Vascular bypass

A vascular bypass (or vascular graft) is a surgical procedure performed to redirect blood flow in a region of the body. It is commonly performed due to inadequate blood flow (ischemia) and as a part of organ transplantation. In general, someone's own vein is the preferred graft material (or conduit) for a vascular bypass, but other materials such as ePTFE, dacron or a different person's vein (allograft) are also commonly used. Arteries can also be redirected and serve as vascular grafts. A surgeon sews the graft to the target vessel by hand using surgical suture, creating a surgical anastomosis.

Common bypass sites include the heart (Coronary artery bypass surgery), and the lower extremities, where vascular bypass is used to treat peripheral vascular disease.

Medical uses

Cardiac bypass

Cardiac bypass is performed when the arteries that bring blood to the heart muscle (coronary arteries) become clogged by plaque.^[1] Such condition may lead to chest pain or heart attack.

Lower extremity bypass

In the lower extremity, bypass grafting is used to treat peripheral vascular disease, acute limb ischemia, aneurysms and trauma. While there are many anatomical arrangements for vascular bypass grafts in the lower extremities depending on the location of the disease, the principle of use is the same: To restore blood flow from an area of normal blood flow to an area without normal flow. For example, a femoral-popliteal bypass ("Fem-Pop") might be used if the femoral artery was occluded. Other anatomic descriptions of lower extremity bypasses include:

• "Fem-Fem" - Femoral to femoral bypass, e.g. from right to left. Used when there is no inflow to one femoral artery (i.e., the iliac artery on the receiving side is diseased) but there is aortic flow.
• "Aorto-Bi-Fem" - Aortic to bilateral femoral arteries. Used when there is disease at the aortic bifurcation or in both iliac arteries.
• "Fem-Tib" - Femoral to one of the three tibial arteries (Anterior, Posterior or Peroneal). Used for disease of the femoral and tibial arteries, this procedures is used most frequently in people with diabetes, as diabetes tends to create disease in the tibial arteries rather than the more proximal arteries.^[2]
• a "DP" bypass refers to any vascular bypass where the distal target is the Dorsalis pedis artery on the dorsum of the foot. It is used in similar situations to those described for the Fem-Tib bypass.

Hemodialysis access

A vascular bypass is often created to serve as an access point to the circulatory system for hemodialysis. Such a bypass is referred to as an arteriovenous fistula if it directly connects a vein to an artery without using synthetic material.

Cerebral artery bypass

In the skull, when blood flow is blocked or a damaged cerebral artery prevents adequate bloodflow to the brain, a cerebral artery bypass may be performed to improve or restore blood flow to an oxygen-deprived (ischemic) area of the brain.^[3]

When several arteries are blocked and thus several bypasses are needed the procedure is called multiple bypass. The number of bypasses needed does not increase the surgery's risks which depend on the patient's overall health.

Other uses

• Human umbilical vein graft, the use of the umbilical vein as a vascular conduit

Contraindications

The lack of an adequate venous conduit is a relative contraindication to bypass surgery, as depending on the location of the bypass, alternatives may be used. Medical comorbidities such as ischemic heart disease or Chronic obstructive pulmonary disease that increase the risk of surgery are relative contraindications.

If a patient is deemed to be too high-risk to undergo a bypass, he or she may be a candidate for angioplasty of the relevant vessel.

Techniques

Standard Techniques

Dogma in vascular bypass technique says to obtain proximal and distal control. This means that in a vessel with flow through it, a surgeon must be have exposure of the furthest and nearest extents of the vessels on which he or she means to create a bypass, such that when the vessel is opened, blood loss is minimized. After the necessary exposure, some variety of clamp is usually used on both the proximal and distal end of the segment. Exceptions exist where there is no blood flow through the target vessel at the area of proposed entry, as is the case with an intervening occlusion.

If the end organ perfused by an artery is sensitive to even temporary occlusion of blood flow, such as in the brain, various measures are taken.

