Table 1 Protocol for measurement of internal jugular venous (IJV) collapsibility index

1. Position patient at 30° head elevation, as standard of care for mechanically ventilated patients, ensuring overall comfort

2. Rotate the head slightly <30° to expose right or left IJV

3. Place transducer transversely across the patient neck, the area lateral to the level of the cricoid cartilage

4. IJV vessel identification was done by identifying 2 vessels lateral to the trachea and IJV is identified by compressibility, color flow or pulse wave Doppler

5. Applying minimum pressure, enough to obtain adequate ultrasound image of the right/left IJV

6. Rotate the transducer clockwise or counter-clockwise to obtain the most circular cross-sectional image of the IJV

7. Store the image of the patient’s complete respiratory cycle

8. Measure the AP diameter during maximum and minimum distention during a respiratory cycle. On occasion, M mode was used to determine max and min AP diameter

9. Calculate IJV collapsibility index = [(Max diameter − Min diameter)/(Max diameter)] × 100%