Zero to Finals : General anaesthesia Flashcards
What are the 2 main categories of anaesthesia?
- General
- Regional
Define general anaesthesia
Making the patient unconcious
Define Regional anaesthesia
Blocking feeling to an isolated area of the body
What type of respiratory support is in place during general anesthesia for an operation?
- Intubation / Supraglottic airway device
breathing suppoerted by ventilator
Patient is continuously monitored at all times immediately before, during and after general anaesthesia
Prior to general anaesthesia, what type of preperation must be done?
If possible:
* Fasting (reduce risk of reflux and spiration)
What are the possible consequences of a patient not fasting prior to undergoing general anaesthesia?
Preperation
- Aspiration of gastric contents into airway -> inflammitory response (pneumonitis)
Highest risk before and during intubation and during extubation
What are the 2 major causes of morbidity and mortality in general anaesthetics?
Preperation
- Apiration pneumonitis
- Pneumonia
Although rare in non-emergency planned procedures
How long is the fasting period typically?
Preperation
- 6hrs (no food/feeds) prior to op
- 2 hrs of no clear fluids (NBM)
NBM: nil by mouth
Why is it important to preoxygenate the patinet prior to undergoing general anaesthesia?
Preperation
To provide a reserve of oxygen for the period between when they lose consciousness and are successfully intubated and ventilated (in case the anaesthetist has difficulty establishing the airway)
Patinet breathes 100& O2 for several mins prior to going under
What medications may be given to a patient prior to the undergoing general anaesthesia?
Preperation
- Benzodiazepines (e.g. midazolam): muscle relaxant/reduce anxiety, causes amnesia
- Opiates (e.g. fentayl/alfentanyl): pain management/reducehypertensive response to laryngoscope
- Alpha-2-adregenic agonist (e.g. clonidine): sedation/pain
When is RSI performed?
What is RSI?
RSI= Rapid Sequance Induction/Intubation
- Gain control over the airway (quickly/safely) in emergency situations
- Non-emergency situations where the airway needs to be secured quickly to avoid aspiration (e.g. GORD/Pregnancy )
How may the risks associated with performing RSI be minimised?
Risk: Aspiration of stomach contents
Minimised by:
* Bed positioned upright
* Cricoid pressure (compress oesophagus/prevent reflux- ONLY used by trained/experinced health professionals)
Whta is the triad of General Anaesthesia?
- Hypnosis
- Muscle relaxation
- Analgesia
What 2 modes may hypnosis be induced in patients?
Hyponsis
- IV
- Inhalational
List some hypnotic IV agents used in GA?
- Propofol (the most commonly used)
- Ketamine
- Thiopental sodium (less common)
- Etomidate (rarely used)
What are some adverse effects of propofol?
- Pain on injection (due to activation of the pain receptor TRPA1)
- Hypotension
What is an adverse effectof thiopental?
Laryngospasm
What are some adverse effects of etomidate?
- Primary adrenal suppression (secondary to reversibly inhibiting 11β-hydroxylase)
- Myoclonus
In cases of hameodynamic instability, what IV hypnotic agent is used and why?
Etomidate
Causes less hypotension than propofol and thiopental during induction
What are some adverse effects of Ketamine?
- Disorientation
- Hallucinations
What IV hyponitic agent is useful in trauma situations and why?
Ketamine
Doesn’t cause a drop in blood pressure
What is the most commonly used IV Hypnosis agent in GA?
Hyponosis
Propofol
Used extensively in intensive care for ventilated patients
List some Inhalational hypnotic agents used in GA?
Hypnosis
Volatile Liquid anaetshtics:
* Sevoflurane (the most commonly used)
* Desflurane (less favourable as bad for the environment)
* Isoflurane (very rarely used)
Other:
* Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)
What are some adverse effects of volatile liquid anaesthetics?
e.g. isoflurane, desflurane, sevoflurane
- Myocardial depression
- Malignant hyperthermia
- Halothane (not commonly used now) is hepatotoxic
Used for both induction and maintenance of GA
What is the most commonly used inhalational hypnotic agent in GA?
Hypnosis
Sevoflurane
What inhalational hypnotic agent is used in GA in children?
Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)
Waht conditions that patients may have CI use fo NO for general anaesthesia?
