Where should the arterial line transducer be positioned to ensure accurate pressure readings?

• A. The phlebostatic axis
• B. The foramen of Monroe
• C. The foramen of Todd
• D. The subscapular axis

Answer: (A)

Accurate arterial pressure readings depend on the transducer being at the same vertical level as the right atrium, because hydrostatic pressure changes with height. The phlebostatic axis is the standard landmark that approximates the right atrial level: at the fourth intercostal space, midaxillary line. Position the transducer at that level and zero it there, and adjust if the patient moves. If the transducer is above this level, readings will read lower than actual; if below, readings will read higher. The other options are unrelated anatomical landmarks for this purpose.