Relationship between Trendelenburg tilt and internal jugular vein diameter.

Objectives: To evaluate the relationship between Trendelenburg tilt and internal jugular vein (IJV) diameter, and to examine any cumulative effects of tilt on the IJV diameter. Methods: Using a tilt table, healthy volunteers were randomised to Trendelenburg tilts of 10°, 15°, 20°, 25°, and 30°. Ultrasound was used to measure and record the lateral diameter of the right IJV at the level of the cricoid cartilage. Following each reading the table was returned to the supine position. Balanced randomisation was used to assess cumulative tilt effects. Results: A total of 20 healthy volunteers were recruited (10 men, 10 women). Mean supine IJV diameter was 13.5 mm (95% CI 12.8 to 14.1) and was significantly greater at 10° (15.5 mm, 95% CI 14.9 to 16.1). There was no significant difference between 10° and greater angles of tilt. The effect of the previous angle of tilt did not prove to be statistically significant. Conclusion: Increasing the degree of Trendelenburg tilt increases the lateral diameter of the IJV. Even a 10° tilt is effective. The cumulative effect of tilt (that is, the effect of the previous angle) is not significant. Ultrasound guided cannulation is ideal, but in its absence Trendelenburg tilt will increase IJV diameter and improve the chance of successful cannulation. While 25° achieved optimum distension, this may not be practical and may be detrimental (for example, risk of raised intracranial pressure).