Drugs in Surgery Flashcards
What are the ways to take general anaesthetics (GAs)?
Inhalational
Intravenous
What are premedications?
Muscarinic antagonist
Analgesic
Local anaesthetic
Muscle relaxant
What do GAs do?
Abolish awareness and response to pain
Why are GAs used in surgery?
Loss of consciousness, including memory
Suppression of pain
Suppression of skeletal muscle reflexes and tone
What are the toxic effect of GAs?
Depresses b.p. and resiration (low therapeutic index)
Liver/kidney damage (rarely)
What are the characteristics of the ideal anaesthetic?
Quick induction High potency Reversibility Good analgesia Amnesia No hangover Low or harmless metabolism Non-flammability Muscle relaxation Low toxicity
What is quick inductio?
Low solubility in blood, giving rapid saturation of bloos
What is high potency?
High lipid solubility
What is reversibility?
Gases give good control, injection less so
What is low toxicity?
Respiratory depression
Cardiovascular depression
Liver damage
What are volatile/ gaseous anaesthetics?
Many, simple, unreactive compounds
Halothane and nitrous oxide are commonly used
What is the compositiong of volatile/gaseous anaesthetics?
Numerous simple, small molecules
Mostly very unreactive compounds
What happens with intravenous agents after injection
Very rapid (high cerebral blood flow) Very short duration (redistribution to other organs)
What is an example of an intravenous agent used?
Thiopentone (barbiturate)
What are the characteristics of thiopentone?
Low therapeutic index
Depresses heart and respiration
Repeat dose-> longer anaesthesia (slow metabolism)
What are intravenous agents?
Induction agents
Short procedures
What are the mechanism of intravenous mechanisms?
Synaptic transmission, not axonal conduction
Where is analgesia caused in intravenous mechanisms?
Reticular formation and thalamus
Where is unconsciousness caused in intravenous mechanisms?
Rf and hippocampus
Where is amnesia caused in intravenous mechanisms?
hippocampus
What mechanism was recognised by is now discredited?
Non-receptor
What is the lipid-solubility mechanism?
Interact with hydrophobic structure Membranes- volume expansion (pressure reversal) Protein binding (hydrophobic sites)
What do receptors encourage?
Opening of chloride channels (e.g. GABA receptors)
What does Cl- entry into a neurone cause?
Hyperpolarisation and inhibition
What do general anaesthetics do in terms of the Cl- entering the neurone?
Enhance the response
What drugs are used as a premedication?
Hyoscine
Morphine
Lignocaine
What is hyoscine?
Muscarinic receptor antagonist- dries up secretions of saliva and bronchial mucus
What is morphine?
Opiate analgesic
Prevents post-operative pain
What lignocaine?
Local anaesthetic- blocks conduction in sensory nerves
What do muscle relaxant drugs do?
Voluntary muscles can be relaxed by drugs which interfere with nicotinic receptors
What are some examples of muscle relaxant drugs?
Tubocurarine
Suxamethonium
What does tubocurarine do?
Non-depolarising
Competes with ACh
Long acting
Reversible with ChE inhibitor
What does suxamethonium do?
Depolarising
Cation channels stay open
Short acting
Not reversible with ChE inhibitor
