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Explain me about primary management of anaphylatic shock

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"anaphylaxis"[MeSH Terms] AND "epinephrine"[MeSH Terms] AND management

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I now have comprehensive information from Rosen's Emergency Medicine. Let me compile the full, detailed answer.

Primary Management of Anaphylactic Shock

Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction. When it progresses to hemodynamic collapse (anaphylactic shock), rapid and simultaneous multi-step management is required. The pathophysiology involves IgE-mediated mast cell and basophil activation, releasing histamine, tryptase, prostaglandin D2, and leukotriene C4, which cause profound vasodilation, increased vascular permeability, bronchoconstriction, and distributive shock.

Diagnostic Criteria (Box 106.5, Rosen's Emergency Medicine)

Anaphylaxis is highly likely when ANY ONE of the following is met:
  1. Sudden onset of skin/mucosal involvement PLUS at least one of: respiratory compromise OR reduced BP/end-organ dysfunction
  2. Two or more of the following occurring rapidly after allergen exposure: skin/mucosal involvement, respiratory compromise, reduced BP, GI symptoms
  3. Reduced BP alone after exposure to a known allergen:
    • Adults: Systolic BP <90 mmHg or >30% drop from baseline
    • Children: Age-specific low systolic BP or >30% drop

Emergency Measures (Taken Simultaneously)

These initial steps are performed at the same time, not sequentially:
ActionDetail
Remove triggering agentStop IV drug infusion, remove insect stinger if present
Patient positioningSupine position (improves venous return and cardiac output)
MonitoringCardiac monitor, pulse oximetry, continuous BP monitoring
Airway assessmentEnsure patent airway; prepare for endotracheal intubation (including awake fiberoptic or surgical airway if angioedema is present)
Supplemental oxygenApply if hypoxia, respiratory distress, or severe reaction
IV accessLarge-bore IV lines (16 or 18 gauge preferred)
IV fluid resuscitationAdults: 1000 mL isotonic saline (NS) in first 5 min - several liters may be needed; titrate to response. Pediatrics: 20-30 mL/kg increments

Treatment Medications

First-Line Agent: Epinephrine (MANDATORY - given immediately)

Epinephrine is the cornerstone of treatment and must never be delayed. It acts on alpha-1 receptors (vasoconstriction, reduces angioedema), beta-1 receptors (increased heart rate and contractility), and beta-2 receptors (bronchodilation, inhibits mediator release).
  • Adults: 0.3-0.5 mg IM (1 mg/mL / 1:1000 concentration) into the anterolateral thigh - may repeat every 5-10 minutes as needed
  • Pediatrics: 0.01 mg/kg IM (1:1000 concentration) into the anterolateral thigh - may repeat every 5-10 minutes as needed
  • Auto-injector alternative: EpiPen 0.3 mg (adult) or EpiPen Jr 0.15 mg (child) into anterolateral thigh
The anterolateral thigh (vastus lateralis) is preferred over the deltoid due to faster absorption and higher peak plasma concentration.
IV Epinephrine is reserved for patients with refractory shock or cardiac arrest:
  • Start at 0.1-0.2 mcg/kg/min IV infusion, titrated to response
  • Bolus IV epinephrine risks severe hypertension and arrhythmias and should only be used by experienced providers

Second-Line Agents (Do NOT replace or delay epinephrine)

H1 Antihistamines

  • Diphenhydramine: Adults 50 mg IV or oral; Pediatrics 1 mg/kg IV or oral
  • Useful for urticaria and pruritus, but do NOT treat cardiovascular collapse or bronchospasm

H2 Antihistamines

  • Famotidine: Adults 40 mg IV or oral; Pediatrics 0.5 mg/kg IV or oral
  • Combined H1 + H2 blockade provides better symptom relief than H1 alone

Corticosteroids

  • Methylprednisolone: Adults 125 mg IV; Pediatrics 1-2 mg/kg IV (max 125 mg)
  • Onset is delayed (4-6 hours), so not useful acutely but help prevent biphasic reactions
  • Dexamethasone 0.3 mg/kg oral/IV is an alternative

Aerosolized Beta-Agonists (for bronchospasm)

  • Albuterol (salbutamol): 2.5 mg in 3 mL NS via nebulizer - may repeat or give continuously
  • Ipratropium: 0.5 mg in 3 mL NS - adjunct for refractory bronchospasm
  • These are adjuncts; epinephrine remains first-line even for bronchospasm

Special Scenarios

Refractory Anaphylaxis (Shock Persists Despite Epinephrine + Fluids)

  • IV epinephrine infusion: 2-10 mcg/min, titrated up
  • Vasopressin: 40 units IV bolus or 0.03-0.04 units/min infusion - useful when beta-blockade blunts epinephrine response
  • Glucagon: 1-5 mg IV over 5 min (then 5-15 mcg/min infusion) - especially important in patients on beta-blockers, as glucagon bypasses the blocked receptor and stimulates adenyl cyclase directly
  • Norepinephrine or dopamine infusions may be added for persistent hypotension

Patients on Beta-Blockers

  • Epinephrine response may be blunted
  • Glucagon is the key adjunct (see above)
  • Atropine 0.3-0.5 mg IV may be used for refractory bradycardia

Airway Management

  • Early intubation is preferable if angioedema of the tongue, uvula, or larynx is progressing
  • Delay can result in a "cannot intubate, cannot oxygenate" scenario
  • Surgical airway (cricothyrotomy) must be immediately available

Biphasic Anaphylaxis

  • Occurs in 1-20% of cases, typically 1-12 hours after initial resolution (rarely up to 72 hours)
  • Unpredictable; not reliably prevented by antihistamines or steroids
  • Observation period: All patients with anaphylaxis requiring epinephrine should be observed for a minimum of 4-6 hours in the ED; those with severe reactions or risk factors (asthma, prior biphasic reaction) require 12-24 hours

Discharge Planning

  • Prescribe self-injectable epinephrine (EpiPen) for all discharged patients
  • Refer to allergist/immunologist
  • Advise allergen avoidance and Medic-Alert bracelet
  • Counsel on when to use auto-injector (any systemic allergic symptoms)

Summary Algorithm

SUSPECT ANAPHYLAXIS
       |
       v
EPINEPHRINE IM (anterolateral thigh) ← FIRST AND IMMEDIATE
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       v
Position supine + O2 + Monitor + Large-bore IV + Rapid IV NS
       |
       v
H1/H2 antihistamines + Corticosteroids + Beta-agonist (if bronchospasm)
       |
       v
Reassess - Is patient improving?
  NO → Repeat epinephrine q5-10 min → IV epinephrine infusion
       → Glucagon (if on beta-blocker) → Vasopressors
  YES → Observe ≥4-6 hours → Discharge with EpiPen + follow-up
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