Studying to be a nurse? Then here is a nursing how-to video that teaches you how to do a central venous access. Every nurse should know the basics of this technique, follow along and see how easy it is to draw blood from a central line. These medical tips are sure to help you pass your nursing exam with flying colors. Remember when performing a central venous access, all caps must be replaced each time blood is drawn. You must swab the port for 1 min prior to withdrawal. Follow your hospital's protocol.