General Anaesthetics Flashcards
How can general anaesthetics be administered?
intravenous injection or inhalation
What three things do general anaesthetics need to achieve?
- need to make the patient unconscious
- need for analgesia (no pain)
- muscle relaxation (loss of reflexes)
How do general anaesthetics work?
by depressing CNS activity
What do all the inhabited anaesthetics have in common?
- simple, unreactive compounds
- short chain
- not one chemical class
What happens in high pressure?
reverses anaesthesia
What proves the lipid solubility case wring?
-as the chain length of long chain anaesthetic compound increases its lipid solubility increases however anaesthetic potency stops beyond a certain length
What gives evidence that the protein theory might be correct?
stereo selectivity (one orientation of an exactly the same molecule has more anaesthetic potency than another orientation of the same molecule) this suggests protein binding
Why is lipid solubility important?
to allow the molecule to enter the membrane and bound to a hydrophobic pocket on a protein
What are the molecular targets for inhaled/gaseous general anaesthetics?
- ion channels but no single target
- GABA A receptor (increase inhibition)
- K+ channel activation (decrease membrane excitability)
- blocking excitatory ligand-gated channels such as NMDA and ACh nicotinic
- increase inhibition by binding to the glycine channel
What are the stages of anaesthesia?
- Analgesia (drowsiness, reflexes intact, still conscious)
- Delirium (induction phase) (excitement, delirium, incoherence, loss of consciousness, unresponsive to painful stimuli) (also some dangerous symptoms such as muscle rigidity, spasmodic movements, cardiac arrhythmias, vomiting and choking)
- Surgical anaesthesia (unresponsive to painful stimuli, regular breathing, abolition of reflexes, muscle relaxation)
- Medullary paralysis (overdose) (pupillary dilation, respiration/circulation ceases, EEG wanes) (can lead to death)
What are two key factors of an anaesthetic agent?
potent and fast acting
How do you measure anaesthetic potency?
MAC
minimum alveolar concentration in man
(the conc of anaesthetic in the alveoli required to produce immobility in 50% of patients when exposed to noxious stimulus)
What is MAC inversely proportional to?
lipid solubility
What is the main determinant of anaesthetic potency?
lipid solubility
Why is it important to have fast acting anaesthetics?
gets through the dangerous phases quickly
What are the factors influencing the rate of induction?
- properties of anaesthetic
- physiological factors
What are the two partition coefficients that the anaesthetic needs to get through in order to reach the brain?
-blood:gas partition constant
-tissue:blood partition constant
(have to reach equilibrium)
When inhaling the anaesthetic, how can you increase the rate of conduction?
increase conc of anaesthetic
increase rate and depth of breathing
In order to make anaesthesia faster do you want an anaesthetic that is highly soluble in the blood?
no, it has to be a bit soluble in the blood but having a high solubility means that the blood has a high capacity so more molecules are required to saturate the blood before it transfers into the brain (slow down speed of conduction)
a relatively low blood insoluble gas means capacity is smaller so saturation occurs faster so the transfer to the brain is faster
What is blood:gas partition coefficient inversely proportional to?
speed of induction
What does a faster rate of pulmonary flow mean?
higher cardiac output so faster transfer
What is the solubility of anaesthetic lie in the brain?
conc of anaesthetic in the brain rises fast because anaesthetics are soluble in lean tissue (grey matter, muscle)
If a patient has a lot of adipose fat, will it increase or decrease the speed of induction?
decrease because anaesthetics are highly soluble in adipose tissue (more soluble than in the brain)
How does tissue blood flow affect induction?
high tissue blood flow eg brain increases induction
How do you eliminate inhaled anaesthetics?
-mainly via the lung (speed of induction in reverse)
Look at advantages and disadvantages of different anaesthetics
on slides
What is balanced anaesthesia?
using combinations of different drugs for optimal clinical effect with lower risk
What are the features of intravenous anaesthetics?
- rapid onset
- short acting
When are intravenous anaesthetics used?
in induction
or used alone in short procedures
How do intravenous anaesthetics work?
through interaction with specific ligand gates receptors e.g GABA A
What types of premedication can you use before using an anaesthetic?
- benzodiazepines (sedation and amnesia)
- opioids (pain relief)
- antimuscarinics (to facilitate intubation and ventilation)
What is a muscle relaxant used for?
to relax deep abdominal, tracheal and diaphragm muscles without the need for deeper anaesthesia
What is an anti-emetic?
prevents the patient from throwing up as they recover
