From the Guidelines
Shock in anaphylaxis is primarily caused by widespread vasodilation and increased vascular permeability, leading to a dramatic drop in blood pressure, as supported by the most recent evidence from 2017 1. During an anaphylactic reaction, mast cells and basophils release massive amounts of inflammatory mediators, particularly histamine, leukotrienes, and prostaglandins. These substances cause blood vessels to dilate significantly and become leaky, allowing fluid to escape from the bloodstream into surrounding tissues. This fluid shift reduces circulating blood volume, decreases venous return to the heart, and ultimately leads to inadequate tissue perfusion. Additionally, bronchial constriction often occurs simultaneously, further compromising oxygen delivery to tissues. The heart may initially compensate by increasing cardiac output, but as the reaction progresses, myocardial depression can occur due to inflammatory mediators and hypoxia. Key factors that can exacerbate anaphylaxis include the use of beta-blockers, which can blunt the response to epinephrine and worsen hypotension and bradycardia, as noted in studies from 2005 1 and 2010 1. Treatment requires immediate administration of epinephrine to counteract these effects by causing vasoconstriction, reducing vascular permeability, and relaxing bronchial smooth muscle. The recommended dose of epinephrine is 0.3-0.5mg intramuscularly in adults and 0.15mg in small children, as indicated by recent guidelines 1. Fluid resuscitation with intravenous crystalloids is also essential to restore circulating volume, typically requiring 1-2 liters rapidly infused in adults. Prompt recognition and treatment of anaphylaxis are critical to prevent severe outcomes, including hospitalization and death, as highlighted by the importance of immediate epinephrine administration in recent studies 1.
From the FDA Drug Label
Through its action on alpha-adrenergic receptors, epinephrine lessens the vasodilation and increased vascular permeability that occurs during anaphylaxis, which can lead to loss of intravascular fluid volume and hypotension The cause of shock in anaphylaxis is vasodilation and increased vascular permeability, leading to loss of intravascular fluid volume and hypotension 2.
- Vasodilation and increased vascular permeability are key factors contributing to shock in anaphylaxis.
- Hypotension is a result of these factors, which can lead to shock.
From the Research
Causes of Shock in Anaphylaxis
- Anaphylaxis is a multisystem disorder that can manifest signs and symptoms related to the cutaneous, respiratory, cardiovascular, and gastrointestinal systems 3
- The condition can cause airway, breathing, or circulatory compromise, leading to shock 4, 5
- Shock in anaphylaxis is often characterized by intravascular volume depletion, which requires aggressive fluid resuscitation 3
- The release of mediators from mast cells, such as histamine, can also contribute to the development of shock in anaphylaxis 6
Treatment of Shock in Anaphylaxis
- Intramuscular epinephrine is the immediate treatment of all patients with anaphylaxis, including those in shock 3, 4, 5
- Intravenous epinephrine should be used in patients in shock, either as a bolus or infusion, along with fluid resuscitation 4, 5
- Additional vasopressors may be needed for shock that is refractory to epinephrine 4, 5
- Airway obstruction must be recognized, and early intubation may be necessary in patients with anaphylaxis and shock 4, 5