Pneumothorax
May diffuse into gas-filled body compartments → increase in pressure
Used for maintenance of anaesthesia and analgesia (e.g. during labour)
What devices are used for inhaled volatile agents? How do these work?
Hypnosis
Vaporiser:
* The liquid medication is poured into the machine.
* The machine then turns it into vapour and mixes it with air in a controlled way.
* During the anaesthesia, the concentration of the vaporised anaesthetic medication can be altered to control the depth of anaesthesia.
a) What mode of administartion is most commonly used for induction of GA?
b)What mode of administartion is most commonly used for maintenance of GA?
Why is this?
Induction
a) IV: infused directly into the blood and so can quickly reach an effective concentration
b) Inhalational: need to diffuse across the lung tissue and into the blood, where it takes a while for them to reach an effective concentration. Convcentration can be controlled easier
What is TIVA?
Total intravenous anaesthesia (TIVA):
- involves using an intravenous medication for induction and maintenance of GA
Propofol is the most commonly used. This can give a nicer recovery (as they wake up) compared with inhaled options.
How do muscle relaxants work?
Muscle relaxants
Block the neuromuscular junction from working
Acetylcholine (the neurotransmitter) is released by the axon but is blocked from stimulating a response from the muscle (msucle is relaxed/paralysed)
What are the 2 categories of muscle relaxants used in GA?
Muscle relaxation
- Depolarising (e.g., suxamethonium)
- Non-depolarising (e.g., rocuronium and atracurium)
What medications can reverse effects of neuromuscular junction blocking medications?
Muscle relaxants
Cholinesterase inhibitors (e.g., neostigmine)
Sugammadex is used specifically to reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium).
What medication category is most frequently used for analgesia?
Analgesia
Opiates
List some common analgesic agents used in GA?
Analgesia
- Fentanyl
- Alfentanil
- Remifentanil
- Morphine
What medications are administered at the end of the ooperative procedure?
What are most common types given to patients?
Antiemeteics: prevent post-operative nausea and vomiting
- Ondansetron (5HT3 receptor antagonist) – avoided in patients at risk of prolonged QT interval
- Dexamethasone (corticosteroid) – used with caution in diabetic or immunocompromised patients
- Cyclizine (histamine (H1) receptor antagonist) – caution with heart failure and elderly patients
What antiemetic medication should be avoided in pts with risk of prolonged QT interval?
Ondansetron (5HT3 receptor antagonist)
What antiemetic medication should be used with caution in diabetic or immunocompromised patients?
Dexamethasone (corticosteroid)
What antiemetic medication should be used with caution in heart failure and elderly patients?
Cyclizine (histamine (H1) receptor antagonist)
What must be done prior to emergence from GA?
- Reversal of muscle relaxants (prevent awareness under anaesthesia)- can be tested with nerve stimulators to ensure muscle relaxant effects have ended (done on ulnar n./facial n using TOF stimualtion)
TOF Stimulation : Train of four stimulation (nerve stimualted 4 times to check for appropriate response
What does the anaesthetist control during the emergence phase of GA?
- Switches off anaesthetics (concentration of anaesthetic in the body falls, the patient regains concioussness)
- Extubation
What are the most common side effecst of GA?
- Sore throat
- Post-op nausea/vomiting
What are some significant risks of general anaesthesia?
- Accidental awareness (waking during the anaesthetic)
- Aspiration
- Dental injury, mainly when the laryngoscope is used for intubation
- Anaphylaxis
- Cardiovascular events (e.g., myocardial infarction, stroke and arrhythmias)
- Malignant hyperthermia (rare)
- Death
What agents increase risk of malignant hypothermia during GA?
- Volatile anaesthetics (isoflurane, sevoflurane and desflurane)
- Suxamethonium
What increases risk of malignant hyperthermia?
Genetic mutation (autosomal dominant)
What does malignant hyperthermia cause?
- Increased body temperature (hyperthermia)
- Increased carbon dioxide production
- Tachycardia
- Muscle rigidity
- Acidosis
- Hyperkalaemia
How is malignant hyperthermia treated?
Dantrolene (interrupts the muscle rigidity and hypermetabolism by interfering with the movement of calcium ions in skeletal muscle)
Waht conditions that patients may have CI use fo NO for general anaesthesia?
Pneumothorax
May diffuse into gas-filled body compartments → increase in pressure
Used for maintenance of anaesthesia and analgesia (e.g. during labour)