塩酸プロピトカインの大量使用によりメトヘモグロビン血症を引き起こした症例

抄録

  Methemoglobinemia is a rare adverse event during dental treatment. Methemoglobinemia can be critical, leading to hypoxemia. In dental treatment, the amide-type local anesthetic propitocaine, which contains nitrites, can cause methemoglobinemia. We report a case of methemoglobinemia caused by propitocaine during general anesthesia. The patient was a 24-year-old woman (height, 163.3 cm ; weight, 46.5 kg) with WPW syndrome. The removal of a fixation plate after an open reduction of the mandible and wisdom teeth extractions were scheduled to be performed under general anesthesia. We chose propitocaine for local anesthesia to prevent tachycardia. Her SpO₂ gradually decreased from 99% to 93%. We tried to optimize her SpO₂ by increasing PEEP, FIO₂ and/or a lung recruitment maneuver but were unsuccessful. We suspected methemoglobinemia and checked her arterial blood gas levels. Since her partial oxygen tension was 435 mmHg and her O₂Hb was 95%, and a methemoglobin value was 4%. We have noticed methemoglobinemia. The total dose of propitocaine was 540 mg, and methemoglobinemia is typically caused by a dose of more than 400 mg without felypressin. The patient had no clinical signs of cyanosis or dyspnea. After surgery, we monitored the arterial methemoglobin value using pulse spectrophotometry (SpMet^® value ; Masimo Rainbow^®). The peak methemoglobin value was 5.6%, occurring 3 hours after the return of the patient to the ward. Orthtoluidine, a metabolite of methemoglobin, was thought to have contaminated the measured value. The SpO₂ recovered to 97%, and the SpMet^® value decreased to 0.6%. In conclusion, we propose a risk of methemoglobinemia that is caused by overdose of propitocaine. Continuous monitoring using pulse-spectrophotometry (SpMet^®) is useful for confirming the trend of the methohemoglobin value.