Before invasive arterial blood pressure measurement, the transducer must be levelled at the phlebostatic axis. The phlebostatic axis corresponds to:

• A Mid-axillary line at the level of the 2nd intercostal space
• B Mid-clavicular line at the level of the 3rd intercostal space
• C Anterior axillary line at the level of the 5th intercostal space
• D Mid-axillary line at the level of the 4th intercostal space ✓

Explanation

The phlebostatic axis is defined as the intersection of the mid-axillary line with the 4th intercostal space, approximating the level of the right atrium. Levelling the transducer here gives true atrial-referenced pressures. Positioning the transducer above this point falsely lowers the displayed pressure and below it falsely raises it. The other choices describe incorrect surface landmarks that would introduce systematic error.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.