RCTs that compared fluid administration before induction of spinal anaesthesia (preloading) in women scheduled for elective Caesarean delivery versus fluid administration at the time of induction (co-loading) were eligible for inclusion. Outcomes of interest in the review were hypotension as defined in the primary studies (primary outcome), lowest blood pressure recorded, nausea and vomiting, umbilical artery pH, total volume of fluid administered and dose of vasoconstrictor used (secondary outcomes). Studies that compared types of fluid were excluded.
Participants in the included studies received approximately 500mL to 1,000mL of colloid or 1,000mL to 1,500mL of crystalloid fluid. Vasopressors used in the studies included ephedrine, phenylephrine and metaraminol in varying doses and combinations. Study definitions of hypotension varied; most common was a 20% reduction in systolic blood pressure. Outcomes reported in the review included Apgar scores under 7 at five minutes.
Four reviewers independently selected the studies. Disagreements were resolved by consensus.