No explicit memory after skin incision without anesthetic except for remifentanil infusion

Abstract

To the Editor: Awareness and memory during general anesthesia is a serious problem. We experienced no explicit memory in a patient who was accidentally not administered anesthetic during skin incision before abdominal surgery. During that time, remifentanil alone was infused continuously. A 76-year-old woman, height 156.8 cm, weight 52 kg, was scheduled for peritoneal metastatic tumor resection. She had no complications or past history, except for lower anterior resection of the rectum with laparoscopic surgery 24 months prior. No premedication was administered. Anesthesia was induced with 200 mg thiopental and continuous infusion of remifentanil at the rate of 0.5 lg/kg/ min. She underwent tracheal intubation with the aid of 7 mg of vecuronium. The ventilation was controlled with 35% oxygen in air. After the induction of anesthesia, we planned to provide inhaled 3% sevoflurane during mask ventilation and 1% after tracheal intubation. We used the sevoflurane vaporizer 953 for servo 900C ventilator (MAQUET Critical Care AB, Solna, Sweden). This vaporizer requires activation of another switch in addition to adjusting the concentration dial to initiate sevoflurane inhalation (Fig. 1). We inadvertently forgot to activate the vaporizer switch to the ‘‘on’’ position. Accordingly, no sevoflurane was inhaled. After intubation, we decreased the rate of remifentanil infusion to 0.25 lg/kg/min during surgical-site sterilization and draping. Just before skin incision, we increased the rate of remifentanil infusion to 0.5 lg/kg/min. Twenty-four minutes after the administration of thiopental, skin incision was performed as usual. There was no apparent change of blood pressure or heart rate. The laparotomy was then continued, and there were no apparent changes in her vital signs. About 6 min after the skin incision, we noticed that the end-tidal concentration of sevoflurane on the monitor (S5, GE Healthcare Japan, Tokyo) was zero, and activated the vaporizer switch. We initially administered 3% sevoflurane, followed by 1–1.5% sevoflurane with 0.1–0.5 lg/kg/min of remifentanil. No other sedatives were administered. The operation was completed uneventfully with a total operation time of 1 h 39 min. The emergence from anesthesia was uneventful, with a total duration of anesthesia of 2 h 29 min. We asked the patient about her memories of the operation later on that same day and the next day. She had no explicit memory during the operation and expressed her thanks for a good anesthetic experience. The hypnotic that we administered to this patient was 200 mg of thiopental alone. Clinically, patients awaken from a single dose of thiopental about 5–10 min after administration because the drug levels in the brain decrease as a result of redistribution [1]. Accordingly, about 15 min after the end of the hypnotic action of thiopental, the patient was sedated only with remifentanil of 0.25–0.5 lg/kg/min. During the procedure, we had closed the eyelids of the patient using a sticking tape. The ears of the patient were free, but the sound in the operating room was minimal. Accordingly, it is possible that the patient was not aware of any stimuli except for the surgical procedure. Remifentanil has some sedative action and has been used for analgesia-based sedation [2, 3]. No implicit or explicit memory was found when a high concentration of remifentanil combined with low hypnotic concentration of propofol was maintained with high bispectral index (BIS) values [4]. Remifentanil 0.5 lg/kg/min might have been M. Yasuda R. Kubota T. Adachi (&) Department of Anesthesiology, Kitano Hospital, The Tazukekofukai Medical Research Institute, 2-4-20 Ohgimachi, Kita-ku, Osaka 530-8480, Japan e-mail: t-adachi@kitano-hp.or.jp