Cross Clamp

Time Pressure

The interruption of arterial flow with temporary clips and the dangers of cerebral ischemia suffuse bypass surgery with tension and stress. We may ask our anesthesiologists to titrate barbiturates to suppress EEG activity, or cool the patient to lower the cerebral metabolic rate, or administer vasoconstrictors to boost the blood pressure, but these interventions only increase ischemic tolerances and do not provide ironclad brain protection. Only one thing ameliorates the dangers of temporary flow arrest, and that is surgeon speed. Therefore, clamp time means that the ischemia clock is ticking and the pressure to perform is on.

Surgeon Speed

Clamp time is simply the duration of flow arrest needed to perform a bypass, but, in reality, clamp time is more about performance than ischemia risk. Differences in neurologic outcomes between a bypass with 30 minutes of clamp time and one with 20 minutes of clamp time are immeasurable, as long as the anastomotic site has been selected carefully on distal recipients without critical perforating arteries and with some collateral circulation. However, clamp time is interpreted as a measure of the bypass surgeon’s skill, dexterity, composure, and prowess, as well as speed. Clamp times can become a competency threshold for surgeons in training, or a contest between more experienced surgeons. Clamp times can become a bragging right for fast surgeons, or an embarrassment for slow ones.

Speed should not supersede meticulous technique and bypass quality; a speedy surgeon with poor technique and suturing errors will produce a sloppy anastomosis. However, clamp times are a metric of efficiency that we can use to improve our technique. The ambitious bypass surgeon should strive for a pace of one stitch per minute, or to complete a typical STA-MCA anastomosis with approximately 20 stitches or bites in 20 minutes. Time targets force the surgeon to eliminate wasted movements, find shortcuts, search for new tricks, and practice more. Shaving time requires staying in the zone at high magnification, preloading the donor artery with the first and second sutures, minimizing instrument transfers, finding a suturing rhythm quickly, tightening the spiral of suture with fewer touches or on the fly, and tying knots with shorter tails and tighter loops. Shaving time requires eliminating mishaps, like an oozing scalp, a malfunctioning suction, a dropped needle, or a broken suture. By paying attention to clamp times and pace, internal pressure to perform faster will make us better bypass surgeons.

Shortcuts

Some bypass steps can be performed before applying temporary clips to shorten clamp time. For example, sutures can be placed in the donor scalp artery or interposition graft before, rather than after, temporary clipping and arteriotomizing the recipient artery. With deep bypasses, “preloading” the donor with the first bite of these stay sutures is performed comfortably outside the zone where it is much easier and brought in later (Fig. 7.1A). Suture needles passed through the donor wall, one at the heel and another at the toe, are locked securely in position and do not back out because the needle’s diameter is wider than the suture’s diameter. The suture length can also be trimmed to size in advance. These shortcuts performed before cross clamping expedite the placement of stay sutures.

Marking the recipient walls with violet ink is essential to visualize these thin, translucent layers during the anastomosis (Fig. 7.1B). Another timesaving step is the inking of the arteriotomy line before temporary clipping. Although applied temporary clips define the course of this line and it is normally drawn during the clamp time, drawing it beforehand eliminates one step, two instrument exchanges, and some precious time.

Fig. 7.1 (A) Sutures can be placed in the donor scalp artery or interposition graft before, rather than after, temporary clipping and arteriotomizing the recipient artery. “Preloading” the donor with the first bite of these stay sutures, before cross clamping, expedites the placement of stay sutures. (B) Marking the recipient walls with violet ink helps visualize these thin, translucent layers during the anastomosis and is done before temporary clipping to eliminate one step and two instrument exchanges.

Temporary Clipping

Temporary clipping is simply the application of temporary clips to the recipient artery distally and proximally, and also to an intracranial donor artery with an IC-IC bypass like an in-situ bypass or a reimplantation. Small temporary clips (usually 3-mm straight clips) are applied horizontally or parallel to the stage to lie flat in the field (Fig. 7.2). Sutures will snag on shanks of larger clips and those applied vertically, and clips standing perpendicular to the stage narrow the working space. Temporary clips must cross the arterial diameter completely to prevent back-bleeding or leaks, and should exclude small branching twigs, which (surprisingly) also back-bleed into the anastomotic site. Larger branches that cannot be excluded by the temporary clips should be occluded with another temporary clip.

There is not much more to temporary clipping than that. However, although any artery can be temporarily occluded, only some are safe. Safe sites for recipient anastomosis do not have perforating arteries to deep central structures, such as the thalamus, hypothalamus, basal ganglia, and brainstem (Fig. 7.3). Perforators are end arteries that, unlike cortical arteries, lack collateral connections that might increase their tolerance to clamp time. Even a few minutes of perforator occlusion can alter intraoperative SSEP and MEP signals and cause significant morbidity. The M2 MCA segment and beyond, A2 ACA segment and beyond, and P2 PCA and beyond are safe, but more proximal sites are not. The M1 MCA segment gives rise to lateral lenticulostriate arteries that supply the basal ganglia. The distal A1 ACA, ACoA, and proximal A2 ACA give rise to medial lenticulostriate arteries and the recurrent artery of Heubner that supply the hypothalamus and caudate nucleus. The P1 PCA gives rise to posterior thalamoperforators that supply the thalamus. In addition, AChA and branches of SHA supply the internal capsule and optic apparatus, making the distal ICA less safe as an anastomotic site. The basilar artery and vertebrobasilar junction are dangerous sites for temporary occlusion because of their direct brainstem perforators, whereas the proximal V4 segment of the VA has few perforators and is safe.