1
Q
Describe the pathway of platelet activation
A
- Remain inactive by prostacyclins and NO constitutionally released from healthy vessels
- vWf, thrombin or colagen activate platetets
- Activated platelets release their dense granules (containing ADP) and thromboxane A2 via COX system
- ADP binds to the P2Y12 receptor triggering Calcium release and GpIIb/IIIa receptor activation
- Thomboxane A2 also does the above
- Circulating fibrinogen binds to vWf at injury site and GpIIb/IIIa receptor to form platelet plug
2
Q
Name anti-platelet drugs and their MOA
A
- COX inhibition - aspirin
- P2Y12 inhibitors - clopidogrel, ticargrelor, prasugrel
- GpIIb/IIIa inhibitors - epitifibitide, tirofiban
- Prostacyclin
3
Q
Causes of raised or low platelets
A
Causes of raised platelets
- Essential thrombocytosis
- Leukaemia
- Malignancy
- Infection
Causes of reduced platelets:
- ITP
- TTP
- DIC
- HELLP
4
Q
What is the guidance and options for stopping DAPT post stent for major surgery
A
Normal guidelines:
- Aspirin should be continued lifelong
- Second agent should be continued for: Bare-metal - 1 month. Drug eluting - 6 months
- Drug eluting stents reduce risk of re-stenosis, but require longer anti-platelet therapy due to the drug therapy promoting platelet activation.
- Bare metal stents used only in patients who longer duration anti platelets may cause issue
Issues with stopping DAPT: stent thrombosis and rebound hypercoagulable state
If stopping:
- Perform surgery within 24h in a centre with PCI
- Continue aspirin if bleeding risk accepted
- Replace ADP antagonist with short acting infusion (epitfibitide or cangrelor)
5
Q
What factors increase the risk of stent thrombosis?
A
○ MI as the indication for PCI+Stent
○ Diabetes Mellitus
○ Active smoking
○ PCI 6 months prior to recent PCI
- Congestive heart failure
6
Q
What are the risk factors for PONV?
A
Patient
○ Female gender
○ History PONV
○ History of motion sickness
○ Non-smoker
○ Young age
Anaesthetic
○ Nitrous
○ Opioids
○ Neostigmine
○ Duration
○ Stomach distention due to BVM
Surgical
○ Middle ear
○ Squint
○ Laparoscopic
- Neuro
7
Q
Complications of PONV
A
- Reduced satisfaction
- Longer recovery times
- Delayed oral intake return
- Aspiration
- Wound dehiscence
- Oesophageal rupture
- Raised ICP
8
Q
What are the classifications of anti-emetics?
A
- H1 receptor antagonists - cyclizine
- Anti muscarinic - hyoscine
- 5HT3 antagonists - ondansetron
D2 receptor antagonists - prochlorperazine, domperidone, metoclopramide - Neurokinin 1 receptor antagonist - aprepitant
9
Q
What are the pharmacokinetics of propofol?
A
- Vd - 4L/Kg
- pKa 11
- Clearance 25-60 ml/kg/min
- Protein binding 99%
10
Q
What are the pharmacokinetics of remifentanil?
A
- Vd 400ml/Kg
- pKa 7.5
- Protein binding 70%
- Clearance 40ml/kg/min
11
Q
Describe the process of TCI
A
- Uses three compartment model (three compartments, and rate of transfer between them)
- Initial bolus: V1 x Cp
- Drug then leaves V1 to V2 (vessel rich tissues) and V3 (vessel poor tissues), so infusion rate slows to keep Cp constant
- Drug is eliminated from V1, so infusion must match this to maintain steady state
12
Q
What is the difference between target and effect site control?
A
- Assumption that effect site is negligible in volume
- Assumption that there is an inward constant (Keo) but no outward constant
- Keo is an experimentally derived constant
13
Q
What are the safety components of a TCI infusion set up?
A
- Leur lock connections
- Anti-syphon valves at syringe injection points
- Anti-reflux valves at infusion site
14
Q
How should intra-op awareness be managed?
