EXTRACORPOREAL CIRCULATION Staff Members of Cardio-thoracic Surgery Departments Egypt

Cardiac Operations 1- Closed heart surgery (without extracorporeal circulation): Congenital (extra-cardiac) carried out on the main vessels outside the heart: closure of PDA, correction of coarctation of aorta, pulmonary artery banding and palliative shunts for cyanotic heart diseases. Valvular: Closed mitral commissurotomy. Ischemic: Off-pump coronary artery bypass surgery (OPCAB). The heart is beating and connected to circulation. Done through thoracotomy or sternotomy.

Cardiac Operations (Cont.) 2- Open heart surgery (with extracorporeal circulation). Congenital defect repair: VSD, ASD, Total repair of Fallot’s Tetralogy. Coronary artery bypass graft (CABG), (ON-PUMP). Heart valve repair or replacement when a heart valve does not function properly. Others: Heart transplant to remove a severely damaged heart and replace it with a donor heart. Cardiac Tumours. Surgery for cardiac arrhythmias.

Cardiac Operations (Cont.) During these operations the heart functionally disconnected from the circulation; heart lung machine (cardiopulmonary bypass, extracorporeal circulation) is used to do the function of the heart and the lung temporarily. The operations performed under direct vision in a bloodless, motionless field within the chambers of the heart or great vessels. Classically performed through median sternotomy with excellent exposure. May be done through thoracotomy.

EXTRACORPOREAL CIRCULATION (ECC), Heart–lung Machine, Cardio-pulmonary Bypass (CPB) Definition: Heart lung machine is a machine which replaces the function of the heart (Pumping) and the lung (Oxygenation) during cardiac surgery. It works by diverting retuned venous blood to extracorporeal circulation (ECC) and pump it back to the aorta i.e. bypassing the heart and lung (Cardio Pulmonary Bypass, CPB).

The main targets of the CPB: Bloodless field. Motionless heart. Protection of vital organs e.g. kidney and brain. Myocardial protection. Blood conservation. Uses: CPB is used in open heart surgery requiring arrested heart either with or without opening of cardiac chambers to support the circulation during that period.

Components: Reservoir: collect all returned venous blood. Oxygenator: for oxygenating deoxygenated blood. It could be bubble or membrane oxygenator. Roller Pump: used to push blood back to the aorta. Heater–Cooler: used to cool down the temperature of the patient during CPB and to warm him up at the end of CPB. Filters: incorporated in the circuit to prevent the passage of micro-emboli (gas bubbles, fibrin and platelet aggregates or calcium particles).

Present Day Heart Lung Machine

STEPS OF PROCEDURE General anesthesia and insertion of monitoring lines (Invasive BP, CVP, temperature prob, ECG). Mid sternotomy. N.B. Right or left thoracotomy may be used in some cases. Heparin before cannulation of the heart to prevent clotting inside the cannulae, tubes and oxygenator during CPB. Using priming fluids: to fill the oxygenator and tubing to augment peripheral circulation and to decrease blood viscosity. May be crystalloid (e.g. isotonic saline) or blood enriched.

Cannulation: 1) Arterial Cannulation: cannula is inserted usually in Aorta (some cases in femoral artery) 2) Venous Cannulation: usually double cannulation in SVC and IVC (sometimes single cannulation in R.A) The deoxygenated blood returning to the heart is diverted through cannulae inserted in SVC and IVC, to the reservoir and then to a blood membrane oxygenator where gas exchange occurs. The oxygenated blood is returned from the oxygenator, using a roller pump, to the patient through a cannula placed in the ascending aorta.

Cooling patient down to desired temperature using a heater-cooler. Aortic cross clamp applied at ascending aorta. Cardioplegia delivered. Cardiac procedure is now done in motionless bloodless field. De-airing at the end of procedure to avoid cerebral air embolism. Aortic cross clamp removed. Defibrillator may be required to restore cardiac rhythm. Re-warming - Weaning from CPB. Protamine sulfate is given to neutralize heparin after removal of the cannulae from the heart.

Myocardial Preservation Cardioplegic solution containing high potassium chloride. Generally, Cold (4°C), but recently there is also warm blood cardioplegia for short procedures. Infused after aortic cross–clamping into: Antegrade into Aortic root, or Directly into the coronary ostia e.g. cases with aortic regurge, Retrograde through coronary sinus e.g. in cases of left main coronary artery disease. Local hypothermia by placing ice or cold saline on the heart. Systemic hypothermia: decreases metabolic rate and oxygen consumption. The oxygenator is equipped with a heat exchanger that can cool and warm blood and thereby control body temperature. Hypothermia may be mild, moderate or severe . Total circulatory arrest can be achieved by profound hypothermia at 16 - 18°C (e.g. in surgery of extensive aneurysms of the aorta).

Myocardial preservation: (Cont.) Hypothermia protects the heart and all body organs including the brain by decreasing metabolic needs and oxygen demand during the procedure. The time from beginning CPB to its end is called CPB Time, while time from aortic cross clamping till aortic de-clamping is called ischemic time.

Complications of extracorporeal circulation Prolonged bypass induces cytokine activation and inflammatory response results in: red cell damage and haemoglobinuria, and thrombocytopenia. Cerebral Stroke and neurocognitive defects. Psychological changes e.g depression, psychosis. Bleeding complications secondary to platelet dysfunction. Renal insufficiency. Pulmonary insufficiency, lung atelectasis, ARDS. Cardiac complications such as perioperative myocardial infarction, low cardiac output syndrome, stone heart syndrome due to bad myocardial preservation and arrhythmias. Immunosuppression. Gastrointestinal complications: ilius, stress ulcer and acute pancreatitis.

Approaches for open heart Surgery Median sternotomy is the standard approach for open heart surgery. Other minimally invasive approaches : Ministernotomy (upper part). Right submammary thoracotomy for ASD closure and mitral valve surgery, Limited left anterior thoracotomy for bypassing a stenosed left anterior descending coronary artery with left internal thoracic( mammary) artery. Recently available, VATS and Robotic cardiac surgery. The main disadvantage of these incisions is the small field they yield, that is insufficient in emergency situations. Advantage cosmetic incision.