9.1 Possible Bypass Errors

We can all learn from our mistakes, particularly early in our training. By taking advantage of the opportunity to learn from our mistakes in the laboratory, we may be able to better avoid mistakes in our future clinical practice. One area of potential improvement is bypass errors.

Amin-Hanjani and Charbel ¹ classified bypass errors into two main types: poor indications for bypass and technical errors with the bypass. They also defined three subtypes of technical errors: donor vessel problems, anastomosis problems, and outflow vessel problems.

Numerous common mistakes can occur during bypass procedures. Most of these mistakes are technical in nature and might be avoided through laboratory practice, which helps you to anticipate and circumvent such mistakes. Although a detailed analysis of clinical management guidelines, such as appropriate selection of treatment strategies, is beyond the scope of this manual, certain aspects of these guidelines are important to consider in order to preclude common mistakes that can be potentially devastating to the patient.

9.2 Patient–Treatment Mismatch

Selecting bypass surgery for a patient who is not a suitable candidate for such treatment is the first mistake that should be avoided. Outcomes for extracranial-intracranial (EC-IC) bypasses from the Carotid Occlusion Surgery Study ² and the Japanese EC-IC Bypass Trial ³ showed the EC-IC bypass to be inferior to the best medical treatment for intracranial ischemic disease, thus greatly reducing indications for this procedure. Clearly, even a technically excellent bypass can fail to benefit patients who were not carefully selected.

Mistiming the bypass for the patient, such as by rushing to perform it, can also be problematic. Enough time should be allowed before surgery to control modifiable risk factors and to adjust the patient’s blood coagulation and platelet profile. Patients are usually given low-dose aspirin (81–100 mg/day) before a bypass and full-dose aspirin (325 mg/day) after the bypass. To overcome aspirin resistance, you should run the aspirin response test and adjust the aspirin dosage as needed. ⁴ A slight increase in bleeding during surgery as a result of aspirin use is preferable to a bypass clot, which can lead to a stroke.

9.3 Operating Room Environment and Operative Team

Extra supplies should be readily available during an anastomosis, as not having them on hand can present problems. All extra microneurosurgery tools that compose the bypass instrument set (microsurgical forceps, scissors, clips, sutures, and bipolar forceps) should be prepared for use before commencing the procedure. Bipolar coagulation power settings should be adjusted to a low setting after switching to the microsurgical bipolar forceps and before starting to coagulate branches on a small recipient cortical artery.

In addition to requiring the right equipment and backup instruments, the bypass procedure also requires a well-trained team and good teamwork. Despite the observation or participation of medical students, residents, and other trainees, the operating room is not the best place to teach bypass workflow, which instead should be practiced in the laboratory.

The operating room setup should offer the surgeon the optimal position and a comfortable posture, because poor posture can result in excessive tremor, which can undermine the skill set of any surgeon (Video 9.1).

9.4 Anesthesia-Related Issues

Errors in blood pressure management can have a huge effect on the degree of cerebral perfusion. Decreasing blood pressure during the operation to a level below what is typical for a particular patient may cause an infarction either near to or distant from the bypass location. The blood pressure levels of patients should be strictly maintained at their awake blood pressure levels while they are under general anesthesia during surgery.

It is important to be aware of several key areas where anesthesia-related mistakes can occur. Communication with the anesthesiologist is therefore key. First, hyperventilation should be avoided during bypass surgery. Second, alpha-adrenergic agonists are not recommended because of their vasoconstrictive effects. Third, if the brain is bulging, mannitol should be administered instead of hyperventilation, and the anesthesia can be deepened by increasing the propofol dose under tight blood pressure control. Fourth, during the temporary clipping and while anastomosis is being performed, barbiturates or propofol should be used routinely for burst suppression under electroencephalogram monitoring.

