Anaesthesia Flashcards
7 stages of general anaesthesia which require drugs
Premed e.g benzodiazepine Induction (most IV but some volatile) Intraop analgesia Muscle paralysis Maintenance Recovery/reversal Provision for post op N&V
Types of IV GA
Propofol
Barbiturates
Ketamine
Types of volatile GA
N20
Isoflurane
Desflurane
Xenon for neonates
What is anaesthesia a combo of
Analgesia
Hypnosis (loss of consciousness)
Depression of spinal reflexes
Muscle relaxation
What are measured in Guedel’s sign
Muscle tone
Breathing
Eye movements - glabellar reflex (blink when tapped between eyes)
4 stages of Geudel’s signs
Analgesia
Excitement
Surgical anaesthesia (the aim)
Respiratory paralysis
Describe analgesia in terms of Guedel’s signs
Analgesia
Conscious
Normal muscle tone and breathing
Describe excitement in terms of Guedel’s signs
Unconscious
Erratic breathing
Increased muscle tone
Describe surgical anaesthesia in terms of Guedel’s signs
Relaxed muscle tone
Subdivided into 4 stages with decreasing resp rate
Describe respiratory paralysis in terms of Guedel’s signs
Resp rate too low leading to death
Definition of MAC
Minimum alveolar concentration measures potency of volatile anaesthetic
Alveolar concentration at which 50% of subjects fail to move to surgical stimulus
Factors increasing MAC
Hyperthermia
Pregnancy
Central stimulants
Alcoholism
Factors decreasing MAC
Increasing age
Opioids
Anaesthetic drugs (N20 added to other volatile anaesthetics to decrease dosing)
Consequence of a low blood:gas partition and a drug example
Fast induction and fast recovery e.g desflurane
Means low water solubility so drug wants to leave blood and go to target sites
Consequence of a high oil:gas partition and a drug example
High lipid solubility so drug has a higher potency because membranes are lipid rich e.g halothane
Possible target receptors of anaesthetics
GABA agonist for most drugs
NMDA antagonist for xenon, N20 and ketamine
Target systems of anaesthetics
Reticular system
Hippocampus (memory)
Brainstem (cvs and resp)
Spinal cord (motor and sensory activity)
Describe potency of IV GA
Plasma concentration at which 50% patients reach an end point e.g loss of glabellar reflex or a specific bispectral index number
Chemical structure of local anaesthesia
Aromatic ring
Amine group
Amide or ester link
What increases LA potency
Higher lipid solubility
What increases speed of LA onset
Lower pKa (dissociation constant)
What type of LA chemical structures are shorter acting
Drugs with an ester link e.g procaine
Broken down by esterases in cells
What type of LA drugs are longer acting
Drugs that are protein bound e.g bupivacaine
Max dose is 2mg/kg
MoA of LA
Unionised and lipophilic so cross plasma membrane and enter cell Become charged (rate related to pKa) Enters and blocks Voltage gated Na channels in nerves
