Where is the phlebostatic axis located for placing the monitoring transducer when measuring continuous arterial blood pressure?

• A. Level of the left atrium at the 5th intercostal space, midaxillary line
• B. Level of the right atrium at the 4th intercostal space, midaxillary line
• C. Level of the right ventricle at the 3rd intercostal space
• D. Level of the aorta at the second intercostal space

Answer: (B)

Measuring continuous arterial blood pressure with an invasive line relies on aligning the transducer with the heart so hydrostatic effects don’t skew the reading. This reference point is the phlebostatic axis, which corresponds to the level of the right atrium. The most practical landmark is the level of the right atrium at the fourth intercostal space along the midaxillary line.

Positioning the transducer at this level ensures the arterial pressure reading reflects the true central pressure. If the transducer is placed higher than this level, the reading will be falsely low; if placed lower, it will be falsely high. So the best placement for accurate, continuous BP monitoring is at the right atrial level, typically the fourth intercostal space, midaxillary line.