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Blood Loss and Posthemorrhagic States

Haemorrhagia

For medical students2 min readUpdated 2026-10-10

Blood loss is the loss of a portion of the body's blood volume, triggering a complex cascade of pathogenic and adaptive responses. The severity of life-threatening disorders depends directly on the volume of blood lost and the initial reactivity of the organism.

Hydremic phaseDevelops on days 2–3 due to tissue fluid shifting into the vasculature

Bone marrow phaseOccurs after 4–5 days and is accompanied by reticulocytosis

Shock stateMassive blood loss leads to critical hemodynamic and biological oxidation failure

Recovery timelineTotal red blood cell mass normalizes within 1–2 months

Causes and Etiology

Blood loss occurs due to various factors leading to vascular damage or functional impairment:

Disruption of vascular and cardiac integrity — mechanical cuts or ruptures, vessel wall arrosion by purulent processes, destruction by tumors, and myocardial ruptures in myocardial infarction zones and aneurysms.
Increased vascular permeability — observed in the microvasculature during radiation sickness, leukemias, severe infections (sepsis, epidemic typhus), and severe vitamin C deficiency (scurvy).
Decreased blood clotting — a significant factor contributing to prolonged bleeding.

Pathogenesis and Compensatory Stages

The pathogenetic process begins with a decrease in circulating blood volume (CBV), a drop in venous return, decreased stroke volume and cardiac output, and a drop in blood pressure. This leads to tissue hypoperfusion, hypoxia, acidosis, and the development of capillariotrophative insufficiency.

To counteract these effects, the body activates compensatory mechanisms:

Protein compensation — liver proteosynthesis is activated, increasing hemostatic potential.
Hydremic phase (days 2–3) — autohemodilution occurs (tissue fluid shifts into the vascular bed), causing a decrease in hematocrit, oligocytemia, as well as relative thrombocytopenia and leukopenia.
Bone marrow phase (days 4–5) — erythropoietins stimulate bone marrow cell proliferation, leading to a reticulocyte crisis and the appearance of hypochromic and microcytic red blood cells.

Chronic Posthemorrhagic Anemia

The chronic form develops against the background of frequent and prolonged bleeding. The main causes include gastrointestinal pathologies (polyps, peptic ulcer disease, esophageal varices), renal diseases (urolithiasis, hemorrhagic nephritis), and congenital or acquired thrombocytopathies.

The pathogenesis is based on progressive iron deficiency, making this pathological condition a specific variant of iron deficiency anemia.

Mnemonic

Compensation timeline: 2–3 days — water dilutes the blood (hydremia); 4–5 days — the bone marrow responds with reticulocytosis (erythropoiesis); 1–2 months are required for complete recovery of red blood cell mass.

Frequently asked questions

What mechanisms mediate the vascular-reflex (early) stage of compensation in acute blood loss?

The vascular-reflex stage of acute blood loss compensation is mediated by the centralization of blood circulation and stimulation of the sympathoadrenal system. Mechanisms include:

Stimulation of the sympathoadrenal system — as a reflex response of baro- and chemoreceptors.
Venospasm and arteriolospasm — reduction of the vascular bed volume via increased tone of veins and peripheral arterioles.
Increased venous tone — compensates for up to 10–15% of CBV loss.
Vasoconstriction of vessels in the skin, kidneys, liver, and abdominal organs.
Preservation of blood flow to the brain, heart, and lungs.
Blood mobilization from depots and increased cardiac output as components of cardiovascular compensation.

What types of hypoxia develop sequentially in acute massive blood loss?

Acute massive blood loss leads to mixed-type hypoxia. Its components include:

Hemic hypoxia — due to decreased blood oxygen capacity caused by falling hemoglobin levels and erythrocyte loss.
Circulatory hypoxia — due to circulatory disorders, drops in CBV and blood pressure, and hemodynamic disturbances.
Respiratory hypoxia — developing due to decreased pulmonary perfusion.

These links of various hypoxia types mutually exacerbate each other.

What is the complete mechanism of protein compensation following acute blood loss?

The mechanism of protein compensation involves the restoration of blood protein composition through the activation of liver proteosynthesis. The process has the following features:

Timing of activation — begins several hours after blood loss; signs of increased synthesis persist for 1.5–3 weeks depending on the blood loss volume and organism reactivity.
Biological significance — the synthesis of procoagulants increases the hemostatic potential of blood.
Result — these reactions promote thrombosis of the vascular defect and cessation of bleeding.

What is the pathogenesis of hemorrhagic shock at the microcirculatory level?

The pathogenesis of hemorrhagic shock at the microcirculatory level is associated with decreased perfusion pressure and hypoperfusion of organs and tissues. Key changes include:

Microcirculatory disturbances and the development of capillariotrophative insufficiency due to impaired transport of oxygen and metabolic substrates to cells, as well as impaired removal of carbon dioxide and metabolic products.
Erythrocyte sludging — erythrocyte agglutination in capillaries due to their spasm and slowed blood flow.
Blood pooling and sequestration in capillaries against the background of impaired hemorheological properties as a link of the terminal shock stage.

These processes are accompanied by tissue hypoxia, predominance of anaerobic processes, and the development of tissue acidosis.

What changes occur in peripheral blood during the hydremic phase?

Oligocytemic hypo- or normovolemia, decreased hemoglobin, erythropenia, low hematocrit, normochromia of red blood cells, as well as thrombocytopenia and leukopenia are observed.

What are the blood picture features during the bone marrow compensation phase?

The anemia becomes hypochromic, microcytic, regenerative, and normoblastic, with prominent reticulocytosis reaching up to 30%.

What is the primary cause of chronic posthemorrhagic anemia?

Progressive iron deficiency in the body resulting from prolonged, recurring bleeding of various etiologies.

Go deeper

Classification of blood loss by source, time, and volume
Principles of water-electrolyte balance correction
Correction of acid-base balance (ABB)
Symptomatic treatment principles for posthemorrhagic states
Mechanisms of posthemorrhagic shock development