How do I locate the mid-level sternum for accurate blood pressure measurement?

Locating the Mid-Level Sternum for Blood Pressure Measurement

For accurate blood pressure measurement, position the patient's arm so the blood pressure cuff is supported at the level of the mid-sternum, which approximates the right atrial level and prevents spuriously elevated readings. 1

Anatomical Location of Mid-Sternum

The mid-sternum corresponds to the middle portion of the sternal body, which can be identified using the following landmarks:

• The mid-sternum is located approximately at the level of the 4th intercostal space, which lies between the manubrium (upper sternum) and the xiphoid process (lower sternum) 2, 3

• This level typically aligns with the 5th intercostal space at the mid-clavicular line, where the apical impulse of the heart is normally located 4

• The sternum consists of three parts: the manubrium (upper), the body (middle), and the xiphoid process (lower), with the mid-level falling in the central portion of the sternal body 2

Clinical Significance for Blood Pressure Measurement

Arm positioning at the mid-sternal level is critical because deviations result in significant measurement errors:

• When the arm is positioned below the mid-sternal (right atrial) level, blood pressure readings are spuriously elevated by approximately 10 mm Hg for both systolic and diastolic measurements 1

• Placing the patient's arm on a chair armrest instead of at the reference right atrial level results in falsely elevated readings of 9.7 ± 9.4 mm Hg (systolic) and 10.8 ± 5.8 mm Hg (diastolic) 1

• The mid-sternum serves as the practical approximation of the right atrial level, which is the reference point for accurate blood pressure measurement 1

Practical Technique for Locating Mid-Sternum

To identify the mid-sternal level for blood pressure measurement:

1. Have the patient sit upright with back supported 5, 1

2. Locate the suprasternal notch (the depression at the top of the sternum between the clavicles) 6

3. Palpate downward along the sternum to identify the sternal body (the flat central portion below the manubrium) 2

4. The mid-point of the sternal body represents the mid-sternal level, typically at the 4th intercostal space 2, 3

5. Position the patient's arm so the blood pressure cuff is supported at this level, with the arm flexed at the elbow and supported horizontally 1

Common Pitfalls to Avoid

• Never allow the arm to rest on chair armrests during measurement, as this positions the arm below the right atrial level and falsely elevates readings 1

• Ensure the arm is supported at the mid-sternal level, not simply "at heart level", as vague positioning leads to inconsistent measurements 1

• Body position matters: Blood pressure is highest in the supine position and lowest in the standing position, so maintain consistent sitting position with proper arm support 5

• The mid-sternum should not be confused with the lower sternum (used for chest compressions in CPR, which targets the lower half of the sternum) 6