基準投与量以下の塩酸プロピトカインの浸潤麻酔により発症したメトヘモグロビン血症の1例

<p>  Methemoglobinemia is reportedly caused by propitocaine administration. According to the clinical statement from the Japanese Dental Society of Anesthesiology, the maximum dose of propitocaine is 400-600 mg (6-8 mg/kg). We experienced a case of propitocaine-induced methemoglobinemia at a dose of 4.3 mg/kg in a 28-year-old woman with a height of 152.8 cm and weight of 50.8 kg. Surgery for placement of a dental implant was scheduled under intravenous sedation. The patient had a diagnosis of schizophrenia and took aripiprazole regularly. We planned to inject 3% propitocaine and 0.03 IU/mL felypressin as local anesthetic because aripiprazole is contraindicated for combined administration of adrenaline. Intravenous sedation was maintained with midazolam and propofol. The patient’s initial SpO₂ was 96% under air, but rose to 94% after administration of 7.2 mL propitocaine. Administration of oxygen resulted in recovery of SpO₂ to 100%, and her final SpO₂ was 96% under air after the need for sedation. However, SpO₂ rose to 91% after 20 min in the recovery room. We started to monitor the hemoglobin concentration ; SpMet^® using a pulse CO oximeter (Rainbow^®, MASIMO Inc.), which was 4.6%. We diagnosed the patient with methemoglobinemia and continued to measure the hemoglobin concentration and this measurement decreased to 2.5% 4h and 25 min after propitocaine injection. We decided to discharge the patient from the hospital because the hemoglobin concentration was lower than normal value ; <3% and the patient strongly wished to be discharged. The patient was ultimately discharged from the hospital without any symptoms of methemoglobinemia.</p>