What does flat neck veins in the supine position a sign of?

In the supine position, flat neck veins are often a sign of low central venous pressure (CVP), which can indicate several possible conditions, including dehydration, hypovolemia (decreased blood volume), or even shock.

It's important to note that flat neck veins alone are not enough to diagnose a medical condition, as other factors and clinical findings should also be considered. When flat neck veins are observed, it's generally recommended to assess overall fluid status, vital signs, and any underlying health conditions to determine the cause.