Seventeen RCTs (n=636) were included.
Sixteen studies scored 3 or less out of 5 on the Jadad scale for quality; the remaining study scored 5. Most studies did not describe the randomisation method and most did not use blinding. None reported adequate allocation concealment. Seven studies explicitly reported the transfusion trigger.
Deliberate hypotension was associated with a significant reduction in blood loss (WMD -286 mL, 95% CI: -447, -127) and transfusion requirements (WMD -667 mL, 95% CI: -963, -370) compared with control.
For blood loss, results were consistent across all surgical procedures (orthognathic, total hip arthroplasty and spinal fusion) apart from knee arthroplasty, which showed an increase in blood loss in the hypotensive group. There was significant heterogeneity between subgroups of all types of surgery except orthognathic surgery, and for all types of hypotensive drugs except prostaglandin E1. The results were similar for high- and low-quality studies and for older and more recent studies.
There was no statistically significant difference between hypotension and control for duration of surgery (WMD -1.9 minutes, 95% CI: -7.2, 3.5) or surgical field quality rating (SMD -0.5, 95% CI: -1.1, 0.2).
There was no evidence for publication bias (funnel plot fairly symmetrical; Egger’s test, p=0.955).
Nine studies reported harms. No deaths were reported and studies reported no differences between hypotensive and control groups for cardiopulmonary, renal or hepatic complications.