Cardiopulmonary Bypass It’s bananas!

And it’s as simple as 1, 2, 3! 1! 3! 2!

Lol, jk, it’s super complex

But it’s also super awesome.

What is Cardiopulmonary Bypass? “Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation in which the patient's blood is diverted from the heart and lungs and rerouted outside of the body. The normal physiological functions of the heart and lungs, including circulation of blood, oxygenation, and ventilation, are temporarily assumed by surrogate technology. This allows a surgeon to operate on a non-beating heart in a field largely devoid of blood while maintaining complete control of tissue oxygenation and perfusion.” Woah. That IS bananas. Marion, DW. Weaning from cardiopulmonary bypass. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on November 25, 2013.)

What do we use CPB for? CPB is used in the following surgical procedures Coronary Artery Bypass Surgery Cardiac valve repair and/or replacement (aortic valve, mitral valve, tricuspid valve, pulmonic valve) Septal defect repair. Repair of congenital heart defects. Organ transplantation (hearts, lungs, heart & lungs). Aortic and cerebral aneurysm repair. Pulmonary thromboendarterectomy (removal of blood clots from the pulmonary arteries). In short, it’s an immensely invasive procedure used for a lot of things, and we’re all going to spend the rest of our medical careers taking care of patients who at one point or other underwent CPB.

A Brief History Maximilian von Frey, a German physiologist, constructed the first prototype heart- lung machine in 1885! Lol max, wtf are we doing? It’s 1885, this is bananas

More History However, the procedure simply wasn't feasible until the discovery of heparin in 1916 and the first known operation involving mechanical takeover of the heart wasn’t conducted until 1951 at the University of Minnesota(it failed). The failed procedure resulted in four years of laboratory experimentation with dogs in a unit known as “Iron Heart.” In 1953, John Gibbon repaired an atrial septal defect on an 18-year-old female, which was the first successful open heart procedure on a human utilizing CPB. Omg u guys we finally did it, good job, high fives all around

Components of CPB Mechanically speaking, CPB consists of “venous and arterial cannula; a membrane or bubble oxygenator that oxygenates the blood, removal of carbon dioxide, and delivery of anesthetic gases; a heat exchanger that allows the blood to be either heated or cooled by conduction; a pump, which keeps the blood moving at a constant speed; filters, which remove particulate or gas emboli and plasma protein or platelet aggregates; a left ventricular vent to prevent distention of the left ventricle during aortic cross-clamp; cardiotomy suction to aspirate blood from the operative field; and sensors, which detect air bubbles, low levels of oxygen saturation, and low levels of blood in collection chambers.” -Up To Date I found a picture with some of those things in it! Marion, DW. Weaning from cardiopulmonary bypass. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on November 25, 2013.)

The Process Placing patients “on” and “off pump” consists of the following sequence of events: Priming of the CPB circuit. Anticoagulation. Vascular cannulation. Initiation and maintenance of CPB. Myocardial protection. Weaning and termination of CPB.

Priming of the Circuit The CPB tubing is primed prior to being connected to the patient to mitigate the risk of air emboli. During CPB, blood sent to the bypass machine is cooled in order to reduce the body’s basal metabolic rate and consequent demand for oxygen. Cooling, however, make the blood more viscous, so the CPB tubing is primed with a crystalloid solution in order to dilute the blood passing through it. Fig. 1: Tubes

2. Anticoagulation It seems counterintuitive for surgery, but large doses of heparin are administered to prevent the formation of massive clots during CPB. “Heparin is used for anticoagulation during CPB to prevent clotting in the CPB circuit. Before initiation of CPB, a heparin dose of 3 mg/kg is administered through a central line. Activated clotting time is monitored a minimum of every 30 minutes during CPB. Once CPB is completed, heparin is reversed using protamine sulfate. Care is taken to administer protamine slowly and watch for a possible protamine reaction, which may vary from mild hypotension to full-blown anaphylaxis.” -Cardiac Nursing Susan Woods - Wolters Kluwer Health/Lippincott Williams & Wilkins - 2010

