A 45-year-old woman, suspected of having colon cancer, is advised to undergo a contrast-CT scan of the abdomen. She has no comorbidities and no significant past medical history. There is also no history of drug allergy. However, she reports that she is allergic to certain kinds of seafood. After tests confirm normal renal function, she is taken to the CT scan room where radiocontrast dye is injected intravenously and a CT scan of her abdomen is conducted. While being transferred to her ward, she develops generalized itching and urticarial rashes, with facial angioedema. She becomes dyspneic. Her pulse is 110/min, the blood pressure is 80/50 mm Hg, and the respirations are 30/min. Her upper and lower extremities are pink and warm. What is the most appropriate management of this patient?

Administer IM epinephrine 1:1,000, followed by steroids and antihistamines

Administer broad-spectrum IV antibiotics

Administer vasopressors (norepinephrine and dopamine)

Perform IV resuscitation with colloids

Obtain an arterial blood gas analysis

A 6-year-old boy is brought to the emergency room by ambulance, accompanied by his kindergarten teacher. Emergency department staff attempt to call his parents, but they cannot be reached. The boy’s medical history is unknown. According to his teacher, the boy was eating in the cafeteria with friends when he suddenly complained of itching and developed a widespread rash. Physical exam is notable for diffuse hives and tongue edema. His pulse is 100/min and blood pressure is 90/60 mmHg. The boy appears frightened and tells you that he does not want any treatment until his parents arrive. Which of the following is the next best step in the management of this patient?

Immediately administer epinephrine and provide supportive care

Continue calling the patient’s parents and do not intubate until verbal consent is obtained over the phone

Obtain written consent to intubate from the patient’s teacher

Wait for the patient's parents to arrive, calm the patient, and provide written consent before intubating

Obtain written consent to intubate from the patient

A 23-year-old woman is brought to the emergency department by her friends because she thinks that she is having an allergic reaction. The patient is visibly distressed and insists on immediate attention as she feels like she is going to die. Her friends say they were discussing future plans while dining at a new seafood restaurant when her symptoms started. The patient has no history of allergies. She takes no medications and has no significant medical history. Her vitals include: pulse 98/min, respiratory rate 30/min, and blood pressure 120/80 mm Hg. On physical examination, she is tachypneic and in distress. Cardiopulmonary examination is unremarkable. No rash is seen on the body and examination of the lips and tongue reveals no findings. Which of the following would most likely present in this patient?

Decreased alveolar pCO2 and increased alveolar pO2

Increased alveolar pCO2 and decreased alveolar pO2

Decreased alveolar pCO2 and unchanged alveolar pO2

Increased alveolar pCO2 and increased alveolar pO2

Decreased alveolar pCO2 and decreased alveolar pO2

A 29-year-old man is outside his home doing yard work when a bee stings him in the right arm. Within 10 minutes, he reports breathlessness and multiple, circular, pruritic rashes over his right arm. He drives to his family physician’s office for evaluation. His past medical history is significant for hypertension and he takes lisinopril. Known allergies include latex, Hymenoptera, and aspirin. His blood pressure is 118/68 mm Hg; heart rate is 104/min and regular; respiratory rate is 22/min; temperature is 37.7°C (99.8°F). There is non-pitting edema but erythema with raised wheels are present in the region of the right arm. Auscultation of the lungs reveals mild wheezing at the lung bases. Which of the following is the best course of action in the management of this patient?

Epinephrine and go to the emergency department

Methylprednisolone and go to the emergency department

Diphenhydramine and go to the emergency department

Albuterol and go to the emergency department

You are working in the emergency room of a children's hospital when a 4-year-old girl is brought in by ambulance due to "difficulty breathing." The patient had been eating lunch on a school field trip when she suddenly complained of abdominal pain. Shortly thereafter, she was noted to have swelling of the lips, a rapidly developing red rash and difficulty breathing. In the ambulance her blood pressure was persistently 80/50 mmHg despite intramuscular epinephrine. In the course of stabilization and work up of the patient, you note an elevated tryptase level. What is the mechanism behind this elevated tryptase level?

Cross-linking of IgE on mast cells

IgM mediated complement activation

Antibody-antigen immune complexes

Cross-linking of IgG on mast cells

An orthopaedic surgeon at a local community hospital has noticed that turnover times in the operating room have been unnecessarily long. She believes that the long wait times may be due to inefficient communication between the surgical nursing staff, the staff in the pre-operative area, and the staff in the post-operative receiving area. She believes a secure communication mobile phone app would help to streamline communication between providers and improve efficiency in turnover times. Which of the following methods is most appropriate to evaluate the impact of this intervention in the clinical setting?

