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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

The effects of mild perioperative hypothermia on blood loss and transfusion requirement

S Rajagopalan, E Mascha, J Na, and DI Sessler.

Review published: 2008.

CRD summary

This review evaluated the impact of mild perioperative hypothermia on surgical blood loss and transfusion requirements. The authors concluded that that even mild hypothermia may significantly increase blood loss by approximately 16 per cent (4-26%) and increase the risk of a transfusion being required by around 22 per cent (3-37%). Due to limitations in the review methodology and reporting, these results should be treated with caution.

Authors' objectives

To evaluate the impact of mild perioperative hypothermia on surgical blood loss and transfusion requirements.

Searching

MEDLINE (1966-2006) and The Cochrane Library (2006) were searched in all languages (search terms reported). Bibliographies of the retrieved articles were checked for relevant citations. Only published articles were considered for inclusion.

Study selection

Eligible studies for this review were randomised controlled trials (RCTs) with 15 or more patients that compared normothermic patients with patients who had mild intra-operative hypothermia. Studies where the average core temperature fell to below 34°C or local cooling had been used to reduce bleeding were excluded. Relevant outcomes were specified as blood loss and transfusion requirement; at least one of these outcomes was reported by all included studies. The population of interest was not pre-specified, but the included studies covered a range of surgical procedures (hip arthroplasty, hysterectomy, CABG, abdominal or cardiac surgery, gastric bypass and spinal surgery). Two reviewers independently assessed studies for inclusion.

Assessment of study quality

Quality of the primary blood loss studies was assessed by method of randomisation, intent to treat, blood loss primary outcome and objective measure of blood loss, and summed as a quality score from 0-7 points with each criteria worth varying numbers of points. The authors did not state how the validity assessment was carried out.

Data extraction

For each included study, data were extracted on intra-operative blood loss and total blood loss. These data were presented as a mixture of means and standard deviations (SD), medians (range) and means and standard errors (SE), which the authors converted to a log-transformed mean (SD) blood loss (transformation procedure detailed in paper). The authors stated neither how the data were extracted for the review nor how many reviewers performed the data extraction, but they stated that study authors were contacted for missing data where possible.

Methods of synthesis

A random-effects meta-analysis was used to calculate effect sizes for each study (ratio of geometric means) as the ratio of normothermic to hypothermic mean blood loss. Transfusion requirements were also analysed using a random-effects analysis. The relative risk (RR) of any transfusion versus no transfusion was calculated for each study in normothermic versus hypothermic patients. Heterogeneity was assessed using the Q statistic and associated p value. Publication bias was assessed using funnel plots. Correlations between study quality and estimated treatment effects were assessed using Pearson's correlations.

Results of the review

A total of 15 RCTs were included (n= 1,419) of which 14 contributed to analysis of blood loss and 10 to the transfusion analysis. Quality assessment was reported in a table ranging from 0 to 7 points out of a possible 7. Overall quality score was not correlated with the observed effect sizes in the blood loss studies. Funnel plots for both outcomes indicated low levels of publication bias from a fairly symmetrical plot.

Blood loss (14 RCTs, n=1,219): pooled analysis found normothermia was associated with significantly lower levels of blood loss than hypothermia; ratio of geometric mean total blood loss = 0.84 (95% CI: 0.74, 0.96). Significant heterogeneity was noted in this analysis (Q: 62.3, p<0.001).

Transfusion requirement (10 RCTs, n=895): pooled analysis found normothermia was associated with significantly lower need for transfusion compared with hypothermia, RR 0.78 (95% CI: 0.63, 0.97, p=0.027). No significant heterogeneity was found in this analysis (Q: 11.4, P=0.25).

Authors' conclusions

This analysis indicated that even mild hypothermia (<1°C) may significantly increase blood loss by approximately 16 per cent (4-26%) and increase the risk of a transfusion being required by around 22 per cent (3-37%).

CRD commentary

This review addressed a clear clinical question, but the inclusion criteria could have been more detailed in terms of the intervention/comparator arms (no definition of normothermic or hypothermic was given) and the populations (no restriction on type of surgery meant a wide variety of procedures were included in this review, potentially resulting in clinical heterogeneity). The variability in included studies was reflected in the heterogeneity identified by the authors and may have resulted in less accurate effect estimates. The searches were limited and did not address unpublished literature. The methodology was not clearly reported and this review may have been vulnerable to bias and/or error at the data extraction/quality assessment stages. Relatively little data on the primary study populations were reported, so it was difficult to ascertain if the decision to pool the studies was appropriate. The results of the meta-analysis and the review overall may not be reliable.

Funding

National Institutes of Health grant no: GM 061655 and Joseph Drown Foundation

Bibliographic details

Rajagopalan S, Mascha E, Na J, Sessler D I. The effects of mild perioperative hypothermia on blood loss and transfusion requirement. Anesthesiology 2008; 108(1): 71-77. [PubMed: 18156884]

Indexing Status

Subject indexing assigned by NLM

MeSH

Blood Loss, Surgical /prevention & control; Blood Transfusion /standards; Humans; Hypothermia, Induced /adverse effects; Intraoperative Complications /epidemiology /etiology; Perioperative Care /adverse effects /methods /standards; Randomized Controlled Trials as Topic /methods

AccessionNumber

12008009311

Database entry date

31/03/2009

Record Status

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.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 18156884

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