Anaesthetics Flashcards
General Anaesthesia
what are the 2 main categories of anaesthesia
General anaesthesia: making the pt unconscious
Regional anaesthesia: blocking feeling to an isolated area of body eg limb
General Anaesthesia
what happens during general anaesthetic
pt intubated or has a supraglottic airway device
breathing supported and controlled by a ventilator
pt continuously monitored at all times immediately before, during and after general anaesthesia
General Anaesthesia
what is the purpose of fasting before a planned general anaesthetic
to make sure they have an empty stomach
to reduce the risk of the stomach contents refluxing into the oropharynx (throat)
then being aspirated into the trachea (airway)
General Anaesthesia
what happens if gastric contents gets into the lungs
an aggressive inflammatory response, causing pneumonitis
General Anaesthesia
when is risk of aspiration highest
before and during intubation and when they are extubated
once the endotracheal tube is correctly fitted, the airway is blocked and protected from aspiration
General Anaesthesia
what are major causes of morbidity and mortality in anaesthetics
aspiration pneumonitis and pneumonia
General Anaesthesia
what does fasting for an operation typically involve
- 6h no food or fedes before operation
- 2h no clear fluids (fully nil by mouth)
General Anaesthesia
what is preoxygenation
before being put under general anaesthetic, the pt will have a period of several minutes where they breathe 100% O2
General Anaesthesia
why do you preoxygenate a pt before surgery
it gives them a reserve of O2 for the period between they lose consciousness and intubated and ventilated (in case difficulty establishing airway)
General Anaesthesia
what premedication is given and why
benzodiazepines eg midazolam: to relax the muscles and reduce anxiety (also causes amnesia)
opiates eg fentanyl or alfentanyl: to reduce pain and reduce the hypertensive response to the laryngoscope
alpha-2-adrenergic agonists eg clonidine: sedation + pain
General Anaesthesia
when is Rapid Sequence Induction/intubation used?
to gain control over the airway as quickly and safely as possible where a pt is intubated in an emergency scenario and detailed pre-planning is not possible
General Anaesthesia
what non-emergency situations is RSI used
when the airway needs to be secured quickly to avoid aspiration eg GOR or pregnancy
General Anaesthesia
why is RSI more riskt
- not fasted so risk of aspiration
- no plan for individual factors and potential problems eg difficult airway
General Anaesthesia
RSI procedure
endotracheal tube intubation asap after induction
General Anaesthesia
biggest concern in RSI
aspiration of stomach contents into the lungs
General Anaesthesia
what can be done to reduce the risk of aspiration in RSI
- position bed more upright
- cricoid pressure: compresses oesophagus
General Anaesthesia
what is the triad of general anaesthesia
- hypnosis
- muscle relaxation
- analgesia
General Anaesthesia
what are hypnotic agents used for
to make the pt unconscious
IV med will be used as an induction agent and inhaled med will be used to maintain the general anaesthetic during the operation
General Anaesthesia
IV options for hypnotic agents
- Propofol (most common)
- Ketamine
- Thiopental sodium (less common)
- Etomidate (rarely used)
General Anaesthesia
inhaled options for hypnotic agents
- Sevoflurane (most common)
- Desflurane
- Isoflurane (rarely)
- NO (combined with other med - may be used for gas induction in children)
General Anaesthesia
why is Desflurane less favourable than Sevoflurane
its bad for the environment
General Anaesthesia
what are Sevoflurane, desflurane and isoflurane?
volatile anaesthetic agents - liquid at room temp and need to be vaporised into a gas to be inhaled
General Anaesthesia
how are volatile anaesthetic agents vapourised?
