The nurse is caring for a patient with a radial arterial line. Prior to obtaining a reading, which action is most appropriate?

Choice D rationale To ensure the accuracy of the hemodynamic data from a radial arterial line, the nurse must reference and zero the system. Referencing involves positioning the transducer at the phlebostatic axis, which is the level of the atria at the fourth intercostal space, mid-axillary line. Zeroing the line negates the effects of atmospheric pressure on the monitoring system. This ensures that the pressure displayed on the monitor represents only the patient's internal physiological blood pressure, preventing false high or low readings. Choice A rationale Flushing the arterial line is done to maintain patency of the catheter and clear the tubing of blood after sampling. However, a continuous flush system usually handles this at a rate of 3 mL per hour. Manually flushing for 10 seconds is not a standard requirement prior to taking a reading and could potentially cause a fluid bolus or damage the artery if done with excessive force. It does not contribute to the calibration or accuracy of the electronic pressure transducer. Choice B rationale While positioning is important, the correct landmark for hemodynamic monitoring is the phlebostatic axis, not the sternal angle. The sternal angle, or Angle of Louis, is used as a landmark for identifying the second rib and auscultating heart sounds, but it does not correspond to the level of the heart's chambers for pressure monitoring. Using the incorrect reference point will lead to hydrostatic pressure errors, where every inch the transducer is below the heart adds approximately 2 mmHg to the reading. Choice C rationale The Allen test is a diagnostic physical exam used to assess the patency of the ulnar artery and the adequacy of collateral circulation to the hand. This must be performed before the arterial line is even inserted into the radial artery to ensure that the hand will remain perfused if the radial artery becomes occluded. Once the line is already in place, performing an Allen test is not a prerequisite for obtaining a routine pressure reading from the monitor.