General anaesthesia Flashcards
What are the two main categories of anaesthesia?
General anaesthesia - making the patient unconscious
Regional anaesthesia - blocking feeling to an isolated area of the body
Why do we fast the patient?
Reduce the risk of stomach contents refluxing into the oropharynx, then being aspirated into the trachea.
What happens if gastric contents get into the airways during intubation?
Inflammatory response, causing pneumonitis.
When is risk of aspiration highest?
Before and during intubation, and when they are being extubated
Major causes of morbidity and mortality in anaesthetics
Aspiration pneumonia and pnuemonia
How do you fast a patient?
- 6 hours no food or feeds before operation
- 2 hours no clear fluids (fully ‘nil by mouth’)
What is preoxygenation?
Before being put under GA, the patient will breathe 100% oxygen for several minutes.
This gives them a reserve of oxygen for the period between losing consciousness and successful intubation and ventilation.
What is premedication?
Meds given before the patient is put under GA to relax, reduce anxiety, reduce pain and make intubation easier.
These may include:
* Benzodiazepines - relax muscles and reduce anxiety (also causes amnesia)
* Opiates - reduce pain, reduce hypertensive response to laryngoscope
* Alpha-2-adrenergic agonists - help with sedation and pain
What is RSI?
Rapid sequence induction/intubation
Gain control over airway asap in emergency scenario and detailed pre-planning is not possible.
Also used in non-emergency situations where the airway needs to be secured quickly to avoid aspiration, eg. patients with GORD or pregnancy.
Triad of GA
- Hypnosis
- Muscle relaxation
- Analgesia
Hypnotic agents and how are they given?
IV:
* Propofol (the most commonly used)
* Ketamine
* Thiopental sodium (less common)
* Etomidate (rarely used)
Inhaled options:
* Sevoflurane (most common)
* Desflurane (less favourable as bad for environment)
* Isoflurane (very rarely used)
* Nitrous oxide (combined with other anaesthetic meds - may be used for gas induction in kids)
Volatile anaesthetic agents?
Sevoflurane
Desflurane
Isoflurane
Are all volatile agents, need to be vaporised into a gas to be inhaled.
Common order of administration of anaesthetics?
Intravenous med first as induction agent (induce unconsciousness) and inhaled med used to maintain GA during the operation.
What is TIVA?
Total intravenous anaesthesia
Involves using IV medication (most commonly propofol) for induction and maintenance - gives a nicer recovery (as they wake up) compared with inhaled options.
What are the two categories of muscle relaxants?
- Depolarising (e.g. suxamethonium)
- Non-depolarising (e.g. rocuronium and atracurium)
How to reverse the effects of muscle relaxants?
Cholinesterase inhibitors (e.g. neostigmine) can reverse the effects of neuromuscular blocking meds.
Sugammadex is used to reverse the effects of non-depolarising muscle relaxants (rocuronium and vecuronium).
Commonly used opiates for analgesia?
- Fentanyl
*.Alfentanil - Remifentanil
- Morphine
Common antiemetics given to prevent post-op N+V?
- Ondansetron - avoid in patients at risk of prolonged QT interval.
- Dexamethasone - used with caution in diabetic or immunocompromised patients.
- Cyclizine - caution with HF and elderly patients.
What is ‘awareness under anaesthesia’?
Patient regains consciousness while still paralysed.
Risks of GA?
Sore throat and post-op nausea and vomiting are common adverse affects of GA.
Significant risks:
* Accidental awareness (waking during the anaesthetic)
* Aspiration
* Dental injury, mainly when the laryngoscope is used for intubation.
* Anaphylaxis
* Cardiovascular events (e.g. MI, stroke and arrhythmias)
* Malignant hyperthermia (rare)
*Death
What is malignant hyperthermia?
Rare but potentially fatal hypermetabolic response to anaesthesia. (Main risk with volatile anaesthetics and suxamethonium)
Malignant hyperthermia:
* Increased body temp
* Increased carbon dioxide production
* Tachycardia
* Muscle rigidity
* Acidosis
* Hyperkalaemia
How do you treat malignant hyperthermia?
Dantrolene
Dantrolene interrupts the muscle rigidity and hyper metabolism by interfering with the movement of calcium ions in skeletal muscle.
