Pharmacology of Anaesthesia Flashcards
What is the most commonly used induction agent?
Propofol which is delivered via an IV canulla
What is the aim of induction agents?
To cause a rapid loss of consciousness and this is then followed with maintainance analgesia
Why are elederly patients more prone to overdose during IV induction?
Due to a poor cardiac output they are more likely to have higher doses of IV induction agents given to them as it takes longer for the induction agent to reach the brain and cause analgesia
This is called the arm brain circulation time
What are some advantages to induction analgesia?
Pleasant for patient
Can cause a rapid loss of consciousness
Relatively predictable
What are some disadvantages to induction agents?
Overdoses in people with poor cardiac output and elderly due to increased arm brain circulation time
Adverse respiratory and cardiovascular effects
What causes rapid falls in plasma concentration of the induction agent?
This is due to redistribution of the drug into the muscle, specifically the fat of muscle.
What causes gradual falls in the plasma concentration of a drug?
This is due to metabolic clearance by the liver and kidneys
What does propofol look like?
It is a cloudy white liquid
What is the most common IV induction agent?
Propofol
Why might etomidate be used as an induction agent?
It is pretty CV stable and so maybe used in cardiac patients
Where is thiopentone used?
Use in obstetrics
It is a potent myocardial depressant
What receptor does ketamine act on?
The NMDA receptor
What is a side effect of ketamine?
It causes a dissociative state and can cause vivid nightmares
Also causes memory suppression so maybe used in children
What are some advantages to inhalational induction agents?
Provides a large amount of control
Easier to control adverse CV and respiratory effects
Stopping allows for quick clearance of the agent
Good is cannulation may be difficult- children, needle phobic
What is a common inhalational agent?
Sevoflurane
What relationship is there for solubility of induction agents and how quick they work?
The less soluble a drug is the quicker it works-
This is because less agent i needed to saturate the blood and then levels of the agent in the brain increase, causing general anaesthesia
What are some disadvantages to inhalational agents?
Speed of onset is dependent on rate and depth of breathing
Requires skill and attention to do it well
Must have good co-operation with patient
When are inhalational anaesthetics commonly used?
Inhalational agents are commonly used for maintenance anaesthesia following induction
What is a dangerous stage of induction for patients for inhalational agents?
Stage 2- The induction phase/Delerium Phase
This is because patients can vomit and choke and this can increase the risk of aspiration and death
What are some important physical properties of inhalational anaesthetics?
Non flammable Stable in light Liquid and vapourisable at room temperature Non irritant to the airways Pleasant to inhale
What is seen with overdose of inhalational agents?
Medullary paralysis
Pupillary dilation
Respiratory Arrest
Cardiac arrest
Death
Why is a lower solubility more desirable for inhalational anaesthetics?
Low solubility means that it takes less time for the anaesthetic to have it’s effect as the delay to saturating the blood is reduced if the anaesthetic is less soluble
What is the minimal alveolar concentration?
This is the concentration of the anaesthetic in the alveoli required to produce immobility in 50% of patients when exposed to noxious stimuli
Or the concentration that prevents movement in response to skin incision is 50% of unpremeditated animals
How can the alveolar concentration be estimated during surgery?
Using the expiratory concentrations of the anaesthetic agent
