Cardiothoracics

Question 1

What are the indications for an endoscopic thoracic sympathectomy?

Answer 1

Palmar, axilliary of facial hyperhydrosis

CRPS of upper limb

Facial blushing

Chronic angina unmanageable by pharmacological or cardiological intervention

Question 2

What is the sympathetic supply to the upper limb?

Answer 2

Presynaptic - Originate in lateral horns of T1-4

Travel via sympathetic chain and synapse in sup, middle and inf cervical ganglion
○ Superior - Cranial nerves, superior cardiac branch, C1-4 anterior rami
○ Middle - Thyroid, middle cardiac branches, C5-6 anterior rami
○ Inferior - Inferior cardiac branch, C7-T1 anterior rami (Often fused with first thoracic ganglion to become stellate ganglion)

Postsynaptic travel via nerves within brachial plexus (C5-T1)

Question 3

What positions can an endoscopic thoracic sympathectomy be performed - an what are the positioning risks?

Answer 3

Supine in reverse trendelemberg, with abducted arm - brachial plexus injury

Prone - increased eye pressure. Pressure on breasts and genitals

Lateral - common peroneal nerve injury

Question 4

What are the intraoperative complications of an endoscopic thoracic sympathectomy?

Answer 4

Airway
○ Malposition of double lumen tube/bronchial blocker

Breathing
○ Hypoxia due to OLV and shunt
○ In bilateral surgery - residual atelectasis may also cause hypoxia

Cardio
○ Hypotension due to capnothorax
○ Risk of haemorrhage
Intrathoracic diathermy may cause cardiac arrythmias

Question 5

What are the post-operative complications of an endoscopic thoracic sympathectomy?

Answer 5

Compensatory hyperhidrosis

Ongoing hypoxia due to residual atelectasis

Question 6

Which vessels can be used for a CABG graft

Answer 6

Long saphenous vein

Radial artery (in young patients with non-calcified vessels)

Internal thoracic artery

Question 7

What are the advantages of OFF pump CABG surgery

Answer 7

Reduced coagulopathy - Reduced platelet dysfunction and clotting factor dysfunction

Reduced end organ damage (reduced neuro and renal disorders)

Reduced surgical complications - aortic damage and air embolism

Reduced risk of fluid overload and electrolyte disturbance

Reduced hypothermia
Reduced/avoided ICU admission

Question 8

What are the disadvantages of OFF pump CABG

Answer 8

Higher risk of incomplete bypass

Higher risk of re-intervention need

Higher risk of haemodynamic instability
○ Ischaemia due to vessel anastomosis
○ Impaired filling due to immobilisation device
○ Impaired filling due to manipulation of heart during surgery (including AV valve reflux)
○ Arrythmias induced by ischaemia , manipulation and reperfusion
○ Bleeding

Question 9

How can haemodynamic instability be reduced in OFF pump CABG

Answer 9

Minimise manipulation

Minimise ischaemia by use of shunts

Keep HR low to minimise myocardial oxygen consumption/demand

Monitor for electrolyte abnormalities and give magnesium to stabilise myocardial electrical activity

Adequate fluid management with cardiac output monitoring

Question 10

What are the neurological complications of a CABG?

Answer 10

Central
- Delirium
- TIA
- Stroke - embolic (patient thrombus or CPB) or haemorrhagic
- Gas embolism
- Acute cord ischaemia

Peripheral
- Brachial plexus injury - prolonged abduction and sternotomy pushing 1st rib/clavicle into retroclavicular space
- RLN injury - prolonged intubation and during IMA harvesting
- Phrenic nerve injury - during IMA harvesting
- Saphenous nerve injury during vein harvesting
- Ulnar nerve injury during radial artery harvesting (due to rotated positioning of arm)

Question 11

What are the risk factors for developing a neurological injury during CABG?

Answer 11

Patient
○ Age
○ Co-morbidities - diabetes, hypertension, hypercholesterolaemia, previous strokes
○ Pre-existing neurological deficits

Surgical
○ Surgical duration
○ Micro-emboli from surgical dissection, cardiac manipulation and CPB
○ Rewarming after hypothermia leads to BBB dysregulation and potential cerebral oedema

Anaesthetic
○ Prolonged/excessive deep hypnotic time
○ If OFF pump - low MAP reducing CPP

Question 12

What are the methods of reducing neurological complications in CABG?

