Lasering of AV anastomoses

Lasering of AV anastomoses

AV anastomoses can be interrupted by lasering the artery, the vein, or both. In theory, lasering of the vein still allows for blood to be lost into the cotyledon, and may be responsible for development of intraoperative fetal anemia. Therefore, when possible, we prefer to laser the artery first. Most placentas will have both AVDRs and AVRDs. 

Whenever possible, we prefer to laser AVDRs first followed by AVRDs, as this may allow for an intraoperative transfusion of the donor twin (sequential technique, or SQLPCV). Lasering of superficial anastomoses Lasering of AA and VV anastomoses requires that the surgeon decide where, along the path of the vessel, the interruption needs to be made (Figure 9.11a and b). 

This is based on the principle of maximum preservation of placental territory for both twins, as determined by the location of the draining or feeding branches (AA and VV, respectively). Figure 9.11a shows an AA anastomosis with an arterial branch to the donor twin. Effective interruption of the vascular communication could be achieved in different ways: a) Lasering at sites 1 and 2. This eliminates all blood exchange at this level. However, it deprives the donor twin from a cotyledon. b) Lasering at site 3. This interrupts the AA anastomosis and allows the donor twin perfuse the placenta at site 2. Figure 9.11b also shows a complex AA anastomosis. 

Interruption of the blood exchange through this vessel could be accomplished by a) Lasering at site 1 and 2. This choice significantly hinders the ability of twin 1 to perfuse the cotyledon (C). b) Lasering at site 3, while technically more challenging, (it is very close to the branching of the AA and to the underlying vein of twin 2) preserves the cotyledon (C) for twin 1. Separation would be completed by lasering at sites 4 and 5. 

Occasionally, interruption of the AA anastomosis cannot be performed where it would anatomically make most sense. In these cases, it is important to follow the vessel along its length to assure that a new functional AV anastomosis is not generated. As an example in Figures 9.11a and 9.11b, lasering only at site 1 creates an AV anastomosis (at site 2 and C, respectively). Step 3: review The last step in the lasering process involves careful review of all lasered vessels. This step assures that the vessels are completely obliterated and have not simply undergone a spastic closure. 

This step may also be used to identify and laser any other vessel that may have been overlooked in the two prior steps. The diagnostic endoscope is again used, as it provides maximum diagnostic power. If a patent anastomosis is identified, relasering with the operating endoscope should be done with care not to cause bleeding from the coagulated tissue. This is best accomplished by not targeting proximal areas of the lasered vessel. Once all lasered communications have been reviewed and relasered if necessary, the operating scope is removed and the endoscopic aspect of the surgery is considered complete.