General Anaestetics Flashcards
What sorts of physical anaesthetics are there?
Low pressure
Hypothermia
What is the MAC concentration for anaestetics?
Concentration of anestetic required to abolish response in 50% of patients
What is lipid theory?
Anestetic potency is related to lipid solubility. The more lipid soluble drugs are, the less concentration required
What are some problems with lipid theory?
Drugs have diverse structures and don’t all enter though lipids.
Larger lipophilic compounds have a loss of activity
Limited response suggests receptors
The higher the oil:gas partition coefficient, the lower the concentration required to lower the concentration needed
What are the targets of general anaesthetics?
Volatile general anaesthetics bind α and β subunits of GABAa
Intravenous general anaestetics bind to the β subunit of GABAa
What do ketamine and nitrous oxide block?
NDMA receptors
How can general anaesthetics affect two-pore potassium channels?
They can hyperpolarise neurons by opening these, making action potentials more difficult to fire
What can high concentrations of general anaesthetics cause?
Loss of motor control
Reflexes
Autonomic regulation leading to death
What parts of the brain do general anaesthetics affect?
Reticular formation- unconsciousness
Hippocampus- short term amnesia
Thalamic sensory relay nuclei- analgesia
Volatile anaesthetics- inhibit spinal reflexes
What are the 4 stages of anaesthesia?
Analgesia
Excitement- exaggerated reflexes
Surgical anaesthesia
Medullary paralysis- can lead to death. loss of autonomic functions
What are some advantages of intravenous anaesthetics?
Relatively easy to administer
Rapid induction (20-30 seconds)
Propofol has rapid metabolism
Short half life so less “hangover” from surgery
What are some disadvantages of intravenous anaesthetics?
Pain at the injection site
Complex pharmacokinetics for duration of action
Respiratory depression
Cardiovascular depression
What are the effects of ketamine use?
Dissociation
Sensory loss
Amnesia
Cardiovascular excitement, involuntary movements
Hallucinations
How do inhaled anaestetics reach receptors?
Lipid soluble molecules cross the alveolar membrane
What does speed of induction of GAs depend on?
Solubility in blood and fat
Depth of anaesthesia
Concentration of the anaesthetic
