How far is the sternal angle from the mid-right atrium?

Background: The central venous pressure (CVP) is commonly estimated at the bedside by measuring the height of the jugular venous pressure (JVP) relative to the sternal angle. Determining the CVP from this measure requires that the distance from the sternal angle to the level of the mid-right atrium be known. Classical clinical teaching quotes this distance as 5 cm, invariable between patients, and invariable with changes in the elevation of the patient's head. The validity of these JVP characteristics has been questioned.

Objectives: To measure the distance from the sternal angle to the level of the mid-right atrium (SA-RA) and determine if the SA-RA distance varies with patient position.

Methods: Cross-sectional study conducted at a single-center teaching hospital on ambulatory patients undergoing computed tomography of the chest.

Results: One hundred sixty patients were included. The median SA-RA distance with the patient lying supine was 5.4 cm (interquartile range, 4.7 to 6.1). Using geometric calculations to estimate the SA-RA distance when the patient's torso was elevated above the supine position, the median SA-RA distance was calculated to be 8 cm, 9.7 cm, and 9.8 cm at 30, 45, and 60 degrees elevation respectively. The SA-RA distance varied extensively between patients and was independently associated with smoking, age, and antero-posterior chest diameter.

Conclusions: The distance from the sternal angle to the level of the mid-right atrium varies considerably between individuals and with patient position. When using the JVP to calculate the CVP, physicians need to consider specific patient factors and the patient's position.