Distinguishing Delayed Post‑Procedural Hypotension from Anaphylaxis

Epidemiology of Anaphylaxis During Anesthesia

• Isolated hypotension occurs in only about 10 % of allergic anaphylaxis episodes that arise under anesthesia. 1, 2, 3
• Cutaneous manifestations (flushing, urticaria, rash) are present in ≈ 72 % of such cases. 4, 1, 2
• Bronchospasm or respiratory distress accompanies roughly 40 % of episodes. 4, 1
• Angio‑edema is observed in about 12 % of cases. 4, 1
• Tachycardia is the usual cardiac response; bradycardia occurs in ≈ 10 % of anaphylaxis events. 4, 1

Timing of Anaphylactic Reactions to Peri‑Procedural Drugs

• Anaphylaxis most commonly develops within minutes of drug exposure, but delayed onset up to 1 hour can occur. 4, 5, 2
• Substances such as antibiotics, IV colloids, and latex may provoke delayed reactions up to 1 hour after administration. 4, 5, 2
• A presentation 2–3 hours after discharge therefore exceeds the recognized window for drug‑induced anaphylaxis. 4

Clinical Presentation Suggesting a Non‑Anaphylactic Cause

• The combination of severe isolated hypotension occurring 2–3 hours post‑procedure, without any cutaneous, respiratory, or airway signs, is highly atypical for anaphylaxis and aligns more with delayed hemodynamic effects or residual sedation. 4, 1

Diagnostic Recommendations – Serum Tryptase

• Drawing tryptase at these intervals is essential; without these measurements, anaphylaxis cannot be definitively excluded retrospectively. 6, 1, 7, 5

Management of Severe Hypotension When Anaphylaxis Is Suspected (Grade III)

• Epinephrine 50 µg IV as the initial bolus if no other vasopressors have been given.
• Epinephrine 100 µg IV if the response to the initial dose is inadequate.
• Crystalloid 1 L rapid IV bolus, repeat as needed until adequate preload is achieved.
• If hypotension persists after 10 minutes, add a norepinephrine infusion (0.05–0.5 µg·kg⁻¹·min⁻¹).
• In the reported case, early initiation of pressors successfully stabilized the patient. 8

Post‑Procedure Monitoring Guidelines

• Patients undergoing outpatient extracorporeal shock‑wave lithotripsy (ESWL) with sedation should remain in a monitored setting for at least 6 hours or until they are clinically stable and symptoms are regressing. 8

Documentation Requirements for Future Cases

• Record the absence of cutaneous signs, respiratory symptoms, and tryptase measurements to support exclusion of anaphylaxis. 8, 6, 1

Bezold‑Jarisch Reflex: Pathophysiology, Clinical Differentiation, and Diagnostic Pitfalls

Pathophysiology

• The Bezold‑Jarisch reflex originates from sensory mechanoreceptors located in the inferoposterior wall of the left ventricle; unmyelinated vagal C‑fibers convey the signal to cranial medullary centers that regulate respiration, heart rate, and vascular tone. 9

Clinical Presentation – Differentiation from Anaphylaxis

• Bradycardia is the hallmark of the reflex, contrasting with the tachycardia seen in >90 % of anaphylactic reactions. 9

Diagnostic Pitfalls

• Anaphylaxis should not be presumed solely on the basis of hypotension; the presence of bradycardia (instead of tachycardia) and the lack of cutaneous or respiratory manifestations are indicative of the Bezold‑Jarisch reflex. 9