SummaryWe searched MEDLINE, Embase, CINAHL, AMED and CENTRAL databases until December 2014 and included 133 randomised controlled trials of peri-operative gabapentin vs placebo. Gabapentin reduced mean (95% CI) 24-h morphine-equivalent consumption by 8.44 (7.26-9.62) mg, p < 0.001, whereas more specific reductions in morphine equivalents were predicted (R 2 = 90%, p < 0.001) by the meta-regression equation: 3.73 + (À0.378 9 control morphine consumption (mg)) + (À0.0023 9 gabapentin dose (mg)) + (À1.917 9 anaesthetic type), where 'anaesthetic type' is '1' for general anaesthesia and '0' for spinal anaesthesia. The type of surgery was not independently associated with gabapentin effect. Gabapentin reduced postoperative pain scores on a 10-point scale at 1 h, 2 h, 6 h, 12 h and 24 h by a mean (95% CI) of: 1.68 (1.35-2.01); 1.21 (0.88-1.55); 1.28 (0.98-1.57); 1.12 (0.91-1.33); and 0.71 (0.56-0.87), respectively, p < 0.001 for all. The risk ratios (95% CI) for postoperative nausea, vomiting, pruritus and sedation with gabapentin were: 0.78 (0.69-0.87), 0.67 (0.59-0.76), 0.64 (0.51-0.80) and 1.18 (1.09-1.28), respectively, p < 0.001 for all. Gabapentin reduced pre-operative anxiety and increased patient satisfaction on a 10-point scale by a mean (95% CI) of 1.52 (0.78-2.26) points and 0.89 (0.22-1.57) points, p < 0.001 and p = 0.01, respectively. All the effects of gabapentin may have been overestimated by statistically significant small study effects.

A conscious individual, as defined in the Oxford English Dictionary, is 'awake and aware of their surroundings and identity'. However, consciousness represents a continuum with varying depths of consciousness. Coma is derived from the Greek 'koma' meaning a state of sleep; more specifically, it is defined medically as 'a state of unresponsiveness from which the patient cannot be aroused'. By convention we use the Glasgow coma scale (GCS) to provide a rapid, reproducible quantification of depth of unconsciousness. Although the GCS was developed for assessment and prediction of outcome in traumatic brain injury, it remains a useful tool to assess conscious state regardless of the causative factor. The GCS scores verbal, movement and visual responses to stimulation; a GCS <8 defines coma.