T1 L21: Anaesthetic agents Flashcards
What is the definition of an anaesthetic agent?
A reversible drug that induces absence of sensation and awareness.
It’s any lipid soluble agent that causes depression of the brain in a predictable order
What is the predictable order in which anaesthesia depresses the brain?
- Cortex
- Midbrain
- Spinal cord
- Medulla
What is the order of levels of intoxication by Ethanol?
Tranquilisation Excitation Dysarthria Ataxia Sedation/Hypnosis Anaesthesia Coma Medullary depression Death
What is Dysarthria?
Slurring speech
What is Ataxia?
Falling over
What is the difference between sedation and being anaesthetised?
Sedated people can wake up and talk to you.
Someone who is anaesthetised won’t wake up. You can preform surgery on them
What structures does anaesthesia work on?
- Cell membranes
- Membrane proteins - modulation of ligand-gated ion channels
- Global depression of neuronal activity
How does Anaesthesia work?
By stimulation of inhibitory receptors (GABA A and Glycine
By inhibition of excitatory receptors (Nicotinic, Serotonin, Glutamate, NMDA)
How do anaesthetic agents work on GABA A?
They cause an influx on Cl- which hyperpolarises the cell
What are the 2 methods of administrating aneasthesia?
Inhaled or injected
What are some rare side effects of administrating O2?
O2 free radicals
CNS convulsion
Pulmonary oxygen toxicity
Retrolateral fibroplasia
What is Retrolateral fibroplasia?
An abnormal proliferation of fibrous tissue immediately behind the lens of the eye, leading to blindness. It affected many premature babies in the 1950s, owing to the excessive administration of oxygen
Why is Nitrous oxide not used as an anaesthetic?
Because it has a MAC of 105% meaning it can’t fully sedate you
What is MAC?
Minimal alveolar concentration. It indicated how powerful an anaesthetic is
A minimum of 20% of O2 is needed so a sedative can’t have a MAC of >80% for it to fully sedate you
What is an analgesic agent?
A painkiller
What is the onset/offset of nitric oxide?
Quick
What are some complications from using nitric oxide as an anaesthetic?
It causes cardiorespiratopry depression
Neuropathy
BM depression
Why is nitric oxide not used with a pneumothorax?
Because it’s so small and soluble that it will go into the affected area making the pneumothorax worse
What is Nitric oxide used for clinically?
As an analgesic agent
What are some physical properties of inhalational agents?
They are chemically stable Non-flammable/explosive Vaporizable Environmentally stable Have an impact on the environment They're non-irritant Low blood : gas solubility High potency (MAC) Minimal side effects Non-toxic Biotransformation
What is the benefit of Inhalational agents being vaporizable?
It’s a liquid at room temperature so it’s vapour can be passed through tubing
What is the benefit of a low blood : gas solubility?
It leads to a rapid induction and recovery due to less retention following tissue distribution
What is biotransformation?
The alteration of the drug within the body
Why can’t Isoflurane be inhaled?
Because it causes irritation
What are some properties of Isoflurane?
Inhaled Cheap Stable Non-flammable Irritable to airways MAC of 1.1% 0.2% metabolised
What are the side effects of Isoflurane?
Causes CV and RS depression
What are some properties of Sevoflurane?
Inhaled Non-irritable Quick onset/offset MAC 2% 5% metabolised CVS stability Gives emergence phenomena Expensive (less so now because it's been out for a while) No nasty side-effects
What is meant by emergence phenomena?
You wake up very quickly after anaesthesia and that’s confusing. This mostly happens in children
What are some properties of Desflurane?
Inhaled Very quick onset/offset 0.02% metabolised Moderately expensive Irritant to airways Needs a special vaporiser because of the boiling point MAC 6.35% Environmentally damaging
Which patients is Desflurane used on?
On larger patients because it wears off quickly. It’s only used on special occasions because it’s so environmentally damaging
What are some properties of intravenous agents?
Rapid and pleasant They are redistributed throughout the body Metabolised CVS/RS depression Short acting
What are intravenous agents used for?
For inducing a patient. Inhaled agents are then used to maintain
What is meant by redistribution of intravenous agents?
They aren’t broken down. They end up in muscles and fat where they cause anaesthetic effects
What are some properties of Thiopentone
Injected Smells like garlic Antiepileptic CVS/RS depression Cause anaphylaxis in arteries Half-life of 10 hours
Why can’t Thiopentone be injected into arteries?
Because it will precipitate due to changes in pH which occur when mixed with blood (pH 7.4) and may eventually block smaller vessels
What are some properties of 2,6-diisopropyphenol (propofol)?
It's a solvent 4min redistribution half-life 4hr elimination half-life Minimal accumulation Anti-emetic Anti-epileptic Painful to inject abnormal movements CVS/RS side effects
Why is Propofol used in TIVA (total intravenous anaesthesia)?
It has minimal accumulation
What is meant by abnormal movements with Propofol?
These are common in children.
It makes it hard to tell if the patient is actually sedated
When is Ketamine used as a sedative?
In the field because it doesn’t cause airway depression unlike other drugs. It can be given intravenous/intramuscular.
But it has lots of side effects
When is Midazolam used as a sedative?
When children are often in the hospital because it erases memory.
Also a date-rape drug
What are the 2 types of muscle relaxants?
Depolarising and non-depolarising
Why are muscle relaxants gievn?
They cause muscle paralysis so can:
Facilitate intubation
Maintain paralysis throughout surgery/ventilation
Why do muscle relaxants have to be given after the anaesthetic?
Because the paralysis process can be painful
Which type of muscle relaxant will cause the patient to contract all over before they relax?
Non-depolarising
What are some properties of depolarising muscle relaxants?
They mimic acetylcholine
Short half-life (2min)
Multiple side-effects
Metabolised by plasma cholinesterase
Where is cholinesterase found?
In nerve endings and red blood cells
What type of drug is Suxamethonium?
A depolarising muscle relaxant
What are some properties of non-depolarising muscle relaxants?
They are competitive with ACh (blockers)
Duration is variable
Slow onset/offset
Last about 30min
Which are more commonly used: depolarising or non-depolarising muscle relaxant?
Non-depolarising
What are the 2 types of non-depolarising muscle relaxants?
Steroid group Eg. Rocuronium
Benzylisoquinoliniums Eg. Atracurium
Why is awareness more common with TIVA?
Because depth of sedation is harder to measure
What is TIVA?
Total intravenous anaesthesia used to induce anaesthesia. Most frequently used is Propofol