the liq med is poured into the vaporiser machine which turns it into vapour and mixes it with air in a controlled way
during the anaesthesia, the conc can be altered to control the depth of anaesthesia
General Anaesthesia
inhaled or IV quicker to reach an effective conc
IV as they are infused directly into the blood whereas inhaled meds need to diffuse across the lung tissue and into the blood
General Anaesthesia
what is total intravenous anaesthesia (TIVA)
using an IV medication for induction AND maintenance of the general anaesthetic
propofol is most common. Can give a nicer recovery
General Anaesthesia
how do muscle relaxants work
they block the neuromuscular junction from working
ACh is released by the axon but is blocked from stimulating a response from the muscle
General Anaesthesia
why are muscle relaxants given
to relax and paralyse the muscles to make intubation and surgery easier
General Anaesthesia
what are the 2 categories of muscles relaxants
- depolarising
- non-depolarising
General Anaesthesia
name an example of a depolarising muscle relaxant
suxamethonium
General Anaesthesia
name an example of a non-depolarising muscle relaxant
rocuronium
atracurium
General Anaesthesia
what can reverse the effects if neuromuscular blocking medications
Cholinesterase inhibitor eg neostigmine
General Anaesthesia
what is used specifically to reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium)
Sugammadex
General Anaesthesia
what common agents are used for analgesia
opiates:
- fentanyl
- alfentanil
- remifentanil
- morphine
General Anaesthesia
why are antiemetics often given at the end
to prevent post-op N + V
General Anaesthesia
antiemetics: Ondansetron
- 5HT3 receptor antagonist
- avoided in patients at risk of prolonged QT interval
General Anaesthesia
antiemetics: Dexamethasone
- corticosteroid
- caution in diabetics or immunocompromised pts
General Anaesthesia
antiemetics: Cyclizine
- histamine 1 receptor antagonist
- caution with HF + elderly pts
General Anaesthesia
what is ‘awareness under anaesthesia’
pt regains consciousness whilst still paralysed
the muscle relaxant needs to be worn off before waking the patient
General Anaesthesia
what is used to ensure the muscle relaxant effects have ended
nerve stimulator ‘the twitchy machine’
General Anaesthesia
where can the nerve stimulator test on?
- ulnar nerve at wrist: watch thumb twitch
- facial nerve: movement in the orbiculares oculi
General Anaesthesia
what is train-of-four stimulation
the nerve is stimulated 4 times to see if the muscle responses remain strong (indicating it has worn off)
or whether they get weaker with additional stimulation (indicating it has not fully worn off)
General Anaesthesia
what are common adverse effects of general anaesthesia
- sore throat
- post-op N+V
General Anaesthesia
what are some significant risks of general anaesthesia
- accidental awareness (waking during the anaesthetic)
- aspiration
- dental injury (laryngoscope)
- anaphylaxis
- CV events (MI, stroke, arrhythmias)
- Malignant hyperthermia (rare)
- death
General Anaesthesia
what is malignant hyperthermia
hypermetabolic response to anaesthesia
genetic mutations increase the risk.
Autosomal dominant
General Anaesthesia
what agents are a risk for malignant hyperthermia
- volatile anaesthetics: isoflurane, sevoflurane, desflurane
- Suxamethonium
General Anaesthesia
what does malignant hyperthermia cause
- increased body temp (hyperthermia
- increased CO2 exhalation
- tachycardia
- muscle rigidity
- acidosis
- hyperkalaemia
General Anaesthesia
what is malignant hyperthermia treated with
dantrolene
General Anaesthesia
how does dantrolene work when treating malignant hyperthermia
it’s a muscle relaxant that works by interfering with the movement of Ca+ in skeletal muscle
Post-op N+V
name 3 types of antiemetics
- 5HT3 receptor antagonist
- D2 receptor antagonist
- H1 receptor antagonist
Post-op N+V
what type of antiemetic is ondansetron
5HT3 receptor antagonist
Post-op N+V
5HT3 receptor antagonist: site of action
- chemoreceptor trigger zone
- GI tract
Post-op N+V
5HT3 receptor antagonist: mechanism
prevents stimulation of vagus nerve by emetogenic stimuli in the gut (a substance that causes vomiting)
Post-op N+V
5HT3 receptor antagonist: side effects
- prolonged QT interval
- headaches
- constipation
- diarrhoea
Post-op N+V
5HT3 receptor antagonist: useful in?
- Chemoreceptor trigger zone stimulation e.g. drugs
- visceral stimuli e,g, gut infection, radiotherapy
Post-op N+V
5HT3 receptor antagonist: avoid in?
pt taking other drugs that prolong the QT interval e.g. antipsychotics, SSRIs
what type of anti-emetic is Metclopramide
D2 receptor antagonist
what type of anti-emetic is domperidone
D2 receptor antagonist
Post-op N+V
D2 receptor antagonist: site of action
- chemotrigger zone
- upper GI tract
Post-op N+V
D2 receptor antagonist: mechanism
prokinetic:
- relaxes the pylorus
- decreases lower oesophagus sphincter tone
- increases gastric peristalsis
Post-op N+V
D2 receptor antagonist: SEs of metclopramide
ESPEs: acute dystonia because it crosses the BBB
more common in young females
Post-op N+V
D2 receptor antagonist: SEs of domperidone
does not cross the BBB so no ESPEs
Post-op N+V
D2 receptor antagonist: general SE
diarrhoea
Post-op N+V
D2 receptor antagonist: useful in?
- CTZ stimualtion (drugs)
- decreased gut motility e.g. opioids, diabetic gastro paresis
Post-op N+V
D2 receptor antagonist: avoid in?
