3 SPECIAL CONSIDERATIONS FOR DEEP VEINS Although a deep arm vein is a challenge to cannulate, sometimes you have no choice because it's all that's E available. Cannulating an arm vein also has the virtue of freeing the patient's hand so he can move around easily. When you stretch a deep arm vein to immobilize it, it may seem to disappear because stretching may flatten it slightly. So you must be able to "see" it by palpating it with your fingers. To cannulate a vein that's palpable but hard to see, follow these steps: