Emergence from anaesthesia: a winding way back

Sir, Accidental awareness with recall during general anaesthesia (AAWR) is a rare complication of general anaesthesia with an overall incidence of ~1:19,000 anaesthetics [1]. About 20% of AAWR cases occur at the emergence from anaesthesia, while 90% of these events are potentially preventable, especially through the use of neuromuscular monitoring [1]. The remaining AAWR emergence episodes could be attributed to an error in anaesthesia management, such as inappropriate anaesthetic administration due to device malfunction or human error [2, 3]. In very rare cases, there is no readily identifiable cause. This letter chronicles the clinical presentation of an AAWR episode manifesting itself at the emergence from anaesthesia, in order to provide a picture of this rare complication (Table 1), and to underline how the pharmacodynamic and operating mechanism of general anaesthetics, and the relationships between consciousness and anaesthesia, pose a puzzle still too difficult to solve. A 58-year-old Caucasian man (86 kg, 178 cm) affected by colon cancer was selected for elective laparoscopic left hemicolectomy. Before the beginning of the surgery, midazolam 2 mg and fentanyl 100 μg were administered as premedication. Anaesthesia was induced with intravenous propofol, titrated (total dose 140 mg) until loss of consciousness (LOC), along with fentanyl 100 μg. Anaesthesia maintenance was obtained through end-tidal concentrations (ETAG) of desflurane (in 40% oxygen) with a minimum alveolar concentration (MAC) of 0.9. The ETAG-guide was achieved through a nomogram to estimate age, gender, weight, and height related MAC (Draeger Fabius® apparatus). Manually controlled remifentanil infusion was titrated on the patient’s response. In addition, haemodynamic variations were managed through the guidance of the non-invasive cardiac output monitoring (NICOM®) system. Neuromuscular blockade was obtained with cisatracurium 15 mg. The monitoring of the neuromuscular blockade was performed (NMT Trident Drager Infinity®) allowing the maintenance of the depth of anaesthesia (DoA) status (ETAG 0.9) until full reversal of the neuromuscular blockade. The operative course was uneventful and according to our standard anaesthetic approach, the ETAG value was maintained for the entire duration of the operation (2 hours and 15 minutes). At the end of surgery, remifentanil infusion was interrupted and extubation performed under recovery of the neuromuscular blockade (sugammadex 100 mg) with spontaneous breathing and the swallowing reflex. Moreover, we usually perform extubation under only a partial recovery of consciousness, usually corresponding to a MAC of about 0.2–0.3 with an anaesthetic expiration concentration ranging from 2 to 4%, in the case of desflurane. Although the recovery of consciousness at emergence was sudden, the patient immediately reported to the anaesthesiologist detailed conversations which had taken place between several professionals in the theatre. The report was so impressive as it described a conversation between two non-Italian visiting medical students speaking in English. The patient provided specific information about the duration of symptoms which lasted an estimated 3 to 5 minutes at the phase of awakening from anaesthesia. The patient did not experience paralysis and the AAWR episode did not cause him concern and distress. Moreover, conversational psychodiagnostic interviews, at 1 and 6 months, demonstrated that the patient had no psychiatric sequelae. The misuse of neuromuscular monitoring is a major risk factor for AAWR during emergence from anaesthesia [1], especially in case of butyrylcholinesterase deficiency [4]. However, a root cause analysis showed that the patient had no risk factors for AAWR, and had never undergone surgery. No equipment malfunction or human errors were detected,