9.5 Donor Vessel

There are several mistakes that can occur during the dissection of a donor vessel. The first potential mistake involves confusing the superficial temporal artery with the superficial temporal vein. To avoid this error, keep in mind that the vein is usually straight, blue, and thin, whereas the artery is usually more curved, white, and pulsatile. A second possible mistake is to mishandle the donor vessel so as to damage it, to allow it to dry out, or to cause it to go into spasm. This mistake can be avoided by keeping the donor vessel or graft moist and warm, which will prevent it from spasming. The heat from newer microscopes can quickly dry out a donor vessel, so be sure to continuously irrigate the vessel. If the vessel does spasm, you can abort the spasming by rinsing it with the papaverine, nicardipine, milrinone, or a local anesthetic.

The occipital artery takes longer to dissect than the superficial temporal artery. Therefore, you should determine beforehand whether the occipital artery will be considered as a donor and should spend precious time on its dissection only after this decision is made.

Scalp necrosis and wound infection after decreasing the scalp blood supply by dissecting and redirecting the temporal or occipital artery is another concern. The reported incidence of wound infection or necrosis associated with bypass procedures varies between 0.7 and 21.4%, and this incidence is considered to be higher than that associated with craniotomies without skin vessel harvesting. ^{5 ,​ 6 ,​ 7 ,​ 8} The major factors predisposing to wound problems include harvesting of both branches of the superficial temporal artery, diabetes, and atherosclerosis obliterans. ^{7 ,​ 8} Other suggested factors include traumatic handling of the tissue edge, damage to the galeal vessels, and marginal location of the harvested vessel within the flap. ⁸ Although studies have not had enough statistical power to show the benefit of a particular incision shape, such as straight skin incision over flaps, in preventing wound complications, ⁷ thoughtful and careful skin incision planning is important to avoid such complications.

A pedunculated donor vessel should be large enough (> 1 mm in diameter) to provide adequate flow. In many cases where direct bypass was found to be technically impossible, it was due to an occluded, atretic, or small donor vessel. ⁵ In cases in which there is a small donor vessel, the bypass strategy can be adjusted in several ways: indirect bypass could be used, the donor vessel could be cut proximally (where it is larger) and an interposition graft could be used, or an alternative donor vessel, such as the maxillary artery, could be used. ^{5 ,​ 9}

9.6 Craniotomy

The most important mistake to avoid in performing a craniotomy is damaging the donor vessel with the drill. To avoid this mistake, place a Farabeuf retractor or Penfield dissector between the craniotome blade and the vessel to protect the soft tissues from being accidentally damaged by the drill. Do not place the donor vessel under a cottonoid patty or gauze, because this material could be caught by the drill. Avoid using a fishhook retractor or another compressive type of retractor on the donor vessel. You can also perform a larger dissection at the proximal and distal ends of the vessel from the galea, so that the vessel can be retracted farther away from the trajectory of the drill foot plate.

9.7 Choosing a Recipient Vessel

In selecting a recipient vessel for a bypass, you should not suture a smaller donor vessel to a larger recipient vessel—even when circulation is compromised—because it will not result in good blood flow. This mistake can be avoided by selecting a recipient vessel that is the same size as or smaller than the donor vessel. The pressure in large intracranial vessels is usually high, and a narrow donor vessel could result in slow flow at the anastomosis. Measuring the blood flow accurately is therefore important for assessing and matching blood flow demand and supply. ¹

9.8 Operative Field

To avoid problems in the operative field, it should be cleaned, cleaned, and cleaned again. Trying to work in a dirty or bloody operative field is a common mistake that can complicate the bypass. Do not hesitate to spend extra time to make the operative field perfectly clean before attempting a bypass, including making sure that the microsuction device is working well. Even when you do everything else perfectly, patient bleeding can severely obscure the view and hamper your every movement. It is often best to use an extra rubber dam around the vessel, so that, when you are sewing, the sutures fall on a clean surface rather than stick to brain, muscle, or clotted blood.