anaesthetics Flashcards
what are the different levels of anaesthesia?
local - one area sensation is loss
regional e.g. central nerve block (spinal or epidural)
sedation
general anaesthesia
what agents can be used for local anaesthetics?
lidocaine
procaine
bupivacaine
what does general anaesthesia involve?
analgesia hypnosis relaxation - reduced reflexes and muscle relaxation amnesia anxiolysis
Chloroform can achieve hypnosis, analgesia and paralysis alone so why don’t we just use this?
It is better to use multiple agents at a lower dose than one agent at a high dose. less side effects.
list some IV drugs that can be used to induce anaesthesia.
propofol - most common - rapid sedation induction
ketamine
midazolam
etomidate
list some inhaled agents used for induction of anaesthesia.
Desflurane
isoflurane
halothane
Briefly outline the steps taken when undergoing general anesthetics
pre-assessment premedication induction maintenance - usually switch to a volatile anaesthetic agent at this point. need to be continuously monitoring and adjusting e.g. phenylephrine to treat hypotension emergence recovery
during the induction phase of anaesthetics. what happens?
check monitors are all working pre-oxygenate IV induction usually with propofol analgesic - opioid muscle relaxation to aid intubation/reduce movement - usually tubocurarine intubate tape over eyes to protect them position to prevent sores/ how surgeon wants
what type of induction is mainly used and when do we use the other type of induction?
usually IV by propofol
but can use gas via airways instead if phobia of needles, non compliant child, poor vein access
what agent is mainly used for induction of anaesthetics?
propofol
why do we pre-oxygenate a patient before inducing anaesthesia?
allows more time to intubate and establish an airway.
normal air is 21% O2 so a patient will desaturate after 2 mins but if we give them 100% O2 before this extends the time frame to 10 mins
what agents are often used for muscle paralysis during anaesthesia? how do these work?
Tubocurarine - blocks nACHr
Succinylcholine - depolarising blocker of nACHr - accommodation
name 2 NMDA receptor antagonists
ketamine
N2O
how does propofol work?
increases GABAa chloride channel current by increasing sensitivity to GABA
positive allosteric modulation
what monitoring do we use throughout general anaesthesia?
capnography and airway gas's - most important pulse oximetry ECG agent analyser BP temperature - malignant hyperpyrexia airway pressure
depending on surgery other things e.g. Doppler in carotid endartectomy
why is N20 a useful agent?
low potency but can be used in conjugation with other gents to lower the MAC of other agents. Therefore less side effects
How do you stop general anaesthesia?
withdraw anaesthetic agents / reverse them.
continue analgesics and anti-emetics
establish sustainable spontaneous respiration with good gas exchange
transfer to recovery
what agents can be used to reverse neuromuscular block?
Neostigmine - reverses neuromuscular blockage
however can lead to reduced HR and bronchoconstriction
therefore mix it with glycopyroate which counters these effects but does not cross BBB so neostigmine reverses the effects required.
what are the stages of anaesthesia?
- analgesia and conscious
- unconscious, excitement, delirium, weird breathing
- surgical anaesthesia - reduced resp and CNS activity, muscle tone and reflexes
- severe medullary depression - resp and CNS depression - cardiac arrest and death.
what are the advantages and disadvantages of total intravenous anaesthesia?
advantages - better recovery, better for neurosurgery, problems of N20 avoided
disadvantages - need secure IV access, may cause profound hypotension.
what is the MAC?
minimum alveolar concentration…
the % of inhaled anaesthetic agent that 50% of patients will not respond to surgical incision
i.e. the lower it is, the more potent an anaesthetic
what MAC value is usually used in practice?
very variable depending on individual and the surgery and the different anaesthetic agents used.
what factors affect MAC?
