The bypass machine needs to be set up for circulatory arrest.
Two arterial lines are needed:
Option 1 - one for central perfusion and one with a second branch in it for selective cerebral perfusion. During the period of selective cerebral perfusion the central perfusion line is inserted into the proximal descending aorta via the open arch for distal body perfusion.
Option 2 - one for femoral perfusion and one with a second branch in it for selective cerebral perfusion.
Venous return is usually via a two stage cannula. Venous Cannulation and Drainage
Venting of the right superior pulmonary vein (RSPV) is the commonest method of venting the heart, however other routes exist.
Diagram shows locations used to vent (decompress the heart).
(A) Aortic root vent, which can also be used to administer cardioplegic solution after the ascending aorta is clamped.
(B) A catheter placed in the right superior pulmonary vein/left atrial junction can be passed through the mitral valve into the left ventricle.
(C) Direct venting of the left ventricle at the apex.
(D) Venting the main pulmonary artery, which decompresses the left atrium because pulmonary veins lack valves.
Cardioplegia line with a branch for anterograde and retrograde cardioplegia.
One or Two pump suckers.
Basic CPB set up
Basic cardiopulmonary bypass circuit with membrane oxygenator and centrifugal pump.
The complete heart-lung machine includes many additional components. Most manufacturers consolidate a membrane oxygenator, venous reservoir, and heat exchanger into one unit. A microfilter-bubble trap is added to the arterial line. Depending on the operation various suction systems are used to return blood from the surgical field, cardiac chambers, and/or the aorta. Aspirated blood passes through a cardiotomy reservoir and microfilter before returning to the venous reservoir. Optionally, but increasingly recommended, field blood is washed in a cell saver system and returned to the perfusate as packed red cells. In addition to adjusting pump flow, partial and occluding clamps on venous and arterial lines are used to direct and regulate flow. Sites for obtaining blood samples and sensors for monitoring pressures, temperatures, oxygen saturation, blood gases, and pH are included, as are various safety devices.
Actual typical CPB setup
Diagram of a typical cardiopulmonary bypass circuit with vent, field suction, aortic root suction, and cardioplegic system. Blood is drained from a single "two-stage" catheter into the venous reservoir, which is part of the membrane oxygenator/heat exchanger unit. Venous blood exits the unit and is pumped through the heat exchanger and then the oxygenator. Arterialized blood exits the oxygenator and passes through a filter/bubble trap to the aortic cannula, which is usually placed in the ascending aorta. Blood aspirated from vents and suction systems enters a separate cardiotomy reservoir, which contains a microfilter, before entering the venous reservoir. The cardioplegic system is fed by a spur from the arterial line to which the cardioplegic solution is added and is pumped through a separate heat exchanger into the antegrade or retrograde catheters. Oxygenator gases and water for the heat exchanger are supplied by independent sources
A separate circuit for administering cardioplegic solutions at controlled composition, rate, and temperature is usually included in the system. Less often a hemoconcentrator (for removal of water and small molecules) is added to the primary circuit.
The following are some of the many perfusion scenarios in aortic surgery
Bilateral antegrade cerebral perfusion obtained by selective cannulation of the innominate and left common carotid artery.
Upper right: retrograde cerebral perfusion via the superior vena cava.
Lower right: regional cerebral perfusion (unilateral antegrade perfusion) via cannulation of the right subclavian artery.
Sequential bilateral antegrade perfusion of the brain. The branch of a multiple-arms graft is initially connected to the left common carotid artery allowing rapid establishment of a bilateral perfusion of the brain. The other anastomoses are performed thereafter. Perfusion of the right subclavian artery through a graft allows monitoring of the perfusion pressure via the right radial artery.
Ascending aortic aneurysm extending into the underside of the aortic arch. (B) Bentall reconstruction of the aortic root with open resection of the hemiarch. Perfusion via the right axillary artery. (C) Completed repair and full systemic perfusion.
(A) Acute type A aortic dissection with the entry point located in the aortic arch.
(B) Cardiopulmonary bypass via the right axillary artery.
