Severe Refractory Hypotension Following Patent Blue V Injection: A Case of Atypical Perioperative Anaphylaxis.

Background and Clinical Significance: Patent Blue V (PBV) is widely used for sentinel lymph node mapping but may rarely cause severe hypersensitivity reactions. These reactions can present atypically, with predominant cardiovascular collapse and minimal cutaneous manifestations, potentially delaying recognition and treatment. Case Presentation: We report the case of a 52-year-old woman who developed sudden and prolonged refractory hypotension shortly after PBV injection during melanoma surgery. The reaction initially occurred in the absence of bronchospasm or early significant cutaneous manifestations. Profound cardiovascular collapse preceded the delayed appearance of erythema and piloerection, making early recognition of perioperative anaphylaxis particularly challenging. Hemodynamic instability required aggressive fluid resuscitation and prolonged vasopressor support. Subsequent diagnostic work-up, including serum tryptase measurement and allergological evaluation, confirmed PBV-induced anaphylaxis. PBV-induced anaphylaxis may present with isolated cardiovascular collapse without typical clinical features. Conclusions: Early recognition and prompt hemodynamic support are essential to optimize outcomes in the perioperative setting.