ACC Flashcards
what three main things present a risk to the patient undergoing surgery?
1) surgery itself - damage to structures, blood loss, complications
2) effects of anaesthesia
3) pre-existing disease
list some possible intra-operative problems that can happen
- fluid balance
- hypoxia
- pain
- PONV
- hypothermia
- anaphylaxis
- PE
- death
what “centre” controls PONV? how does it work?
the vomiting centre - linked to other parts of the brain responding to different stimuli, via different receptors.
- inner ear –> cerebellum (H1)
- emotion (fear) –> higher centres
- blood-borne emetic –> chemoreceptor trigger zone (5HT-3, D2, H1)
- pharynx/GI tract –> solitary tract nucelus (5HT-3, D2, H1)
blood borne emetics / GI tract interact between each other.
all these different pathways act on vomiting centre, mediated by 5HT-3, D2
I think?? maybe look this up to actually understand it
give an example of an antiemetic that works on serotonin pathways? indications?
ondansetron - useful for both PONV and for vomiting post acute opioid administration
give an example of an antiemetic that works on histamine (H1) pathways? indications?
cyclizine
commonly used for travel sickness
can cause tachycardia
give examples of antiemetics that work on dopamine (D2) pathways? indications?
domperidone = premedication if at risk of PONV
metoclopramide = long term opioid use (counteracts gastric stasis
procholperazine = vertigo
what 5 steps make up pre-op preparation?
1) optimise medical conditions
2) adjust medication
3) check Ix
4) check wt
5) EXPLAIN AND CONSENT
explain the ASA grading system
1) healthy individual
2) mild systemic disease not limiting activity
3) severe systemic disease limiting activity but not incapacitating
4) incapacitating systemic disease, life threatening
5) emergent case - expected survival <24hrs without surgery
(6 = brain stem dead, for organ retrieval)
how do the 5 ASA grades related to predicted mortality?
1 = 0.05%
2 = 0.5%
3 = 5%
4 = 25%
5 = 50%
what key conditions do you want to know about when asking the anaesthetic history in pre-op?
pts prev. experience and FHx relevant.
* malignant hyperpyrexia
* suxamethonium apnoea
also:
- previous airway problems
- PONV (ask about travel sickness etc too)
what is malignant hyperpyrexia?
inherited skeletal muscle disorder that can be triggered by volatiles and suxamethonium.
causes hyperkalaemia, hypoxia, temperature, rhabdomyolysis.
can reverse with dantralene.
what is suxamethonium apnoea?
patient doesn’t have the enzyme to break down suxamethonium - use propofol instead.
inherited disorder of acetylcholinesterase.
what allergies is it important to ask about in pre-op assessment?
anaesthetic agents, analgesics, abx, latex, EGGS (propofol)
what is the protocol for peri-op adjustment if a patient is on: ACE inhibitors ?
stop as the anaesthetic will drop BP
what is the protocol for peri-op adjustment if a patient is on: angiotensin 2 receptor blockers ?
stop 24hrs before
what is the protocol for peri-op adjustment if a patient is on: ranitidine ?
increases pH so if aspiration occurs it’s less bad - continue
what is the protocol for peri-op adjustment if a patient is on: warfarin ?
stop.
if pt has AF use LMWH.
if thrombophilia/metallic heart valve (?) = stop 3-5 days before, use bridging protocol.
what is the protocol for peri-op adjustment if a patient is on: inhalers?
continue - should be brought with the patient into the anaesthetic room, and taken round to recovery.
what is the protocol for peri-op adjustment if a patient is on: clopidogrel?
stop 5 days before
what is the protocol for peri-op adjustment if a patient is on: beta blockers?
continue
what is the protocol for peri-op adjustment if a patient is on: PPIs?
continue
what is the protocol for peri-op adjustment if a patient is on: aspirin?
stop high does (200mg) - can continue 75mg only if spinal/epidural
what is the protocol for peri-op adjustment if a patient is on: steroids?
continue
what is the protocol for peri-op adjustment if a patient is on: insulin/oral hyperglycaemia?
insulin dependent people need a variable rate insulin infusion (sliding scale). avoid starving them - place first on the list!
what should you ask about at pre-op assessment for the CVS?
