CRD Summary: The authors concluded that adding clonidine to intrathecal local anaesthetic had beneficial effects on some, but not all measures of motor and sensory block. Adding clonidine reduced intra-operative pain but increased the risk of arterial hypotension. Given the low quality of the included studies and the possibility of publication bias, the reliability of the results is questionable.

[Included studies used a clonidine dose ranged from 15 to 150 μg. Local anaesthetics used were hyperbaric or isobaric bupivacaine, hyperbaric mepivacaine, isobaric prilocaine or hyperbaric tetracaine.]

CRD Commentary: The authors addressed a clear research question and intervention criteria were clearly stated. Participant and outcome inclusion criteria were not specified, and few data were given regarding the patients included in the review, making it hard to assess the generalisability of the results. The authors searched several computerised databases. Having no language restriction excluded the possibility of language bias. However, the search and study selection was performed by only one reviewer, meaning that there could have been bias and/or error during this phase of the review. No attempt was made to assess publication bias in the review, and the authors acknowledge that such bias is a possibility. Three authors independently assessed validity, which minimised the risk of error. The authors reported that the included studies were generally of poor quality and acknowledged that this was likely to have led to an overestimation of effect. No subgroup analysis of high quality trials was reported. Assessing multiple outcomes may have led to some results being reported as statistically significant by chance.

The a priori decisions regarding when to synthesise the results using meta-analysis were appropriate. Most of the results were reported using a narrative synthesis, grouped according to outcome. In these cases, when the authors decided not to conduct a meta-analysis because of statistical heterogeneity, they reported the median treatment effect between groups. This value was misleading, as it was not a weighted summary measure; it has not been reported in this abstract.

Given the low quality of the included diverse studies and the possibility of publication bias, the reliability of the results is questionable.