(C) Separate graft anastomosis to the brachiocephalic vessels.
(D) Selective cerebral perfusion and elephant trunk construction.
(E) Arch reconstruction with graft-to-graft anastomosis.
(F) Completed repair.
(A) Atherosclerotic ascending and arch aneurysm.
(B) Fabrication of the trifurcated graft.
(C) Selective cerebral perfusion and construction of the elephant trunk.
(D) Completed repair.
(A) Recurrent arch proximal descending aneurysm.
(B) Selective cerebral perfusion and arch reconstruction.
(C) Completed repair.
(A) Distal arch descending thoracic aortic aneurysm with femoral artery perfusion.
(B) HCA and anastomosis to the distal arch.
(C) Selective cerebral perfusion.
(D) Reattachment of the left subclavian artery and completed repair.
(A) Technique for extensive thoracoabdominal aortic aneurysm repair utilizing proximal aortic isolation with distal aortic perfusion employing left atrial to left common femoral artery bypass with a centrifugal pump.
(B) Following completion of the proximal anastomosis, visceral and renal arteries are perfused using 9 F Pruitt catheters with oxygenated blood from the bypass circuit during intercostal arterial reattachment.
(C) Prior to completion of distal reconstruction, visceral and renal perfusion are continued during reattachment of the aortic graft. Sequential clamping provides intercostal perfusion.
Crawford extent IV thoracoabdominal aortic aneurysm with visceral and renal oxygenated blood perfusion from left atrium during the ischemic period of aortic reconstruction.
(A) Crawford extent I thoracoabdominal aortic aneurysm using atrio-femoral bypass, with beveled distal anastomosis, includes visceral and renal arterial reattachment that is carried out first.
(B) Sequential clamping of graft provides renal and visceral perfusion during reattachment of a patch of intercostal arteries.
(C) Sequential placement of the clamp allows distal perfusion of reattached intercostal arteries during the proximal aortic anastomosis.
Diagram showing a typical setup for partial left heart bypass in a patient with aortic disruption at the isthmus.
Iliac artery exposure
This is sometimes necessary when the femoral arteries are too diseased to cannulate or are too small for stent insertion.
Antegrade Cerebral Perfusion
Antegrade perfusion of the brain through cannulae inserted in the innominate (or more distally in the right common carotid artery) and left common carotid artery provides the most physiologic and efficient perfusion of the brain. Perfusate temperature is usually set at 18°C and flow is set between 10 and 20 mL/kg/min or adjusted to maintain a pressure between 40 and 50 mm Hg in the right radial artery. Clinical results, especially regarding swift recovery of cerebral function, have been outstanding with this method of perfusion. The necessity to cannulate relatively small and often diseased arch arteries and the presence of additional cannulae in the operating field constitute the main drawbacks of the technique. Cannulation of the common carotid arteries can result in dissection of the arterial wall and embolism of atheromatous plaque material or air. Furthermore, the flow in the artery is dependent on proper positioning of the tip of the cannula within the vessel. For these reasons, many surgeons rely on a unilateral perfusion of the brain, with the sole cannulation and perfusion of the right subclavian artery. The right vertebral and right common carotid artery territories are perfused in an antegrade fashion. The blood reaches the left cerebral hemisphere through the circle of Willis and, to a lesser extent, through cervicofacial connections. It is, therefore, important that the left common carotid and left subclavian arteries be occluded to avoid a steal of blood down these arteries. Occlusion (usually with an inflatable balloon) of the descending aorta is also a useful maneuver to improve overall body perfusion. Effective somatic perfusion (including the abdominal organs, spinal cord, and lower limb musculature) has been documented with this maneuver.
The presence of an aberrant right subclavian artery (also called arteria lusoria) is obviously a contraindication to the use of this perfusion method. The aberrant origin of the artery is usually readily identified by computed tomography or magnetic resonance. The burst of blood from the descending aorta during the opening of the aortic arch should alert the surgeon to this anatomic variation, and prompt a direct cannulation of the ostium of the right and left common carotid arteries.