Answer 12

• Reduce stress response - minimally invasive surgery where possible
• Maintaining MAP
• Gas and emboli filters in CPB circuit
• Assessment of aorta prior to cross clamp to prevent plaque disruption
• Depth of anaesthesia monitoring
• Avoidance of rapid rewarming
  Cerebral oxygen monitoring and responding to drops

Question 13

What are the benefits of cardiopulmonary bypass?

Answer 13

Bloodless surgical field

Motionless surgical field

Minimises blood loss

Question 14

Outline the comments of a cardiopulmonary bypass

Answer 14

Drainage of blood
- Right atrium catheter which drains deoxygenated blood into a reservoir
- Suction pump which drains blood from surgical field into reservoir
- Ventricular pump which drains heart of any air or residual blood

Blood is then pumped into
- a heat exchanger
- Then a gas exchanger

Blood is then either
- Pumped through a filter and back into peripheral circulation (into aortic arch post-cross clamp)
- Through a cardioplegia pump, where the caridoplegia solution is added and fed back into aortic root to deliver cardioplegia to the coronary arteries.

Question 15

What are the functions of cardioplegia?

Answer 15

Myocardial protection through cooling

Myocardial protection through diastolic cardiac arrest with extracellular environment minimising metabolic activity

Facilitate surgery through still heart

Facilitate surgery through bloodless heart

Question 16

What are the constituents of cardioplegia?

Answer 16

High potassium (20mmol/L) - shifts resting potential to -50mV, preventing repolarisation, inactivating fast inward voltage gated sodium channels

High magnesium - competes with calcium reducing calcium induced contraction

Low calcium - reduces amount available for myocyte contraction

Normal sodium and chloride levels

Bicarbonate - buffer due to metabolic acidosis

Mannitol - raise osmolarity to reduce oedema

Procaine - reduce risk of arrythmia at perfusion

Question 17

How can cardioplegia be administered?

Answer 17

Anterograde - into ascending aorta or coronary route (requires patent coronary system)

Retrograde - via coronary sinus

Question 18

What are the risks with cardioplegia?

Answer 18

Damage to vessel being cannulated

Dislodgement of plaque causing embolism (stroke/MI)

Gas embolism

Failure to get global cardioplegia due to perfusion issues (remaining warm but ischaemic)

Post op electrolyte abnormalities causing arrythmias

Post op oedema

Post op acid base balance disturbance

Question 19

Describe appropriate anticoagulation for cardiac surgery

Answer 19

Heparin 400IU/kg given via CVC

ACT should be checked after 5 minutes and then every 30 minutes

Target: >480 seconds or 3x more than baseline

Normal ACT: 120 seconds

Question 20

What tests of coagulation can be used during cardiac surgery? What are the pros and cons?

Answer 20

Activated clotting time
- General test of clotting time
- Fast and cheap, however lacks specificity to aspects of clotting

APPT
- Cheap but slow

Anti-Xa activity
- Correlates well with heparin activity but slow to perform

TEG
- Graphical representation of blood clot
- Can add heparinase to negate heparin effect, to guide blood product administration
- Expensive and needs training to interpret

Question 21

What could the reasons be for inadequate anticoagulation in cardiac surgery?

Answer 21

Human error - non-patent CVC, not flushing

Pharmacodynamics - Malignancy or critical illness increasing circulating proteins

Anti-thrombin III deficiency - consumption (sepsis), genetic deficiency, decreased hepatic synthesis

Question 22

How can heparin be reversed? What are the potential complications?

Answer 22

Protamine
- Forms a salt with heparin (which is a strong acid)
- 1mg of every 100 units of heparin

Potential reactions
- Anaphylaxis
- Arterial hypotension and reduced cardiac output
- Pulmonary vasoconstriction and pulmonary oedema
- Platelet inhibtion

Question 23

Describe how an intra aortic balloon pump works

Answer 23

Inflate during diastole, deflate before systole

Inflation forces blood proximally to perfuse coronaries and increase myocardial oxygen supply

Deflation reduces afterload, reducing myocardial oxygen demand

Endothelial stretch by pump releases nitric oxide, resulting in coronary vasodilation

Helium used to inflate balloon due to its low density (promoting laminar flow) - and would be rapidly absorbed in event of rupture

Question 24

Describe the indications and contraindications for an intra aortic balloon pump

Answer 24

Indications
- Cardiogenic shock (e.g. acute heart failure with hypotension)
- Post MI (e.g. failing LV or acute MR from papillary muscle rupture)
- Failure to come off bypass

Contraindications
- Severe aortic disease (e.g. regurgitation/dissection/aneurysm)
- Uncontrolled sepsis
- Tachycarrythmia (at a rate that the device cannot sync with)
Severe coagulopathy

Question 25

Describe the methods of triggering in an intra-aortic balloon pump, and the complications of mistriggereing

Answer 25

Triggering - ECG triggered - inflate at T wave, deflate on R wave - Pressure triggered - Inflate at dicrotic notch, deflate before arterial upstroke - In cardiac arrest - must be changed to pressure trigger Mis-triggering - Early inflation = increased afterload and myocardial work - Late inflation = no improvement in coronary perfusion - Early deflation = no improvement in afterload reduction - Late deflation = increased afterload and myocardial work

Question 26

What are the complications of an intra-aortic balloon pump?

