Is haemoglobin below 7.0 g/dL an optimal trigger for allogenic red blood cell transfusion in patients admitted to intensive care units? A meta-analysis and systematic review

Abstract

Objectives: We employed a comprehensive systematic review and meta-analysis to assess benefits and risks of a threshold of haemoglobin level below 7 g/dL versus liberal transfusion strategy among critically ill patients, and even patients with septic shock.

Design: Systematic review and meta-analysis.

Data sources: We performed systematical searches for relevant randomised controlled trials (RCTs) in the Cochrane Library, EMBASE and PubMed databases up to 1 September 2019.

Eligibility criteria: RCTs among adult intensive care unit (ICU) patients comparing 7 g/dL as restrictive strategy with liberal transfusion were incorporated.

Data extraction and synthesis: The clinical outcomes, including short-term mortality, length of hospital stay, length of ICU stay, myocardial infarction (MI) and ischaemic events, were screened and analysed after data collection. We applied odds ratios (ORs) to analyse dichotomous outcomes and standardised mean differences (SMDs) to analyse continuous outcomes with fixed or random effects models based on heterogeneity evaluation for each outcome.

Results: Eight RCTs with 3415 patients were included. Compared with a more liberal threshold, a red blood cell (RBC) transfusion threshold <7 g/dL haemoglobin showed no significant difference in short-term mortality (OR: 0.90, 95% CI: 0.67 to 1.21, p=0.48, I²=53%), length of hospital stay (SMD: -0.11, 95% CI: -0.30 to 0.07, p=0.24, I²=71%), length of ICU stay (SMD: -0.03, 95% CI: -0.14 to 0.08, p=0.54, I²=0%) or ischaemic events (OR: 0.80, 95% CI: 0.43 to 1.48, p=0.48, I²=51%). However, we found that the incidence of MI (OR: 0.54, 95% CI: 0.30 to 0.98, p=0.04, I²=0%) was lower in the group with the threshold <7 g/dL than that with the more liberal threshold.

Conclusions: An RBC transfusion threshold <7 g/dL haemoglobin is incapable of decreasing short-term mortality in ICU patients according to currently published evidences, while it might have potential role in reducing MI incidence.

Keywords: intensive care units; red blood cells; septic shock; transfusion.

Figure 1

Flow chart for study selection. Online databases, including Cochrane Library, EMBASE and PubMed, were systematically searched. Finally, nine RCTs with 3415 patients were included in the meta-analysis. RCTs, randomised controlled trials.

Figure 2

Forest plot of all-cause short-term mortality in ICU patients. The OR and 95% CI for short-term mortality between the restrictive and liberal transfusion thresholds are presented in the forest plot. The threshold of haemoglobin <7 g/dL showed no obvious improvement in short-term mortality when compared with the liberal threshold. ICU, intensive care unit; M-H, Mantel-Haenszel.

Figure 3

Forest plot of the length of hospital stay. The forest plot shows the mean difference and 95% CI for the length of hospital stay between the two groups. Blood transfusion at the restrictive threshold resulted in no significant difference of hospital stays compared with blood transfusion at the more liberal threshold.

Figure 4

Forest plot of the length of ICU stay. The difference in the length of ICU stay in the groups with different transfusion thresholds is shown by the mean difference and 95% CI in the forest plot. No marked improvement was seen in the length of ICU stay with a transfusion threshold of haemoglobin <7 g/dL. ICU, intensive care unit.

Figure 5

Forest plot of myocardial infarction in ICU patients after RBCs transfusion. The forest plot shows the ORs and 95% CI for myocardial infarction in the groups of ICU patients with different transfusion thresholds. Blood transfusion at a threshold of haemoglobin <7 g/dL significantly decrease in the rate of myocardial infarction compared with the more liberal threshold. ICU, intensive care unit; M-H, Mantel-Haenszel; RBC, red blood cell.

Figure 6

Forest plot of ischaemic events/thromboembolic events in ICU patients after RBC transfusions. The ORs and 95% CI for ischaemic/thromboembolic events are presented in the forest plot. No significant difference was noted in ischaemic/thromboembolic events between the group with the threshold of 7 g/dL haemoglobin compared with the group with the more liberal threshold. ICU, intensive care unit; M-H, Mantel-Haenszel; RBC, red blood cell.

Figure 7

Forest plot for short-term mortality following subgroup analysis. The forest plot shows the ORs and 95% CI for the all-cause short-term mortality of patients receiving RBC transfusions at various thresholds according to the subgroup analysis of the septic shock and non-sepsis groups. Restrictive transfusion was incapable of decreasing short-term mortality in septic ICU patients. ICU, intensive care unit; M-H, Mantel-Haenszel; RBC, red blood cell.