16) Anaesthetics Flashcards
Describe general anaesthetic:
IV, inhalational or volatile
Affects the whole body - patient unconscious
Describe regional anaesthetic:
Involves rendering larger, specific regions of the body insensate, patient conscious
Describe local anaesthetic:
More defined, peripheral nerve block
What is conscious sedation?
Use of small amounts of anaesthetic or benzodiazepines to produce a sleepy like state
Describe the main stages of anaesthetic procedure over the course of a surgery:
Pre-medication Induction Intra-operative analgesia Muscle paralysis to facilitate intubation or ventilation Reversal and recovery
What are some examples of volatile anaesthetics?
N20, chloroform, fluranes, xenon
What are some examples of IV anaesthetics?
Propofol, barbiturates, etomidate, ketamine
What are Guedel’s signs (stages of anaesthesia)?
Stage 1: analgesia
Stage 2: unconscious, breathing erratic, increased muscle tone
Stage 3: surgical anaesthesia - decreasing muscle tone and breathing
Stage 4: respiratory paralysis
What are the main effects of anaesthesia?
Analgesia
Hypnosis
Muscle relaxation
How is the potency of volatile anaesthetics described?
Minimum alveolar concentration
What is the MAC (minimum alveolar concentration)?
Alveolar concentration at which 50% of subjects fail to move to surgical stimulus
How does the MAC relate to potency?
Lower the MAC, the more potent the inhaled anaesthetic
What is the absorption of an anaesthetic determined by?
Blood:gas co-efficient (water solubility)
What does the lipid solubility of the anaesthetic determine?
Potency (greater lipid solubility = greater potency
What factors can affect the MAC?
Age (lower in elderly) Pregnancy (increased) Central stimulants (increased) Opioids (decreased) Hyperthermia (increased|) Alcoholism (increased)
What are some receptor targets of anaesthetics?
GABAa receptors
NMDA receptors
What anaesthetics don’t potentiate GABAa receptors?
Xenon, N2O, ketamine
What effects do anaesthetics have in the brain?
Depression of: Reticular system Hippocampus Brainstem Spinal cord (dorsal horn and motor neurones)
When are local and regional anaesthetics often given?
Dentistry Obstetrics Regional surgery Post op Chronic pain
What is the main target of local anaesthetic?
Voltage gated sodium channels
Where can regional anaesthetic be administered?
Applied to peripheral nerves
Extradural (around spinal cord)
Intrathecal (through meninges
What are the main side effects of general anaesthetics?
PONV
Hypotension
Post op cognitive dysfunction
Chest infection
What are the main side effects of local anaesthetics?
Cardiovascular toxicity
