Send to

Choose Destination
Anaesthesia. 2018 Mar;73(3):365-374. doi: 10.1111/anae.14065. Epub 2017 Oct 16.

Nitrous oxide-based vs. nitrous oxide-free general anaesthesia and accidental awareness in surgical patients: an abridged Cochrane systematic review.

Author information

Liverpool Reviews and Implementation Group, University of Liverpool, Liverpool, UK.
Patient Safety Research Unit, Department of Anaesthesia, Royal Lancaster Infirmary, Lancaster, UK.
Royal United Hospital Bath NHS Foundation Trust, Bath, UK.
School of Clinical Sciences, University of Bristol, Bristol, UK.
Department of Anaesthesia, Royal Lancaster Infirmary, Lancaster, UK.


Accidental awareness during general anaesthesia can arise from a failure to deliver sufficient anaesthetic agent, or from a patient's resistance to an expected sufficient dose of such an agent. Awareness is 'explicit' if the patient is subsequently able to recall the event. We conducted a systematic review into the effect of nitrous oxide used as part of a general anaesthetic on the risk of accidental awareness in people over the age of five years undergoing general anaesthesia for surgery. We included 15 randomised controlled trials, 14 of which, representing a total of 3439 participants, were included in our primary analysis of the frequency of accidental awareness events. The awareness incidence rate was rare within these studies, and all were considered underpowered with respect to this outcome. The risk of bias across all studies was judged to be high, and 76% of studies failed adequately to conceal participant allocation. We considered the available evidence to be of very poor quality. There were a total of three accidental awareness events reported in two studies, one of which reported that the awareness was the result of a kink in a propofol intravenous line. There were insufficient data to conduct a meta- or sub-group analysis and there was insufficient evidence to draw outcome-related conclusions. We can, however, recommend that future studies focus on potentially high-risk groups such as obstetric or cardiac surgery patients, or those receiving neuromuscular blocking drugs or total intravenous anaesthesia.


awareness; nitrous oxide; systematic review

[Indexed for MEDLINE]
Free full text

Supplemental Content

Full text links

Icon for Wiley
Loading ...
Support Center