Anaesthetics Flashcards
What is conscious sedation
Conscious sedation - use of a small amount of anaesthetic or benzodiazepine to produce a sleepy-like state
Name some inhaled anaesthetics
Nitrous oxide
Xenon - protects against neuronal damage so used in children at risk of neuronal damage
Choloform
Fluroxene
Diethyl-ether
Name some intravenous anaesthetics
Propofol
Barbiturates
Etomidate
Ketamine
Describe the Guedel’s signs
Stage 1 - analgesia and consciousness
Stage 2 - unconscious, erratic breathing, delirium and possibly an excitment phase
Stage 3 - surgical anaesthesia. Four levels with breathing getting slower and weaker
Stage 4 - respiratory paralysis and death if not treated
What is MAC
MAC - minimum alveolar concentration. Is used to describe the potency of a volatile anaesthetic
MAC is the alveolar concentration at which 50% of subjects fail to move to surgical stimulus
Name some factors affecting MAC
Age - MAC high in infants and low in elderly
Increased in hyperthermia and decreased in hypo
Increased in pregnancy
Increased in alcoholism
Increased with a central stimulus
Decreased with other anaesthetics and sedatives
Decreased with opioids
What are the two partition coefficients
Blood:Gas partition - low value means fast induction and fast recovery
Oil:Gas partition - high value, high potency of the drug
Which inhaled anaesthetic lower the MAC of other anaesthetics and what does this help achieve
Nitrous oxide lowers the MAC of other anaesthetics
This helps to reduce the dose and so reduce the side effect profile while maintaining a good anaesthetic profile
What is the main target in anaesthetics
GABA-A receptor
How do anaesthetics act on the GABA-A receptor
Anaesthetics potentiate the GABA-A receptor to increase Cl ion conduction to cause hyperpolarisation and prevent action potentials firing
What is the other target of anaesthetics and which anaesthetics act on this target
NMDA receptors
Xenon, nitrous oxide and ketamine act by blocking NMDA receptors to cause anaesthesia
Name some local anaesthetics
Lidocaine
Bupivacaine
Ropivacaine
Procaine
Describe how local anaesthetics work
Local anaesthetics block the VGSCs to prevent an action potential firing
The block is use dependent and selectively blocks pain fibres which are being activated
Local anaesthetics block small myelinated nerves first - this causes nocicepetive and sympathetic block
The anaesthetic crosses into the plasma membrane where it then either enters the cell or enters the VGSC where it picks up a positive charge and blocks the channel
If the anaesthetic enters the cell, it picks up a positive charge and then enters the VGSC
Where do regional anaesthetics block and how might they be given
Regional anaesthetics block a nerve to selectively anaesthatise part of the body
May be given extradural, intrathecal or combined
Name some side effects of anaesthetics
General - PONV, hypotension, POCD, chest infection
Local and regional - depends on agent used. May enter circulation and stop heart
Local - headaches, twitching muscles, dizziness, continuing paraesthesia
Allergic reaction and anaphylaxis
