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 10-year-old boy is brought to the emergency room after a fall from a horse. He has severe pain in his right forearm. He has a history of asthma and atopic dermatitis. His current medications include an albuterol inhaler and hydrocortisone cream. Examination shows an open fracture of the right forearm and no other injuries. The patient is given a parenteral infusion of 1 L normal saline, cefazolin, morphine, and ondansetron. The right forearm is covered with a splint. Informed consent for surgery is obtained. Fifteen minutes later, the patient complains of shortness of breath. He has audible wheezing. His temperature is 37.0°C (98.6°F), heart rate is 130/min, respiratory rate is 33/min, and blood pressure is 80/54 mm Hg. Examination shows generalized urticaria and lip swelling. There is no conjunctival edema. Scattered wheezing is heard throughout both lung fields. Which of the following is the most appropriate next step in management?

Administer intramuscular epinephrine

Administer intravenous diphenhydramine

Administer intravenous methylprednisolone

Administer vancomycin and piperacillin-tazobactam

A 23-year-old woman comes to the emergency department because of a diffuse, itchy rash and swollen face for 6 hours. That morning, she was diagnosed with an abscess of the lower leg. She underwent treatment with incision and drainage as well as oral antibiotics. She has no history of serious illness. She is not in acute distress. Her temperature is 37.2°C (99°F), pulse is 78/min, and blood pressure is 128/84 mm Hg. Physical examination shows mild swelling of the eyelids and lips. There are multiple erythematous patches and wheals over her upper extremities, back, and abdomen. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. After discontinuing all recently administered drugs and beginning continuous vital sign monitoring, which of the following is the most appropriate next step in management?

Oral diphenhydramine and close monitoring

Endotracheal intubation and mechanical ventilation

Intramuscular epinephrine and intravenous hydrocortisone administration

Intravenous famotidine administration

Watchful waiting and regular reassessments

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

A 12-month-old boy presents for a routine checkup. The patient immigrated from the Philippines with his parents a few months ago. No prior immunization records are available. The patient’s mother claims that he had a series of shots at 6 months of age which gave him a severe allergic reaction with swelling of the tongue and the face. She also remembers that he had the same reaction when she introduced solid foods to his diet, including carrots, eggs, and bananas. Which of the following vaccinations are not recommended for this patient?

Intramuscular influenza vaccine

Measles, mumps, and rubella (MMR) vaccine

A 16-month-old male patient, with no significant past medical history, is brought into the emergency department for the second time in 5 days with tachypnea, expiratory wheezes and hypoxia. The patient presented to the emergency department initially due to rhinorrhea, fever and cough. He was treated with nasal suctioning and discharged home. The mother states that, over the past 5 days, the patient has started breathing faster with chest retractions. His vital signs are significant for a temperature of 100.7 F, respiratory rate of 45 and oxygen saturation of 90%. What is the most appropriate treatment for this patient?

Nasal suctioning, oxygen therapy and IV fluids

Albuterol, ipratropium and IV methylprednisolone

IV cefotaxime and IV vancomycin

Humidified oxygen, racemic epinephrine and intravenous (IV) dexamethasone

A 4-year-old girl is brought to the emergency department by her parents with a sudden onset of breathlessness. She has been having similar episodes over the past few months with a progressive increase in frequency over the past week. They have noticed that the difficulty in breathing is more prominent during the day when she plays in the garden with her siblings. She gets better once she comes indoors. During the episodes, she complains of an inability to breathe and her parents say that she is gasping for breath. Sometimes they hear a noisy wheeze while she breathes. The breathlessness does not disrupt her sleep. On examination, she seems to be in distress with noticeable intercostal retractions. Auscultation reveals a slight expiratory wheeze. According to her history and physical findings, which of the following mechanisms is most likely responsible for this child’s difficulty in breathing?

