Cardiothoracic Surgery Dr.Mohammed J. Jameel FIBMS.Th.CVS.Senior Lecturer. Department of Surgery, College of Medicine, Al-Mustansiriyah University, Baghdad, Iarq.

Lec:1 Cardiopulmonary Bypass (CPB) Is the method by which the physiological function of the heart and lung is replaced by a machine in anesthetized patient for a limited period of time during cardiac operation, it is required for most of cardiac operations. The CPB machine is composed mainly of three parts Part one: act as a mechanical pump to pump the blood instead of the heart during the period of cardiac stand still. Part two: Called the Oxygenator which acts instead of patients' lung to provide O2 and remove CO2 i.e. to do the gas exchange function during cardiac operation. Part Three: Called heat exchanger which control body temperature by cooling the blood at the beginning and during the cardiac operation and then by re-warm the blood after the completence of operation to return to normal body temperature.

The benefit of cooling the body during the operation is to decrease the basal metabolic rate and O2 requirement this allows reduction of blood flow rate (cardiac output) of the mechanical heart and when blood flow rate is decreased surgeon will get a bloodless field in human heart to facilitate doing of intended procedure. The reduction of temperature during cardiac operation is done according to length and complexity of operation, the longer and more complex the operation the more the reduction in temperature is needed.

Hypothermia is categorized to 4 Levels:- Mild Hypothermia: - the body temperature is decreased to 32C at which machine flow rate can be decreased to 2 Litre/minute/ Square meter. Moderate Hypothermia:- the temperature is decreased to 28C and flow rate decreased to 1.5 Litre / minute/ m2. Deep Hypothermia:- the temperature is decreased to 23C and flow rate decreased to 1Litre/minute/m2. Profound Hypothermia:- the temperature is decreased to 18C and the flow rate decreased to 0.5 Litre /minute/m2.

HOW CPB IS STARTED:- The sternum is divided by mechanical saw. 1. After the patient is anesthetized in supine position the chest is opened by Median Sternotomy which is the classical route for cardiac operation The sternum is divided by mechanical saw. The pericardium is opened. The patient is heparinised (given Heparin) the dose is 4 mg/Kg . 2. The Ascending Aorta is cannulated by special size cannula according to body weight and surface area, the cannula is fixed to aorta by purse-string suture. 3. The venous cannula is inserted to the venous circulation through the right atrial appendage, after the insertion of the arterial and venous cannulae both are connected to CPB machine by special plastic tubes which are designed to decrease damage to blood element.

4. When the circuit is completed CPB is started by an order from surgeon, the blood is cooled to the temperature necessary for operation. 5. A cross clamp is put on Ascending Aorta proximal to site of aortic cannula and cold cardioplegic solution is infused to aortic root by small needle, the cardioplegic solution contains high potassium concentration will induce diastolic arrest of heart ,then the surgeon can do the operation. 6. When operation is finished the blood is re-warmed, Aortic clamp is removed and the heart will return to beat again either spontaneously or by D.C shock. 7. When general condition of patient become stable Protamine is given to reverse the heparin effect, the dose is 1 mg Protamine for each 1 mg of heparin. 8. CPB is stopped, Aortic and venous cannulae are removed and sternum is closed by steel wires.

Surgical Management Of Ischemic heart Disease:- The Coronary circulation to heart is composed of Left and Right coronary arteries. Left Coronary artery arise from Left coronary sinus and supply most of anterior wall, the apex and interventricular septum, it is divided to left anterior descending and circumflex artery. Right Coronary artery arise from Right coronary sinus and supply SA and AV nodes and part of interventricular septum. The coronary arteries liable to develop atherosclerotic changes this will narrow them and when the obstruction reaches the critical level it will prevent the transient of blood to myocardium and this will produce ischemic symptoms.

Indications of Coronary Artery By-pass Graft 1. Disease involves Left Main Stem Coronary Artery. 2. Two vessel disease including Left anterior descending artery. 3. Three vessel disease not including Left anterior descending artery. 4. Symptoms refractory to medical treatment. 5. Complex lesion not amenable for PTC. During CABG usually 3 to 4 grafts are used to transmit blood directly from Ascending Aorta to coronary arteries distal to site of atherosclerotic obstruction.

The grafts may be arterial or venous 1.Arterial graft like Left internal mammary artery which is harvested from chest wall, the proximal end remain attached to subclavian artery and the distal end is anatomised to left anterior descending coronary artery. 2. Venous graft like Long Saphenous Vein Which is harvested from the leg and used as free graft. After surgery most patients will get benefit by relief of symptoms in 97% of cases ,5 to 10 years later symptoms may develop again because of the development of atherosclerosis in the grafts which may obstruct them, the internal mammary artery is more resistant to atherosclerosis than saphenous vein graft the restenosis can be treated nowadays by Redo- CABG.