Answer 26

Bleeding/pseudoaneurysm at site of insertion Limb compartment syndrome in insertion limb Organ or limb ischaemia due to malpositioning Aortic dissection/rupture Thromboembolism / plaque rupture Balloon rupture with gas embolism

Question 27

Indications for a pneumonectomy

Answer 27

Trauma with uncontrolled haemorrhage Infection in single lung (e.g. TB, empyema, fungal) Inflammatory lung disease Congenital lung disease

Question 28

How can a patient be assessed for suitability for a pneumonectomy?

Answer 28

PPO FEV1 - <30% = poor predictor and should prompt CPET PPO DLCO - <30% = poor predictor and should prompt CPET CPET (VO2 peak) - <10ml O2/Kg/Min = contra-indication - >20 O2/kg/min = 'safe' for pnuemonectomy Pulmonary pressures via echo - will increase once circulating volume directed to only 1 lung RESECT90 or Thoracoscore systems

Question 29

How can a patient be pre optimised for a pneumonectomy?

Answer 29

Smoking cessation Optimising concurrent diseases Physical exercise to improve lung function and muscle mass Nutritional support Anaemia management

Question 30

What are the contraindications for a pneumonectomy?

Answer 30

- <10ml O2/Kg/min as per CPET - Severe pulmonary hypertension - Metastatic disease or subdiaphragmatic extension

Question 31

What are the complications of a pneumonectomy?

Answer 31

Bronchopleural fistula (breakdown of bronchial stump) Atrial arrythmias (40%+ get AF) Pulmonary hypertension with right heart failure Phrenic or recurrent laryngeal damage

Question 32

Describe the clinical, echo, CXR, ECG and PA catheter findings of a cardiac tamponade

Answer 32

Clinical - Hypotension (Becks Triad) - Muffled heart sounds (Becks Triad) - Distended jugular veins (Becks Triad) - Dyspnoea - Tachycardia - Pulsus Paradoxus - abnormal drop in systolic BP during inspiration Echo - Compressed cardiac chambers - IVC dilation due to R heart compression Chest Xray - Evidence of cardiac failure (e.g. pulmonary congestion/oedema) - Globular heart (effusion) ECG - Electrical alternans - Low amplitude QRS PA catheter - Equal pressures in al 4 chambers - High PCWP

Question 33

What are the causes of a cardiac tamponade?

Answer 33

Recent surgery (e.g. CABG) Penetrating trauma Aortic dissection Pericarditis - infectious, idiopathic, uraemic, autoimmune

Question 34

Describe the landmarks for a pericardiocentesis

Answer 34

Parasternal: 5th intercostal space close to the sternum

Question 35

Describe the anaesthetic management for a cardiac tamponade

Answer 35

Early cardiothoracic support for potential decompressive sternotomy Cardiovascular 'Fast full and tight' ○ Fast - Avoid bradycardia - SV will be fixed and low, so CO maintained with HR ○ Full - Maintain adequate preload ○ Tight - Maintain afterload to ensure adequate coronary perfusion ○ Avoid myocardial depressants (excess anaesthetic agents)

Question 36

Describe the affect of IPPV on a cardiac tamponade

Answer 36

RV likely to go into failure due to increased pulmonary pressures Increased thoracic pressure reduces venous return to right heart, consequently reducing preload to left and reduciong overall cardiac output LV will get transient increase in output due to increased thoracic pressure compressing pulmonary vasculature

Question 37

What are the methods of achieving one lung ventilation?

Answer 37

Double lumen tube Normal ET tube with bronchial blocker ET tube with capnothorax

Question 38

What are the indications for one lung ventilation?

Answer 38

Absolute - Isolation to prevent contamination (e.g. empyema or massive haemorrhage) - Control ventilation distribution (e.g. bronchopulmonary fistula) - Unilateral lung lavage (e.g. cystic fibrosis) Relative - Oesophagectomy - Lobectomy/Pneumonectomy - Thoracic aorta surgery - Minimaly invasive cardiac surgery

Question 39

Why is a left sided DLT preferred? What are the indications for a right sided DLT?

