The authors concluded that there was some evidence that deliberate hypotension could reduce blood loss and transfusion requirements in orthopaedic surgery patients, but the evidence was generally limited to small poor-quality studies and further research is required. Despite the limitations of the search strategy, and the differences between the studies, the authors’ cautious conclusion appears appropriate.

To evaluate the effects of deliberate hypotension on blood loss and transfusion requirements in patients undergoing orthopaedic surgery.

MEDLINE, EMBASE and the Cochrane Library were searched from inception to January 2006; the search terms were reported. In addition, the reference lists of selected studies and reviews were screened and local experts in the field were contacted for details of other studies. Only English language reports were included.

Study designs of evaluations included in the review

Randomised controlled trials (RCTs) were eligible for inclusion in the review.

Specific interventions included in the review

Studies that evaluated any method of inducing deliberate hypotension were eligible for inclusion. The included studies evaluated six methods of inducing deliberate hypotension: sodium nitroprusside, volatile anaesthetics, prostaglandin E1, epidural blockade, remifentanil and propranolol. Two studies used haemodilution as a cointervention. All studies used no hypotension as the control treatment. In one study of knee arthroplasty patients, an intra-operative tourniquet was used in the control group only.

Participants included in the review

Studies of patients undergoing orthopaedic surgery were eligible for inclusion. The majority of included studies were in patients undergoing orthognathic surgery or total hip arthroplasty; other studies were in patients undergoing total knee arthroplasty or spinal fusion.

Outcomes assessed in the review

Studies that assessed intra-operative blood loss were eligible for inclusion; this was the primary review outcome. Secondary review outcomes included volume of intra-operative blood transfused, duration of surgery and surgical field quality. The included studies assessed the quality of the surgical field using various ordinal scales (details were reported). Where reported, transfusion triggers varied among studies (details were reported). The review also assessed harms.

How were decisions on the relevance of primary studies made?

Two reviewers independently selected the studies. Any disagreements were resolved by consensus.

Two reviewers independently assessed validity on the basis of randomisation method, allocation concealment, blinding and completeness of follow-up. Study quality was scored using a modified version of the Jadad scale. Studies scoring more than 3 out of 5 points were classified as high quality.

Two reviewers independently extracted data on the outcomes of interest from each study. Any disagreements were resolved by consensus. The effect size and corresponding standard deviation were extracted where possible. When standard deviations were not available, they were estimated using reported methodology. Where studies used multiple treatment groups, only the first reported group treated with hypotension was used.

How were the studies combined?

Pooled weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated for outcomes measured in the same way across homogeneous studies, while pooled standardised mean differences (SMDs) with 95% CIs were calculated where different outcome measures were used or the studies were heterogeneous. The random-effects model of DerSimonian and Laird was used. Publication bias was assessed using a funnel plot and Egger’s test.

How were differences between studies investigated?

Statistical heterogeneity was assessed using an inverse variance test (p<0.5 indicated significant heterogeneity). Subgroup analysis was performed to explore the influence on blood loss of type of surgery, methodological quality and publication date.

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.

There was some evidence that deliberate hypotension could reduce blood loss and transfusion requirements in patients undergoing orthopaedic surgery, but the evidence was generally limited to small poor-quality studies and further research is required.

The review addressed a clear question that was defined in terms of the participants, intervention, outcomes and study design. Several relevant sources were searched but no attempts were made to minimise publication or language bias. The potential for publication bias was assessed and no evidence of it was found. Methods were used to minimise reviewer error and bias in the study selection, validity assessment and data extraction processes. Validity was assessed and the results were reported. Studies were pooled using meta-analyses, statistical heterogeneity was assessed, and forest plots were presented. Where significant heterogeneity was found, potential causes were examined. However, heterogeneity remained significant for most subgroups. Despite the limitations of the search strategy and the heterogeneity between the studies, which were predominantly small and of poor quality, the authors’ cautious conclusion appears appropriate.

Practice: The authors did not state any implications for practice.

Research: The authors stated the need for further larger studies to assess the potential harms of deliberate hypotension; a large prospective cohort study may be the most appropriate study design.

Hamilton Health Sciences, Department of Anesthesia Academic Fund.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.