Cardiopulmonary Bypass

1. 1. Expose great vessels
2. 2. Purse string inserted into ascending aorta (adventitia) + aortic perfusion cannula + connect to bypass circuit
   • Impracticalities: Aortic root surgery, dissection, severe adhesions - fem-fem bypass can be employed
3. Purse string inserted into Rt atrium by appendage Cardiopulmonary bypass machine takes over circulation + ventilation
   • Pumped from venous reservoir
   • Oxygenated in membrane oxygenator (gas exchange across silicone membrane)
   • Heat exchanger
   • Filtered: remove particulate emboli
   • Infused via roller pump (achieves even arterial pressure)

Post cardiopulmonary bypass
Air excluded from cardiac chambers
Restore beat is VF present
Epicardial wires for post-op bradycardia/heart block
Warm
Correct acidosis
Correct K
When BP acceptable, CPB discontinued
+ Protamine to reverse effects of heparinisation
+/- inotropic support
+/- intra-aortic balloon pump

Myocardial protection

1. 1. Cardioplegic arrest
   • Topical cooling + cardioplegic (intentional + temporary cessation of cardiac activity) solution
   • K+ - containing (arrests heart in diastole by membrane depolarisation)
   • Cold isotonic crystalloid - reduce metabolic rate
   • Safe cardiac arrest can be maintained for 2hours
2. Intermittent cross-clamp fibrillation
   • Induce VF (by electrical voltage)
   • Cross clamp aorta to render heart ischaemic
   • Allow perfusion (10-20minutes) by intermittently releasing cross-clamped aorta + electrical cardioversion
3. 3. Total circulatory arrest

Complications

1. Access
   • Infection, pulmonary injury, vascular injury
2. Bypass
   • Embolism
   • Bleeding disorder (from heparin)
3. Stress/consequences
   • Tamponade
   • Emboli - heart: infarction, brain: stroke, gut: ischaemia