General Anaesthetics Flashcards
What are the two broad types of anaesthesia
- General anaesthesia - makes patient unconscious
- Local/regional - blocks feeling to localised region e.g. limb
Fasting before GA
1. Purpose
2. When is the patient at highest risk of aspiration
3. Major causes of morbidity/mortality in anaesthetics
4. Fasting time-frames
- empty stomach = reduced risk of reflux = reduced risk of aspiration pneumonitis
- Before and during intubation, and when they are extubated (once the endotracheal tube is correctly fitted, the airway is blocked and protected from aspiration)
- Aspiration pneumonitis and pneumonia
- 6 hours of no food or feeds before the operation
2 hours of no clear fluids (fully “nil by mouth”)
Emergency –> RSI (rapid-sequence induction)
Preoxygenation
1. What is it
2. What physiological measure of spirometry is it relevant to
- Before GA, patient on 100% O2 –> O2 reserve for period between loss of consciousness and intubation + ventilation.
Emergency –> may be skipped
- Functional reserve capacity - the volume remaining in the lungs after a normal, passive exhalation
Premedication
1. Purpose
2. Examples (BOA)
- relaxation, reduce anxiety, reduce pain and make intubation easier
Benzodiazepines (e.g., midazolam) –> muscle relaxation + reduce anxiety (also causes amnesia)
Opiates (e.g., fentanyl or alfentanyl) –> reduce pain and reduce the hypertensive response to the laryngoscope
Alpha-2-adrenergic agonists (e.g., clonidine), which can help with sedation and pain
Rapid Sequence Induction/Intubation (RSI)
1. What is it
2. Why is it higher risk than normal intubation
3. What are its uses non-emergency
4. What is the single highest risk of RSI
5. How can you reduce the risk of 4.
- Gain airway control quickly and safely in emergency scenario using an ET tube as soon as possible after induction (patient unconscious)
- No fasting
- No pre-planning e.g. difficult airway
3.GORD or pregnancy
- Aspiration
5.
1. more upright bed
2. Cricoid pressure?
Hypnotic agents
1. What is their use
2. How can they be delivered to the patient
- Make patient unconscious
- IV or inhaled
What is the triad of general anaesthesia (HMA)
Hypnosis
Muscle relaxation
Analgesia
Examples of IV hypnotic agents (PKTE)
Propofol (the most commonly used)
Ketamine
Thiopental sodium (less common)
Etomidate (rarely used)
Examples of inhaled hypnotic agents (SDI fluranes + NO)
Sevoflurane (the most commonly used)
Desflurane (less favourable as bad for the environment)
Isoflurane (very rarely used)
Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)
- What characteristic do sevoflurane, desflurane and isoflurane share in common?
- What device is used to deliver these agents?
- All are volatile anaesthetic agents i.e. liquid at room temperature and need to be vaporised into a gas to be inhaled.
- Vaporiser (liquid poured into and turned to vapour mixed with air –> conc can be altered to control depth of anaesthesia)
Which agent is usually given first (IV or inhaled)?
1. Why
2. What is TIVA?
IV to induce, inhaled to maintain
1. IV acts quicker, while inhaled must diffuse across lung tissue until ideal concentration is reached
2. TIVA = Total intravenous anaesthesia i.e. IV used throughout (easier wake up)
Muscle relaxants (Neuromuscular blockers)
1. MoA
2. Types
3. How to reverse
- Block nicotinic N1 receptors in neuromuscular junctions, preventing skeletal muscle stimulation –> relax and paralyse muscle –> intubation is easier
- Depolarising - suxamethonium
Non-depolarising - Rocuronium, atracurium - Cholinesterase inhibitors e.g. neostigmine
What is Sugammadex
Used specifically to reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium)
Adverse effects of volatile anaesthetic agents
- Myocardial depression
- Malignant hyperthermia
- Halothane (not commonly used now) is hepatotoxic
Adverse effects of nitrous oxide
May diffuse into gas-filled body compartments → increase in pressure → avoid in pneumothorax