GI obstruction , perforation
what type of antiemetic is cyclizine
H1 receptor antagonist
what type of antiemetic is cinnarizine
H1 receptor antagonist
what type of antiemetic is promethazine
H1 receptor antagonist
Post-op N+V
H1 receptor antagonist: site of action
vomiting centre, vestibular system
Post-op N+V
H1 receptor antagonist: SEs
anti-cholinergic effects:
- drowsiness
- dry mouth
- blurred vision
transient tachycardia after IV
Post-op N+V
H1 receptor antagonist: useful in?
motion sickness and vertigo
Post-op N+V
H1 receptor antagonist: avoid in?
prostatic hypertrophy as it can precipitate urinary retention
what is ondansetron used in
5HT3
- PONV
- vomiting after acute opioid administration
what is cyclizine used in
H1
- PONV
- motion sickness
- vomiting after acute opioid administration
what is metclopramide used in
long term opioid use
(opioids cause gastric stasis which can be counteracted by prokinetic effect of metclopromide
what is domperidone used in
premedication for pts at risk of PONV
what is prochlorperazine used in
vertigo
Local
what us the principle drug used in spinal anaesthesia
Bupivacaine
Local
what is bupivacaine especially used in
continuous epidural analgesia in labour or for posop pain relief
Local
what is the duration and onset of action in bupivacaine
- longer duration fo action that other locals
- takes up to 30m for full effect
Local
what is Levobupivacaine
an isomer of bupivacaine but fewer adverse effects
Local
solutions of lidocaine should not exceed what % strength
1% except for surface and dental anaesthesia
Local
what is the duration of block (w/ adrenaline) of lidocaine
90m
Local
what happens to blood vessels
they dilate
Local
why is a vasconstrictor (adrenlaine) added to the local
it diminishes local blood flow, slowing the rate of absorption and therefore prolonging the anaesthetic effect
Local
when should you not add adrenaline to local?
in pts with severe HTN or unstable cardiac rhythm
Local
toxicity can lead to>
cardiovascular toxicity –. cardiac arrest
Local
mnx of local anaesthetic-induced cardiac arrest
- standard resus
- 20% lipid emulsion (Intralipid) bolus then infusion
- 5 min? 2 more boluses and increase infusion rate
what is the anti-emetic of choice in bowel obstruction
Cyclizine
which anti-emetic is more suitable for patients with bowel obstruction secondary to stasis or ileus.
metclopromide because it increases intestinal peristalsis
which anti-emetic is prescribed for nausea and vomiting secondary to chemotherapy
Ondansetron
SE of ondansetron
constipation
what is rapid sequence induction
- administration of rapidly acting induction agents
- to produce anaesthesia and muscle relaxation
- followed by prompt intubation
- resulting in a secure airway with the minimal risk of aspiration
what are the steps forming the sequence of RSI
1) Preparation: optimise environment - equipment, staff
2) Preoxygenation: high flow O2 for 5m prior
3) Pretreatment: opiate analgesia or fluid bolus to counteract hypotensive effect of anaesthesia
4) Paralysis: induction agent (e.g. Propofol or Sodium Thiopentone) + paralysing agent (e.g. Suxamethonium or Rocuronium)
5) Protection + positioning: Cricoid pressure to protect airway
6) Placement and proof: Intubation via laryngoscopy, with proof obtained (direct vision, end-tidal CO2, bilateral auscultation)
7) Post-intubation management
Taping or tying the endotracheal tube, initiating mechanical ventilation + sedation agents
what is a complication from epidural anaesthesia (c-section)
Maternal and foetal distress secondary to hypotension
how much to increase opioid dose if pain is not controlled
increase total dose by 1/3
what is the method of delivering oxygen to treat type II respiratory failure
BiPAP
what is the first line treatment for spasmodic pain in palliative care patients
diazepam
family history of difficulty ventilating during anaesthesia, which drug to aid intubation and why
Rocuronium
risk of suxamethonium apnoea if Suxamethonium used
what is the total recommended maintenance fluid a day
25-30ml/day
mnx for patients peri op if anaemic
blood transfusion
unless pt has CKD4 (as less EPO so anaemia is normal for them)
at what GCS score should intubation be considered
GCS <8
How do you predict a difficult intubation?
- previous difficult intubation
- small mouth opening
- Mallampti score
- BMI
- neck mobility
What from the WHO checklist do you do once the patient has arrived for surgery before anaesthetic (4)
- Check pt name, number and DOB
- allergies
- check consent form
- check operation Mark site
- machine and drug check
- pulse check
- assess airway risk
- ask blood loss risk
which airway device provides protection for the lungs from regurgitated stomach
contents?
Tracheal tube
What is the purpose of cricoid pressure
It prevents the passage of gastric contents into the airway
