Cardiopulmonary bypass
The machine that takes over the heart and lungs so the surgeon can stop the heart and work on it.
Why it's done
- Most open-heart operations need a still, bloodless heart. Bypass keeps oxygenated blood flowing to the brain and body while the heart is stopped.
- Understanding bypass makes every other operation on this list easier to follow, because the same steps open and close almost all of them.
The steps
- Anticoagulate: Full-dose heparin is given before any cannula goes in. The team checks the activated clotting time (ACT), usually aiming above about 400–480 seconds, because blood clots on the circuit's plastic otherwise.
- Cannulate: An arterial cannula goes into the ascending aorta and a venous cannula into the right atrium (or both venae cavae). Other sites, like the axillary or femoral artery, are used when the aorta itself is diseased.
- Go on bypass: Venous blood drains into a reservoir, passes through the oxygenator (which adds oxygen, removes CO₂ and controls temperature) and is pumped back into the aorta.
- Cross-clamp: A clamp goes across the ascending aorta between the arterial cannula and the heart. From this point the heart receives no blood of its own.
- Cardioplegia: A cold or warm potassium-rich solution is given into the aortic root (antegrade) and/or the coronary sinus (retrograde). The high potassium stops the heart in diastole and cuts its oxygen demand.
- Operate: The surgeon does the repair while the perfusionist manages flow, pressure, temperature and blood gases.
- Unclamp and de-air: The clamp comes off and blood reperfuses the heart. It may restart on its own or need a shock. Air is removed from the left heart before it starts ejecting.
- Wean off: Ventilation restarts, the pump flow is turned down and the heart gradually takes over, often with inotropes.
- Reverse heparin: Protamine reverses the heparin, the cannulae come out and the team checks carefully for bleeding.
Risks
- Bleeding from heparin, haemodilution and platelet dysfunction
- Stroke from emboli (air, calcium, clot)
- A whole-body inflammatory response and vasoplegia (low blood pressure with warm, dilated vessels)
- Acute kidney injury
Recovery
Bypass itself doesn't have a recovery period. What matters is the operation it supports. Longer bypass and cross-clamp times are linked with more complications, which is why surgeons and perfusionists track them closely.
St George's Cardiothoracic Surgery Society, City St George's, University of London.