often used for reconstruction of larger defects in the head and neck, so it is very common. The examination can be performed preoperatively and intraoperatively. With this test, which is called the Allen test, the existence and patency of the anastomosis between the supercial palmar arterial arch and the profound palmar arterial arch in the ipsilateral hand is assessed (Fig.10.26; Video 10.8). The existence of an anastomosis between the radial and ulnar artery is required before the ap (which is usually pedicled at the radial artery) can be harvested. The profound palmar arte­rial arch is a prolongation of the radial artery and courses beneath the long exor strings. It is identied on the ultra­sound screen, and then the radial artery is compressed under continuous observation of the blood ow in the pal­mar arch. The test is positive if there is signicant blood ow during compression. It is advantageous to perform pulse oximetry with a sensor at the index nger during the test, because this provides additional information about the pulsation, oxygen saturation, and perfusion of the nail bed during compression of the radial artery. It is very likely that the blood supply of the second and third nger is sufcient and the anastomosis is intact when no signicant decrease of the pulsation curve occurs. The ap can then be harvested.