Anaphylactic Shock and Histamine Shock
Anaphylaxis is an allergic condition in which thecardiac output and arterial pressure often decrease drastically. It results primarily from an antigen-antibody reaction that takes place immediately after an antigen to which the person is sensitive enters the circulation. One of the principal effects is to cause the basophils in the blood and mast cells in the pericapillary tissues to release histamine or a histamine-like substance. The histamine causes (1) an increase in vascular capacity because of venous dila-tion, thus causing a marked decrease in venous return; (2) dilation of the arterioles, resulting in greatly reduced arterial pressure; and (3) greatly increased capillary permeability, with rapid loss of fluid and protein into the tissue spaces. The net effect is a great reduction in venous return and sometimes such serious shock that the person dies within minutes.
Intravenous injection of large amounts of histamine causes “histamine shock,” which has characteristics almost identical to those of anaphylactic shock.