How does cardiopulmonary bypass work

In adults with moderate hypothermia, alpha-stat is beneficial. This maximises cerebral cooling and avoids severe acidosis with prolonged pH-stat. Ultrafiltration during and after CPB removes inflammatory mediators and excess fluid thereby producing haemoconcentration. Conventional ultrafiltration uses a haemofilter inserted into the bypass circuit. Modified ultrafiltration MUF is used after completion of the surgical repair before protamine administration, with blood removed from the arterial line and returned to the venous line after passing through the haemofilter.

It was first described by Naik et al. Weaning is the process where extracorporeal support is gradually withdrawn as the heart takes over the circulation. Several steps are required for successful completion of weaning. The use of hypothermia requires a period of rewarming. Rapid rewarming and hyperthermia are associated with cerebral injury. The high gradient between core and peripheral temperature can lead to after drop in temperature. Use of vasodilators can help in homogenous rewarming and to increase venous capacitance during transfusion of circuit blood.

Supplemental doses of anaesthetics are administered; acid-base balance, electrolytes, PaO 2 , PaCO 2 , sugar and haematocrit are kept within normal limits. Serum potassium of 4. After open-heart procedures, deairing of the heart is done. TOE is useful to assess the adequacy of deairing. Air embolism, frequently involving the right coronary artery due to its anterior location, can cause arrhythmias, ST-elevation and myocardial dysfunction.

It is treated by increasing the perfusion pressure and maintaining pulsatile perfusion by partially clamping the venous line. Heart rate, rhythm and contractility are assessed. Removal of the aortic cross-clamp can be associated with ventricular fibrillation, especially in conditions causing left ventricular hypertrophy like severe aortic stenosis.

Defibrillation is achieved using internal paddles with the biphasic energy of 5—20 J. Antiarrhythmics such as amiodarone, lidocaine and magnesium[ 33 ] can be added for persistent dysrhythmias. Mechanical ventilation is started, and the perfusionist gradually occludes venous return and fills the heart while incrementally reducing pump flows. Difficulties in weaning manifested by systemic hypotension may be due to either hypovolaemia, ventricular dysfunction or low SVR.

Hypovolaemia is treated by giving controlled boluses of blood from the circuit. Low SVR is treated with vasopressors such as phenylephrine, noradrenaline or vasopressin. The need for inotropes should be evaluated by visually assessing contractility and with TOE. Prior left ventricular dysfunction, severe pulmonary hypertension, inadequate myocardial protection and prolonged cross-clamp time are factors to consider in determining the post-bypass use of inotropes. A variety of inotropes are available, but the evidence base to advocate one inotrope over another is lacking.

Inodilators such as milrinone, dobutamine and levosimendan can be used in the setting of ventricular dysfunction with increased afterload. Use of levosimendan may be associated with a reduction in mortality. In spite of all measures, if the patient fails to wean, mechanical support devices like intra-aortic balloon pump, ventricular assist device or extracorporeal membrane oxygenation should be considered.

After separation from CPB, heparin is reversed with protamine in a ratio of — Protamine is administered over 10—15 min. Protamine can cause various reactions, namely type I hypotension, due to fast infusion , type II anaphylaxis and type III pulmonary hypertensive crisis.

Once protamine administration is complete, ACT is checked to confirm normalisation. Additional protamine should be given if circuit blood containing heparin is transfused.

High doses of protamine also cause anticoagulation. Residual re-heparinisation may also occur as the drug emerges out of poorly perfused compartments, especially in obese patients heparin rebound.

The final step is arterial decannulation. Post CPB, radial arterial catheters may underestimate central aortic systolic pressure but mean pressure is equivalent , due to vasodilation and arteriovenous shunting in the upper limb. Arterial cannulation can be associated with bleeding, cannula malposition causing selective cerebral perfusion, plaque dislodgement and dissection. It can be diagnosed with TOE. Repair of the dissection is necessary under DHCA.

Massive air embolism is due to pumping from an empty reservoir. Treatment is cessation of the pump and commencing retrograde cerebral perfusion.

Other complications include oxygenator failure, pump malfunction, clotting in the circuit, tubing rupture, gas supply failure and electrical failure due to which hand cranking must be available at all times. CPB causes qualitative and quantitative platelet dysfunction. The concentration of pro-coagulants decreases due to haemodilution. Inflammatory, coagulation, complement and fibrinolytic pathways are activated. Thromboelastography can help in knowing the cause of bleeding diathesis.

Bleeding is greater with prolonged bypass time, redo-surgery and preoperative use of anticoagulants. Studies have shown decreased blood loss and transfusion requirement in cardiac surgery patients with prophylactic anti-fibrinolytics. Inflammatory response and hypotension can cause acute kidney injury AKI. Risk factors are prolonged bypass time, sepsis and diabetes. Treatment includes maintenance of high perfusion pressure, use of early biomarkers to detect AKI and dialysis.

