The patient was a 46-year-old man, 169 cm in height, and weighing 60 kg. He was diagnosed with myotonic dystrophy type 1 5 years previously, with weakness in the distal muscles and electrophysiological tests. The patient complained of vision disability due to cataracts, and phacoemulsification and intraocular lens implantation for both eyes were scheduled under general anesthesia.
Serum creatine phosphokinase level was 2921 U/L (normal range, 43–272 U/L). There were no further abnormal findings on preoperative tests, including an electrocardiogram and transthoracic echocardiogram. Although the relationship between myotonic dystrophy and malignant hyperthermia is controversial, we planned to use total intravenous anesthesia in this case.
The use of propofol, which is a commonly used intravenous anesthetic, might cause prolonged recovery after anesthesia in patients with myotonic dystrophy [2]. Therefore, we planned to use remimazolam to achieve fast recovery in this case.
No premedication was administered. We administered 6 mg/kg/h of remimazolam intravenously for 1 min. The patient lost the response to the verbal command after the infusion of remimazolam (Fig. 1). Continuous infusion of remifentanil (0.2 μg/kg/min) and remimazolam (0.5 mg/kg/h) was started. Neuromuscular monitoring of the left ulnar nerve was commenced using a train-of-four (TOF) stimulus (TOF watch, MSD). Three minutes after administration of 40 mg rocuronium, all four twitch responses disappeared, and tracheal intubation was performed. During surgery, the remimazolam dose was planned to maintain a bispectral index (BIS) value between 40 and 50 with continuous remifentanil infusion (0.1 μg/kg/min). However, the BIS value remained below 40 at a continuous infusion rate of 0.25 mg/kg/h, a 1/4 dose of the standard infusion rate. At this dose, the electroencephalogram showed continuous alpha wave spindles and delta waves (Fig. 2). Therefore, we judged that an appropriate anesthesia level was achieved. An additional 5 mg rocuronium was administered 60 min after the first dose because the first twitch response was observed. The surgery time was 46 min, and the infusion of all anesthetics was stopped. At the end of the procedure, TOF showed the first twitch response, and then 180 mg(3 mg/kg) of sugammadex was administered. Three minutes after administering sugammadex, the TOF recovered to 100%. Six minutes after remimazolam discontinuation, the patient opened his eyes on verbal command with sufficient spontaneous respiration. Next, the tracheal tube was removed. Finally, flumazenil (0.2 mg) was administered to boost the recovery, and the postanesthetic course was uneventful. A post-operative interview with the patient was performed on the day and the next day. He had no memory during the surgery.