[healthresearch (OP)]

How you can tell (from symptoms or signs) that someone has either hypovolemia or he or she has already gone into a hypovolemic shock?

I understand the difference between compensated and decompensated shock - in the later, the blood pressure falls.

But what is the deciding symptom/sign between hypovolemia and compensated shock? For example, a severely dehydrated person probably has hypovolemia, but not every severely dehydrated person is in the hypovolemic shock. So, is it tachycardia, pale or sweaty skin or capillary refill time that can tell the difference? I'm not asking about precise moment when hypovolemia becomes a shock, but about the judging symptom/sign

[cheryl j]

Hypovolemia just means low volume or low blood pressure from low volume. And as you mentioned, the body will compensate by constricting blood vessels and raising heart rate, and if the volume is low enough, shunting blood to vital areas (the brain, the heart) from less vital areas (skin, muscles, digestive tract, even the kidneys.)  I would guess symptoms and signs progress in severity, if blood pressure keeps dropping or remains critically low.

Shock occurs when blood pressure is low to the point where blood does not perfuse the organs and stays low long enough that cells start to malfunction and die.

I don't think there is a single test or sign that indicates at what point progressive shock has become irreversible, and it may depend on the initial health status of the patient, the health of his kidneys, etc.  In addition, some forms of shock have a better prognosis than others. Hypovolemic shock, if you can replace the fluids and find the leak and plug it, has much better odds than shock resulting from a bacterial infection or heart failure.

An interesting thing about shock, though, it's one medical emergency in which being old may be better. In a lecture on the cardiovascular system, I heard a surgeon say old people just look and feel bad when they are getting shocky, and have symptoms, because their bodies cannot compensate as well. It's obvious to the doctor right away that something is wrong. A healthy 22 year old male whose been in a car accident will be sitting up, talking, his color is good, his heart rate might be a little higher, but nothing alarming, and then his pressure crashes right through the floor, and even if you get him into surgery it might be too late. Therefore, according to this doctor, there would be know way to tell how much trouble someone is in just by their initial appearance.

[chris]

As quite rightly put above, hypovolaemia refers merely to a lower than normal circulating volume but does not take into account the physiological impact of this. Hypovolaemic shock is the clinical consequence of hypovolaemia.