Cardiopulmonary Bypass Principles

CPB: Introduction & Goals - Heart's Holiday Helper

• Cardiopulmonary Bypass (CPB): "Heart-Lung Machine." An extracorporeal circuit temporarily replacing heart & lung functions. Diverts venous blood to an oxygenator & pump, returning it oxygenated to the arterial system.
• Primary Goals:
  • Provide a still, bloodless surgical field.
  • Maintain systemic perfusion & oxygenation.
  • Allow myocardial protection (cardioplegia).
  • Preserve end-organ function.
• Key Uses: Cardiac surgeries (CABG, valve repair), heart/lung transplant.

⭐ CPB allows surgeons to operate on a non-beating heart while maintaining vital organ perfusion.

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CPB: Circuit Components - The Life Support Loop

• Venous Drainage: Blood via cannulae (SVC/IVC/RA) to venous reservoir (collects, defoams).
• Main Pump (Artificial Heart):
  • Roller: Occlusive, fixed output.
  • Centrifugal: Non-occlusive, afterload-dependent.
• Oxygenator (Artificial Lung): Membrane type (microporous fibers) for gas exchange (O2↑, CO2↓).
• Heat Exchanger: Integrated; controls patient temperature (cooling/rewarming).
• Arterial Filter & Bubble Trap: Safety; removes particulates (≥ 20-40 µm) & air.
• Arterial Return: Oxygenated blood to patient (e.g., aortic cannula).
• Accessory: Cardiotomy suction (salvage), Vent (cardiac decompression).

⭐ > Most modern oxygenators are membrane oxygenators, offering superior biocompatibility and less blood trauma compared to older bubble oxygenators.

CPB: Physiological Management - Balancing Act

• Anticoagulation: Heparin 300-400 IU/kg. Target ACT > 480s.
• Hemodynamics:
  • MAP: 50-70 mmHg.
  • Pump Flow (CI): 2.2-2.5 L/min/m². Monitor SvO2 > 70%.
• Gas Exchange:
  • PaO2: 150-250 mmHg. PaCO2: 35-45 mmHg.
  • Adjust sweep gas (CO2) & FiO2 (O2).
• Temperature: Moderate hypothermia (28-32°C) ↓O2 demand. Careful rewarming.
• Acid-Base: Alpha-stat (pH uncorrected for temp) vs pH-stat.

  ⭐ Alpha-stat strategy: better cerebral autoregulation in adults.

• Hematocrit: Target Hct 20-25%.
• Electrolytes: Monitor K+, Ca2+, Mg2+. oka

CPB: Complications & Weaning - Homestretch Hurdles

• Complications:

  • SIRS: Due to blood-circuit interaction.
  • Bleeding: Coagulopathy (factor dilution, platelet dysfunction), heparin rebound.
  • Neurological: Embolic/hypoperfusion stroke, cognitive dysfunction ("pump head").
  • Renal: AKI from hypoperfusion/hemolysis.
  • Pulmonary: "Pump lung" (capillary leak).
  • Myocardial dysfunction: Stunning, ischemia.

• Weaning Prerequisites:

  • Core temperature >36°C (normothermia).
  • Adequate hemodynamics (e.g., MAP >65 mmHg, acceptable CVP).
  • Effective oxygenation (SaO2 >92%) & ventilation (normocapnia).
  • Corrected electrolytes (K+, Ca++), glucose & acid-base balance.
  • Satisfactory cardiac function (rhythm, contractility via TEE).
  • Anticoagulation reversal: Target ACT <130-150s after protamine.

⭐ Protamine administration can cause hypotension, pulmonary hypertension, or anaphylactoid reactions. Careful, slow administration is crucial.

High‑Yield Points - ⚡ Biggest Takeaways

• Cardiopulmonary bypass (CPB) diverts blood from the heart and lungs, enabling open-heart surgery by providing gas exchange and systemic circulation.
• Key components include venous drainage cannulae, a reservoir, an oxygenator, a heat exchanger, an arterial pump, and an arterial line filter.
• Systemic heparinization (target ACT > 480 seconds) is crucial before CPB initiation and is reversed with protamine after bypass.
• Induced hypothermia (e.g., 28-32°C) reduces tissue oxygen consumption and provides organ protection.
• Cardioplegia, a high-potassium solution, is administered to induce electromechanical cardiac arrest, creating a still, bloodless surgical field.
• Major adverse effects include systemic inflammatory response (SIRS), coagulopathy, hemodilution, neurological injury, and renal dysfunction.
• The CPB circuit prime (crystalloid/colloid) significantly impacts hematocrit and colloid oncotic pressure post-initiation.