Cardiothoracic

Question 1

42. What interventional (non-pharmaceutical) options are there for treating chronic (not acute) coronary artery insufficiency?

Answer 1

Coronary artery insufficiency : almost always atherosclerotic – rarely due to vasospasm, embolism or trauma

Interventional options:

• Percutaneous transluminal coronary (Balloon) Angioplasty (PTCA) and insertion of intra-coronary artery stents
• Coronary artery bypass Grafting (CABG)

Interventional revascularisation is recommended for:

• Patients in whom maximal medical therapy has not satisfactorily improved angina symptoms or who are intolerant of medical therapy
• Patients with high risk, or some intermediate risk, of adverse cardiovascular event because of a large amount of myocardium supplied by disease vessel(s) or because of significant underlying LV dysfunction (regardless of angina severity)
  
  • Left main coronary artery stenosis
  • Three vessel coronary artery disease, particularly with a reduced LVEF (usually <40%)
  • Two vessel disease with more than 75% stenosis of the LAD proximal to the first major septal artery

PCI

• It is achieved under local anaesthetic by passing a catheter and guidewire from femoral or radial artery through the stenotic coronary artery
• A balloon is then inflated to achieve patency of the vessel +/- the placement of a stent
• The stents may be bare metal or drug eluting (which gradually releases antiproliferative/immunosuppressant drugs to prevent restenosis
• The restenosis rate of drug eluting stents is much lower than bare metal stents

CABG:

• This procedure can be performed either on or off a cardiopulmonary bypass pump, however so far RCTs comparing the two techniques have failed to demonstrate benefit of off pump procedures (i.e. avoiding the complications of cardiopulmonary bypass)
• Bypass of the arterial occlusion is achieved with grafting of the internal thoracic (mammary) artery, the great saphenous vein (reversed) or rarely the radial artery, right gastro-epiploic, or inferior epigastric
• The combination of left internal throracic artery to the LAD and saphenous vein grafts to the other vessels remains the current surgical favourite.
• In elective patients, the overall mortality risk of CABG is close to 1%, in addition there is a 2% chance of stroke

PCI vs CABG:

• PCI is preferred for single vessel disease and patients who would not tolerate CABG or patients who refuse CABG
• CABG is preferred for multivessel disease, diabetic patients, patients with left main artery disease

Question 2

43. What are the indications for a pneumonectomy in a patient who has been found to have a primary non-small cell lung cancer?

Answer 2

• Primary lung cancers are classified into small cell lung cancer (SCLC) (10-15%) and non-small cell cancer (NSCLC) (85-90%%)
  
  • SCLC is usually treated non-surgically due to the very high risk of metastasis and better responsiveness to chemoradiotherapy than NSCLC
  • NSCLC is further classified into the main types
    
    • Squamous cell carcinoma
    • Adenocarcinoma
    • Large cell carcinoma
• Pneumonectomy Is a resection of the whole lung and is performed less commonly than lobectomy in modern surgical management
  
  • Pneumonectomy is indicated for central tumour involving the distal main stem bronchus, or involvement of ipsilateral peribronchial/ hilar lymph nodes that are otherwise not resectable.
• Surgical management is indicated for patients
  
  • With stage I or II NSCLC (and some patients with stage III disease after pre-operative chemotherapy or chemoradiation) i.e. patients with:
    
    • Disease limited to one lung
    • No nodal involvement or some ipsilateral nodal involvement
    • No distant metastasis
  • Medically fit for operation:
    
    • Adequate pulmonary function
      
      • FEV1 >80% predicted
      • DLCO >80% predicted
      • Predicted post-operative (PPO) FEV1 and DLCO >60% predicted
    • Without other serious medical co-morbidities

Question 3

44. What are the principles of a heart lung bypass perfusion circuit (machine)?

Answer 3

• The cardiopulmonary bypass machine temporarily replaces the function of the heart and lungs during surgery to maintain systemic circulation and oxygenation of the blood. It is commonly used in cardiac surgery to provide a bloodless, stable surgical field
  
