Cardiopulmonary Bypass (CPB): From Induction to Weaning

Cardiopulmonary bypass (CPB) is a cornerstone of modern cardiac surgery, allowing the surgeon to operate on a bloodless, motionless heart while maintaining systemic perfusion and oxygenation. The transition from initiation to termination of CPB involves a sequence of well-defined steps, each with specific physiologic considerations [1].

1. Cannulation and Heparinization

Before initiating CPB, systemic anticoagulation with heparin is administered to prevent thrombosis in the extracorporeal circuit (dose and monitoring per institutional protocol, typically ACT-guided). Arterial and venous cannulas are then placed—commonly the ascending aorta for arterial return, and the right atrium or venae cavae for venous drainage. Correct cannula positioning and secure fixation are essential for adequate flow and safety [1,2].

2. Initiation of CPB and Gradual Increase in Flow

Once the circuit is primed and connected, venous blood is diverted into the CPB circuit and oxygenated blood is returned via the arterial cannula, progressively replacing native cardiac output (CO). During this phase, assess venous drainage (cannula position, preload) and systemic perfusion (pressure and end-organ signals), and coordinate temperature strategy and monitoring as the circuit assumes heart–lung function [3].

3. Full CPB Flow

At full bypass, the CPB circuit provides 100% of systemic perfusion. Flow rates are sized to the patient:

• Infants <10 kg: Flow = weight × 150 mL/min
• ≥10 kg: Flow = BSA × age-specific cardiac index (CI)

Ventilation is stopped, and cooling may be used for organ protection. Continuous surveillance of perfusion adequacy, oxygen delivery, hematocrit, temperature, and metabolic parameters is essential. Infant CPB requires tailored management (prime composition, temperature and perfusion goals, organ immaturity) to mitigate hemodilution and inflammatory load [4,5]. Contemporary infant pathways often emphasize higher flows and higher hematocrit to optimize DO₂ and reduce complications, applied judiciously to patient context [7,8].

4. Cardiac Repair

With circulation supported by CPB, surgical repair proceeds on a beating heart or under cardioplegic arrest. Cardioplegia (blood or crystalloid; antegrade ± retrograde) plus hypothermia reduces myocardial oxygen demand and protects against ischemia–reperfusion injury [3,5].

5. Weaning from CPB

After repair, reperfusion and rewarming are coordinated while gradually transferring work back to the heart. Key points: restore preload, assess contractility and rhythm, and titrate vasoactives/inotropes as needed. TEE (when available) helps guide filling, ventricular performance, valve function, and de-airing during separation and early post-bypass stabilization [6].

6. Termination of CPB

When native CO and perfusion are stable, the pump is stopped and cannulas removed with meticulous hemostasis. Protamine reverses heparin (dose guided by ACT and institutional protocol). Final checks include pressure stability, bleeding control, and secure closure of cannulation sites [1,5].

Clinical Perspective

Transitions on and off CPB are periods of high physiologic vulnerability. Risks include air embolism, malperfusion, inadequate myocardial protection, low-output states/arrhythmias, and systemic inflammatory responses. Protocolized conduct (anticoagulation, perfusion pressure/flow and temperature/rewarming targets, hematocrit strategy) and team checklists improve reliability; cautious rewarming helps mitigate neurologic risk. Individualize MAP, Hct, and flow targets to patient risk and age while adhering to consensus guidance [7,8].

References

[1] Shore-Lesserson L, Baker R, Ferraris V, Greilich P, et al. The Society of Thoracic Surgeons, The Society of Cardiovascular Anesthesiologists, and AmSECT Clinical Practice Guidelines (anticoagulation/monitoring for CPB). Anesth Analg. 2018. doi:10.1213/ANE.0000000000002613.

[2] Shore-Lesserson L, Baker R, Ferraris V, Greilich P, et al. STS/SCA/AmSECT Clinical Practice Guidelines (perfusion practice & safety). J Extra-Corporeal Technol. 2018. doi:10.1051/ject/201850005.

[3] Shore-Lesserson L, Baker RA, Ferraris VA, Greilich PE, et al. Guidelines for CPB (comprehensive conduct/monitoring). Ann Thorac Surg. 2018. doi:10.1016/j.athoracsur.2017.09.061.

[4] Dönmez A, Yurdakök O. Cardiopulmonary bypass in infants. J Cardiothorac Vasc Anesth. 2014. doi:10.1053/j.jvca.2013.12.024.

[5] Hessel E, Groom R. Guidelines for Conduct of Cardiopulmonary Bypass. J Cardiothorac Vasc Anesth. 2020. doi:10.1053/j.jvca.2020.04.058.

[6] Licker M, Diaper J, Cartier V, Ellenberger C, et al. Management of weaning from cardiopulmonary bypass (clinical review; role of TEE). Ann Card Anaesth. 2012. doi:10.4103/0971-9784.97977.

[7] Ramakrishnan K, Kumar T, Boston U, Allen J, Knott-Craig C, et al. CPB in neonates and infants—high-flow, high-hematocrit considerations (review). Transl Pediatr. 2023. doi:10.21037/tp-23-94.

[8] Murphy G, Hessel E, Groom R. Optimal Perfusion During Cardiopulmonary Bypass (pressure/hematocrit/temperature). Anesth Analg. 2009. doi:10.1213/ane.0b013e3181875e2e.