Anaesthetics Flashcards
3 components of anaesthesia?
hypnosis (amnesia)
analgesia
muscle relaxation (akinesis)
3 levels of hypnosis? how do anaesthetic agents therefore act?
awake (LA)
sedation (sedation)
asleep (GA)
3 local techniques:
local - minor surgery - laceration repair
regional - target specific nerves (brachial plexus or sciatic) - for post-op pain relief
neuraxial - spinal/epidural - intra-op, post-op use
what is the difference between spinals and epidurals?
Spinal (subarachnoid block) goes through both ligaments and dura to CSF via an injection at lumbar region, single bolus, faster onset, smaller dose, anaesthetic only
Epidural - needle goes between ligaments and dura and a catheter is passed
continuous infusion, slow onset, larger dose required, anaesthesia+analgesia, T or L spine
where are spinals and epidurals incisions done?
below the highest nerve root affected by the block
normally this is T10 dermatome - umbilicus
why is incision for epidurals/spinals not done above this level?
GA would be required
also epidurals would be insufficient post-op analgesia
MODA: LA:
reversibly blocks Na+ channels
inhibits generation of action potentials in nerve cells
smaller diameter, unmyelinated fibres blocked first
order of block: L.A:
b fibres (autonomic - vasoconstriction)
C and A(d) - pain and temp
A(b) - light touch and pressure
A(a) and A(Y) - motor and proprioception
what is often used in combination with LA? why?
adrenaline - vasoconstriction leads to reduced bleeding and prolonged effects of the LA through reduced absorption from tissues
where should adrenaline not be used?
in end arteries such as fingers
examples of L.A?
lidocaine
bupivicaine
lidocaine onset and duration, when used?
immediate onset, lasts 15m
small procedures - laceration repairs, chest drains, large cannulae
bupivicaine onset and duration, when used?
regional, spinal, epidural
10m onset - lasts 2h anaesthetic, 12-24h as analgesic
what do epidural infusions have running through them commonly and what should this indicate?
opioids
do not prescribe further opioids
what does induction and maintenance mean regarding general anaesthesia?
induction - sending to sleep
maintenance - keeping asleep
how are hypnotic drugs given?
inhaled or IV
3 examples of inhalational hypnotic drugs:
Isoflurane - cheapest - maintains sedation
Desflurane - maintains sedation - quick wears off
Sevoflurane - induces+/-maintains sedation
3 examples of IV hypnotic drug:
Propofol - quick onset - commonest - also antiemetic - fast redistribution (fast recovery of consciousness)
Thiopenthal - quick - emergency anaesthetics
Ketamine - used in CVS instability - also analgesic
pros and cons of induction via inhaled and IV:
IV - commoner, requires cannula, rapid onset, depresses airway reflexes, apnoea common
Inhaled - good for needle phobics, slow onset, irritates airway, usually keep breathing
once GA has taken effect, patients often stop breathing, how is their airway managed? (2)
spontaneous breathing
controlled ventilation
t1rF caused by what specific problem?
alveolar collapse or fluid in alveoli
name an agent which reverses the effects of midazolam?
Flumazenil
which drug is hepatotoxic and also can harm theatre staff if accumulated use?
halothane
name an anaesthetic agent which has anti emetic properties
propofol