A
- Stop surgery
- Verbal reassurance
- Ensure anaesthesia delivery method ok (check TIVA lines)
- Deepen anaesthesia
- Document
15
Q
Compare the Marsh and Schneider models
A
Marsh
○ Bodyweight is the only variable
○ Larger variable V1 (elderly vs young of same weight get same bolus)
○ Fixed low and fast redistribution
○ Fixed elimination
Schneider
○ Age, gender, weight and height required to calculate LBW
○ V1 fixed at 4.7L
○ Variable low and fast redistribution
○ Variable elimination
16
Q
Describe the categories of pulmonary hypertension
A
Definition: Mean pulmonary arterial pressures >25mmHg at rest or >30mHg on exercise
- Group 1 - Pulmonary arterial hypertension
- Group 2 - Left heart disease
- Group 3 - Chronic lung disease
- Group 4 - Chronic thromboembolic disease
- Group 5 - Multisystemic disorders
17
Q
What are the cardiovascular consequences of pulmonary hypertension?
A
- RV hypertrophy
- Increased RV O2 demand leading to ischaemia and fibrosis (diastolic dysfunction)
- Tricuspid regurgitation
- Coronary perfusion reduces as RV pressures increase
- Reduced RV output and increase pressure into LV leads to LV failure
18
Q
What are the anaesthetic goals in pulmonary hypertension?
A
- Minimise RV afterload (minimise pulmonary vasoconstriction) - Avoid hypoxia/hypercarbia/acidosis/pain/nitrous/high airway pressures
- Maintain RV preload- Treat blood loss and cardiac output guided fluid monitoring
Maintain normal rhythm and rate
19
Q
How is pulmonary hypertension treated?
A
- Acute
○ Nebulised prostacyclin
○ IV sildenafil
○ Inodilators (enoximone)
○ Inotropes (doputamine) - Chronic
○ Underlying conditions (inhalers, anticoags, diuretics)
○ Pulmonary vasodilation (Amlodipine, sildenafil inhaled iloprost)
20
Q
What is frailty?
A
A state of increased vulnerability to poor resolution of homeostasis after a stressor
21
Q
What are the cardiovascular changes associated with the elderly?
A
- Reduced arterial elasticity/atherosclerosis = Exaggerated pressor responses
- Reduced atrial pacemaker cells and reduced SV = Reduced response to hypotension
- Reduced AV node cells = Increased risk of arrythmias
- Decreased beta receptor number = Impaired catecholamine response
22
Q
What are the respiratory changes associated with the elderly?
A
Reduced chest wall compliance
Increased closing capacity due to increased residual volume
Reduced chemoreceptor response to O2/CO2
Reduced cough and mucocilliary clearance
23
Q
What are the pharmacokinetic changes associated with the elderly?
A
- Reduced protein binding
- Reduced cardiac output - slower brain arm circulation time
- Decreased total body water = high concentration of water soluble drugs
- Increased fat mass = prolonged effect of lipid soluble drugs
- Reduced nephrons = reduced renal clearance
- Reduced hepatic mass = reduced hepatic metabolism
24
Q
What is post-operative cognitive dysfunction? What are the risk factors?
A
Cognitive decline compared to baseline after surgery over a longer period (compared to delirium) which does not affect consciousness.
- Increased age
- Increased surgical duration
- Pre existing cognitive dysfunction (e.g. stroke)
- Post op infections
25
What is lean body weight? What drugs are dosed by LBW?
Actual body weight minus weight deemed to be fat - Bolus propofol, opioids and NMB
26
Side effects of tacrolimus
- Risk of malignancy
- Risk of infection
- Arrythmias
- Seizures
27
What are the respiratory impacts go obesity?
- Increased basal oxygen consumption = faster desaturation
- Reduced FRC = faster desaturation
- Increase adipose on chest = collapsed smaller airways and higher ventilation pressures
- Higher airway reactivity due to proinflammatory obesity state - less responsive to beta agonsits
- Co-existing OSA or obesity hypoventilaiton syndrome = need for CPAP
28
Side effects of mycophenolate
- Risk of malignancy
- Risk of infection
- Bone marrow suppression
29
Physiological effects of cardiac transplant
- Loss of vagal tone - HR held at 90-100 due to circulating catecholamines
- Blunted sympathetic reflex (no direct sympathetic stimulus)
- Loss of baroreceptor reflex
- Loss of carotid sinus/occulogyric reflex
30
Co-morbidities associated with cardiac transplantation
Cardiac
- CAV (Cardiac allograft vasculopathy) - increased atherosclerosis of donor coronaries
- Rejection
- Arrythmias due to tacolimus
Non-cardiac
- Seizures due to tacrolimus
- Ongoing issues with underlying disease (e.g. amyloid/sarcoid)
31
Effects of drugs in cardiac transplant
- Atropine/glyco - no effect
- Adenosine/adrenaline - exagerated effect
- Vasodilators - BP drop but no sympathetic response
32
Physiology of hyperoxia
- Damages DNA and impairs its repair
- Damages RNA and impairs its repair
- Lipid peroxidation damaging membranes
- Oxidises enzymes leading to loss of function
33
Complications of hyperoxia
Respiratory
- ARDS
- Absorption atelectasis
Cardiovascular
- Systemic vasoconstriction (Inc cerebral and coronary)
- Prothrombotic state
34
Conditions where hyperoxia is used clinically
- Carbon monoxide poisoning
- Spontaneous pnuemothorax
- Cluster headache
- Peri-operatively to reduce anastamotic breakdown
35
What factors increase and decrease FRC?