Sequential perfusion of the cerebral arteries provides additional safety to unilateral cerebral perfusion, and avoids cannulation of small or diseased arch arteries. The right subclavian artery remains perfused during the whole procedure. A vascular graft is immediately sewn on a common patch of aortic wall including all the arch vessels, or the second branch of a multiple-arm prosthesis is anastomosed to the left common carotid artery. Perfusion is then instituted through this additional graft and enhances, after a short period of time, cerebral perfusion.
Retrograde Cerebral Perfusion
The value of retrograde cerebral perfusion in protecting the human brain has still not been clearly elucidated. No animal model truly replicates the complex anatomy and physiology of the human brain, and none allows a fine neuropsychologic evaluation. Conflicting results and conclusions in clinical and experimental studies have, therefore, been reported. Accepted facts include a deep and homogenous cooling of the brain hemispheres (the cooling scalp effect) and the expulsion of solid particles or gaseous bubbles from the arch arteries. Controversies surround the possible nutritive value of retrograde perfusion. The nutritive value has been demonstrated in rabbits but not in dogs, pigs, or baboons. In humans, signs of cerebral perfusion and oxygen uptake have been documented, but the amount of perfusate providing cerebral nutrition is low, corresponding to about 5% of total retrograde flow. The blood delivered in the superior vena cava flows preferentially in the low-pressure inferior vena cava, via the azygos system, the perivertebral venous plexus, and the thoracic wall veins. Even within the brain, the distribution of retrograde flow is uneven, with a preferential distribution in the sagittal sinus and hemispheric veins. The large steal of blood to the inferior venous territory is corroborated by the clinical finding of an extremely small proportion of perfused blood flowing out of the arch arteries. Occlusion of the inferior vena cava to decrease the pressure gradient between the two venous territories effectively reduces the amount of stolen blood, but increases the sequestration of fluid in the interstitial tissue. Interstitial edema is another potential problem of retrograde perfusion, which can lead to cerebral edema and hypertension, particularly when the perfusion pressure exceeds 25 mm Hg. Finally, the finding that the human jugular system may contain competent valves casts definitive doubts regarding the reliability of retrograde cerebral perfusion.
Clinical series, however, have reported encouraging results. A reduction in both mortality and incidence of neurologic damage has been regularly documented with the adjunctive use of retrograde cerebral perfusion to classical hypothermia. Some studies confirmed the limited capacity of retrograde perfusion to sustain cerebral metabolism, and stressed the fact that the occurrence of neurologic damage was only delayed. Indeed, the risk rises sharply after 60 minutes of deep hypothermic circulatory arrest, perhaps at the extinction of intracellular energy substrates. If most surgeons acknowledge the capacity of retrograde cerebral perfusion to prolong the period of safe circulatory arrest, they consider the method a valuable but not an alternative adjunct to conventional methods when long periods of circulatory arrest are contemplated.
Integrated Perfusion
Probably the safest approach to a patient requiring a long period of circulatory arrest resides in the integration of complementary methods of perfusion and monitoring. Retrograde perfusion of the aorta through the femoral artery should be avoided in the presence of a thoracic aortic aneurysm in order to reduce the risk of particulate dislodgment with embolization in the brain and myocardium. Antegrade perfusion of the aorta is performed with cannulation of the ascending aorta or right subclavian artery. The body is cooled to 18°C. Electroencephalogram and venous jugular saturation are monitored to ensure adequate reduction of cerebral metabolism. Circulatory arrest is established only after electrocerebral silence is obtained and jugular venous saturation is superior to 95%. During the 10 to 20 minutes preceding circulatory arrest, the temperature of the perfusate can be lowered to 13°C to further reduce brain temperature and metabolism. The arch arteries are connected to a graft (either with the use of a patch of aortic wall or separately), and antegrade perfusion of the brain is resumed before more extensive resection and repair of the aorta is performed. When the risk of particle embolization to the brain is substantial (old age, severe atherosclerosis of the aorta, arch aneurysm with thrombotic material), a short period of retrograde cerebral perfusion can be performed to wash out the arch arteries before antegrade perfusion is definitively reestablished.
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