Definition of "Hypovolemia"

Last modified: 16 hours



Hypovolemia (aka hypovolemic shock, oligemia) is a state of decreased blood volume, specifically, of blood plasma (i.e. intravascular component of volume contraction).

Patient information

What is hypovolemia?
Low volume... and in this case, blood volume !

Cause
  • Hemorrhage (internal and/or external), including:
    • Burns
  • Loss of fuid from the circulation, including:
    • Vomiting
    • Diarrhea
    • Excess loss in urine due to DKA or diabetes insipidus
    • Dehydration

Patient information

What causes low blood?
So it can be loss of blood, or loss of fluid. So loss of blood is bleeding, whether that's internal or external. And loss of fluid can happen from the 2 ends, so vomiting at the top end, and diarrhea or excess urination at the bottom. And dehydration.

Pathophysiology
  • Characterized by salt/sodium depletion, thus differs from dehydration (i.e. excessive loss of body water)
Classification

Stages of hypovolemic shock, include:

  • Stage 1, which is <15% blood volume loss (blood volume is 7% of body weight in adults)
  • Stage 2, which is <30% blood volume loss
  • Stage 3, which is <40% blood volume loss
  • Stage 4, which is >40% blood volume loss

This therefore depends on blood volume, which is 85mL/kg in neonates (so 300mL blood in 3.5kg baby), 80mL/kg in children, and 70mL/kg in adults (so 5L blood in 70kg adult).

Patient information

There are different stages of low blood?
Yep. So it's divided into 4 stages. Where you have LESS than 15% loss. <30% loss. <40% loss. And then MORE than 40% loss.

Ix
  • Blood tests, including:
    • FBC
    • UEC
    • LFT
    • Glucose
    • Cross match
  • Central venous catheter or BP
  • Arterial line or ABG's
  • Urine output measurements, via urinary catheter
  • BP
  • SpO2 oxygen saturations

Patient information

How do you check out low blood?
So blood tests, like FBC to check blood, UEC to check kidneys, LFT to check livers. Cross match, to ensure donor blood is compatible with the recipient. Check blood pressure. Blood gases. Urine output. And oxygen saturation.

Tx
  • Emergency oxygen, as required, immediately, to increase the efficiency of the Pt's remaining blood supply. This can be life saving
  • IV fluids, thus IV access. It may help compensate for lost fluid volume, but IV fluids can't carry oxygen in the way that blood can, however blood substitutes are being developed which can. Infusion of colloid or crystalloid IV fluids will also dilute clotting factors within the blood, increasing the risk fo bleeding. Fluid replacement is beneficial in hypovolemia stage 2, and is necessary in stage 3-4
  • FFP (fresh frozen plasma) or whole blood
  • Allow permissive hypotension in Pt's, both to ensure clotting factors aren't overly diluted, but also to stop BP being artificially raised to a point where it "blows off" clots that have formed
  • Surgical repair at sites of hemorrhage
  • Inotrope therapy (dopamine, noradrenaline) which increases the contractility of the heart muscle

Patient information

What do you do to fix low blood?
So ABC's, so we start with airways, the patient might need emergency oxygen. Circulation, so IV fluids. In fact, if bleeding is bad enough, we might need FFP which is the liquid part of blood, or even whole blood itself, to pump up the blood volume. We might allow permissive hypotension, so let blood pressure be low, so that blood is allowed to clot, and bleeding can stop. We then do surgical repair at sites of bleeding. Inotropes can help, these are drugs that increase the force of the heart's contractions.

Prognosis
  • As kids have a larger circulating blood volume per kg of body weight, smaller losses have big consequences.
See also
  • Shock
  • Bleeding (uses same classification system as for hypovolemic shock)

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Definition of Hypovolemia | Autoprac


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