Factors reducing
○ Supine
○ Anaesthesia
○ Pregnancy/obesity
○ Young age
Factors increasing
○ Upright
○ Emphysema/COPD
○ PEEP/CPAP
○ Increasing age
36
How is an ultrasound image generated?
- Electrical current applied against piezoelectric generating sound waves within ultrasound frequency
- US waves penetrate tissues and are reflected back due to different electrical impedences
- Crystals also receive reflected US waves and generate voltage
- Higher intensity = brighter image
- Slower return = deeper structure
37
Which probes are used for ultrasound?
- Linear - 5-15MHz
- Curvilinear - 2-5MHz
- Phased Array 1-5mHz
38
Acoustic artefacts seen in US
- Anisotropy - some structures reflect more waves depending on the angle
- Contact - air before probe
- Refraction - if not perpendicular, will deviate from probe
- Post-cystic enhancement - because US waves travel well through fluid
39
What is the Doppler effect?
- Change in perceived frequency of a sound wave when the source is moving in relation to the observer
V=∆F . C / 2 Fo CosO
40
Describe how an oesophageal doppler works?
- Tip rotated to face descending aorta (T6)
- Doppler equation calculates velocity of RBCs
- Cross section of aorta calculated from gender, age and weight
- Velocity-time integral gives stroke distance
- Stroke distance x cross section = stroke volume (x HR = CO)
- Correction factor of 70% applied to take into account arm/brain perfusion
41
Limitations of oesophageal doppler
- Requires sedated patients
- Arrythmias make it difficult to calculate accurately
- Incorrect assumptions (cross section, 70%)
- Cant be used with oesophageal pathology
42
What measurements are taken from an oesophageal doppler?
- Peak velocity = contractility
- Correct flow time = afterload (time increases in sepsis, decreases in hypovolaemia)
- Stroke distance = stroke volume
- Derived: CO = stroke distance x cross section x HR
43
Describe sensitivity, specificity, PPV and NPV
- Sensitivity = Correctly identifying those with the disease
- Specificity = correctly identifying those without the disease
- PPV = Likelihood of having disease with positive test
- NPV = likelihood of not having disease with negative test
44
Describe the levels of statistical evidence
1: Meta-analysis (quantitative) or systematic review (qualitative) of RCTs
2: RCT
3: Cohort, Matched case control or non-randomised trials
4: Case series/reports
5: Expert opinion
45
How does capnography work?
- Molecules with dissimilar atoms absorb infrared light
- Made of crystal that only lets a specific wavelength of light through (4.3 microns for CO2)
- Beers law - absorption of IR is proportional to the concentration of the sample
- Lamberts law - absorption is proportional to the path length
46
Reasons for arterial cannulation
Diagnostic
- ABGs
- CO monitoring
- Angiography
Treatment
- ECMO
- EVAR
- PCI
- Balloon pump insertion
- RRT
- Embolization procedures
47
What is damping? What causes it? What would an under damped trace look like?
