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Flashcards in General anaesthetics Deck (19)
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How on a graph is lipid solubility of a anaesthetic measured

Y - axis - MAC - anaesthetic potency in humans - minimal alveolar concentration required to remove a response in 50% of patients upon incision
X axis - Oil:gas partition coefficient - Predicts the ease of partition into membrane lipids
As MAC goes down the oil:gas coefficient goes up - the lower the MAC value the more potent the anaesthetic , higher solubility


What were the lipid theories used to explain anaesthetic function

1. Volume expansion of the plasma membrane - CNS function altered
2. Increased lipid fluidity
Anaesthesia results from an alteration of membrane function


What is the current theory of anaesthetic action

Protein theory - Different GAs target different types of proteins found on neurons
They target different ion channels in the neuron membrane
Binding sites for GAs on the ion channels are often varied in their hydrophobic domain


What is the main target for GAs

Potentiation of the GABAa receptor - ligand gated chloride channel


Which interfaces to volatile GAs bind to

Alpha and Beta subunits


What interfaces do intravenous GAs bind to

Only the Beta subunit


What receptor is blocked by ketamine

NMDA (glutamate) receptors


What do low concentrations of volatile GAs activate

two pore domain K channels - Modulate neuronal activity - reduce membrane excitability - analgesia, hypnosis


What are the effects of GAs on neurotransmission at the cellular level

1. Enhance tonic inhibition (enhancing GABA), reduce excitation (open K channels) and inhibit excitatory synaptic transmission (depressing transmitter release and ligand gated ion channels)


What are the four stages of anaesthesia

1.Analgesia - loss of pain
2.Excitement - dangerous stage - exaggerated reflexes, imbalance between inhibitory and excitatory neurotransmission
3. Surgical anaesthesia - Unconscious, loss of reflexes, loss of response to pain, short term amnesia
4. Medullary paralysis - Loss of cardiovascular reflexes and respiratory paralysis


Which two stages of anaesthesia are wished to be avoided

2 and 4


Give advantages of intravenous anaesthetics

Speed of conduction is very fast (20-30 seconds)
Easy to administer


Give advantages of using the drug propofol

Rapid metabolism - good for the induction of anaesthesia
T0.5 = 2.4mins - rapid recovery and les hangover - can be used as a day case surgery


What are general disadvantages of using intravenous GAs

Pain at the site of injection, complex pharmacokinetics


What are the disadvantages of thiopental

High lipid solubility so rapid induction - BUT - short duration of action due to redistribution and hangover due to accumulation in fat -
Respiratory depression and CV depression 9i4


What is the action of ketamine

Dissociative anaesthesia, sensory loss, analgesia, amnesia, no complete loss of consciousness or respiratory depression, CV excitement


What are inhaled anaesthetics advantages for use

Useful for maintaining anaesthesia
Only route of entry and exit is via the lungs
Small lipid molecules - so cross the alveolar membrane easily


How is the speed of induction and recovery modified

Properties of the anaesthesia - blood:gas coefficient (solubility in blood)
Oil:gas coefficient (solubility in fat)
Physiological properties
Cardiac output
Alveolar ventilation rate


How can body tissue be split into compartments and how do they differ

Lean tissue (brain) - havre large blood flow and low partition coefficient for anaesthetics therefore equilibrate rapidly with the blood
Fat tissues - have a small perfusion and large partition coefficient - Act as a reservoir of drug during the recovery phase