Therapy
Is a low transfusion threshold safe in critically ill patients with cardiovascular disease?
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Summary
Posted By: Gordon S. Doig
E-Mail: gdoig@med.usyd.edu.au
Posted Date: March 7, 2003
Title: Is a low transfusion threshold safe in critically ill patients with cardiovascular disease?
Authors: Hebert PC, Yetisir E, Martin C et al
Reference: Crit Care Med 2001;29(2):227-234
Link: Click here for a direct link to the paper. A password may be required for access to fulltext.
Abstract: OBJECTIVE: To compare a restrictive red blood cell transfusion strategy with a more liberal strategy in volume-resuscitated critically ill patients with cardiovascular disease.
SETTING: Twenty-two academic and three community critical care units across Canada.
STUDY DESIGN: Randomized controlled clinical trial.
STUDY POPULATION: Three hundred fifty-seven critically ill patients with cardiovascular diseases from the Transfusion Requirements in Critical Care trial who had a hemoglobin concentration of <90 g/L within 72 hrs of admission to the intensive care unit.
INTERVENTIONS: Patients were randomized to a restrictive strategy to receive allogeneic red blood cell transfusions at a hemoglobin concentration of 70 g/L (and maintained between 70 and 90 g/L) or a liberal strategy to receive red blood cells at 100 g/L (and maintained between 100 and 120 g/L).
RESULTS: Baseline characteristics in the restrictive (n = 160) and the liberal group (n = 197) were comparable, except for the use of cardiac and anesthetic drugs (p <.02). Average hemoglobin concentrations (85 +/- 6.2 vs. 103 +/- 6.7 g/L; p <.01) and red blood cell units transfused (2.4 +/- 4.1 vs. 5.2 +/- 5.0 red blood cell units; p <.01) were significantly lower in the restrictive compared with the liberal group. Overall, all mortality rates were similar in both study groups, including 30-day (23% vs. 23%; p = 1.00), 60-day, hospital, and intensive care unit rates. Changes in multiple organ dysfunction from baseline scores were significantly less in the restrictive transfusion group overall (0.2 +/- 4.2 vs. 1.3 +/- 4.4; p =.02). In the 257 patients with severe ischemic heart disease, there were no statistically significant differences in all survival measures, but this is the only subgroup where the restrictive group had lower but nonsignificant absolute survival rates compared with the patients in the liberal group.
CONCLUSION: A restrictive red blood cell transfusion strategy generally appears to be safe in most critically ill patients with cardiovascular disease, with the possible exception of patients with acute myocardial infarcts and unstable angina.
 
Are the Results Valid?
1. Was the assignment of patients to treatments randomized? ( Was allocation concealment maintained?)
Yes. The authors report using sealed opaque envelopes, distributed to each study center.
2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?
2a. Was followup complete?
Yes. Of the 357 patients in this a priori specified sub-group from the original TRICC trial, 30 day mortality was available on all patients and only 1 patient was lost to follow-up at 60 days.
2b. Were patients analyzed in the groups to which they were randomized?
Yes. A true intention to treat analysis was carried out. All patients were analyzed in the group to which they were originally randomzied.
3. Were patients, health workers, and study personnel blind to treatment?
No. Blinding was not possible.
4. Were the groups similar at the start of the trial?
The authors report that all baseline characteristics were similar at the start of the trial except for the less frequent use of diuretics in the restrictive transfusion group (43% vs. 58%, p<0.01) and the previous use of epidural anesthetics (8% vs. 2%, p <0.01). The effect of these imbalances were investigated with a multivariate logistic regression model.
5. Aside from the experimental intervention, were the groups treated equally?
Co-interventions that could have potentially modified oxygen delivery, including use of vasoactive drugs, PA catheter use, and maintenance of fluid balance were similar between groups throughout their ICU stay. The groups were also similar in regards to dialysis days, medication use, days of mechanical ventilation and surgical intervention.
What are the Results?
1. How large was the treatment effect?
Primary outcome:
  • 30 day mortality in both the restrictive and liberal transfusion groups was 23%

  • There was a 53% relative decrease in the number of red blood cell units transfused in the restrictive transfusion group (2.4 vs. 5.2 units, p<0.01).
  • 2. How precise was the estimate of the treatment effect?
    Primary outcome:
  • The 95% CI surrounding 30 day mortality ranged from -8.4% to 9.1% (p=1.00)
  • Will the Results Help Me In Caring For My Patients?
    1. Can the results be applied to my patient care?
    Although this is technically not an equivalency trial, it is an a priori defined subgroup analysis from a well conducted large RCT. As such, it does provide evidence to suggest that ICU patients with cardiovascular disease can be managed at a lower hemoglobin level.
    2. Were all clinically important outcomes considered?
    Yes. The investigators followed-up all patients to at least 60 days or hospital discharge, which ever is longer. Costs were not considered, but there is no evidence of increased resource utilization in the restrictive transfusion group and fewer units of RBCs were used.
    3. Are the likely treatment benefits worth the potential harms and costs?
    Although this study has reasonably wide confidence estimates around 30 day mortality (IF there is harm, we are reasonably certain this harm does not exceed a 10% mortality difference), there are absolutely no indications that any harm might result from a restrictive transfusion management plan. An evidence-based recommendation, which is the building block for an evidence-based guideline, that summarizes this topic can be found in the EBR section.

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