Hypervolemia: volume excess
The condition hypervolemia is characterized by an increase in total blood volume. The key marker is a change in hematocrit, i.e., the ratio of plasma to formed elements.
Main consequences:
- Increased cardiac output: the myocardium is forced to pump a larger volume of fluid.
- Arterial hypertension: an increase in pressure within the vascular bed.
- Rheological shifts: in the polycythemic form, blood becomes viscous, cells tend to aggregate, which creates a high risk of disseminated thrombosis.
Hypovolemia: volume deficit
The condition hypovolemia is a decrease in total blood volume accompanied by an imbalance of its components. There are three types: normocythemic, oligocythemic, and polycythemic forms.
Why polycythemic hypovolemia occurs:
- Fluid loss: frequent vomiting, prolonged diarrhea, excessive sweating, polyuria, or extensive burns.
- Inadequate intake: water deprivation, when the body does not receive enough fluid from the outside.
General vascular threats
Regardless of the direction of volume changes, microcirculation suffers. When blood thickens (polycythemic forms), the following are observed:
- Increased blood viscosity.
- Aggregation of formed elements in microvessels.
- Development of disseminated microthrombosis.
These processes are often complications of shock states, burn disease, or renal failure.
Briefly: answers to topical questions
What pathological processes lead to the development of oligocythemic hypovolemia?
The development of oligocythemic hypovolemia is caused by:
- states following acute blood loss — during the period of restoring circulating blood volume at the expense of tissue fluid, the erythrocyte deficit persists;
- erythropenia.
What causes normocythemic hypervolemia?
Normocythemic hypervolemia is caused by factors leading to an equivalent increase in the volume of formed elements and the liquid portion of circulating blood.
Main causes:
- Large-volume blood transfusion.
- Acute hypoxic states.
- Prolonged significant physical exertion leading to hypoxia and the release of blood from blood depots.
How does polycythemic hypervolemia differ from oligocythemic hypervolemia?
The main difference between these forms lies in changes in hematocrit, blood rheological properties, and developmental mechanisms.
| Sign | Polycythemic hypervolemia | Oligocythemic hypervolemia |
|---|---|---|
| Hematocrit | Enlarged | Decreased (below normal) |
| Blood rheology | Significantly increased viscosity, aggregation, and agglutination of formed elements | Hemodilution (increase in the liquid portion) |
| Consequences | Microcirculatory disorders, disseminated thrombosis | Increase in total blood volume due to plasma |
What are the causes of oligocythemic hypervolemia?
The development of oligocythemic hypervolemia (hemodilution) occurs during body hyperhydration.
Two main groups of causes are distinguished:
- Excessive fluid intake — includes pathological thirst and the administration of large amounts of plasma expanders or blood plasma into the vascular bed.
- Decreased fluid excretion — occurs with renal excretory dysfunction, hyperproduction of antidiuretic hormone (ADH), and blood plasma hyperosmolarity, leading to water retention.
Hyper — "too much" (pressure up), Hypo — "too little" (volume down). The polycythemic form always makes the blood "thick" (viscous), which leads to thrombi.
Class and exam questions
What is the main criterion for differentiating types of hypervolemia?
Differentiation is carried out based on the hematocrit indicator — the ratio of the volume of formed elements to plasma volume.
Why are blood clots dangerous in polycythemic hypervolemia?
Due to high blood viscosity and the increased tendency of formed elements to aggregate and agglutinate, conditions are created for disseminated thrombosis.
What factors most commonly lead to polycythemic hypovolemia?
This is either excessive fluid loss (vomiting, diarrhea, burns, polyuria) or its insufficient intake into the body.
What else to study on this topic
- Compensation mechanisms in acute blood loss.
- The influence of hormonal regulation (ADH, aldosterone) on circulating blood volume.
- Differences between normo-, oligo-, and polycythemic forms.
- Pathophysiological features of shock as a cause of hypovolemia.
- The role of the kidneys in maintaining volemic homeostasis.
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