- HTN - well controlled? end organ damage?
- IHD - angina, MI
- pacemaker (causes problems for diathermy)
- PVD - exercise tolerance
- cerebrovascular disease - tight BP control needed to maintain perfusion
what should you ask about at pre-op assessment for resp system?
- COPD
- Asthma - inhalers, also can they take NSAIDs??
- OSA (STOP BANG)
- exercise tolerance - can they get up stairs without pause?
what other qus should you ask at pre-op assessment in terms of PMHx (apart from for CVS/resp)?
- GI - reflux (lying down?), liver disease
- DM
- thyroid
- DVT/PE
- rheumatoid
- social: smoking, alcohol, other drugs
what are the components of the STOP BANG score for obstructive sleep apnoea?
high risk if yes to 3+:
Snoring
Tiredness
Observed apnoea
Pressure (high BP)
BMI > 35
Age >50
Neck circumference >40cm
Gender - male
what medical conditions make airway assessment/management difficult?
- Downs
- RA
- ankylosing spondylitis
- obesity
- dental abscess
what examination should be done as part of pre op assessment?
- listen to chest
- check teeth for loose/broken/crowns
- neck flexibility
- airway assessment
how do you assess the difficulty of a patient’s airway at pre-op assessment?
1) anatomy - small mouth/chin, large tongue, big neck, beard
2) mechanical limitation - limited mouth opening/neck movement
3) dentition - poor dentition, expensive dental work
what predictive tests can be used pre-op to assess the airway?
- Mallampati score assesses oropharynx
- extension of upper cervical spine <90 degrees = bad sign
- thyromental test - distance from tip of thyroid to tip of mandible at gull extension should be >6.5cm. <6cm means difficult laryngoscopy.
explain how the Mallampati score works
get patient to stick tongue out and open wide.
Class IV = soft palate not visible
Class III = soft palate only
Class II = uvula tip masked
Class I = pillars, soft palate and uvula all visualised.
Class III or IV will be difficult airway.
what are the three components of the anaesthetic triad?
- anaesthesia (unconsciousness)
- analgesia (local or systemic)
- muscle relaxation
define anaesthetisa
a pharmacologically induced, reversible state of sleep characterised by lack of pain, awareness of surroundings and memory of events
what are the 3 phases of general anaesthesia?
1) induction - usually IV, then secure/manage airway, then oxygenate (often pre-oxygenate as well)
2) maintenance
3) reversal
two routes - IV (propofol), inhaled (iso/sevo/desfluorane) - used for young kids, needle phobics
give some basic info on the different induction agents
- propofol - painful on injection
- sevofluorane - minimal vasodilation, almost no metabolism (taken up by and excreted via lungs), irritant, taken up in fat tissue (so get prolonged drowsiness)
- nitrous oxide - analgesic properties, low solubility means rapid onset and offset
Opioids - risk of respiratory depression
- remifentanil - tiny doses, breaks down spontaneously in 10-15s, used in TIVA
- alfentanyl - potent, rapid onset, duration 2-3 mins
- fentanyl - onset 1-2 mins, duration 10-15 mins
- morphine - causes more histamine release so not great for PONV, slow onset (10-15 mins) and causes constipation
what agents are used in maintaining anaesthesia?
gases - volatiles. nitric oxide/oxygen.
TIVA - propofol infusion + remifentanil infusion.
either method can involve paralysis + ventilation or spontaneous breathing.
give some basic info on the volatiles
- isofluorane = cheapest, maintains sedation, most irritant (coughing), not used for induction
- desfluorane = maintains sedation, wears off quickly
- sevofluorane = induces/maintains sedation
give some info on the use of muscle relaxants when under GA
will the patient breathe spontaneously?
if you do use muscle relaxants then you need to ventilate!
at what GCS level are you unable to maintain airway control?
8 or below
GCS 8 or lower ?? = AIRWAY MANAGEMENT NEEDED
what simple manoeuvres can be used in airway management?
