As a future cardiothoracic anesthesiologist, it’s important for me to consider the surgical steps and potential areas of difficulty/complications which may arise during the intraoperative course. Although each procedure must be tailored to a patient’s unique set of comorbidities and surgical factors, I wanted to outline the basic steps involved in a routine coronary artery bypass grafting (CABG).
First, a median sternotomy is made using a pneumatic saw (“cracking the chest”) to access the left pleural space. The left internal mammary artery (LIMA) is carefully dissected off the chest wall while an assistant simultaneously performs ultrasound mapping of the saphenous vein system and harvests vein grafts from the legs endoscopically or with an open incision. Bypass-dose heparin (usually 4 mg/kg) is administered as the pericardial sac is opened. The remainder of the LIMA dissection is performed and the vessel is clamped distally.
Next, the ascending aorta is cannulated through two purse string sutures. At this point, it’s possible to begin cardiopulmonary bypass as long as sufficient volume is provided through suctioning or transfusion from the venous side. Usually, a venous cannula is inserted through two purse string sutures into the right atrial appendage. By doing this, blood is siphoned from the right atrium, goes to the cardiopulmonary bypass machine, and reenters circulation in the ascending aorta. Once bypass is initiated, systemic cooling occurs and an ascending aorta cross-clamp is placed.
If the heart is going to be bloodless (ie, virtually no oxygen supply), we better make sure its demand for oxygen is also minimal. This is achieved through a diastolic arrest with high potassium cardioplegia solution. An antegrade cardioplegia catheter is placed into the aortic root (uses normal coronary plumbing to flush cardioplegia into the heart) and a retrograde catheter is placed into the coronary sinus (perfuses the coronary network backwards). Additionally, cold ice solution is applied to the heart for topical cooling. The combination of cooling the heart, emptying it with bypass/venting to decrease wall stress, and arresting it with cardioplegia helps mitigate the mismatch between oxygen supply and demand after the aortic cross-clamp makes the heart ischemic.
Epicardial vacuum stabilizers allow cardiothoracic surgeons to stabilize a coronary artery for bypass without completely arresting the heart on cardiopulmonary bypass ("off pump CABG"). In the video, you can see a left internal mammary artery (LIMA) to left anterior descending (LAD) bypass on a stationary piece of epicardium thanks to the stabilizer. Note how the heart is still beating and perfused during the grafting.
Next, vessel grafting commences. The posterior, distal grafts (ie, right coronary artery) are performed first. Reversed saphenous vein grafts (SVGs) are anastomosed end-to-side distal to the diseased coronary artery in running fashion. Since the LIMA is already connected to the aorta proximally and the left anterior descending (LAD) coronary artery is on the anterior heart, the LIMA-LAD end-to-side anastomosis is usually done last.
All the vein grafts now need to have their proximal anastomoses completed onto the ascending aorta in an end-to-side fashion. Systemic rewarming is initiated and a partial occluding clamp is placed on the aorta prior to beginning these proximal anastomoses. Once finished, de-airing is performed of all the grafts and right ventricular pacing wires are placed.
Weaning from cardiopulmonary bypass is its own topic but requires careful coordination between the surgeon, anesthesiologist, and perfusionist. Transesophageal echocardiography (TEE) is especially useful at this point to guide weaning. Once successfully weaned, the bypass cannulas are removed and systemic heparinization is reversed with protamine sulfate. Chest tubes are left in the mediastinum and left pleural space. The sternum is closed with stainless steel wires, and the overlying fascial layers are closed with absorbable sutures.
… all easier said than done. 😀