Cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is a technique to temporarily replace the function of the heart and lungs during cardiac surgery using a mechanical pump-oxygenator system. The system takes venous blood from the patient, oxygenates and removes carbon dioxide from the blood, then returns it to the arterial circulation. The use of CPB allows for cardiac decompression and a bloodless surgical field. This technique is often used in open-heart procedures where cardiac arrest is required, including valve repair or replacement, coronary artery bypass grafting. It is different from extracorporeal membrane oxygenation (ECMO) in that it has an open reservoir, allowing for direct volume management.

Surgical Procedure

• Full heparinization
  • Typically heparin 400 units/kg to achieve goal ACT of 480 seconds
  • For patients with heparin-induced thrombocytopenia (HIT), bivalirudin (direct thrombin inhibitor) can be used
• Aortic cannula placement
  • Goal SBP 80-100 during placement to reduce risk of aortic dissection
  • After placement, it will be tested by the perfusionist to confirm that it is 1) pulsatile, 2) correlating to arterial line, and 3) responds to test bolus of fluid by increasing pressure
• Venous cannula placement
  • Monitor for atrial arrhythmias, which can be common during placement
• Cardioplegia line placement
  • Antegrade (via coronary arteries)
  • Retrograde (via coronary sinus to feed myocardium)
    • Indications:
      • Aortic insufficiency
      • Severe coronary artery stenosis
      • Prior coronary artery bypass graft
      • Anticipated prolonged pump run
    • AVOID IN:
      • Persistent left superior vena cava (when the left brachiocephalic vein drains into coronary sinus; as retrograde cardioplegia in this context will go into the left ventricle)
• Left ventricle vent placement
  • Used to decompress the left ventricle during CPB, which often fills with blood draining from Thesbian veins, bronchial circulation

Cannulas

1. Aortic cannula (ascending aorta, distal to aortic cross-clamp)
2. Venous cannula (right atrium appendage)
3. Cardioplegia
   • Antegrade (coronary arteries)
   • Retrograde (coronary sinus to feed myocardium)
4. Left ventricle vent
5. Pump sucker (takes blood from the field and puts it in reservoir bucket, retaining plasma and platelets)

Priming

• Fluid
• RAP (retrograde autologous priming)
  • Use patient's blood to prime aortic cannula
  • Need to make sure the patient can tolerate a drop in preload
  • Avoids hemodilution and associated with better outcomes, less transfusion
• AAP (anterograde autologous priming)
  • Use patient's blood to prime venous cannula

Complications

Complications of CPB are often due to:

• Low flow, ischemia
• Thromboembolic events
• Anticoagulation
• Systemic inflammatory response syndrome (SIRS)
• Prolonged hypothermia

	Complications
Neurological	CVA, watershed infarcts (due to air or circuit related microemboli, sluggish low-flow state following CPB) Neurocognitive impairment
Cardiac	Myocardial stunning (direct effect of cardiotomy, cardioplegia) Myocardial infarction (coronary ischemia due to air emboli) Right ventricular dysfunction (pulmonary hypertention related to protamine) Arrhythmias, heart blood (electrolyte disturbances, hypothermia)
Pulmonary	Left lower lobe collapse (phrenic nerve neuropraxia due to cold slush cardioplegia) Pulmonary hypertension (protamine) Acute lung injury (complement activation, SIRS)
Renal	Post-bypass AKI (thromboembolic events, low-flow state) Post-operative diuresis (due to intra-op cooling, delayed re-warming)
Endocrine	Hyperglycemia (hypothermia-related insulin resistance)
Gastrointestinal	Splanchnic ischemia Hepatic dysfunction Pancreatitis
Hematologic	Coagulopathy (residual AC, dilutional coagulopathy, consumption of clotting factors by bypass circuit) Platelet dysfunction (SIRS) Anemia (hemolysis, hemodilution)
Immunologic	Coagulation cascade activation (contact of blood with non-biological surfaces) SIRS Anaphylaxis (protamine reaction)