Damping is the resistance to oscillations within a measuring system when the input changes and rests at a stable value
Causes of damping:
- Compliant tubing
- Long tubing
- Air bubbles
- Blood clots
Under damped traces:
- Over reads systolic
- Under reads diastolic
- MAP should be the same
48
Describe the categories if acetylcholine esterase
Short acting - edrophonium
- Binds to aninic site and is a competitive antagonist of AChE
Intermediate acting - neostigmine, pyridostigmine, galantamine, rivastigmine
- Those used in dementia cross BBB to have central effects
- Binds to esteratic site of AChE acting as a non-competitive antagonism
- Increases Ach at synaptic cleft to compete with rocuronium
Long acting- organophosphatides
- Irreversibly phosphorylates AChE
- Ach spills out and causes systemic features of cholinergic crisis
49
Describe the innervation of the eye
Sensory
- Special sense (sight) - optic nerve
- Somatic sense - Ophthalmic division of the trigeminal nerve (lacrimal, nasocillary and frontal branches via superior orbital fissue)
Motor
- Superior oblique - trochlear nerve (IV)
- Lateral rectus - abducens nerve (VI)
- Inferior oblique, superior, inferior, medial rectus, levator palpebrae superioris - occulomotor nerve (III)
Parasympathetic
- Edinger Westphal nucleus via the occulomotor nerve to synpase at the cilliary ganglion
- Travels via short cilliary nerve
- Effects - Constricts pupil - contracts pupilary constricter by M3 - Accommodate for near vision - contracts cilliary muscle by M3
Sympathetic (constrict,
- Hypothalamic nucleus flows into spinal cord and sympathetic chain, out via T1 to synapse in superior cervical sympathetic ganglion. (C2/3 posterior to carotid sheath).
- Travels to eye via long cilliary nerve (bypassing cilliary ganglion) or short cilliary nerve
- Effects - Dilated pupil - contracts pupillary dilater via a1 receptors
- Accommodate for far vision - relaxes cilliary muscle via B2
- Also innervates superior tarsal muscle to elevate lid
50
Describe the reflexes of the eye
Light reflex
- Optic nerve -> Edinger Westphal nucleus of midbrain -> Occulomotor nerve (cilliary ganglion and short cilliary nerve) -> constrictor pupilae
Corneal reflex
- Nasocilliary branch of the ophthalmic division of trigeminal nerve -> Trigeminal sensory nucleus -> Facial nerve motor nucelus -> Facial nerve to orbicularis occuli
Occulocardiac reflex
- External muscle traction -> short/long cilliary nerves -> cilliary ganglion -> nasocilliary nerve -> V1 -> Trigeminal ganglion -> Sensory trigeminal ganglion -> Motor nucleus of vagus (nucleus ambiguus) -> Vagus nerve -> SA node -> Bradycardia/asystole
Can be triggered also by LA during blocks, surgical pressure or Honans balloon
51
Describe the production and flow of aqueous humour
- Regulated by aqueous humor of the anterio and posterior chamber (also provides nutrition to avascular tissues)
- Produced by cilliary processes of cilliary body in the posterior chamber.
- Flows between iris and lens into the anterior chamber
- Drains via the trebecular meshwork and them angle of Schlem at the iridocorneal angle
52
Factors that affect normal intraoccqular pressure
- Choroidal blood flow (internal carotid->opthalmic artery->posterior cilliary arteries)
- Aqueous humour drainage (pupil dilation (sympathetic stim) -> relaxed cillairy body -> reduced angle of schlem) - also affected by episceral venous pressures
- Extrinsic pressure (e.g. haematoma, trauma)
- Drugs
Beta blockers - reduce sympathetic stimulation and humour production
Acetazolamide - CA inhibitor to reduce humor production
Ketamine - causes external pressure by eye muscles, plus sympathetic stimulation
53
Nuclei of the vagus nerve
Dosal nucleus (medulla) - Parasympathetic innervation for thorax and abdominal viscera
Nucelus ambiguus (medulla). Motor to larynx, oropharynx. Parasympathetic to heart
Nucleus tractus solitarius (medulla) - Sensory to pharynx, larynx, thoracic and abdominal viscera
Spinal trigeminal nucleus (spinal cord) - Somatosensory to outer ear canal, pinna and dura
54
Anatomy of the vagus nerve
Path of vagus nerve:
- Leaves skull via jugular foramen (alongisde glossopharyngeal, accessory and IJ vein)
- Travels in carotid sheath posterior to internal carotid and internal jugular (between sternocleidomastoid and anterior scalene)
- Right vagus nerve. Anterior to right subvlavian and posterior to superior vena cava
- Left vagus nerve - Anterior to common carotid and posterior to subvlacian artery
Branches of vagus nerve:
- In the neck
○ Pharyngeal branches - motor supply to pharynx
○ Superior laryngeal nerves - motor to cricothyroid and sensory to superior larynx
○ Right recurrent laryngeal (loops around subclavian)- motor to laryngeal muscles
- In the thorax
○ Left recurrent laryngeal (loops around aortic arch) - motor to laryngeal muscles
