Twenty-three RCTs (1,504 patients) were included.
Larger versus smaller crystalloid preload (9 RCTs, 533 patients).
Only 3 RCTs had a quality score of greater than 2. Crystalloid preload was inconsistent in preventing hypotension; only 3 of the 9 RCTs reported a significant effect of a larger preload on the incidence of hypotension. There was a wide variation in the preload volume in the control and experimental groups. In 5 RCTs, the control group received little or no preload, whilst in 4 RCTs, the control groups received a preload volume between 750 and 1,800 mL. The use of prophylactic and therapeutic ephedrine varied among studies. Umbilical cord pH (5 RCTs): only 1 of the 5 RCTs reported a significant difference between the intervention groups. Apgar score of less than 7 (6 RCTs): only 1 of the 6 RCTs reported a significant difference between the intervention groups.
Maternal nausea and vomiting (2 RCTs): neither RCT reported a significant difference between the intervention groups.
Colloid (7 RCTs, 559 patients).
The quality scores ranged from 2 to 5, with 5 RCTs scoring more than 2. Colloid versus crystalloid (6 RCTs): 5 of the 6 RCTs reported a statistically-significant decrease in the incidence of hypotension for colloid, compared with crystalloid. Some investigators used equal volumes of crystalloid and colloid, whilst others used larger volumes of crystalloid.
Apgar scores or umbilical artery pH (6 RCTs): only 1 of the 6 RCTs showed an improved neonatal outcome in the colloid group.
Maternal nausea and vomiting (2 RCTs): neither RCT reported a significant difference between the intervention groups.
Mechanical interventions (7 RCTs, 447 patients).
Most studies were small with low quality scores; only 1 RCT scored more than 2. All patients received between 500 and 2,000 mL of prophylactic crystalloid.
Leg wrapping (3 RCTs, 203 patients): all 3 RCTs reported significant reductions in hypotension for leg wrapping, compared with control or leg elevation.
Inflatable splints (1 RCT, 46 patients): compared with control, inflatable splints significantly decreased hypotension after a crystalloid preload; hypotension was reduced from 83 to 48%. Inflatable boots (1 RCT, 79 patients): no difference was found in the rates of hypotension between the intervention groups. Tilting the patient's head down was of no significant benefit (1 RCT, 34 patients).