For doing CABG, Allen test is done to test which vessel:

Ans is 'b' i.e. Radial aery Allen test is done to test the patency of the Radial aery and the Ulnar aery and also the Collateral circulation of the hand through superficial palmar arch. Radial aery is being used in CABG. Allen test methodology: The radial and ulnar aeries at the wrist are simultaneously compressed by the examiner while the patient clenches his fist for several seconds before relaxing; the hand should now be pale. The radial aery is then released; if the hand flushes it means that the radial blood supply is intact. The test is repeated for the ulnar aery. Allen test is being used: Before CABG, before cannulation of either ulnar or radial aery, and also the check the patency of vessels after trauma.