Answer 39

Left side preferred due to short length of Right main bronchus Indications for right sided: - Surgery involving left main bronchus (e.g. left pnuemonectomy/transplant) - Distortion of the left main bronchus

Question 40

What are the disadvantages of using a DLT?

Answer 40

Larger and more difficult to insert - increased airway trauma Cant be used for ongoing (ITU) ventilation - needs swapping to SLT Movement/dislodgement of tube = failure of OLV

Question 41

Describe the insertion of a DLT - and how to verify its placement

Answer 41

Intubation ○ 40Fr for men, 36Fr for women ○ Insert with stylet and remove once through the cords ○ Rotate 90o anticlockwise to pass thyroid cartildge ○ Insert until tube is snug (aprox 29cm) ○ Inflate tracheal cuff Verification ○ Ventilate with only tracheal cuff inflated. Both lungs should ventilate and etCI2 should be present ○ Clamp tracheal tube and open to air - only left lung should ventilate ○ Assess for leak around bronchial cuff at the open tracheal tube. Inflate cuff until no leak felt ○ Clamp bronchial limb and check only right lung is ventilating Perform bronchoscopic check - RUL look for clover sign

Question 42

Describe the management of hypoxia in OLV

Answer 42

Airway ○ 100% FiO2 ○ Assess tube for dislodgement, blockage or detachment - bronchoscopy if needed Breathing ○ Assess capnograpy trace and ventilation pressures ○ Auscultate if able and treat findings Circulation ○ Ensure haemodynamically stable and no ongoing signifiant blood loss ○ Consider recruitment manouveres if haemodynamically stable ○ Consider CPAP to non-ventilated lung to reduce shunt ○ Consider PEEP to ventilted lung if in lateral position to counteract weight of mediastinum ○ Consider intermittent two lung ventilation

Question 43

Causes of high pressure in OLV

Answer 43

Mechanical ○ DLT is narrower, therefor pressure already higher, but also more easily blocked by secretions ○ DLT slips forward with accidental intubation of smaller branches ○ External compression of circuit ○ Excessive TV given that only 1 lung being ventilated Patient ○ Atelectasis - increased given positioning (ventilated side usually down) ○ Pre-existing lung disease ○ Obesity Acute events ○ Bronchospasm ○ Barotrauma and pneumothorax ○Anaphylaxis

Question 44

What are the risks of repeat sternotomy surgery?

Answer 44

Intrathoracic adhesions Prolonged CPB time Increased risk of coagulopathy due to CPB Increased risk of surgical damage (coronary/chambers) due to surgical dissection

Question 45

What are the indications for repeat sternotomy?

Answer 45

Revascularisation in previous CABG Revision valve surgery (valve thrombosis, stenosis or endocarditis)

Question 46

What are the anaesthetic concerns with repeat sternotomy?

Answer 46

ICD assessment due to significant diathermy around site Defibrillator pads applied Peripheral CPB (rather than central) Management of blood loss: TXA, cell salvage,

Question 47

Describe the histology of the coronary arteries

Answer 47

Tunica intima - single layer of endothelial cells Tunica media - smooth muscle Tunica adventitia - fibroblasts, vasa vasorum and inflammatory cells

Question 48

Describe the coronary arterial supply

Answer 48

LCA ○ Left main stem gives off LAD and Circumflex ○ LAD gives off diagonal and septal branches (all supplying the LV) ○ Circumflex gives off branches to supply lateral LV wall RCA ○ Wraps posteriorly after supplying the RA, RV, SA node and AV node ○ Becomes the posterior descengin artery which supplies the posterior third of the septum (70%) Co-dominance (20%) Circumflex (10%)

Question 49

Describe the coronary venous supply

Answer 49

- Anterior surface via the anterior intraventricular vein, forming the great cardiac vein - Right sided chambers are drained by the small cardiac vein - Posterior drained by middle cardiac veins The remainder drains via thebesian veins into n the LV (shunting)

Question 50

What are the determinants of coronary blood flow?

Answer 50

- Perfusion pressure (Best estimated as MAP-LVEDP) - Myocardial extravascular compression - Myocardial metabolism (O2, CO2 and adenosine) - Neural control (symp vs parasymp) - Humoral control (e.g. vasopressin and VIP) Autoregulation (myogenic vs metabolic theory)