Cardiopulmonary BypassPrinciples of Cardiopulmonary Bypass
The heart is responsible for pumping blood around the body (systemic circulation) and around the lungs (pulmonary circulation). If this circulation is interupted, irreversible neurological damage begins within 3 minutes under normal circumstances.
In order to perform surgery on the heart a technology has been developed over the last 60 years which performs the function of pumping blood around the body and the respiratory functions of the lungs. This technique of circulatory and respiratory support is termed cardiopulmonary bypass. Blood is syphoned from the body via cannulae usually placed via the right atrium to a reservoir from where it is pumped under pressure through an oxygenator and back to the circulation via a cannula in the aorta. The modern oxygenator has hundreds of fine pipes with oxygen and other gases being perfused through them and blood is pumped around them. Oxygen and anaesthetic gases perfusues through the permeable pipe wall into the blood and carbon dioxide diffuses out. The circulation is maintained by a roller pump usually at 2.4-2.6 litres per metre squared body surface area.
The circuit has many built in safety mechanisms to protect the patient. These include in line oxygen saturation monitoring as well as arterial pressure monitoring and monitoring for air. There are filters to both filter out air and any particulate matter which may get suched into the pump by suckers which are used to salvage any shed blood from the operation site.