L9 - General Anaesthetics Flashcards
Who was general anaesthetic first discovered by?
Horace Wells
What was first used to discover general anaesthetic?
Nitrous Oxide
What was the second chemical discovered for use as a general anaesthetic?
Chloroform
What are some kinds of intravenous anaesthetics?
- Halogenated hydrocarbons (isoflurane, proponol)
- Barbiturates (thiopental)
- Steroids (alphaxalone)
What are some kinds of physical anaesthetics?
- Low-pressure (atmosphere)
- Hypothermia
How do drugs cause membrane expansion?
By entering into the lipids of the membrane, making it more fluid.
What is the relationship between lipid solubility and drug concentration?
The more lipid souble the drug is the less concentration of the drug is needed for effect.
What is the Meyer-Overton Rule?
The anaesthetic effect is proportional to molar effect of concentration of agent in lipid.
What is the lipid theory?
Drugs work at the level of the plasma membrane to cause volume expansion or increasing lipid solubility.
What are some problems with the lipid theory
- The temperature effect - lipids solidify in
colder conditions. - The increase GABAa receptor affinity for
agonists,
What are some problems with the lipid theory
- The temperature effect - lipids solidify in
colder conditions. - The increase GABAa receptor affinity for
agonists,
What is the protein theory?
Drugs extert their effect by interacting with proteins.
How do many anaesthetics work?
By increasing the action of GABA at GABAa receptors.
How do volatile anaesthetics work?
They bind at the interface of alpha and beta subunits of GABAa
How do intravenous anaesthetics work?
Bind only to the beta subunit of GABAa receptors.
What is the action of ketamine and nitrous oxide?
they block NMDA receptors.
What are the effects of general anaesthetics on neurotransmitters at low concentrations?
- Synaptic transmission in CNS is
decreased. - Reticular formation leading to
unconsciousness. - Reduces signalling to the hippocampus
leading to short term amnesia. - Thalamic sensory relay nuclei parts of the
cortex affected leading to analgesia.
What are the effects of general anaesthetics on neurotransmitters at high concentrations?
All brain function affected - loss of motor control, reflexes, respiration, autonomic regulation.
DEATH
What are the 4 stages of anaesthesia?
- Analgesia
- Excitement
- Surgical Anaesthesia
- Medullary Paralysis
Analgesia
Reduced responsiveness to pain
Excitement
Exaggerated reflexes eg, gagging or kicking
Surgical Anaesthesia
Unconsciousness, loss of response and reflexes, short-term amnesia
Medullary Paralysis
Loss of cardiovascular reflexes and respiratory paralysis - causes death.
What 2 stages should be avoided when under general anaesthetics?
Stages 2 and 4
Examples of intavenous anaesthetics?
Propofol, thiopental, etomidte
Advantages of intravenous anaesthetics?
- easy to administer
- rapid induction
- Prpofol has rapid metabolism ad rapid
recovery.
Disadvantages of intraveonous anaesthetics?
- Pain at the site of injection
- Complex Pharmacokinetics
- Thiopental has a short duration of action.
Ketamine
- A dissociated anaesthetic similar to PCP
(Phencyclidine) - Causes sensory loss
- Powerful analgesic
- Used in paediatrics and vetinery
Examples of inhalation anaesthetics
Nitrous oxide, isoflurane, desflurane, seroflurane.
Advantages of inhalation anaesthetics
- useful for maintaining surgical
anaesthesia. - Small lipid soluble molecules can easily
cross the alveolar membrane.
What is the depth of anaesthesia deteremined by?
The tension of inhalation anaesthetic in brain blood and alveolar air