The spectrum of cerebral injury ranges from cognitive dysfunction to stroke. The strategy includes maintenance of higher perfusion pressure, adequate HCt, and alpha stat management. Contact of blood with artificial surfaces, ischaemia-reperfusion injury, endotoxaemia and operative trauma can cause systemic inflammatory response after CPB. Acute phase reaction is initiated by the release of complement, cytokines, endotoxins and NO leading to increased capillary permeability.

Rewarming can cause stress response and release of inflammatory mediators. The role of steroids is controversial in view of the lack of adequate benefit and flaring of postoperative infection. Subclinical myocardial injury can occur due to cross clamping of the aorta in spite of cardioplegia. Stunning of the myocardium is responsible for immediate dysfunction.

Factors include metabolic acidosis, preoperative ventricular function, reperfusion injury and inflammatory mediators. Optimisation of electrolytes, temperature and pH helps to reduce arrhythmias. Acute respiratory distress syndrome can be present due to the effects of CPB. Anaesthesia-induced atelectasis and reduced mucociliary clearance further contribute to acute lung injury. As a result atelectasis and pleural effusions are common pulmonary abnormalities after cardiac surgery.

Therefore, lung protective lung strategies are required in the pre- and post-operative periods of cardiac surgery. Vasoplegia is characterised by severe, vasopressor-resistant vasodilation due to activation of nitric oxide synthase, vascular smooth muscle ATP-sensitive potassium channels and relative deficiency of vasopressin.

Treatment includes fluid resuscitation and vasopressors such as phenylephrine, norepinephrine and vasopressin. Methylene blue 1. CPB has made increasingly complex cardiac surgeries possible in the current era.

Over the years, CPB has undergone immense modifications in the form of novel defoaming agents, heparin coated circuitry, ultrafiltration, miniaturised circuit design, integrated arterial filters with oxygenator. However it is not without its share of side effects, it is important to continue to search for strategies to further minimise them for better outcomes. National Center for Biotechnology Information , U.

Journal List Indian J Anaesth v. Indian J Anaesth. Manjula Sarkar and Vishal Prabhu. Author information Copyright and License information Disclaimer. Department of Anaesthesia, Seth G. Medical College, Mumbai, Maharashtra, India. Address for correspondence: Dr. E-mail: moc. This article has been cited by other articles in PMC.

Abstract Cardiopulmonary bypass CPB provides a bloodless field for cardiac surgery. Key words: Cardioplegia, cardiopulmonary bypass, heparin, oxygenator, protamine, ultrafiltration.

Open in a separate window. Cardiopulmonary bypass provides patients with cardiac and pulmonary support, while bypassing the heart and lungs. Cardiopulmonary bypass artificially provides patients three physiologic processes or functions:.

Once the cannulas from the patient have been connected to the cardiopulmonary bypass circuit, the blood is drained from the veins into the heart-lung machine while the blood is pumped into an artificial lung oxygenator , which adds oxygen and removes carbon dioxide.

The oxygenated blood is pumped back to the aorta to provide oxygen to the tissues and organs of the patient. The person responsible for performing cardiopulmonary bypass is called a cardiovascular perfusionist. The perfusionist works in tandem and under the supervision of the surgeon and anesthesiologist. Arrhythmias are usually treated first with medicines.

Other treatments may include. When these treatments do not work, surgery may be needed. One type of surgery is called Maze surgery. Maze surgery is used most often to treat a type of arrhythmia called atrial fibrillation. Atrial fibrillation is the most common type of arrhythmia.

An aneurysm is a balloon-like bulge in a blood vessel or in the wall of the heart. An aneurysm occurs when the wall of a blood vessel or the heart becomes weakened.

Pressure from the blood forces it to bulge outward, forming what you might think of as a blister. An aneurysm can often be repaired before it bursts.

Surgery involves replacing the weakened section of blood vessel or heart with a patch or artificial tube called a graft. Aneurysms in the wall of the heart occur most often in the lower-left chamber called the left ventricle. These aneurysms are called left ventricular aneurysms, and they may develop after a heart attack. A heart attack can weaken the wall of the left ventricle. If a left ventricular aneurysm leads to an irregular heartbeat or to heart failure, the surgeon may perform open heart surgery to remove the damaged part of the wall.

Angina is the pain you feel when a diseased vessel in your heart called a coronary artery can no longer deliver enough blood to a part of the heart to meet its need for oxygen. Angina usually occurs when your heart has an extra need for oxygen-rich blood, such as during exercise.

Angina is nearly always caused by coronary artery disease CAD. Transmyocardial laser revascularization TMLR is a procedure that uses lasers to make channels in the heart muscle, in an attempt to allow blood to flow from a heart chamber directly into the heart muscle.

If the blood flow is increased, more oxygen can reach the heart. This procedure is only done as a last resort. For example, TMLR may be done in patients who have had many coronary artery bypass operations and cannot have another bypass operation.