Anaesthetics Flashcards
what are the 2 routes for general anaesthetic ?
Volatile or Inhalation
IV
define conscious sedation
use of small amount of anaesthetic or benzodiazapines to produce sleepy like state - maintain verbal contact but feel comfortable
what is anaesthesia a combination of ?
Analgesia , Hypnosis, Depression of spinal reflexes muscle relaxation
what are stages of Guedel’s signs ?
Stage 1- Analgesia and consciousness
stage 2 - Unconscious, breathing erratic . Maybe delirium = excitement phase
Stage 3- Surgical Anaesthesia, 4 levels going down until breathing weak
Stage 4- Respiratory Paralysis and death
what is the order that brain functions go in Volatile anaesthetics?
Memory , Consciousness , Movement and CV response
what is potency ?
Docile concentration range at which you see a response
how is volatile anaesthetic potency described ?
Minimum Alveolar Concentration
MAC
What is MAC?
The Alveolar conc at which 50% of subjects fail to move to surgical stimulus
why is MAC used ?
at equilibrium conc of Alveolar = Conc of spinal cord
What is MAC-BAR used for ?
potency at which autonomic responses go
what factors affect induction and recovery ?
Partition Coefficient - Solubility :
Blood: Gas partition (in blood) lower the quicker
Oil: Gas (In fat)
higher the longer as it accumulates so longer induction
What can increase MAC?
Low age Hyperthermia Pregnancy alcholism Central stimulus
What can decrease MAC?
Elderly
hypothermia
other anasethetics
Opioids
what is the effect of MAC by adding NO? What does this lead to ?
decrease in MAC
Allows less side effect profile as lower the MAC the better
what does the Meyer-Overton graph tell us ?
the higher the lipid solubility the higher the potentcy
what other factor is involved in Potency of Anaesthetics?
GABA receptor interaction
what are effects of GABA?
anxiolysis
sedation
Anaestheisa
How do GABA receptors work ?
LGIC - Cl- conductance . out to in to hyperpolarise neurones
How do Anaesthetics work ?
Potentiate Cl- conductance in the GABA receptor
How do Xe, N2O and Ketamine work ?
block NMDA receptor to stop glutamate receptor
what is a feature of Reticular formation ?
lots of GABA receptors
what does the thalamus do in consciousness ?
Transmits and modifies sensory information
What other brain circuitry does Anaesthesia target ?
Hippocampus - Memory
Brainstem - Resp and CVS
Spinal cord - Dorsal horn for analgesia
what are the main IV anaesthetics and what is their onset of action ?
Propofol - rapid
Barbiturates - Rapid
Ketamine - Slower
what is TIVA?
All 3 IV aneasthetics combined - uses defined PK algorithm to infuse at certain rate with bolus to start
how do we measure potency of IV anaesthetics ?
Plasma conc to achieve a specific end point
What is done after induction of IV anaesthetics ?
Switch to volatile
What are uses of local anaesthetics?
dentistry Obs regional surgery post op Chronic pain
What chemical properties determines time of onset of local anaesthetics ?
Lower pKa = faster onset
what determines potentcy of local Anaesthetics ?
Lipid solubility
What can affect duration of local anaesthetics ?
Protein binding
Ester based = ultra Short acting
Amide linked = long acting
how does Bupivacaine work ? what can increase block?
Block VG SCs
the higher the rate of activity = higher the block
block small myelinated afferent nerves = prefencer in nociceptive
what is given with locals ? why?
adrenaline to vasoconstrictor
opioids given as well
what is difference between Bupivacaine, Lidocaine, Ropivacaine?
see table and interpret
where do you give locals?
Upper = interscalene, supraclavicular,
infraclavicular, axillary.
• Lower extremity (e.g.,) ; femoral, sciatic, popliteal,
saphenous.
what are General anaesthetic side effects ?
N+V with opioids
hypotension
Post - op cog dysfunction = delirium
chest infection
