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Difficulty: MediumImmunologic and Inflammatory Processes

A 35-year-old man is hospitalized for the treatment of infective endocarditis and is currently receiving his first dose of intravenous penicillin G. Ten minutes into the infusion, he develops severe pruritus, a sensation of throat tightness, and sudden shortness of breath. His temperature is 37.1°C (98.8°F), blood pressure is 82/50 mm Hg, pulse is 122/min, and respirations are 26/min. Physical examination reveals diffuse urticaria across his torso and audible expiratory wheezing.

Arrange the following management and diagnostic steps in the most appropriate chronological order for this patient's acute condition.

  1. 1Immediate cessation of the intravenous penicillin G infusion
  2. 2Intramuscular administration of epinephrine into the anterolateral thigh
  3. 3Administration of a rapid intravenous bolus of normal saline
  4. 4Intravenous administration of adjunctive medications, including H1-antihistamines and corticosteroids
  5. 5Measurement of serum tryptase levels to retrospectively confirm the immunopathologic diagnosis

Answer

The correct chronological sequence is: 1) Cessation of the intravenous penicillin G infusion, 2) Intramuscular administration of epinephrine, 3) Administration of a rapid intravenous bolus of normal saline, 4) Intravenous administration of adjunctive medications (antihistamines and corticosteroids), and 5) Measurement of serum tryptase levels.
The established standard of care for in-hospital anaphylaxis dictates a strict hierarchy of interventions. Removing the immunologic trigger (stopping the infusion) is the universal first step. Intramuscular epinephrine is the primary life-saving medication and must be given immediately thereafter to reverse smooth muscle spasm and cardiovascular collapse. Normal saline addresses the profound third-spacing and distributive shock that follow mast cell degranulation. Adjunctive therapies like corticosteroids and antihistamines modulate the secondary inflammatory cascade and are given next. Diagnostic markers, such as serum tryptase, are only measured retrospectively once the patient is no longer in extremis.

Step-by-Step Solution

1
Identify the clinical presentation as an acute Type I IgE-mediated hypersensitivity reaction (anaphylaxis).
The patient is experiencing distributive shock and airway compromise triggered by an antibiotic infusion.
Recognizing anaphylaxis is critical for initiating the standard life-support protocol rather than treating isolated symptoms.
2
Prioritize immediate removal of the inciting antigen.
The penicillin G infusion is stopped.
Continuing the infusion would result in ongoing systemic mast cell degranulation, worsening the patient's hemodynamic collapse.
3
Administer definitive first-line pharmacotherapy.
Intramuscular epinephrine is administered into the anterolateral thigh.
Epinephrine directly reverses the life-threatening manifestations of anaphylaxis (bronchospasm and vasodilation) and stabilizes mast cell membranes.
4
Address the resulting distributive shock with volume expansion.
An intravenous bolus of normal saline is infused.
Systemic capillary leak causes significant intravascular volume depletion, necessitating rapid fluid resuscitation alongside vasopressor support.
5
Provide symptomatic relief and prevent delayed reactions.
Adjunctive corticosteroids and antihistamines are administered.
These medications do not work fast enough to be life-saving but are necessary second-line agents for ongoing inflammatory suppression.
6
Obtain diagnostic laboratory studies.
Serum tryptase levels are drawn 1 to 2 hours post-reaction.
Laboratory confirmation of mast cell degranulation must be deferred until the patient is completely stabilized.

Key Concept

The precise sequencing of interventions in anaphylaxis mandates that halting the inciting antigen and administering intramuscular epinephrine precede all fluid resuscitation, adjunctive pharmacotherapies, and diagnostic testing.
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Topics

Immunologic and Inflammatory Processes

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