General anaesthetics Flashcards
What does anaesthesia mean?
The abolition of sensation
What does analgesia mean?
The abolition of pain
What is the triad of general anaesthesia?
The need for:
Unconsciousness
Analgesia
Muscle relaxation/loss of reflexes
What is the structure of inhalational anaesthetics like?
Simple, unreactive compounds
Short chain molecules
No one chemical class
What does the lipid theory state?
The concentration of agents require to immobilise tadpoles is inversely proportional to its lipid:water partition coefficient
What does the protein theory state?
Lipid solubility is the gateway to accessing proteins in the cell
Binding to hydrophobic pockets on proteins
What are the targets of inhaled anaesthetics?
GABAa receptor
K+ channel activation
NMDA receptor, 5-HT3, Ach nicotinic
Glycine
What are the four responses to anaesthetic?
Memory
Consciousness
Movement
CVRS response
What is the first stage of anaesthesia?
Analgesia
Drowsiness
Reflexes intact
Still conscious
What is the second stage of anaesthesia?
Delirium (induction phase)
Excitement, delirium, incoherent speech
Loss of consciousness
Unresponsive to non-painful stimuli
What is dangerous about the second stage of anaesthesia?
Muscle rigidity, spasmodic movements
Cardiac arrhythmias
Vomiting and choking
What is the third stage of anaesthesia?
Surgical anaesthesia
Unresponsive to painful stimuli Regular breathing Abolition of reflexes Muscle relaxation Synchronised EEG
What is the fourth stage of anaesthesia?
Medullary paralysis (overdose)
Pupillary dilation
Respiration/circulation ceases
EEG wanes
Death
What two factors make a good anaesthetic agent?
Fast acting
Potent
What is MAC?
Minimum alveolar concentration
What does MAC mean?
The concentration of anaesthetic in the alveoli required to produce immobility in 50% of patients when exposed to a noxious stimulus
expressed as v/v%
What is the main determinant of anaesthetic potency?
Lipid solubility
How are MAC and lipid solubility related?
Inversely proportional
What factors influence the rate of induction?
Properties of anaesthetic
Physiological factors
Why is the blood:gas partition coefficient important?
A low coefficient = faster induction
Why is tissue:blood partition coefficient important?
If it is high in lean tissue there will be fast induction
If it is high in adipose tissue it will accumulate, low induction
An increase in anaesthetic concentration and rate of breathing will result in what effect on induction?
Increased speed of induction
An increase in solubility in the blood will result in what effect on induction?
Decreased speed of induction
What has to happen before blood transfers anaesthetic to the brain?
Blood has to be saturated
