Which of the following statements is true concerning the insertion of a radial arterial line?

1. The catheter tip must face upstream.
2. The catheter tip must face downstream.
3. The transducer must be higher than the catheter tip.
4. The transducer must be level with the catheter tip.
a. 1 and 3 only
b. 1 and 4 only
c. 2 and 3 only
d. 2 and 4 only

ANS: B
When a catheter faces the source of blood flow it is "looking" upstream. An arterial line placed in the radial artery needs to face the blood flow to accurately measure pressures that are a result of left heart work. If the catheter faces downstream it reads the pressures ahead of it. To accurately measure pressure, the transducer needs to be at the same height or level with the tip of the cathe-ter. If the transducer is higher than the catheter tip the fluid will be flowing away from the transducer and will produce a reading lower than the actual pressure.