Defined as a gradual or abrupt decrease in the volume of blood in the bloodstream, hypovolemia can lead to cardiovascular collapse and pose a fatal risk if no treatment is provided quickly. Its causes are manifold.
What is hypovolemia?
Volemia is the body’s total blood volume including both blood cells (red blood cells, white blood cells, platelets, etc.) and plasma (the liquid in which these cells are bathed).
Its normal value is between 65 and 75 ml per kg or 5,600 liters of blood in total for a person weighing 80 kg. Two-thirds of this volume is contained in the bloodstream, veins, arteries, and heart… and the rest is in the tissues (muscles, fats, organs…).
It is a decrease in the total blood mass of the body. It leads to a reduction in blood pressure, most often, and the return of blood through the veins to the heart. This decrease in blood circulation will be the cause of a deficit of perfusion of organs by oxygen.
This hypovolemia may be related to bleeding losses or severe dehydration. It can also be relative to a decrease in vascular tone (the vessels dilate) and an increase in the passage of part of the plasma out of the bloodstream to go into the peripheral tissues.
It is often a life-threatening emergency that requires care to be quickly put in place.
What causes hypovolemia?
There are many causes of hypovolemia. When it is brutal, it can be related to different reasons:
- externalized blood hemorrhage (accident, wounds) or internal (aneurysm rupture, digestive hemorrhage, gynecological …);
- a state of sudden shocks such as septic shock (microbes that pass into the blood), or anaphylactic shock (antibiotic allergy or other drugs, sting or bite of insects, snakes, or other animals …);
- chemical poisoning;
- severe dehydration (heat stroke, profuse diarrhea, diabetic coma…);
- crushing tissues, especially muscles during road accidents (AVP), or during earthquakes with falling rubble on the body (crush syndrome). It is also sometimes found when lifting a tourniquet that has been held too long around a limb,
- deep and extensive burns.
What are the symptoms of hypovolemia?
The symptoms of hypovolemia vary depending on the cause. In case of sudden bleeding:
- the tension drops and sometimes become impregnable (cardiovascular collapse);
- the heart rate accelerates (tachycardia);
- the pallor of the skin and mucous membranes, especially the lips, is manifested;
- sweating may appear;
- a feeling of dizziness and loss of consciousness is present;
- a feeling of thirst with a dry mouth;
- cooling of the extremities by contraction of the small arteries (vasoconstriction);
- decreased urine volume (oliguria)
- an acceleration of the respiratory rate (polypnea)
These symptoms manifest themselves from 10 to 20% fluid loss to go up to a cardiovascular collapse (pulse impossible to take, the collapse of blood pressure …).
Mechanisms can be put in places such as the reduction of the diameter of the vessels (vasoconstriction), an acceleration of the heart rate, and a reduction of renal function with a decrease in the volume of urine.
They allow as much as possible to maintain the perfusion and oxygenation of the organs (especially the heart and brain) through the bloodstream. But these mechanisms can then be overcome if the fluid losses are too large or prolonged. The vital prognosis is then engaged.
At the biological level, there is progressive anemia in case of hemorrhage, metabolic acidosis related to the lack of oxygen in the tissues, and reduced or no renal function (acute renal failure). Blood clotting disorders can also occur with an increased risk of thrombosis.
What are the treatments for hypovolemia?
Treatments for hypovolemia depend on the cause. They are always urgent to implement. The patient lies on his back, head a little raised, covered with a sheet or aluminum blanket to reduce the loss of heat and sweat, oxygen is delivered to oxygenate the body as well as possible.
At the same time, treatment of the cause is implemented (stopping bleeding, treating acute diarrhea, the antidote for poisoning …). Then it is necessary to quickly fill the bloodstream by blood transfusions in case of massive and sudden hemorrhages, by filling liquids (filling solution such as saline) or products with large molecules (colloids, albumin more rarely …).
Finally, medications may be dispensed to help the venous return of blood to the heart (dopamine).
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