July 30 2020: This Cochrane Review has been withdrawn from publication. The review was temporarily withdrawn in 2013. Cochrane Anaesthesia has now decided to permanently withdraw the review. Cochrane Anaesthesia intends to publish a new review on this topic in the future.
October 17 2013: Following comments received via direct correspondence which have challenged the eligibility criteria and interpretation of the evidence summarized in this review, the CARG editorial team has decided to temporarily withdraw the review from the CDSR whilst the comments are considered further and addressed.
The editorial group responsible for this previously published document have withdrawn it from publication.