The Effect of Intradermal Methylene Blue Application on Hemodynamic Stability Under General Anesthesia in Breast Surgery: A Prospective Observational Study

Sentinel lymph node biopsy is a standard procedure in breast cancer surgery to assess lymphatic spread. Methylene blue is widely used as a dye for sentinel lymph node mapping due to its safety, practicality, and cost-effectiveness. However, recent studies have suggested that methylene blue may have systemic vasopressor effects, particularly when it enters the circulation, by inhibiting guanylate cyclase and blocking nitric oxide pathways. This mechanism has been utilized in the management of refractory hypotension in septic shock, but its intraoperative hemodynamic effects during breast surgery remain unclear.

This prospective observational study will be conducted at Dr. Abdurrahman Yurtaslan Training and Research Hospital, Department of Anesthesiology and Reanimation, between August 1, 2025, and February 1, 2026. The study population will consist of two distinct cohorts: the Methylene Blue Group and the Control Group. Adult patients (aged 18-70) scheduled for elective breast surgery (mastectomy, lumpectomy, or sentinel lymph node biopsy) will be included. The Methylene Blue Group will consist of patients who receive intradermal methylene blue for sentinel lymph node mapping, while the Control Group will consist of patients undergoing breast surgery where no methylene blue or other mapping dyes are administered. All patients will be informed and written consent will be obtained prior to surgery. The study is entirely observational, with no intervention or alteration in the standard clinical management of patients.

Demographic data (age, BMI, ASA score), comorbidities, anesthesia protocols, methylene blue dose and timing (for the study group), and intraoperative hemodynamic parameters (blood pressure, heart rate, oxygen saturation) will be recorded for all participants. The incidence of intraoperative hypotension (defined as MAP <65 mmHg or a decrease of more than 20% from baseline) and the need for vasopressor support will be analyzed and compared between the two groups. Hemodynamic data will be collected at baseline (before anesthesia induction), immediately before methylene blue administration (or at a corresponding surgical time point for the control group), and at 5, 10, 15, 30, and 60 minutes after administration/reference point, as well as at the end of surgery.

The primary aim of this study is to assess and compare the impact of intradermal methylene blue on intraoperative hemodynamic stability against a control group in patients undergoing breast surgery under general anesthesia. By including a control group of patients who do not receive the dye, the study aims to isolate the specific hemodynamic effects of methylene blue from the general physiological changes associated with anesthesia and surgical stress. The results are expected to provide valuable information regarding the safety and potential vasopressor benefits of methylene blue in this context, helping anesthesia and surgical teams anticipate and manage possible hemodynamic changes during surgery. The findings may also contribute to the development of evidence-based protocols for the use of methylene blue in breast cancer surgery and guide future research in this area.