An aortic cannula is a surgical instrument used to create a bypass opening in the aortic lumen during cardiovascular surgery. It has flexible bend-resistant tubing and a soft plastic tip. Some cannulas feature a stylet and obdurator that are built-in, allowing for a less invasive implantation procedure. Another type of aortic cannula has three lumen, or tunnel-like openings, to simultaneously perfuse blood into three locations in the heart.
The aortic cannula may be used during a coronary artery bypass surgery, which is an operation that enables patients with arteriosclerosis or atherosclerosis to live longer. Most surgeons prefer to harvest a suitable saphenous vein from the patient to graft onto the narrowed artery. In some cases, an aortic cannula is implanted when a proper vein for transplant is unavailable.
One type of procedure used to implant the aortic cannula is called cannulation during an ascending aortic aortotomy. It is reversible during an operation called decannulation. An aortic cannulation site may not have any major sites of calcification.
A surgical method called the Seldinger technique is used to insert the cannula into the aorta. The surgeon will use a transesophageal echocardiography (TEE) to visualize the heart during the operation, enabling him to ensure the correct placement of the cannula during the procedure. It can also help calculate the perfusion rate of blood through the cannula.
At the beginning of the cannulation procedure, an opening is created into which an arterial entry catheter is inserted and directed towards the aortic arch. Then a surgical guide wire is inserted through the catheter and advanced to the aorta. The next step is the removal of the catheter.
Before the aortic cannula can be implanted, the aortic wall needs to be dilated to allow enough space for the cannulation. Three dilators are threaded onto the guide wire in succession to slowly widen the aorta and then removed. After the dilation is complete, the cannula is inserted and moved along the guide wire until the proximal descending aorta is reached. It is carefully positioned within the aortic lumen, with the tip of the aortic cannula placed into the descending aorta to reduce the possibility of an embolism.
The use of the aortic cannula may cause an increase in the velocity and turbulence of the flow of blood within the heart called a sandblast effect. Implanting the cannula with the tip in the descending aorta reduces the risk of sandblast cellular debris entering the carotid arteries and causing an embolism. If an embolism or blockage does occur, the damage from a clot in the descending aorta is less likely to cause a person’s death because the flow of blood to the brain is not significantly interrupted.