Lecture 14 - Anaesthetics Flashcards
What is the mechanism of anaesthetic related to?
Disruption of lipid membrane of cells
What is the potentiation of GABA A receptor?
Inhibitory receptor for the inhibitory amino acid transmitter GABA amino butyric acid
What are examples of certain anaesthetics?
Isoflurane
Propofol
What is GABA A receptor?
Chloride Ion channel
What examples of potentiation?
GABA A
Glycine
What are examples of inhibition?
NAChR
5HT3
NMDA
What is NMDA?
Receptor for excitatory amino acid neurotransmitters
Acted upon by Glutamate
What is the result of receptor mediated mechanism?
Dampening down/quester effect on the cell
What is the effect of nervous system?
Enhancement of tonic inhibition
What is anaesthesia?
Constellations of effects which incorporate but not limited to Analgesia
What happens when depth of Analgesia increases?
Pass through stages of unconsciousness and loss of reflexes
What are various parts of the brain affected by?
Anaesthetic compounds
What do many anaesthetics lead to?
Some form of Amnesia
Interference with the hippocampal function
What is the hippocampal function closely tied up with?
Processes of short-term memory
What is the stage I of anaesthesia?
Analgesia
What is the effects produced by stage 1 of anaesthesia?
Analgesia without amnesia or loss of touch sensation
Consciousness retained
What is stage II of anaesthesia?
Excitation
What are the effects produced of stage II of anaesthesia?
Excitation and delirium with struggling
Respiration rapid and irregular
Frequent eye movements with increased pupil diameter
Amnesia
What is stage III of anaesthesia?
Surgical anaesthesia
What are the effects produced of stage III of anaesthesia?
Loss of consciousness
Plane I: decrease in eye movements and some pupillary constriction
Plane II: loss of corneal reflexes
Plane III and IV: increasing loss of pharyngeal reflex
Progressive decrease in thoracic breathing and general muscle tone
What is IV of anaesthesia
Medullary depression
What are the effects produced of stage IV of anaesthesia?
Loss of spontaneous respiration and progressive depression of cardiovascular reflexes
What is intravenous anaesthetics used for?
Induction
Rapidly induce anaesthesia than inhalational/gaseous anaesthetics
What is Thiopental?
Capable of quickly inducing anaesthesia
It’s use is widespread
It is a barbiturate
Largely replaced by Propofol
What is ketamine?
Dissociative anaesthesia
Patient retains some degree of consciousness but dissociated from their environment
Causes perceptual disturbance
What compound can maintain anaesthesia?
Propofol
With slow infusion
What compound is used during endoscopy procedure?
Midazolam
What are some examples of drugs of intravenous anaesthetics?
Propofol Thiopental Etomidate Ketamine Midazolam
What is the speed of induction and recovery of Propofol?
Fast onset
Very fast recovery
What is the main unwanted effect of Propofol?
Cardiovascular and respiratory depression
Propofol
Rapidly metabolised
Continuous infusion
Causes pain at injection site
What is the speed of induction and recovery of Thiopental?
Fast
Accumulation occurs
Slow recovery
‘Hangover’
What is the main unwanted effects of Thiopental?
Cardiovascular and respiratory depression
Thiopental
Largely replaced by Propofol
Causes pain at injection site
Risk of precipitating porphyria I’m susceptible patients
What is the speed of induction and recovery of Etomidate?
Fast onset
Fairly fast recovery
What is the main unwanted effects of Etomidate?
Excitatory effects during induction and recovery
Adrenocortical suppression
Etomidate
Less cardiovascular and respiratory depression than with Thiopental
Causes pain at injection site
What is the speed of induction and recovery of ketamine?
Slow onset
After effects common during recovery
What is the main unwanted effects of ketamine?
Psychotomimetic effects following recovery
Postoperative nausea, vomiting and salivation
Raised intracranial pressure
Ketamine
Produces good Analgesia and amnesia
What is the speed of induction and recovery of Midazolam?
Slower than other agents
Midazolam
Little respiratory or cardiovascular depression
Inhalational anaesthetics
Ranges from nitrous oxide to Ether
What is the most commonly used compound for inhalational anaesthetics?
Isoflurane
How is certain concentration of inhalational anaesthetics within bloodstream achieved?
Low blood: gas coefficient (relatively low solubility in blood)
What does the oil:gas coefficient dictate?
How easily an anaesthetic once in body passes to blood into fat and other tissues
What are the factors affecting the rate of induction and recovery?
Solubility in blood
Solubility in fat
Why is induction/recovery quicker with low blood solubility?
Equilibrium is reached quicker
What does oil:gas coefficient determine?
Potency
What happens when there is a small partition coefficient?
Small proportion of anaesthetic passing into fat/lean tissue
What are the properties of the ideal anaesthetics?
Inherently stable Non-flammable Non-explosive Potent Low blood solubility (rapid induction) Rapid emergence from anaesthesia Rapid adjustment of depth of anaesthesia Non-irritant to the airways Non-toxic Lack of sensitisation of the heart to catecholamines Analgesic Easily reversible Minimal interaction with other drugs Inexpensive
What do local anaesthetic do?
Stop the local propagation of action potentials along the neuron
What are local anaesthetics?
They are all weak bases
Why is it crucial to have some unionised form of local anaesthetics?
No penetration through axonal membrane
How do anaesthetics become ionised?
Significant inflammation that will lower the local PH
What happens at normal physiological PH?
Anaesthetics can cross axonal membrane
What does the ionised form block?
Sodium channel
What happens if the sodium channel gate remain closed?
The local anaesthesia can’t get in
What is the use-dependent pathway?
Local anaesthetics is reversing axonal membrane and getting inside and existing in equilibrium with ionised form which can block the sodium channel
What is inhibited when a local anaesthetic is administered?
All fibres
