Circulatory hypoxia is a pathological condition in which body tissues experience oxygen deprivation due to inadequate blood supply. The pathology develops when blood delivery to organs is impaired, leading to a critical decrease in venous oxygen levels and the development of metabolic acidosis.
Main causeCirculatory system failure and decreased cardiac output.
Blood gas profileArterial blood is normal, venous blood is depleted of oxygen.
Acid-base balanceDecreased blood pH, development of acidosis.
Classification and Causes
In pathophysiology, two types of circulatory hypoxia are distinguished:
Local: limited to a specific body area. It occurs during local blood flow disorders: ischemia, venous hyperemia, or stasis. Impaired oxygen diffusion at the microcirculatory level can also be a cause.
Systemic: affects the entire body. The main cause is general circulatory system failure.
Mechanisms of Systemic Hypoxia
The systemic form develops due to three key factors:
Hypovolemia: a critical reduction in circulating blood volume (CBV).
Heart failure: the heart is unable to provide adequate cardiac output, even if venous return is normal.
Vascular failure: generalized decrease in arterial and venous tone, which increases the vascular capacity and slows down blood return to the heart.
Changes in Blood Gas Composition
In systemic circulatory hypoxia, arterial blood parameters remain within normal limits because the lungs function properly. However, tissues extract more oxygen from the passing blood, leading to the following changes:
Parameter
Change
$P_vO_2$ and $S_vO_2$
Decreased
$C_vO_2$
Decreased
Arteriovenous difference
Increased
Blood pH
Decreased (acidosis)
Mnemonic
Remember the formula "System — Heart — Vessels": if failure occurs in any of these links, blood does not reach the tissues, and circulatory hypoxia develops.
Frequently asked questions
Which pathological conditions or types of shock lead to vascular failure in hypoxia?
Acute circulatory failure or vascular failure includes conditions and types of shock described in literature:
Vascular (distributive) shock — includes the neurogenic form (traumatic, pain, spinal cord injury, anesthesia complication) and anaphylactic form (generalized hypersensitivity reaction). Pathogenesis: marked vasodilation, increased capillary permeability, and arteriovenous shunting; hemodynamically — redistribution of intravascular blood volume and a significant decrease in systemic vascular resistance (SVR).
Septic (toxic-infectious) shock — associated with an infection, most commonly gram-negative flora (E. coli, Proteus, Klebsiella), less often gram-positive; accompanied by the release of endotoxins, activation of complement, coagulation, fibrinolysis, platelet and neutrophil pathways, stimulation of nitric oxide (NO) production, TNF-α, and interleukins. The result is acute circulatory failure.
Collapse — acute vascular failure; may be associated with rapid reduction in circulating blood volume, blood pooling, or an acute drop in total peripheral vascular resistance.
What compensatory mechanisms are activated in the body during systemic circulatory hypoxia?
In response to systemic circulatory insufficiency and a deficit in circulating blood volume (CBV), the following mechanisms are activated:
With CBV deficits up to 10%, venous vessels adapt to the reduced volume (venomotor mechanism).
Centralization of circulation — an adaptive response aimed at preserving core blood flow to the brain and heart via marked peripheral vasoconstriction.
Tissues maximally extract oxygen due to falling volumetric blood flow velocity, leading to a drop in venous blood oxygen content from 14–15 vol.% to 4–5 vol.% and an increased arteriovenous oxygen difference.
What specific causes lead to hypovolemia resulting in circulatory hypoxia?
Hypovolemia (reduction in circulating blood volume) develops due to absolute or relative loss of fluid and plasma.
Acute massive hemorrhage.
Loss of a large volume of blood plasma (e.g., in extensive burns).
Acute and significant dehydration: severe vomiting, profuse diarrhea, excessive sweating, massive losses of isotonic fluid (as in cholera).
Blood redistribution with pooling in venous vessels, sinuses, and capillaries (in shock, intoxications).
Why does arterial blood remain normal in circulatory hypoxia?
Because in this form of hypoxia, lung function and the process of hemoglobin oxygenation are unimpaired. The problem lies exclusively in the delivery of already oxygenated blood to the tissues.
What is the arteriovenous difference and why does it increase?
This is the difference between the oxygen content in arterial and venous blood. It increases because tissues, experiencing deprivation, extract more oxygen from the blood than usual due to slowed blood flow.
What is the difference between local and systemic forms?
The local form is restricted to a specific organ or tissue area (e.g., in ischemia), whereas the systemic form affects the entire body due to cardiac dysfunction or overall blood volume reduction.
Go deeper
Mechanisms of ischemia and venous hyperemia development.
Influence of humoral factors on vascular tone.
Compensatory reactions of the body in acute heart failure.
Differential diagnosis of circulatory and hemic hypoxia.
Pathophysiological consequences of metabolic acidosis on the myocardium.