  • Oxygenation of blood
  • Removal of CO2 from blood
  • Non-pulsatile circulation of blood
• Components
  
  • Cannula is inserted into the right atrium to drain venous return from venae cava
  • Venous blood passes into the venous reservoir under gravity
  • The membrane oxygenator removes CO2 and oxygenates the blood
  • The heat exchanger controls the blood temperature (important because surgery is often performed with cooling)
  • The pump returns non-pulsatile flow to the aorta (distal to the clamp but proximal to the innominate artery)
  • A filter is included to remove air bubbles from circulation
  • Suction is used to remove blood from the operative field and return it to the patient via the reservoir
• Preparation
  
  • Full anticoagulation (with heparin)
  • Prime bypass circuit with crystalloid, heparin +/- mannitol
  • Just before aortic cannulation reduce SBP to 80-100 mmHg
  • Administer cardioplegic solution to decrease electrical and mechanical action, thereby reducing metabolic demand
• During bypass
  
  • Turn-off ventilator to deflate lungs and clear surgical field
  • Maintain MAP at 50-70mmHg with vasopressors/ vasodilators
  • Induce slight hypothermia
• Coming off bypass
  
  • Warm to 37 degrees
  • K+ levels to 4.5 -5.0
  • Haematocrit >20%
  • Normal acid base status
  • HR 70-100bpm
  • SaO2 100%
  • Start inotropes if inadequate CO
  • Protamine once surgeon is happy

Question 4

45. What are the advantages and disadvantages of using a mechanical valve to replace an aortic or mitral valve, rather than a tissue valve?

Answer 4

Mechanical valve

• Advantages
  
  • Greater durability
  • Lower risk of infective endocarditis
  • Good availability
• Disadvantages
  
  • Thrombogenic (increased risk of thromboembolism)
  • Lifelong anticoagulation needed – warfarin with INR 2.5-3.5 (therefore increased risk of bleeding)
  • Sometimes audible when opening and closing
  • Haemolytic anaemia can occur (usually subclinical)
  • If endocarditis develops the valve will need replacement

Tissue Valve

• advantages
  
  • Reduced risk of thromboembolism
  • Reduced need for anticoagulation (usually aspirin alone), thus decreased bleeding risk
• Disadvantages
  
  • 10-15 year lifetime, less in younger patients
  • May need replacement, with significant mortality risk
  • Higher rates of infection

Question 5

46. What are the indications for surgery in a patient who has been stabbed in the chest?

Answer 5

Chest wall injuries

• Many penetrating injuries do not require surgery and can be managed conservatively with
  
  • Serial CXR
  • Simple tube thoracotomy
• 15-30% of chest wall traumas will require surgery

Approach:

• Primary survey and resuscitation
• Detect and treat immediate life threatening conditions
  
  • Tension pneumothorax
  • Massive haemothorax
  • Open pneumothorax
  • Cardiac tamponade
  • Flail chest
• Rapid diagnostic testing
  
  • CXR
  • FAST scan
  • ABG
• Cardiac tamponade:
  
  • Presentation: distended neck veins, muffled heart sounds, hypotension
  • Diagnoses: FAST scan
  • Immediate management: pericardiocentesis + placement of catheter
  • Definitive management: thoracotomy (pericardial window or median sternotomy) to release tamponade and control haemorrhage
• Significant haemorrhage (haemothorax):
  
  • Chest tube drainage > 1-1.5L initial loss or >200mL/hr ongoing losses for more than 2 hours
  • Ongoing bleeding suggests major vascular injury that is unlikely to stop without surgical intervention
• Massive air leak (tracheobronchial injury):
  
  • Air leak during all phases of respiration, and preventing full expansion of the lung or impairing ventilation through diminished tidal volume
• Laceration to the great vessels
• Cardiac injuries
• Impaled objects (foreign body)
• Haemoperitoneum