Cholinergic Urticaria Triggered by Active Forced-Air Warming in the Post-Anesthesia Care Unit: A Case Report and Literature Review

Technical Summary: Cholinergic Urticaria Triggered by Active Forced-Air Warming in the PACU

Problem Statement
Cholinergic urticaria (CU), a subtype of chronic inducible urticaria triggered by core body temperature elevation, is frequently underrecognized in the Post-Anesthesia Care Unit (PACU). While postoperative shivering, active warming measures, and extubation-related sympathetic activation are known to increase core temperature, the specific convergence of these factors precipitating acute CU in the immediate postoperative period remains a diagnostic challenge. Clinicians often misdiagnose these cutaneous manifestations as perioperative drug hypersensitivity, anaphylaxis, or transfusion reactions due to the lack of systematic evaluation guidelines and the scarcity of literature regarding CU in this specific setting.

Methodology
This study employs a single-case report design combined with a narrative literature review.

• Case Subject: An 18-year-old male (ASA II) undergoing cochlear implantation under general anesthesia. The patient had a documented history of self-limiting, pruritic rashes following strenuous exercise or hot baths, though previously undiagnosed.
• Clinical Protocol: The patient underwent standard anesthesia induction (midazolam, propofol, sufentanil, rocuronium) and maintenance (sevoflurane). Intraoperative temperature dropped to a nadir of 36.1°C.
• Intervention and Observation: Upon transfer to the PACU, the patient exhibited post-extubation shivering. An active forced-air warming blanket was applied. The clinical team monitored vital signs, skin manifestations, and temperature changes over a 30-minute window following the application of warming.
• Diagnostic Approach: Diagnosis was established through a process of exclusion and correlation. The team ruled out drug hypersensitivity based on the temporal relationship between the rash and temperature rise, the absence of hypotension or bronchospasm, and the patient's specific history.
• Literature Review: The authors synthesized existing data on CU pathophysiology, differential diagnosis, and management guidelines (specifically EAACI/GA²LEN/EDF/WAO) to contextualize the case findings.

Key Results

• Clinical Presentation: Approximately 10 minutes after the initiation of forced-air warming, the patient developed diffuse, punctate wheals (1–3 mm) with pale centers and peripheral erythematous halos on the upper trunk. This was accompanied by severe pruritus and tachycardia (110–126 beats/min).
• Physiological Dynamics: Core body temperature rose from 36.1°C to 36.8°C (ΔT +0.7°C) during the episode. Hemodynamics remained stable (BP ~120/75 mmHg) with no respiratory compromise (SpO₂ 98%, clear breath sounds).
• Therapeutic Outcome: Immediate cessation of the warming device, reduction of ambient PACU temperature, and administration of intravenous diphenhydramine (20 mg) resulted in significant symptom relief within 20 minutes. The rash faded, and vital signs returned to baseline within 30 minutes. No recurrence was observed during a 24-hour follow-up.
• Pathophysiological Mechanism: The case demonstrates a synergistic effect where post-anesthetic shivering (increasing metabolic rate by up to 500%), exogenous active warming, and extubation-induced sympathetic activation collectively caused a rapid thermal spike. This triggered cholinergic nerve endings to release acetylcholine, leading to mast cell degranulation and histamine release.

Key Contributions

• Identification of a Specific Trigger Sequence: The paper highlights a distinct triad of triggers in the PACU—shivering, active forced-air warming, and extubation stress—that can precipitate CU, a mechanism often overlooked in favor of drug allergy hypotheses.
• Differentiation Framework: It provides a clear clinical distinction between CU and perioperative anaphylaxis. Key differentiators include the morphology of the rash (small, punctate, "satellite-like" wheals vs. generalized hives), the preservation of hemodynamic stability (absence of hypotension/bronchospasm), and the direct correlation with rapid temperature elevation.
• Management Strategy: The study advocates for a targeted, non-pharmacologic approach as the primary intervention: immediate cessation of warming measures and environmental cooling, followed by antihistamines only if necessary. This contrasts with the aggressive epinephrine protocols typically reserved for anaphylaxis.

Significance and Claims
The authors assert that while CU in the post-anesthesia period is infrequently reported, its clinical significance is substantial given the ubiquitous use of active perioperative temperature management. The paper claims that:

1. Diagnostic Precision: Clinicians must rigorously differentiate this benign, self-limiting condition from life-threatening anaphylaxis to avoid unnecessary escalation of treatment.
2. Synergistic Pathophysiology: The convergence of endogenous heat production (shivering) and exogenous warming creates a unique pathophysiological substrate for CU in the PACU.
3. Optimized Care: Prompt recognition allows for rapid resolution through temperature management and reassurance, ensuring patient safety without the risks associated with misdiagnosis and overtreatment.

The paper concludes that enhanced awareness of this specific etiology is essential for improving perioperative safety and patient outcomes in the recovery phase.