Which of the following results from severe allergic reaction producing overwhelming systemic vasodilatation and relative hypovolaemia?

Appeared in: AIIMS Patna NO - 2020

Explanation

Anaphylactic shock is a type of distributive shock resulting from a severe, systemic allergic reaction.
The reaction causes mast cells and basophils to release massive amounts of histamine and other inflammatory mediators.
Histamine leads to widespread vasodilation (widening of blood vessels) and increased capillary permeability (leakage of fluid from vessels).
This combination results in a 'relative hypovolemia,' where the vascular space is too large for the amount of blood in it, causing a drastic drop in blood pressure and tissue perfusion.

Option A: Hypovolaemic shock is caused by an absolute loss of blood or fluid volume (e.g., from bleeding or severe dehydration), not the relative hypovolemia from vasodilation described in the question.
Option C: Neurogenic shock is caused by a loss of sympathetic tone due to damage to the nervous system (e.g., spinal cord injury), not by an allergic reaction.
Option D: Septic shock is triggered by a systemic inflammatory response to a severe infection, not an allergic reaction. While it also involves vasodilation, the cause is different.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pathophysiology of different types of shock, specifically anaphylactic shock as background academic context rather than a clinical decision trigger.
Rapid recognition of anaphylactic shock is critical for patient survival. Nurses must be able to identify key signs like urticaria (hives), angioedema, respiratory distress, and sudden hypotension, especially after administration of a new drug or exposure to a known allergen.
The immediate nursing priority is to maintain the airway, administer epinephrine as prescribed (which counteracts vasodilation and bronchoconstriction), and activate emergency medical services.
What if? If the patient had hypotension and tachycardia but also a high fever, chills, and a known source of infection (e.g., a urinary tract infection), the diagnosis would shift to septic shock. The treatment would then focus on antibiotics, fluid resuscitation, and vasopressors, rather than epinephrine as the primary intervention.

How to Approach the Question

First, analyze the question to identify the core components of the described condition.
Note the three key phrases: 'severe allergic reaction,' 'systemic vasodilatation,' and 'relative hypovolaemia.'
The phrase 'severe allergic reaction' is the most specific and crucial clue.
Evaluate each option against this primary trigger.
Anaphylactic shock is, by definition, a shock state caused by a severe allergic reaction.
Rule out the other options based on their distinct causes: Hypovolaemic shock (absolute volume loss), Neurogenic shock (nervous system damage), and Septic shock (infection).

Concept Tested & Keywords

Concept Tested: Pathophysiology of different types of shock, specifically anaphylactic shock.
Stem keywords: severe allergic reaction, systemic vasodilatation, relative hypovolaemia
Lead-in keywords: Which of the following
Negative lead-in flag: false

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E6 Physiology Guyton 4SAE Part 2A p. 30-32

E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 143-145

Practise the full AIIMS Patna NO - 2020

Attempt every question from this paper in a timed mock, then review the full solution for each one.