Intraoperative decrease in pulse oximeter readings following injection of isosulfan blue

Sentinel lymph node mapping, involving injection of isosulfan blue dye around a tumour, is beginning to be used in patients with carcinoma of the breast. Absorption of the dye into the circulation may interfere with pulse oximetry, causing falsely low readings. This report describes changes in pulse oximeter readings following injection of isosulfan blue for sentinel lymph node mapping in a patient with carcinoma of the breast.

An 83-yr-old female patient underwent sentinel node biopsy of the axilla followed by partial mastectomy for carcinoma of the left breast. Isosulfan blue was injected in the area of the tumour in the left breast. The SpO2 began to decrease 15 min after dye injection, reaching a nadir of 89-90% 30 min after injection. Arterial blood gas analysis showed normal arterial partial pressure of oxygen. Pulse oximeter readings did not return to normal until more than six hours after dye injection.

Review of the literature reveals a small number of case reports of similar occurrences of low pulse oximeter readings following injection of isosulfan blue or patent blue dye for lymphatic mapping. Data from these reports and the case described here suggest that the latency, magnitude and duration of effect on pulse oximeter readings following injection of these dyes is highly variable. It is important to rule out other causes of low pulse oximeter readings when this effect occurs; normal oxygenation can be verified with arterial blood gas analysis. Co-oximetry can be done to rule out methemoglobinemia as a cause of decreased SpO2.