Prilocaine-induced methemoglobinemia evidenced by pulse oximetry

Methemoglobinemia was suspected in a healthy 19-year-old woman, when the pulse oximeter reading (SpO2) was 88% after a plexus brachialis block with 550 mg (35 ml, 1.5%) prilocaine. The patient was receiving 50% oxygen, and the PaO2 was 48.6 kPa (365 mmHg). After start of methylene blue treatment, with a total dose of 1 mg/kg, the SpO2 showed a gradual increase. This case report emphasises the potential advantage of arterial oxygen saturation monitoring with a pulse oximeter, but also the importance of the correct interpretation of the SpO2 reading.