Intrauterine Methylene Blue Injection Influences the Accuracy of Pulse Oximetry Readings

Objective: Intrauterine injection of methylene blue may disturb the accuracy of pulse oximetry readings. I report a case where false low readings on pulse oximetry were obtained after the patient received a transcervical injection of methylene blue during laparoscopy to assess tubal patency. Case Report: A young woman suffering from secondary infertility was scheduled for diagnostic laparoscopy under general anesthesia. Anesthesia was maintained with desflurane and pure oxygen. To evaluate tubal patency, a bolus dose of methylene blue was injected via the cervix into the uterine cavity. Shortly after the injection, the pulse oximeter reading decreased progressively from 100% to 89%. An arterial blood sample showed that arterial oxygen saturation was 100%. The reading slowly returned to the pre-injection level 30 minutes later. The patient recovered from the anesthesia and surgery uneventfully. Conclusions: Intraoperative administration of methylene blue may induce false low readings on pulse oximetry. The patient was not hypoxemic. If there is any doubt, arterial blood gas analysis should be done to ensure that the patient is well oxygenated.