Cardiopulmonary bypass is vital to the performance of open heart surgery. This is the most commonly performed cannulation strategy, called the ‘aorto-bicaval cannulation.’
- Blood returning from the body via the SVC and IVC (hence, bicaval) enter two separate cannulae, which drain passively into an open reservoir (see below). Note the close proximity of the hepatic veins to the IVC cannula; even a mild degree of obstruction to hepatic venous return can manifest as ascites and postoperative hepatic dysfunction, including coagulopathy, hypoglycemia, and delayed lactic acid metabolism.
- A separate cannula may be placed into the LV through the mitral valve via a pulmonary vein, called an LV vent. This is particularly important in adult patients or in children with ventricular hypertrophy, who may be prone to subendocardial ischemia.
- One or more field suckers are placed onto the field and have continuous suction applied by a roller pump. These catheters can be used to drain blood from the field, to remove actively draining blood from a specific location (commonly the coronary sinus), or can be used in emergencies when the venous cannula has not yet been placed (called ‘sucker bypass’).
- Blood drains from all of these venous lines passively or actively (in the case of field suckers) into an open reservoir (see below). Blood is then filtered, oxygenated, and pumped back into a single arterial cannula that is commonly placed into the ascending aorta, transverse aortic arch, or (in neonates) a graft sewn onto the innominate artery (called a chimney graft).
- A separate cardioplegia cannula is placed into the aortic root that is used to administer cold blood cardioplegia solution (here we use del Nido cardioplegia solution), which is a solution that contains oxygenated blood, potassium, magnesium, lidocaine, and other cytoprotective molecules. The purpose of this solution is to stop myocardial activity (to enable us to operate on the heart) and also myocardial oxygen consumption (to prevent myocardial injury while there is no coronary blood flow).
- When a dry field is desired, snares are tied around the outside of the vessel to ensure that all blood passes into the cannula (thus, staying out of the surgical field). This is called ‘tightening the caval snares’ (and some people call it a caval tape).
The anatomy of the cardiopulmonary bypass circuit is different than that of an ECMO circuit in several ways:
- The most obvious and important is the presence of an open craniotomy venous reservoir (CVR) that permits simultaneous drainage from multiple sources, some of which are actively drained from the body.