Defined as a gradual or sudden decrease in the volume of blood in the bloodstream, hypovolaemia can lead to cardiovascular collapse and pose a risk of death if no treatment is given quickly. Its causes are manifold.

Volume is the total blood volume of the body including both blood cells (red blood cells, white blood cells, platelets…) and plasma (liquid in which these cells bathe). 

Its normal value is between 65 and 75 ml per kg, or 5,600 liters of blood in all for an 80 kg person. Two thirds of this volume is contained in the blood circulation, veins, arteries, heart… and the rest in the tissues (muscles, fats, organs…).

What does hypovolemia correspond to? 

It is a decrease in the body’s total blood mass. 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 in perfusion of the organs by oxygen.

This hypovolaemia may be related to bleeding losses or severe dehydration. It can also be related with 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 to the peripheral tissues.

It is often a life-threatening emergency that requires prompt care.

There are many causes of hypovolaemia. When it is brutal, it can be linked to different reasons: 

• externalized (accident, wounds) or internal blood hemorrhage (ruptured aneurysm, digestive, gynecological hemorrhage, etc.); 
• a sudden state of shock such as septic shock (microbes which pass into the blood), or anaphylactic shock (antibiotic or other drug allergy, sting or bite of insects, snakes or other animals…);
• poisoning by a chemical; 
• severe dehydration (heat stroke, profuse diarrhea, diabetic coma, etc.);
• crushing of tissues, in particular muscles during road accidents (AVP), or during earthquakes with rubble falling on the body (crush syndrome). It is also sometimes found when lifting a tourniquet that has been kept around a limb for too long,
• deep and extensive burns.

Symptoms of hypovolaemia vary depending on the cause. In the event of sudden bleeding: 

• blood pressure drops, sometimes becomes impregnable (cardiovascular collapse);
• the heart pulse quickens (tachycardia);
• 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 dry mouth;
• cooling of the extremities by a contraction of the small arteries (vasoconstriction);
• decreased urine volume (oliguria);
• increased respiratory rate (polypnea).

These symptoms appear from 10 to 20% of liquid losses to go up to a cardiovascular collapse (pulsing pulse impossible to take, collapse of the tension…).

Mechanisms can be put in place such as a reduction in the diameter of the vessels (vasoconstriction), an acceleration of the heart rate, a reduction in 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 (in particular the heart and the brain) by the blood circulation. But these mechanisms can then be overcome if the fluid losses are too great or prolonged. The vital prognosis is then engaged.

At the biological level, there is progressive anemia in the event of bleeding, metabolic acidosis linked to the lack of oxygen in the tissues, and reduced or even no renal function (acute renal failure). Blood clotting disorders can also occur with an increased risk of thrombosis.

Treatments for hypovolaemia depend on the cause. They are always urgent to implement. The patient is lying on his back, his head a little elevated, covered with a sheet or an 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 the bleeding, treating acute diarrhea, antidote for poisonings, etc.). Then it is necessary to quickly fill the blood circulation by blood transfusions in the event of massive and sudden hemorrhages, by filling liquids (filling solution such as physiological serum) or products with large molecules (colloids, albumin more rarely …) .

Finally, drugs can be given to help the venous return of blood to the heart (dopamine).