- head tilt
- chin lift
- jaw thrust
list the different options for airway management
- simple manoeuvres
- oropharyngeal (guedel)
- nasopharyngeal (beware in base of skull #)
- supraglottic - LMA
- ET tube
also bag and mask ventilation
list three ways of determining correct placement of ET tube
1) chest movement
2) misting of mask
3) **trace on capnography
places tube shouldn’t be = oesophagus, endobronchial
briefly outline the mechanism of action of local anaesthetics
1) unionised LA enters the cell
2) LA becomes ionised
3) blocks Na channel so pain signals can’t be sent
what 4 different types of sites might be used for regional anaesthesia?
- peripheral nerve blocks
- plexus block
- epidural block
- spinal block
give some basic info on lidocaine
onset = immediate
duration = 15 minutes
used for = small procedure, lacerations, chest drains
give some basic info on bupivocaine
onset = 10 minutes
duration = 2hrs anaesthesia, 12hrs analgesia
used for = regional blocks
give some advantages for the use of regional anaesthesia
- avoids GA
- can be awake
- avoids airway problems
- less PONV
- better peri-operative pain control
what dermatome supplies the shoulder?
C5
what dermatome supplies the thumb?
C6
what dermatome supplies the middle finger?
C7
what dermatome supplies the little finger?
C8
what dermatome supplies the nipples?
T4
what dermatome supplies the umbilicus?
T10
what dermatome supplies the knee?
L4
what dermatome supplies the little toe?
S1
how do spinals work vs epidurals?
spinal goes through ligaments and dura into CSF. uses LA as a bolus, will last c.2 hrs.
epidural goes between the ligaments and dura (into the epidural space, obvs). LA give via a catheter as continuous infusion.
both allow operation below highest nerve root affected by block.
what are the 3 reasons you want muscle relaxation during surgery?
1) relaxes the opening to the trachea (glottis) for intubation
2) relax muscles for surgery
3) so patient doesn’t fight ventilation
what are the two main categories of muscle relaxants, and give examples of each?
Depolarising = suxamethonium. onset is within 30s so used only for EMERGENCIES.
Non-polarising = atracurium, rocuronium, vecuronium. onset 120-180s, duration 30mins. used routinely.
briefly explain the normal mechanism of muscle contraction (so you can understand how muscle relaxants work)
1) nerve impulse releases ACh to the neuromuscular junction (NMJ)
2) ACh binds to sites on muscles and open a pore for Ca2+ to cross membrane and cause contraction
how do non-depolarising muscle relaxants work (e.g . atracurium, rocuronium)
they competitively inhibit ACh by blocking binding site, preventing depolarisation.
- onset 1 minute.
how do depolarising muscle relaxants work?
- suxamethonisum is 2 ACh molecules bound together
- binds BOTH sites simultaneously
- causes contraction then keeps pore open preventing further contraction
- onset 30s, duration 3 mins - see muscle contractions then flaccid paralysis.
what drug can be used to reverse muscle relaxants? how does it work?
neostigmine
- ACh blockers
- causes build up of ACh at the receptor, and competition with the muscle relaxant for binding site
what drugs are used in theatre to speed up the HR? how do they work?
atropine, glycopyrrolate, hyoscine = anticholinergics, increase HR - these inhibit the vagus nerve as the parasymp. NS uses ACh as a neutrotransmitter.
dobutamine = beta-agonist (used in heart failure in ITU) - increases HR and contractility by stimulating beta adrenoreceptors in myocardial cells.
what drugs might you give to increase BP in theatre? (without raising heart rate)
- want to stimulate alpha adrenoreceptors
- causes vasoconstriction
- use alpha agonists to increase BP via increasing SVR (?)
- may cause decrease HR as body tries to correct
what drugs can you use in theatre to increase BP and HR?
e.g. ephedrine or adrenaline (very potent, therefore only @arrest/ITU).
- stimulate alpha and beta adrenoreceptors with combined alpha/beta agonist
briefly describe the WHO pain ladder
mild = paracetamol and NSAIDs
mod = codeine and tramadol
severe = morphine
who should you be careful about using paracetamol with?
liver failure
low weight (elderly, children)