Failure modes and effects analysis

A 29-year-old woman with hypothyroidism comes to her primary care physician for advice on a health insurance plan. She works as a baker and owns a small bakery. The patient explains that she would like to have affordable monthly premiums. She would be willing to make additional payments to be able to see providers outside her network and to get specialist care if referred by her primary care physician. Which of the following health insurance plans would be most appropriate?

Health maintenance organization

Preferred provider organization

Anaphylaxis and allergic emergencies for USMLE Step 3: High-Yield Management Lessons

Pathophysiology & Triggers - The Reaction Ignition

Type I (Immediate) Hypersensitivity: Initial exposure to an allergen prompts IgE antibody production. Subsequent exposure leads to allergen cross-linking of IgE on mast cells and basophils.
Massive Mediator Release: This triggers degranulation, releasing pre-formed mediators like histamine and tryptase, causing vasodilation, increased vascular permeability, and smooth muscle spasm.

IgE-mediated mast cell activation vs. cytokine activation

Common Triggers:
- Foods: Peanuts, tree nuts, shellfish, milk
- Medications: Penicillin, NSAIDs, anesthetics
- Insect Stings: Bees, wasps, fire ants
- Other: Latex, exercise

⭐ Serum tryptase is a specific marker for mast cell activation and helps confirm an anaphylaxis diagnosis, peaking 1-2 hours post-reaction.

Clinical Presentation - Signs of System Shock

Symptoms manifest rapidly, often within 5-30 minutes of allergen exposure across multiple systems.

Cutaneous (~90%):
- Urticaria (hives), diffuse pruritus
- Angioedema (swelling of lips, tongue, face)
Respiratory:
- Dyspnea, wheezing (bronchospasm)
- Stridor, hoarseness (laryngeal edema)
Cardiovascular:
- Hypotension (SBP < 90 mmHg or >30% drop)
- Tachycardia, dizziness, or syncope
Gastrointestinal:
- Nausea, vomiting, abdominal cramps

⭐ Be aware: Cutaneous findings may be absent in up to 20% of cases, especially in rapid-onset, profound shock.

Diagnostic Criteria - Nailing the Diagnosis

Diagnosis is clinical. Any 1 of the following 3 criteria confirms anaphylaxis.

Confirmatory Test: Serum tryptase can confirm the diagnosis retrospectively; levels peak 1-2 hours after reaction onset.

⭐ Hypotension is not required for diagnosis. The most common presentations involve skin and respiratory symptoms without a drop in blood pressure.

Acute Management - The Epi‑sode Response

Immediate Action: ABCs & Epinephrine

FIRST-LINE: Intramuscular (IM) Epinephrine is critical.
- Adult Dose: 0.3-0.5 mg (1:1000 solution) into anterolateral thigh.
- Pediatric Dose: 0.01 mg/kg (max 0.3 mg).
- May repeat every 5-15 minutes.
ADJUNCTIVE THERAPY:
- Antihistamines: H1 blockers (Diphenhydramine) + H2 blockers (Ranitidine/Famotidine).
- Glucocorticoids: (Methylprednisolone) to prevent biphasic reactions.
- Supportive: IV fluids for refractory hypotension; nebulized albuterol for bronchospasm.

⭐ A biphasic reaction (symptom recurrence 1-72 hours after initial resolution without re-exposure) can occur in up to 20% of patients. Observation is key.

Epinephrine auto-injector administration steps

Biphasic & Refractory - The Second Wave

Biphasic Anaphylaxis: Symptom recurrence 1-72 hours post-resolution without re-exposure to the allergen.
Refractory Anaphylaxis: Persistent symptoms despite receiving ≥2 doses of epinephrine.
- Management: IV epinephrine drip. Consider glucagon for patients on beta-blockers.
Disposition: Observe patients for 4-8 hours after complete symptom resolution to monitor for a potential second wave.

⭐ Corticosteroids are administered with the aim of preventing biphasic reactions, though evidence for efficacy is varied.

High‑Yield Points - ⚡ Biggest Takeaways

Anaphylaxis is a Type I (IgE-mediated) hypersensitivity reaction; requires prior sensitization.

Intramuscular epinephrine is the first-line, life-saving treatment and should never be delayed.

Airway compromise (stridor, hoarseness) is a primary cause of death; secure the airway early.

Biphasic reactions can occur 1-72 hours after apparent resolution; always observe patients.

Aggressive IV fluids are critical to counter distributive shock from massive vasodilation.

Adjunctive therapies (antihistamines, corticosteroids) treat symptoms but do not replace epinephrine.

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