T1 L21: Anaesthetic agents Flashcards by Malgorzata Szymaniak

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

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What is the predictable order in which anaesthesia depresses the brain?

Cortex
Midbrain
Spinal cord
Medulla

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What is the order of levels of intoxication by Ethanol?

Tranquilisation
Excitation
Dysarthria 
Ataxia
Sedation/Hypnosis
Anaesthesia
Coma
Medullary depression
Death

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What is Dysarthria?

Slurring speech

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What is Ataxia?

Falling over

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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

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What structures does anaesthesia work on?

Cell membranes
Membrane proteins - modulation of ligand-gated ion channels
Global depression of neuronal activity

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How does Anaesthesia work?

By stimulation of inhibitory receptors (GABA A and Glycine

By inhibition of excitatory receptors (Nicotinic, Serotonin, Glutamate, NMDA)

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How do anaesthetic agents work on GABA A?

They cause an influx on Cl- which hyperpolarises the cell

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What are the 2 methods of administrating aneasthesia?

Inhaled or injected

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What are some rare side effects of administrating O2?

O2 free radicals
CNS convulsion
Pulmonary oxygen toxicity
Retrolateral fibroplasia

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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

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Why is Nitrous oxide not used as an anaesthetic?

Because it has a MAC of 105% meaning it can’t fully sedate you

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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

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What is an analgesic agent?

A painkiller

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What is the onset/offset of nitric oxide?

Quick

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What are some complications from using nitric oxide as an anaesthetic?

It causes cardiorespiratopry depression
Neuropathy
BM depression

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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

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What is Nitric oxide used for clinically?

As an analgesic agent

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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

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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