Session 9: Anaesthesia Flashcards
Give broad types of anaesthesia.
General or local
Types of general anaesthesia.
Inhalation/volatile
Intravenous
Give examples of conscious sedation.
Small amounts of anesthetic or benzodiazepines to produce a sleepy-like state.
Explain the process of anaesthesia before, during and post-surgery.
Premedication of something sedative/hypnotic such as benzodiazepine.
Induction usually intravenous but can also be inhalational to put the person to sleep.
Intraoperative analgesia which is usually an opioid.
Intubation/assisted ventilation if muscle paralysis.
Reversal of muscle paralysis and recovery.
Post-operative analgesia.
Provide medication for post-operative nausea and vomiting.
Give example of gases-volatiles-delivered via lungs.
(Inhalation)
N2O
Halothane
Fluroxene
Methoxyflurane
Enflurane
Isoflurane
Xenon
Give examples of intravenous anaesthesia.
Propofol
Barbiturates
Etomidate
Ketamine
Explain Guedel’s signs.
(Stages 1-4)
1 - Analgesia and still conscious
2 - Patient is unconcious and breathing has become erratic. This is an excitement phase where muscle tone can increase.
3 - Surgical anaesthesia with four levels describing increasing depth until breathing is weak. This is where you want to the patient to be in.
4 - Respiratory paralysis and possible/imminent death (not where you want to go).
What is anaesthesia a combination of?
Analgesia
Hypnosis (loss of consciousness)
Depression of spinal reflexes
Muscle relaxation
How is volatiles drug potency measured?
By minimum alveolar concentration (MAC).
Explain what MAC is.
It’s a measure of the anaesthetic concentration in the alveolus at which 50% of subjects fail to move to surgical stimulus.
It’s like EC50, Km etc…
How does the alveolar concetration to spinal cord concentration relate at equilibrium?
They are equal.
Give examples of MAC.
Mac
MAC-BAR
MACawake
Give factors that affect induction as well as recovery.
Blood:Gas partition
Oil:Gas partition
What does a low Blood:Gas partition value indicate?
Fast induction and recovery
What does Oil:Gas partition determine?
Potency and slow accumulation due to partition into fat.
Give factors affecting MAC.
Why is Nitrous Oxide often given with volatiles?
Because it decrease MAC.
This means that less of a volatile agent is needed to achieve the same result.
Why is it preferable that Nitrous oxide reduces MAC?
Because that means that you won’t have to give as much of the volatile agent and therefore reduced side-effects.
Explain the role of GABA receptors in anaesthesia.
Since GABA is the major inhibitory transmitter you target the receptor and increase the Cl- conductance.
This potentiates GABA activity and leads to anxiolysis, sedation, and anaesthesia.
Give exception of anaesthesia not acting to potentiate GABA activity.
Xenon
N2O (Nitrous oxide)
Ketamine
What do xenon, nitrous oxide and ketamine act on instead?
They interact with NMDA receptors instead and inhibit glutamate activity.
Explain the effects of anaesthesia on the brain circuitry.
The connectivity between the reticular formation and cortex is lost.
The thalamus is inhibited.
Hippocampus is depressed leading to no memory.
Brainstem is depressed (can affect resp and CVS)
Spinal cord and depression of the dorsal horn. This leads to analgesia (suppression of pain)
When are IV anaesthetics used?
As induction
Can also be given as sole anaesthetic in TIVA (Total Intravenous Anaesthesia)
How does the target sites and system targets differ between volatiles and IV?
Same target sites and same system targets.
Ketamine however inhibits NMDA
How do we describe IV anaesthetic potency?
Plasma concentration to achieve a specific end point
TIVA uses a defined PK based algorithm.
In simple terms how does mixed anaesthesia work.
Bolus of IV anaesthesia to end point then switch to volatile.
Causes to give local and regional anaesthesia.
Dentistry
Obstetrics
Regional surgery where the patient is awake
Post-op
Chronic pain management
Give examples of local anaesthetics.
Lidocaine
Bupivacaine
Ropivacaine
Procaine
Characteristics of local anaesthetics.
Lipid solubility - higher lipid solubility = more potent
pKa - lower pKa = faster onset
Protein binding - refers to duration
Briefly explain how local anaesthetics work.
Prevent depolarisation by blocking sodium channels.
Side effects of general anaesthesia.
Post-operative nausea and vomiting
CVS and hypotension specifically
Post-operative cognitive dysfunction
Chest infection
Allergic reactions and anaphylaxis
