Hypovolemia
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2008-07-08T19:42:43Z
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ICD10 = {{ICD10|E|86||e|70}}, {{ICD10|R|57|1|r|50}}, {{ICD10|T|81|1|t|80}} |
ICD9 = {{ICD9|276.52}} |
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MeshID = D020896 |
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In [[physiology]] and [[medicine]], '''hypovolemia''' (also hypovolaemia) is a state of decreased [[blood]] volume; more specifically, decrease in volume of [[blood plasma]].
Volumetric thirst can be caused by a number of things including bleeding and diarrhea. Volumetric thirst arises when the volume of blood plasma decreases.
== Causes ==
Common causes of hypovolemia can be [[dehydration]], [[bleeding]], vomiting<ref name="Carlson">Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.</ref>, severe [[Burn (injury)|burns]] and drugs such as [[diuretic]]s or [[vasodilator]]s typically used to treat [[hypertension|hypertensive]] individuals. Rarely, it may occur as a result of a [[blood donation]]<ref>{{cite journal |author=Danic B, Gouézec H, Bigant E, Thomas T |title=[Incidents of blood donation] |language=French |journal=Transfus Clin Biol |volume=12 |issue=2 |pages=153–9 |year=2005 |month=June |pmid=15894504 |doi=10.1016/j.tracli.2005.04.003 |url=}}</ref>, sweating<ref name="Carlson"/>, and alcohol consumption<ref name="Carlson"/>.
==Bodily response==
To respond to hypovolemia is a task for the body [[fluid balance]] systems as well as [[osmotic balance]] systems.
Following an acute response, this function is accomplished by two sets of receptors; one in the kidneys and the other in the heart.
====Acute response====
{{See|Baroreflex}}
The first response to hypovolemia is an inversed [[baroreflex]], where a lack of activation of [[baroreceptor]]s results in elevation of [[total peripheral resistance]] and [[cardiac output]] via increased [[contractility]] of the heart, [[heart rate]], and arterial [[vasoconstriction]],<ref>{{cite journal |author=Banic A, Sigurdsson GH, Wheatley AM |title=Influence of age on the cardiovascular response during graded haemorrhage in anaesthetized rats |journal=Res Exp Med (Berl) |volume=193 |issue=5 |pages=315–21 |year=1993 |pmid=8278677 |doi= |url=}}</ref>which tends to increase blood pressure.
====Kidney====
{{Main|Renin-angiotensin system}}
The kidneys have a specialized set of cells that enable the recognition of changes in blood flow to the kidneys.<ref name="Carlson">Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.</ref> Naturally, these cells detect the presence of hypovolemia and react accordingly to the loss of blood volume. These cells secrete a hormone called renin when there is a decrease in the flow of blood to the kidneys.<ref name="Carlson">Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.</ref> Renin flows into the blood and there, initiates the conversion of a protein called angiotensinogen to angiotensin.<ref name="Carlson">Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.</ref> In order to exert its effects on the body, angiotensin I must be converted by enzymes into its active form, angiotensin II. Physiologically, angiotensin II stimulates the release of hormones by the posterior pituitary gland (ADH, also known as [[vasopressin]]) and the adrenal cortex ([[aldosterone]]). Aldosterone causes the kidneys to reabsorb sodium, leading to the reabsorption of water. ADH (vasopressin) also causes the kidneys to reabsorb water. Angiotensin II increases blood pressure by contracting arterial muscles.
====Heart====
:''Further reading:[[Atrial natriuretic peptide]]''
The next set of receptors responsible for detecting volumetric insufficiency are located in the heart atria. Commonly referred to as stretch receptors, these atrial [[baroreceptor]]s detect the amount of blood that is being pumped back into the heart from the veins.<ref name="Carlson">Carlson, N. R. (2005). Foundations of Physiological Psychology: Custom edition for SUNY Buffalo. Boston, MA: Pearson Custom Publishing.</ref> The body constantly returns blood to the heart through veins. Therefore, when the volume of blood being transported back to the heart is decreased, these receptors detect the change in the amount of blood thereby reducing the release of [[atrial natriuretic peptide]].