use of multiple agents e.g. N20, opioids
elderly - lower MAC
infants - higher MAC
hypotension, hypothermia and hypothyroid - lower MAC
hyperthyroid, hyperthermia - increase MAC
stimulants alcohol and smoking - increase MAC
pregnancy - increases MAC
1 MAC of sevoflurarane is 2.2 % what does this mean? how many MAC would you use?
at a concentration of 2.2% , 50% of people will not be responsive to surgical incision.
you would want to use 1.2-1.5 MAC to ensure all patients are not responsive. therefore would use 3%
however take into account individual and other agents which will agent adjust the MAC
if only old patients were tested 1 MAC of this agent may instead be 1.8% because elderly lowers MAC i.e. drug becomes more potent.
what alters the speed of conduction of an anaesthetic agent?
how well it dissolves in blood or lipid. if it leaves blood to tissues it will induce anaesthesia fast. i.e. the better soluble in lipid the faster acting.
also the more lipid soluble the more potent because the more will leave into nerve cells across myelin and work.
what are common post op complications related to anaesthesia?
PONV, sorethroat,
Pain: headache, itching, aches, bruising, soreness
confusion, shivering
chest infection, bladder problems.
less common: damage to lips, teeth, allergy, breathing difficulties, damage to eyes, nerve damage, death
what are the main risks of anaesthesia?
reduced CO and low BP - shock
reduced resp rate
list some common problems of fluranes
resp and CVS depression (reduced medulla activity)
arrhythmias and hypotension - due to reduced vascular resistance by direct effect on arterial smooth muscle
increased cerebral flow and therefore increased ICP due to vasodilation
malignant hyperthermia
isofluranes and desflurane are airway irritants and can lead to laryngospasm
list the common problems of propofol
CVS and resp depression
propofol infusion syndrome (RARE) - impaired mitochondrial resp leading to metabolic acidosis, hyperkalaemia, rhabdomyolysis - can lead to cardiac arrest
list the ADRs of N20
expansion of airway cavities - sinuses, middle ear, bowel
dangerous in pneumothorax
diffuses rapidly out of blood and rises in alveoli and therefore become temporarily hypoxic (problem if there is already resp problem)
state an ADR of benzodiazepines
resp depression
state an ADR of neuromuscular blockers
Apnoea therefore hypoxia
list the roles of Anaesthetists
I - intensive care T - theatre A - anaesthetics P - pain S - sleep
including epidurals in obs and gynae
state symptoms and signs of an allergy
symptoms: itching,sneezing, wheezing, tightness, swelling of face/airways, eyes watering, N and V and D, tingling, rash
signs: hypotension , pale and sweaty, tachypnoea , tachycardia
what happens in the stress response to surgery? what factor can increase this response?
ADH and cortisol are secreted
ADH: fluid retention
Cortisol and aldosterone: sodium and fluid retention, potassium loss.
results in dehydration and electrolyte imbalances
Pain
what are the indications for lignocaine/lidocaine and what are the contraindications?
indication: local anaesthetic, arrhythmias,
contraindications: heart block, WPW
how does lignocaine/ lidocaine/ bupivacaine work?
blocks fast acting VG na channels in neuronal cell membrane preventing depolarisation of post synaptic neuron therefore no pain transmission.
in heart it can also do this making heart less likely to conduct early AP and thus prevents arrhythmias
all act on internal side of these channels.
why is levobupivacaine often used over lidocaine?
levobupivacaine last longer
what happens if local anaesthetic agent gets into blood in high concentrations? how is it treated?
can lead to seizures/arrhythmias - i.e. avoid vessels when giving local anaesthetic
Can give intralipid to mop this up
what type of block is used for
a) shoulder
b) arm/elbow
c) hand
a) intrascalene
b) supraclavicular
c) axillary
for intrascalene block, what structure do we need to be careful of?
phrenic nerve
what are the indications for ITU?
patient needs close monitoring
needs support of more than one of their body functions e.g. ventilation and dialysis
large amount of blood loss in surgery etc
when is ITU not indicated?
An individual is unlikely to gain much out of intensity of care e.g. incurable cancer. in this case palliative care is more appropriate
