Sentinel node mapping affects intraoperative pulse oximetric recordings during breast cancer surgery

In invasive breast cancer lymphatic mapping with patent blue vital dye (PBV) is used intraoperatively to identify the sentinel lymph nodes: the first axillary node draining the mammary lymphatic basin and first involved by the metastatic growth in breast cancer. Patent blue vital dye spreads to tissues giving a bluish tinge to patients. We have noted the possibility that intraoperative peripheral pulse oximetric (SpO2) values are artificially low when intradermal PBV is used.

Twenty patients with normal pulmonary function undergoing breast cancer surgery in standardized anesthesia either did or did not receive intradermal PBV sentinel node marking. The radial artery was cannulated for blood-gas-analysis; arterial oxygen tension (PaO2); and arterial oxygen saturation (SaO2). Peripheral oxygen saturation was measured using the light absorption technique. Red and infrared light (660 and 900 nm), used by pulseoxymetry, is partially absorbed when passing through the tissue. The amount of light absorbed is sensed and saturation calculated. The color of the skin was evaluated.

Peripheral oxygen saturation decreased only immediately after the injection of PBV, and remained at a significantly lower level (P<0.001) throughout the operation and up to 90 min postoperatively. Arterial oxygen tension and SaO2 values did not decrease after intradermal PBV. Patent blue vital dye made patients' skin more bluish (P<0.001). No changes in SpO2, PaO2 and SaO2 were found in control patients.

The spectrum of PBV has a peak absorption at 640 nm, thus making the SpO2 values incorrect. Peripheral oxygen saturation values are falsely low and true arterial oxygenation is not impaired when PBV is used during sentinel node mapping.