ELANA

In Neurosurgery, excimer laser assisted nonocclusive anastomosis (ELANA) is a technique use to create a bypass without interrupting blood supply in the recipient blood vessels. This is preferred manipulation is minimized, reducing risk of stroke or a rupture of an aneurysm.

The ELANA technique is a subtle modification of existing methods to establish a connection between blood vessels (anastomosis) to create a bypass in or to the brain. The only real differences involve how the recipient artery is opened. In conventional techniques the recipient artery is temporarily interrupted (occluded with clips) and opened using microscissors or scalpel while in the ELANA technique blood flow is not interrupted and the opening (arteriotomy) is created with radiation from a 308 nm Excimer Laser delivered through a catheter inserted in the vessel that will become the bypass while blood continues to flow through the artery that receives the bypass. This subtle difference, however, is very important for the safety of the procedure and eliminates the risk of ischemia to the regions supplied by the artery receiving the bypass. The technique is most valuable in neurosurgery, as brain cells are particularly sensitive to the lack of blood supply (ischemia) that would be caused by traditional methods of bypass creation. The bypasses created with the help of the ELANA can be to one of the major arteries in the brain (extracranial to intracranial EC-IC bypass) or between two arteries in the brain (intracranial to intracranial).

Surgeons are creating such a bypass mainly as a step in the treatment of patients with unclippable and uncoilable giant aneurysms or tumors at the skull base or to treat patients at risk of stroke who can not be treated otherwise.

The ELANA technique has been extensively described in medical literature. It was developed in 1993 by Cornelis A.F. Tulleken,^[4] professor of neurosurgery at the University Medical Center Utrecht, the Netherlands, to find a way to treat patients with a bypass to a major cerebral artery without the risk of cerebral ischemia during the procedure. The use of this technique has been reported upon in the media e.g., in The New York Times in December 2006.^[5]

Risks and complications

A number of complications can arise after vascular bypass.

Risks related to bypass:

• Acute Graft Occlusion is the occlusion (blockage) of a vascular bypass graft shortly after the bypass is performed. Its causes, which are distinct from those of chronic graft occlusion, include technical failure (e.g. anastomotic stricture, incomplete valve lysis in non-reversed vein) and thrombosis. It is rare, but almost always requires reoperation.

Risks related to surgery:

• Hemorrhage (Bleeding)
• Infection
• Embolism

Recovery

Immediately following vascular bypass surgery, patients recover first in the intensive care unit or Coronary care unit for one to two days. Provided that patients recover normally and without complications, then are then allowed to move to a less intensively monitored unit such as a step-down unit or a ward bed. Monitoring immediately after all types of bypass surgery focuses on signs and symptoms of bleeding. If bleeding is detected, treatment can range from transfusion to reoperation. Later on in the hospital course, common complications include wound infections, pneumonia, urinary tract infection and acute graft occlusion.

At discharge, patients are prescribed oral painkillers, and should be prescribed a statin and an anti-platelet medication if their bypass was performed for atherosclerosis (PVD or CAD as tolerated. Some patients start feeling normal after one month, while others may still experience problems up to six months after the procedure.^[6]

During the first twelve weeks after the procedure patients are advised to avoid heavy lifting, hose work as well as strenuous recreation like golf, tennis, or swimming while surgical wounds (particularly the sternum after coronary bypass) heal.^[7]

Part of the recovery after any bypass surgery includes regular visits to a physician to monitor the patient's recovery. Normally a follow up visit with a surgeon is scheduled for two to four weeks after surgery. The frequency of these visits gradually lessens as the patient's health improves.

For vascular bypass operations performed for atherosclerosis (PVD and CAS), the operation does not cure the underlying disease. Instead, lifestyle changes that include quitting smoking, making diet changes, getting regular exercise, and lowering stress improve the underlying condition.^[8]

References