The arterial line transducer should be positioned at which reference axis?

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

Answer: (A)

Positioning the arterial line transducer at the phlebostatic axis ensures the reading reflects the true level of the right atrium, providing an accurate reference for arterial pressures. The phlebostatic axis is an imaginary point at the level of the right atrium, typically identified where a horizontal line through the RA level intersects a vertical line along the midaxillary line around the fourth intercostal space. Set the transducer at that level and zero to atmospheric pressure so measurements aren’t distorted by body height or position. If the transducer sits higher than this axis, pressures read lower than they truly are; if it sits lower, readings appear higher. The other landmarks listed aren’t used for this purpose and don’t provide an accurate reference for arterial pressure monitoring.