Makindo Medical Notes.com

The use of cardiopulmonary bypass (CPB) technology allows cardiac surgical procedures to be performed in a motionless, bloodless surgical field.

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• In order to operate safely in a bloodless, immobile field whilst maintaining an adequate circulation to the rest of the body cardiopulmonary bypass is most commonly used.
• A cannula is placed in the right atrium in order to divert blood away from the heart. The blood is then oxygenated by one of two methods: Bubble or membrane oxygenators
• Bubble oxygenators work by bubbling 95% oxygen through a column of blood.
• Modern machines use Membrane oxygenators work by bringing the blood and oxygen together via a gas permeable membrane (e.g. sheet and hollow-fibre oxygenators)
• However gas exchange is less efficient. Diffusional distances are greater (approximately 200 micrometres in comparison with 10 micrometres in the human alveolus)
• Bubbles are then removed by passing the blood through a sponge. The blood is then heated or cooled as required.
• A roller pump compresses the tubing driving the blood back into the systemic side of the circulation at an arterial perfusion pressure of between 50 to 100 mmHg.
• If the myocardium is to be opened, cross-clamping the aorta gives a bloodless field; the heart is protected from ischaemia by cooling to between 20 and 30C. Systemic cooling also lowers the metabolic requirements of other organs during surgery. CPB is performed over a range of temperatures (37-15C).
• Beating heart bypass grafting is now possible using a mechanical device to stabilise the target the surface area of the heart, but access to the posterior surface of the heart can be difficult.
• Important to confirm adequate patient anticoagulation before initiation of CPB.
• Cardiac surgery with CPB can promote a systemic inflammatory response syndrome

References

• Cardiopulmonary bypass (CPB)