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