Airway hyperreactivity to external allergens causing intermittent airway obstruction

Defective chloride channel function leading to mucus plugging

Chronic mucus plugging and inflammation leading to impaired mucociliary clearance

Inflammation leading to permanent dilation and destruction of alveoli

Destruction of the elastic layers of bronchial walls leading to abnormal dilation

Anaphylaxis management — USMLE Lesson

Anaphylaxis - The Allergic Overload

Intramuscular injection sites: deltoid, vastus lateralis

Core Principle: Acute, life-threatening, multi-system allergic reaction. Early recognition and treatment are key.
First-Line Tx: Intramuscular (IM) Adrenaline is the single most important step.
Dose: 0.01 mg/kg of 1:1000 solution (max 0.5 mg) into anterolateral thigh. Repeat every 5-15 mins if no response.
Adjuncts: High-flow O₂, IV fluids for hypotension, nebulized salbutamol for bronchospasm, antihistamines (H1+H2 blockers), and corticosteroids.

⭐ Biphasic Anaphylaxis: A recurrence of symptoms can occur 1-72 hours after initial resolution, even without re-exposure. Mandates observation for at least 4-6 hours.

Immediate Response - Adrenaline First, Fast!

Drug of Choice: Adrenaline (Epinephrine) is the single most important, life-saving intervention.
Dose: 0.01 mg/kg of 1:1000 solution.
- Max dose: 0.5 mg in adults, 0.3 mg in children.
Route: Intramuscular (IM) injection into the mid-anterolateral thigh (vastus lateralis).
Frequency: Repeat every 5-15 minutes if no significant improvement.

Adjunctive (Second-Line) Therapies: Administer after adrenaline.
- Antihistamines: H1 blockers (e.g., Cetirizine) and H2 blockers (e.g., Ranitidine).
- Corticosteroids: IV Hydrocortisone or Methylprednisolone to prevent delayed/biphasic reactions.

⭐ Exam Favourite: The most common cause of fatality in anaphylaxis is delayed administration of adrenaline. Subcutaneous injection is no longer recommended due to slower absorption compared to the IM route.

Adjunctive Therapies - The Backup Crew

Antihistamines (H1 & H2 Blockers): For cutaneous symptoms.
- H1 Blocker (e.g., Cetirizine): 0.25 mg/kg.
- H2 Blocker (e.g., Ranitidine): 1 mg/kg.
- ⚠️ Do NOT relieve life-threatening respiratory or cardiovascular symptoms.
Corticosteroids: To prevent late-phase/biphasic reactions.
- Hydrocortisone: 5-10 mg/kg IV.
- Methylprednisolone: 1-2 mg/kg IV.
- - Onset of action is slow (4-6 hours).
Bronchodilators:
- Salbutamol/Albuterol nebulization for persistent bronchospasm despite adrenaline.

⭐ Corticosteroids are crucial to prevent biphasic reactions, where symptoms can recur 4-12 hours after initial resolution, even without re-exposure to the allergen.

Post-Crisis Care - Watch, Warn, & Ward

Observation: Monitor all patients for 4-8 hours post-resolution. Extend to 24 hours if severe, refractory, or history of biphasic reaction.
Biphasic Reaction: Symptom recurrence 1-72 hours later without re-exposure. Occurs despite initial steroid use.
Discharge Plan (The 3 E's):
- Epinephrine Auto-Injector: Prescribe TWO.
- Education: On avoidance & symptom recognition.
- Expert Referral: To an Allergist/Immunologist.

⭐ High-Yield: Biphasic reactions occur in up to 20% of anaphylaxis cases. Corticosteroids have NOT been definitively shown to prevent them.

Anaphylaxis Discharge Management and Prevention

High‑Yield Points - ⚡ Biggest Takeaways

Intramuscular Adrenaline (IM) is the first-line, life-saving drug for anaphylaxis, given in the anterolateral thigh.

The dose is 0.01 mg/kg of 1:1000 adrenaline, with a maximum of 0.5 mg.

Antihistamines (H1/H2 blockers) and corticosteroids are adjunctive therapies, not first-line treatment.

Repeat IM adrenaline every 5-15 minutes for persistent symptoms.

Always provide supplemental oxygen and secure IV access for fluids.

Observe patients for 4-8 hours due to the risk of a biphasic reaction.

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