Hypovolemia
Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This could be caused to a loss of salt and water, or a reduction in blood volume. Hypovolemia refers to the loss of extracellular fluid and should not be confused with dehydration.
Hypovolemia can be caused by a number of factors, but they can be divided into two groups: those that are linked to renal function and those that aren’t. As the amount of fluid lost rises, the signs and symptoms of hypovolemia worsen. Headache, weariness, weakness, dizziness, or thirst may occur immediately or shortly after modest fluid loss. Hypovolemia that goes untreated, or high and rapid volume loss, can lead to hypovolemic shock. Increased heart rate, low blood pressure, pale or chilly skin, and altered mental status are all signs and symptoms of hypovolemic shock. When these symptoms appear, prompt action should be taken to recover the volume that has been lost.
Fig.1. Hypovolemic Shock (Histopathology. guru)
The body’s baroreceptors detect a decrease in circulating fluid and send signals to the brain, causing the sympathetic response to increase. This sympathetic response causes adrenaline and norepinephrine to be released, causing peripheral vasoconstriction to save circulating fluids for essential organs. Cold extremities, higher heart rate, and increased cardiac output are all symptoms of peripheral vasoconstriction. The kidneys will eventually receive less blood, resulting in decreased urine output.
Reference:
https://www.healthgrades.com/right-care/symptoms-and-conditions/hypovolemia