3. Vascular Cannulation Link

4. Initiation and Maintenance of CPB “The perfusionist controls oxygen delivery and carbon dioxide removal from the patient's blood. The perfusionist can administer anesthetic gases, remove fluid (hemoconcentration), deliver cardioplegia solution to cause cessation of all mechanical and electrical myocardial activity, apply suction to remove blood from the surgical field, and control patient temperature.” - Cardiac Nursing Fig. 1: A Perfusionist I mostly just see them writing the patient’s UOP and CT output on paper towels. You’d think they would have their own paper or something. Susan Woods - Wolters Kluwer Health/Lippincott Williams & Wilkins - 2010

5. Myocardial Protection “Cross-clamping the aorta without protection for more than 15 to 20 minutes would result in profound myocardial dysfunction. Cardioplegia is infused to arrest the heart and provide a bloodless, motionless operative field as well as protect the heart during cardiac surgery. Cardioplegic solution is infused into the aorta or coronary sinus or into the coronary arteries themselves to cause cardiac arrest. [Cardioplegia solutions are made of crystalloid, oxygenated crystalloid, or crystalloid-blood mixtures. Although cardioplegic solutions vary widely, typical components include potassium, magnesium, or procaine to provide immediate diastolic arrest; oxygen, glucose, glutamate, or aspartate as energy substrate; bicarbonate or phosphate to buffer acidosis; and calcium, steroids, or procaine to stabilize membranes.]” - Cardiac Nursing Susan Woods - Wolters Kluwer Health/Lippincott Williams & Wilkins - 2010

6. Weaning and Termination of CPB This is easily the most complex part of this process, and is summarized with the acronym WAAARRRRMM (no, seriously). Warm: The perfusionist begins warming the patient ~30m prior to the end of CPB. Anesthesia: Formulate a plan for postoperative sedation. Adjuvant Drugs: Ensure antiarrhythmic, inotropic and vasoactive infusions expected to be needed after cessation of CPB are available. Air: Air bubbles that accumulate in the aorta during DPB are vented out of the heart (the surgeon might massage them out). Rhythm: A perfusing rhythm must be established before weaning bypass. Epicardial pacing is place if NS isn’t achieved. Rate: Maintain a rate of 80-90 BPM to maximize CO. Resistance: Patients with a low SVR need vasopressors. Respiration: Weaning requires adequate lung function patient lung function. Metabolism: Calcium, acid-base and potassium abnormalities must be treated in order for normal cardiac function to resume. Monitoring: Turn your monitors on. Why did you turn them off? We’re doing heart surgery.

WAAARRRRMM!

Problems During and After Weaning “CPB is associated with an intense inflammatory response that is primarily induced by contact of blood with non-endothelial extracorporeal surfaces [1]. This results in platelet activation, initiation of the coagulation cascade, and decreased levels of coagulation factors. Endothelial cells and leukocytes are activated, releasing more mediators and resulting in capillary leakage and tissue edema. Many of the challenges encountered during weaning from CPB and the postbypass period (eg, myocardial dysfunction, vasodilation, and bleeding) are thought to be consequences of this inflammatory sequence.” -Up To Date Marion, DW. Weaning from cardiopulmonary bypass. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on November 25, 2013.)

Problem List There are literally a billion different things that can go wrong after CPB, here are a few highlights: LV dysfunction, diastolic dysfunction, RV dysfunction, vasodilatory shock, arrhythmias, air embolization, airway obstruction, bronchospasm, pulmonary edema, bleeding, anemia, coagulopathy, thrombocytopenia, all the metabolic abnormalities (hypo and hyper-everything), hypothermia...the list goes on. Approximately 0.7% of CPB patients will experience an incidence of cardiac arrest within 24 hours of surgery.

Case Study (If there’s time).

Summary Cardiopulmonary Bypass is bananas.