o Cardiac branches
55
Anatomy of the upper limb arterial supply
- Brachiocephalic or directly off arch of aorta
- Subclavian -> Axillary at lateral border of first rib
- Axillary -> Brachial artery at inferolateral border of teres major
- Brachial -> Radial and ulnar in ACF
- Radial forms deep palmar arch and joins with a deep ulnar branch
- Ulnar forms superficial arch and joins with a superficial radial branch
56
Factors affecting radial artery size
Bigger = CCF, nitrates, ACEi, hypertension
Smaller = smokers, young, female
57
Complications of arterial cannulation
- Infection
- Thrombosis with occlusion
- Haematoma
- Haemorrhage
- Pseudoaneurysm
- Ischaemic injury to distal limb
58
Arterial line insertion best practice
- Site consideration (upper limb preferred)
- Sterile precautions for insertion and maintenance
- Optimise radial artery position through 45 degree wrist extension
- Use ultrasound
- Classical seldinger procedure has highest rates of success
- Ensure system properly set up and calibrated
59
Anatomy of the lower limb arterial system
- Aorta trifurcates to left and right common iliac and median sacral arteries
- Common iliac bifurcates to external and internal
- External iliac becomes the femoral as it passes under the inguinal ligament
- Femoral artery bifurcates into superficial and deep femoral artery
- Superficial travels medially and becomes the popliteal artery
- Popliteal artery becomes the anterior tibial that becomes dorsalis pedis
- Popliteal also becomes the tibioperoneal trunk, which bifurcates to become the posterior tibial artery and peroneal artery, which terminate at the heel.
60
What is ionising radiation?
Energy that travels through space in the form of waves or particles, that have enough energy to release electrons from atoms
61
How can radiation exposure be measured?
- Exposure - amount of radiation at one point
- Absorbed dose - amount of radiation per unit of mass
- Equivalent dose - compensates for type of radiation and its relative biological effect
- Effective dose - takes into account body type being irradiated
62
What are the risks to radiation exposure?
Risks of burns: related to single doses og high energy
Risk of carcinogenesis/cataracts: related to cumulative effects of radiation
63
What factors affect degree of radiation exposure?
Patient related
- Body thickness.- more needed and increased scattering
- Complexity of procedure - may need more imaging
Technical factors
- Position of Xray tube
- C-arm angulation
- Source of radiation
- Image detector positioning
- Collimation (narrowing exposed field)
64
What are the legal occupational radiation exposure limits?
20mSv per year (averaged over 5 years)
Maximum 50 mSv per year
During pregnancy 1mSv
65
What are the uses for a PA catheter?
- Guidance of shock management
- Diagnosis of pulmonary hypertension
- During cardiac surgery
- Differentiating between pre and post capillary pulmonary hypertension
66
What are the contraindications for a PA catheter?
- Severe coagulopathy
- Mechnical TV or PV
- Right sided endocarditis
- Large ASD
- Risk of RV perforation (e.g. extreme pressures)
67
Describe the components of a PA catheter
- 110cm in length
- 1.5ml balloon at tip
- Thermister 4cm from tip
- Thermal filament allowing temperature dilution (15-25cm from tip)
- Optical module connector for SvO2
68
Describe the insertion process of a PA catheter
- Sheath inserted via R IJV usually
- Inserted to 20cm and then balloon filled with air
- Passed through the SVC and RA (Typical JVP waveform seen) - Pressures 0-8mmHg
- Then RV - Systolic 15-25, diastolic 0-8
- Then PA - Systolic 15-25, diastolic 8-15 (occurs due to pulmonary artery resistance to flow)
- Then becomes wedged 6-12mmHg
- This should reflect left atrial pressures as it is a continuous column of blood between them (assuming it is in west zone 3)
- Usually PCWP used as a proxy for LVEDP
69
How are PA catheters confirmed to be in West zone 3?
- PCWP is less than the pulmonary artery diastolic pressure
- PCWP changes with PEEP (Change is reflected by 50% chance in PCWP)
- A and V waves noted on waveform
70
What measurements can be taken from a PA catheter?
Direct
- CVP
- RA pressure
- RV pressure
- PA pressure
- PCWP
- Mixed venous oxygen saturations
- Core body temperature
- Cardiac output (by thermodilution)
Indirect
- SVR
- PVR
Stroke volume
71
How is CO measured from a PA catheter? What are its limitations?
- Indirect Ficks principle
- Copper filament heats blood and temp change is detected at thermistor
Limitations
- Overestimates if any L-R intra-cardiac shunts
- TR prevents accuracy
- Extreme temperatures (therapeutic hypothermia) will affect calibration
- Coadministration of fluids affects readings
Final FRCA
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