From the Guidelines
Distributive shock in anaphylaxis requires immediate treatment with epinephrine as the first-line therapy, administered 0.3-0.5 mg (1:1000 concentration) intramuscularly in the mid-outer thigh, which can be repeated every 5-15 minutes if needed, as recommended by the most recent guidelines 1. The management of anaphylactic distributive shock involves a multifaceted approach to counteract the pathophysiology of the condition.
Key Components of Management:
- Administer epinephrine as the first-line treatment, which works by causing vasoconstriction, increasing cardiac output, and reducing mediator release and bronchospasm 1.
- Place the patient supine with legs elevated unless respiratory distress prevents this position.
- Provide high-flow oxygen to manage respiratory symptoms.
- Establish IV access for fluid resuscitation with crystalloids, such as normal saline or lactated Ringer's, at 1-2 L rapidly for adults.
Second-Line Medications:
- H1 antihistamines, such as diphenhydramine 25-50 mg IV/IM.
- H2 blockers, such as ranitidine 50 mg IV or famotidine 20 mg IV.
- Corticosteroids, such as methylprednisolone 125 mg IV, although their role in the acute management of anaphylaxis is less clear 1.
Persistent Hypotension:
- Consider vasopressors, such as norepinephrine (0.1-0.5 mcg/kg/min) or vasopressin (0.01-0.04 units/min), for persistent hypotension despite epinephrine and fluid resuscitation. Anaphylactic distributive shock is characterized by massive vasodilation and increased vascular permeability due to inflammatory mediators released during severe allergic reactions, primarily driven by mast cell and basophil degranulation 1. The most recent guidelines emphasize the importance of prompt epinephrine administration in the management of anaphylaxis, highlighting its critical role in improving outcomes 1.
From the Research
Distributive Shock in Anaphylaxis
- Distributive shock is a hyperdynamic process resulting from excessive vasodilatation, which can lead to inadequate tissue perfusion and end-organ damage 2.
- Anaphylaxis is a potentially life-threatening, multisystem allergic reaction that can cause airway, breathing, or circulatory compromise, including distributive shock 3, 4.
- The treatment of anaphylaxis-induced distributive shock involves the administration of epinephrine, either intramuscularly or intravenously, along with fluid resuscitation to replace lost volume 5, 3, 4, 6.
- Aggressive fluid resuscitation is crucial in treating the intravascular volume depletion characteristic of anaphylaxis, and crystalloids or colloid volume substitutes can be used depending on the severity of the shock 5, 6.
Diagnosis and Management
- Early diagnosis of anaphylaxis is critical, and the diagnosis is purely clinical, with laboratory tests being of no help in the acute situation 6.
- The treatment of anaphylaxis should not be delayed, and epinephrine should be administered as soon as the diagnosis is suspected, followed by additional therapy such as supplemental oxygen, intravenous fluids, antihistamines, and corticosteroids 5, 3, 4.
- Patients with anaphylaxis should be observed for a period of time after resolution of signs and symptoms, as biphasic reactions can occur, although the exact observation period is not well-defined 5, 3, 4.