Editing Cardiopulmonary bypass (section)

==Components==
Cardiopulmonary bypass devices consist of two main functional units: the [[pump]] and the [[oxygenator]]. These units remove oxygen-depleted blood from a patient's body and replace it with oxygen-rich blood through a series of tubes, or hoses. Additionally, a [[heat exchanger]] is used to control body temperature by heating ''or'' cooling the blood in the circuit. All components of the circuit are coated internally by [[heparin]] or another anticoagulant to prevent clotting within the circuit.<ref name=":33"/>

[[File:Perfusionist opearting heart lung machine.jpg|thumb|250px|Perfusionist operating a modern heart lung machine]]

===Tubing===
The components of the CPB circuit are interconnected by a series of tubes made of [[silicone rubber]] or [[PVC]].<ref>{{Cite web|url=https://www.ebme.co.uk/articles/clinical-engineering/cardiopulmonary-bypass-machine-cpb|title=Cardiopulmonary bypass machine — CPB| vauthors = Davies H |website=www.ebme.co.uk|language=en-GB|access-date=2019-11-21}}</ref>

===Pumps===

====Centrifugal pump====
Many CPB circuits now employ a [[centrifugal pump]] for the maintenance and control of blood flow during CPB. By altering the speed of revolution (RPM) of the pump head, blood flow is produced by [[centrifugal force]]. This type of pumping action is considered to be superior to the roller pump because it is thought to prevent over-pressurization, clamping, or kinking of lines, and causes less damage to blood products ([[hemolysis]], etc.).<ref name=":0" />

====Roller pump====
The pump console usually comprises several rotating, motor-driven pumps that [[peristalsis|peristaltically]] "massage" the tubing. '''This action gently propels the blood through the tubing.''' This is commonly referred to as a roller pump, or [[peristaltic pump]]. The pumps are more affordable than their centrifugal counterparts but are susceptible to over-pressurization if the lines become clamped or kinked.<ref name=":0" /> They are also more likely to cause a massive air embolism and require constant, close supervision by the perfusionist.<ref name=":33"/>

===Oxygenator===
The [[oxygenator]] is designed to add [[oxygen]] to infused [[blood]] and remove some [[carbon dioxide]] from the [[venous blood]].

=== Heat exchangers ===
Because hypothermia is frequently used in CPB (to reduce metabolic demands), heat exchangers are implemented to warm and cool blood within the circuit. Heating and cooling is accomplished by passing the line through a warm or ice water bath, and a separate heat exchanger is required for the cardioplegia line.<ref name=":33"/>

===Cannulae===
Multiple [[cannula]]e are sewn into the patient's body in a variety of locations, depending on the type of surgery. A venous cannula removes oxygen depleted venous blood from a patient's body, and an arterial cannula infuses oxygen-rich blood into the arterial system. The main determinants of cannula size selection is determined by the patient's ''size'' and ''weight'', ''anticipated flow rate'', and the ''size of the vessel'' being cannulated.<ref name=":33"/> A [[Cardioplegia]] cannula delivers a Cardioplegia solution to cause the heart to stop beating.

Some commonly used cannulation sites:
{| class="wikitable"
|-
! Venous
! Arterial
! Cardioplegia
|-
|[[Right atrium]]
| Proximal [[aorta]], distal to the [[aortic cross-clamp|cross-clamp]]
| Proximal [[aorta]], proximal to the [[aortic cross-clamp|cross-clamp]]
|-
|[[Vena cavae]]
|[[Femoral artery]]
|[[Coronary sinus]] (retrograde delivery)
|-
|[[Femoral vein]]
|[[Axillary artery]]
| Coronary ostia
|-
|
| Distal [[aorta]]
| Bypass grafts (during [[CABG]])
|-
|
| Apex of the [[heart]]
|
|-
|}

===Cardioplegia===
{{main|Cardioplegia}}
Cardioplegia is a fluid solution used to protect the heart during CPB. It is delivered via a cannula to the opening of the coronary arteries (usually by way of the aortic root) and/or to the cardiac veins (by way of the coronary sinus).<ref name=":0" /> These delivery methods are referred to '''antegrade''' or '''retrograde''', respectively. Cardioplegia solution protects the heart by arresting, or stopping the heart. This then decreases the heart's metabolic demand. There are multiple types of cardioplegia solutions, but most work by inhibiting [[Sodium channel|fast sodium currents]] in the heart, which prevent conduction of the [[action potential]]. Other types of solutions act by inhibiting calcium's actions on [[myocyte]]s.<ref name=":2">{{Cite book |title=TSRA Primer of Cardiothoracic Surgery |vauthors=Youssef SJ, Williams JA |publisher=TSRA/TSDA |year=2013 |isbn=978-0-9894023-0-9 |location=Chicago, IL}}</ref>