Introduction: Perioperative anaphylaxis is a critical emergency that is difficult to diagnose under general anesthesia due to the inability to assess subjective symptoms and the frequent absence of cutaneous signs.

Case Report: A 56-year-old female patient with a history of anaphylactic shock caused by ceftriaxone three weeks prior was scheduled for breast-conserving surgery. Following anesthetic induction and 10 minutes after the administration of methylene blue, she developed severe hypotension (50/26 mmHg) and an abrupt drop in ETCO2 (28 mmHg) without any cutaneous manifestations.

Intervention or Treatment: Given the lack of response to the administration and increased infusion rate of norepinephrine, anaphylactic shock was suspected, and titrated IV epinephrine boluses (50 mcg) were initiated, followed by a continuous infusion, in conjunction with aggressive volume replacement with crystalloids and 100% oxygen therapy, resulting in an immediate and adequate response.

Course and Outcomes: The patient achieved hemodynamic stabilization with epinephrine, allowing for the gradual withdrawal of vasopressors, uncomplicated extubation in the operating room, and hospital discharge on the third postoperative day.

Conclusions: Sudden cardiovascular collapse without cutaneous signs should raise suspicion of transanesthetic anaphylaxis. Epinephrine is the indispensable first-line medication; a recent history of anaphylaxis requires prior allergy evaluation to identify risk factors before a new procedure. Although the acute event was resolved according to standard protocol and consultation with an allergist was pending for follow-up, the absence of such an evaluation following the first event in our case is undeniable.