Prediction of a small internal jugular vein by external jugular vein diameter.

The relationship between internal jugular vein diameter as measured with an ultrasound imaging machine (SiteRite, Dymax) and external jugular vein diameter was studied in 50 anaesthetised patients undergoing elective cardiac surgery. There was an inverse correlation between external jugular vein diameter and internal jugular vein diameter (r = -0.47, p < 0.001). All patients with an external jugular vein diameter of 7 mm or greater had an internal jugular vein diameter of less than 15 mm. No patient with an external jugular vein diameter of less than 7 mm had an internal jugular vein diameter of less than 20 mm. No other patient dimension (height, weight, body mass index, neck circumference) predicted internal jugular vein size. These results suggest that a large external jugular vein (i.e. 7 mm or greater in external diameter) may be associated with a small internal jugular vein. A size 5.0-mm internal diameter tracheal tube may be used to provide a rapid assessment of external jugular vein diameter.