Intravascular volume status

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In medicine, intravascular volume status refers to the volume of blood in a patient's circulatory system, and is essentially the blood plasma component of the overall volume status of the body, which otherwise includes both intracellular fluid and extracellular fluid. Still, the intravascular component is usually of primary interest, and volume status is sometimes used synonymously with intravascular volume status.

It is related to the patient's state of hydration, but is not identical to it. For instance, intravascular volume depletion can exist in an adequately hydrated person if there is loss of water into interstitial tissue (e.g. due to hyponatremia or liver failure).

Clinical assessment[edit]

Intravascular volume depletion[edit]

Volume contraction of intravascular fluid (blood plasma) is termed hypovolemia,[1][2] and its signs include, in order of severity:

  • a fast pulse
  • infrequent and low volume urination
  • dry mucous membranes (e.g. a dry tongue)
  • poor capillary refill (e.g. when the patient's fingertip is pressed, the skin turns white, but upon release, the skin does not return to pink as fast as it should - usually >2 seconds)
  • decreased skin turgor (e.g. the skin remains "tented" when it is pinched)
  • a weak pulse
  • orthostatic hypotension (dizziness upon standing up from a seated or reclining position, due to a drop in cerebral blood pressure)
  • orthostatic increase in pulse rate
  • cool extremities (e.g. cool fingers)

Intravascular volume overload[edit]

Signs of intravascular volume overload (high blood volume) include:

Pathophysiology[edit]

Intravascular volume depletion[edit]

The most common cause of hypovolemia is diarrhea or vomiting. The other causes are usually divided into renal and extrarenal causes. Renal causes include overuse of diuretics, or trauma or disease of the kidney. Extrarenal causes include bleeding, burns, and any causes of edema (e.g. congestive heart failure, liver failure, etc.).

Intravascular volume depletion is divided into three types based on the blood sodium level:

  1. Isonatremic (normal blood sodium levels) Example: a child with diarrhea, because both water and sodium are lost in diarrhea.
  2. Hyponatremic (abnormally low blood sodium levels). Example: a child with diarrhea who has been given tap water to replete diarrheal losses. Water is replenished, but sodium is not, so water flows out of the vasculature into the interstitial tissue.
  3. Hypernatremic (abnormally high blood sodium levels). Example: a child with diarrhea who has been given salty soup to drink, or insufficiently diluted infant formula. Here sodium has been replenished, but not enough water has been provided with it.

Intravascular volume overload[edit]

Intravascular volume overload can occur during surgery, if water rather than isotonic saline is used to wash the incision. It can also occur if there is inadequate urination, e.g. with certain kidney diseases.

References[edit]

  1. ^ MedicineNet > Definition of Hypovolemia Retrieved on July 2, 2009
  2. ^ TheFreeDictionary.com --> hypovolemia Citing Saunders Comprehensive Veterinary Dictionary, 3 ed. Retrieved on July 2, 2009

See also[edit]