====Thirst====
{{Main|Extracellular thirst}}
Both the activation of the [[renin angiotensin system]] and the decrease in [[atrial natriuretic peptide]], along their other functions, contribute to elicit [[thirst]], by affecting the [[subfornical organ]].<ref>{{cite journal
| author=M.J. McKinley and A.K. Johnson
| title=The Physiological Regulation of Thirst and Fluid Intake
| journal=News in Physiological Sciences
| volume=19
| issue=1
| year=2004
| pages=1–6
| url=http://physiologyonline.physiology.org/cgi/content/full/19/1/1
| accessdate=2006-06-02
| pmid=14739394
| doi=10.1152/nips.01470.2003 }}</ref>
===Other response===
Furthermore, as intravascular fluid decreases, blood pressure is reduced and the body attempts to compensate by moving fluid from other cellular compartments into the vasculature. Fluid is transferred from all of the fluid compartments in the body, including [[intracellular]], [[interstitial]] and other extravascular compartments.<ref name="Carlson"/>
== Diagnosis ==
Clinical symptoms may not present until 10-20% of total whole-blood volume is lost.
Hypovolemia can be recognized by [[elevated pulse]], diminished blood pressure, and the absence of [[perfusion]] as assessed by skin signs (skin turning pale) and/or [[capillary refill]] on [[forehead]], [[lips]] and [[nail beds]]. The patient may feel dizzy, faint, nauseated, or very thirsty. These signs are also characteristic of most types of [[Shock (medical)|shock]].
Note that in children, compensation can result in an artificially high blood pressure despite hypovolemia. This is another reason (aside from initial lower blood volume) that even the possibility of internal bleeding in children should always be treated aggressively.
Also look for obvious signs of external bleeding while remembering that people can bleed to death internally without any external blood loss.
Also consider possible mechanisms of injury (especially the [[steering wheel]] and/or use/non-use of seat belt in motor vehicle accidents) that may have caused internal bleeding such as ruptured or bruised internal organs. If trained to do so and the situation permits, conduct a secondary survey and check the chest and abdominal cavities for pain, deformity, guarding or swelling. (Injuries to the pelvis and bleeding into the thigh from the femoral artery can also be life-threatening.)
== Treatment ==
Minor hypovolemia from a known cause that has been completely controlled (such as a blood donation from a healthy patient who is not anemic) may be countered with initial rest for up to half an hour. Oral fluids including moderate sugars ([[apple juice]] is good) and rich in [[electrolytes]] are needed to replenish the organism of lost sodium ions. Furthermore the advice is to the donor to eat good solid meals with proteins for the next few days. Typically, this would involve a fluid volume of less than one liter (1000 ml), although this is highly dependent on body weight. Larger people can tolerate slightly more blood loss than smaller people.
More serious hypovolemia should be assessed by a nurse or doctor. When in doubt, treat hypovolemia aggressively.
=== First Aid ===
External bleeding should be controlled by direct pressure. If direct pressure fails, other techniques such as elevation and pressure points should be considered. The [[tourniquet]] should be used in the case of massive hemorrhage i.e. arterial bleeds, such as the [[femoral artery]], as a last resort, for the use of a tourniquet can easily kill all the tissue below its application upon a limb, making amputation necessary. If a first-aider recognizes internal bleeding, the life-saving measure to take is to immediately call for emergency assistance.
=== Field Care ===
Emergency oxygen should be immediately employed to increase the efficiency of the patient's remaining blood supply. This intervention can be life-saving.
The use of [[intravenous drip|intravenous fluids]] (IVs) may help compensate for lost fluid volume, but IV fluids cannot carry oxygen in the way that blood can. See also [[emergency medical services]] for a discussion of techniques used in IV fluid management of hypovolemia.
=== Hospital Treatment ===
If the hypovolemia was caused by medication, the administration of antidotes may be appropriate but should be carefully monitored to avoid shock or the emergence of other pre-existing conditions.
[[Blood transfusion]]s coupled with surgical repair are the definitive treatment for hypovolemia caused by [[Physical trauma|trauma]]. See also the discussion of [[Shock (medical)|shock]] and the importance of treating reversible shock while it can still be countered.
==History==
Hypovolemia has historically been termed ''desanguination'' (from Latin ''sanguis'', blood), meaning a massive loss of blood. The term was widely used by the [[Hippocrates]] in traditional medicine practiced in the Greco-Roman civilization and in Europe during the Middle Ages. The word was possibly used to describe the lack of personality (by death or by weakness) that often occurred once a person suffered [[hemorrhage]] or massive blood loss.
==References==
<references/>
==See also==
* [[Volume status]]
* [[Hypervolemia]]
* [[Exsanguination]]
==External links==
* {{CrispThesaurus|00004050}}
* {{DiseasesDB|29217}}
{{Water-electrolyte imbalance and acid-base imbalance}}
[[Category:Medical emergencies]]
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