the need for bag + mask ventilation before intubation
–> risk of gastric insufflation + regurgitation is reduced
What are the different types of muscle relaxants?
Depolarising –> e.g. suxamethonium
Non-depolarising –> e.g. atracurium, rocuronium
When is suxamethonium a good muscle relaxant to use?
RSI Difficult airway (as wears off quickly)
What are some side effects of suxamethonium?
Muscle pain (as causes fasciculations during the operation) Jaw rigidity Hyperkalaemia (can be toxic) Bradycardia Malignant hyperthermia
How is muscle relaxation monitored during surgery?
Peripheral nerve stimulator used to monitor NMJ function
What are the options for maintaining the airway in an anaesthetised patient?
Supraglottic device e.g. LMA
ET tube
Where does an LMA sit?
Above the vocal cords –> no protection against aspiration
Where does an ET tube sit?
Passes through vocal cords, cuff inflated
–> airway protected (secure)
What are the options for maintenance of anaesthesia?
Usually inhaled volatile agents (induction with propofol, maintained with volatile agent)
Or continuous infusion of IV agent
What are some of the systemic effects of GA?
Reduced BP
Ventilation can impede venous return –> reduced preload + CO
Respiratory depression
Loss of airway reflexes + tone
Why is BP reduced during GA?
Vasodilation (reduced SVR) Negative inotropy (reduced SV) Negative chronotropy (reduced HR)
Are induction agents anti-emetic or emetogenic?
Propofol –> antiemetic
Volatile agents –> emetogenic
Why is ketamine different to other anaesthetic agents?
Maintains CV stability
Preserves muscle tone + airway patency
Bronchodilator
In which situations is ketamine useful for anaesthesia?
Haemodynamically unstable patients
In the developing world + field medicine
What must be ensured before emergence from GA?
Adequate analgesia
Anti-emetic
NMJ function restored
Why is analgesia still given during GA when the patient is unconscious?
Surgery will elicit a sympathetic response –> analgesia presents this
Also essential for smooth emergence and comfort immediately after surgery
Which analgesia is most often used during surgery?
Fentanyl
Why is temperature monitored during surgery?
Patient susceptible to hypothermia due to:
- vasodilation
- convection
- radiation
- conduction
- evaporation
- loss of shivering
How might a patient be warmed during surgery?
Warm air devices
Warmed fluids
What is ‘awareness’ during anaesthesia?
Unplanned recall of events under GA
Which drugs might be used to increase HR during surgery?
Antimuscarinic e.g. atropine
Which drugs might be used to reduce HR during surgery?
Beta-blockers
Which drugs might be used to increase BP during surgery?
Alpha agonists e.g. metaraminol
Which drugs might be used to reduced BP during surgery?
Alpha antagonists e.g. phentolamine
