Critical Care Medicine-Infections and Immunologic Disease>>>>>Immunological Effects of Infections
Question 3#

A 68-year-old man with bronchiectasis and severe pneumonia is mechanically ventilated in the ICU. He is treated with empiric meropenem and vancomycin based on the culture data obtained during prior admission, and his blood pressure is supported with norepinephrine. On ICU day 3, his sputum culture reveals ceftriaxone-susceptible Streptococcus pneumoniae. Thirty minutes after the dose of ceftriaxone, he is noted to have worsening hypotension and requires increasing doses of norepinephrine. As ICU physician prepares to perform cardiac ultrasound, he notices urticaria on his chest.

Which of the following laboratory tests would clarify the diagnosis?

A. Angiotensin-converting enzyme (ACE) level
B. Tryptase level
C. Histamine level
D. Complete blood count (CBC)

Correct Answer is B


Correct Answer: B

Anaphylactic shock is a life-threatening condition that may be difficult to recognize in sedated, intubated patients. Clinical manifestations include increased peak airway pressures, urticarial rash, hypotension, or cardiac arrhythmias. The patient in the vignette has bronchiectasis and history of previous admissions for pneumonia, for which he likely received cephalosporin antibiotics in the past.

Anaphylaxis may either be IgE mediated or non-IgE mediated. In IgEmediated anaphylaxis, mast cell degranulation, and histamine and protease release (ie tryptase) lead to the clinical manifestations. Non-IgE– mediated anaphylaxis occurs via neutrophil, eosinophil, and complement activation. Common triggers of anaphylaxis include antibiotics, nonsteroidal anti-inflammatory medications, certain anesthetic agents, food and insect venom.

Biomarkers, if positive, are useful in diagnosing anaphylaxis. Tryptase has a plasma half-life of approximately 2 hours. For comparison, a baseline tryptase level should be measured 24 hours after resolution of anaphylaxis to ensure accurate interpretation. Owing to the kinetics of tryptase release, it is the most clinically useful serum marker of anaphylaxis. While histamine is released by mast cells during anaphylactic reactions, peak serum levels occur within 5 to 10 minutes and return to baseline within 1 hour, making it a suboptimal clinical biomarker. ACE level is not a marker of anaphylaxis. Nonspecific changes during anaphylaxis may be seen on CBCs including leukocytosis, neutrophil predominance, and possibly increased eosinophilia. However, this pattern may be seen in a variety of conditions and would not confirm the diagnosis. Further, in a patient with suspected infection, leukocytosis and neutrophil predominance would be expected.


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