The aim of this cross-sectional, descriptive analysis is to compare 3 different ultrasound-based protocols to measure the internal jugular vein pressure (uJVP) in healthy individuals.

Proper hydration is crucial for health, and imbalances-like dehydration or fluid overload-can cause serious health problems including increased morbidity, hospitalization rate, and even mortality. Currently, assessing hydration is challenging, and there is no standardized method in clinical use.

Ultrasound (US) of the internal jugular vein (IJV) and ultrasound-guided estimation of jugular venous pressure (uJVP) is a promising, non-invasive method to assess the hydration status. Several measure methods have been described, however, there is no univocal protocol for US IJV-assessment.

In this study, three existing protocols including 4 measurements are compared to measure uJVP, which reflects the body's fluid balance. The study aims to find out which method is most accurate, easy to perform, and consistent when done by the same or different medical professionals. They will also look at how long each method takes and how acceptable these tests are to participants.

The study is performed in healthy individuals and all 4 measurements are applied cross-sectional during one visit. The whole ultrasound assessment will have a duration of maximum 45 minutes.

For all protocols, uJVP will be calculated by measuring with a ruler the vertical distance between IJV-height and sternal angle (cm) and then adding 5cm to this value.

Protocol 1: IJV tapering portion is portrayed in a transverse view. The IJV height is marked and measured as soon as IJV is smaller than Common Carotid Artery (CCA) throughout the whole respiratory cycle.

Protocol 2: IJV tapering portion is portrayed in a transverse view. The IJV height is marked and measured as soon as IJV is completely collapsed throughout the whole respiratory cycle.

Protocol 3: IJV tapering portion is portrayed in a longitudinal view. The IJV height at the end of expiration is marked and measured at the following two positions:

1. Measurement 1: at the very end of the tapering portion (collapsing point / top of pulsation).
2. Measurement 2: at the beginning of the tapering portion (taper point).

Inclusion Criteria:

1. Healthy adults aged 18 years or older, 15 women and 15 men.

Exclusion Criteria:

1. Major cardiovascular event in the last 3 months
2. Pregnant or lactating women
3. Heart failure of any grade
4. Kidney failure
5. Thrombosis V. jugularis interna
6. Atrial Fibrillation
7. Valves impairment
8. Uncontrolled Diabetes mellitus
9. Uncontrolled Diabetes insipidus (AVP resistance or deficiency)
10. Respiratory Distress of any grade
11. Signs/Symptoms of volume loss (diarrhea, vomiting, bleeding) in the past 3 days
12. Medication: Angiotensin-converting enzyme inhibitors, Angiotensin receptor blockers, any diuretic therapy
13. Inability to follow procedures or insufficient knowledge of project language.
14. Inability to give consent
15. Abnormal vital signs: tachycardia > 90/min, systolic blood pressure < 90 mmHg

Recruitment will take place at university hospital of Basel through flyers and word of mouth addressed to healthy visitors and employees.