Intraoperative awareness during general anaesthesia: results of an observational study

Background: Intraoperative awareness is a rare but extremely unfavourable phenomenon affecting 0.1–0.2% of patients who undergo surgery under general anaesthesia. The event exposes patients to stress and its remote, severe outcomes. The aim of the present study was to determine the incidence of intraoperative awareness in patients undergoing general anaesthesia. Methods: The observational questionnaire-based study was carried out in patients treated in one centre during a period of 8 months. Anaesthesia depth was monitored clinically using measurements of end-tidal concentration of volatile anaesthetic agent. After anaesthesia, accounts of patients regarding possible intraoperative awareness were analysed. Awareness was defined as recall events are confirmed or have a high likelihood of occuring in the intraoperative period. Results: Data from 199 patients were analysed. None of them experienced awareness during general anaesthesia (category A). Possible intraoperative awareness was observed in one patient (0.5%) (category B), and 17 patients (8.5%) experienced intraoperative dreaming. Conclusion: The incidence of intraoperative awareness in our study was low. The intraoperative monitoring including clinical analysis of anaesthetized patient as well as measurement of end-tidal concentration of volatile anaesthetic agent seems to be sufficient for prevention of episodes of awareness during general anaesthesia.