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It has been known for more than one hundred years that an intravenous injection of histamine causes a fall in the blood pressure. [30] The underlying mechanism concerns both vascular hyperpermeability and vasodilation. Histamine binding to endothelial cells causes them to contract, thus increasing vascular leak.
Vasodilation is also a major component of anaphylaxis. [12] Inflammation causes not only vasodilation but also causes increased vascular permeability, allowing neutrophils, complement proteins, and antibodies to reach the site of infection or damage. [7]
Anaphylactic shock is caused by a severe anaphylactic reaction to an allergen, antigen, drug, or foreign protein causing the release of histamine which causes widespread vasodilation, leading to hypotension and increased capillary permeability. Signs of anaphylaxis Signs typically occur after exposure to an allergen and may include:
The main factor involved in causing vasodilation is histamine. [3] [15] Histamine also causes blood vessels to become porous, allowing the tissue to become edematous because proteins from the bloodstream leak into the extravascular space, which increases its osmolar load and draws water into the area. [3]
Vasodilation and its resulting increased blood flow causes the redness (rubor) and increased heat (calor). Increased permeability of the blood vessels results in an exudation (leakage) of plasma proteins and fluid into the tissue ( edema ), which manifests itself as swelling ( tumor ).
Firstly, at the site of infection histamine release causes vasodilation of the capillaries near the injured area which slows down the blood flow in the region and encourages leukocytes, such as neutrophils, to come closer to the endothelium, and away from the centre of the lumen where the rate of blood flow is highest.
Reversing the underlying causes of vasodilatory shock, stabilizing hemodynamic, preventing renal, myocardial, and other organs from injuries due to hypoperfusion and hypoxia, and taking necessary measures to safeguard against complications including venous thromboembolism are served as the top priorities during the treatment.
A vasoactive substance is an endogenous agent or pharmaceutical drug that has the effect of either increasing or decreasing blood pressure and/or heart rate through its vasoactivity, that is, vascular activity (effect on blood vessels).