Cardiothoracic Flashcards
42 What interventional (non-pharmaceutical) options are there for treating chronic (not acute) coronary artery insufficiency?
Coronary artery insufficiency is almost always atherosclerotic, only rarely due to vasospasm, embolism, or trauma
Interventional options for revascularisation are:
1) PCI - percutanous transluminal coronary balloon angioplasty with drug-eluting stent
2) CABG - bypass of occlusive disease to provide flow to patent distal coronary artery segments
PCI:
- Indications: single vessel with proximal stenosis, ineligible for CABG, patient dissatisfaction with quality of life under medical therapy
- Advantages: better short-term survival, lower cost, faster recovery
- Disadvantages: higher revascularisation rates in multi-vessel disease
CABG:
- Indications: symptomatic angina not relieved by/intolerant of medical therapy, patient believed to have better prognosis than with medical therapy alone
- Improved survival in left main stenosis, triple vessel disease with impaired LV contractility, 2-vessel including proximal LAD
- Graft conduits: left internal mammary artery (gold standard, 90% 10-year patency), saphenous vein (30-50% 10-year patency)
- Advantages: better long-term survival, better rates of patency
- Disadvantages: risk of surgery (1% mortality, 2% stroke)
43 What are the indications for a pneumonectomy in a patient who has been found to have a primary non-small cell lung cancer?
Standard treatment for patients who are:
1) Medically operable
- Adequate pulmonary function: FEV1>80%, DLCO >80%, predicted post-op FEV1 and DLCO >60% (considered low risk), VO2max >20mL/kg/min considered suitable for any type of lung resection
- Without serious medical comorbidity
2) Clinical stage 1 or 2 NSCLC
- Stage 1 = tumour <3cm without invasion more proximal than lobar bronchus
- Stage 2 = tumour <7cm with some ipsilateral node involvement OR >7cm with no node involvement
3) Proximal tumours that cannot be resected by lobectomy
44 What are the principles of a heart lung bypass perfusion circuit (machine)?
Machine temporarily replaces heart and lung function during surgery to maintain systemic circulation and oxygenation while providing a bloodless, stable surgical field
Principles:
- Maintain adequate gas exchange
- Generate flow and pressure against a degree of resistance
- Protect the myocardium to preserve function and prevent cell death
- Manage temperature to decrease oxygen consumption and increase tolerance to ischaemia of vital organs
- Adequately filter bypassed and recycled suctioned blood prior to reintroducing into the systemic arterial circulation
- Adequately conduct blood through the machine circuit while minimising haemodilution, without generating excessive resistance or pressure, and without clotting
Each part of the prep and machine circuit adheres to one of these principles
Prep:
- Anticoagulate with high dose systemic heparin
- Prime machine circuit with crystalloid + heparin + mannitol
- Reduce SBP prior to aortic cannulation
- Administer cardioplegic solution (K+, Mg2+, procain) to decrease electrical and mechanical action, thereby reducing metabolic demand
Circuit:
- Siphon heparinised systemic venous blood through RA/IVC+SVC cannula into cardiotomy reservoir
- Blood pumped under pressure through a membrane oxygenator (also filters micro-bubbles)
- Blood pumped under pressure through a heat exchanger
- Blood passed into the roller pump that maintains flow through the circuit
- Blood passed through a filter before being returned via arterial cannula into the ascending aorta
45 What are the advantages and disadvantages of using a mechanical valve to replace an aortic or mitral valve, rather than a tissue valve?
Mechanical/prosthetic - bi-leaflet (90%) or ball-and-cage
- Advantages: durability, availability
- Disadvantages: thrombogenic, lifelong anticoagulation required (INR 2.5-3.5), slightly higher infective endocarditis risk after first 18 months with very high mortality rate
Tissue - homograft (human) or xenograft (usually pigs)
- Advantages: reduced risk of thromboembolism, reduced need for anticoagulation, lowest infarction risk (homografts)
- Disadvantages: more prone to failure (10-15 year lifespan, less in younger patients), Significantly higher rates of re-operation due to valve deterioration
Also:
- Younger patients are usually given a homograft due to the decreased need for anticoagulation
- Patients >60yo are given xenografts since 90% are free of structural degeneration at 10 years
46 What are the indications for surgery in a patient who has been stabbed in the chest?
1) Cardiac tamponade
- Dx on FAST scan
- Indication: pulseless ECG activity in the past 6-10mins
- Initial: pericardiocentesis + catheter placement
- Definitive: thoracotomy (pericardial window or median sternotomy) to release tamponade and control haemorrhage
2) Significant haemorrhage from chest tube
- Def: >1000-1500mL initial OR >200mL/hr ongoing for more than 2-4hrs
- Ongoing bleeding suggests major vascular wall injury that is unlikely to stop without surgical intervention
3) Massive air leak
- Def: present during all phases of respiration and preventing full expansion of affected lung or impairing ventilation through diminished tidal volume
- Suggests major bronchial injury that is unlikely to heal without surgical repair
