Search results and characteristics of included trials
After removing duplicates, 2265 records were identified during the search conducted in November 2020. Twenty-eight full-text articles were identified and assessed for their eligibility, and nine RCTs with a total of 701 patients were included in the qualitative synthesis (see Figure 1. For PRISMA flow chart). Table 1 summarizes the published studies included in the synthesis. Data from seven trials were analysed and are shown in Figure 2 and supplementary figures 1-4. The risk of bias assessment is summarized in Supplementary Figures 5. The summary of findings is shown in Table 2.
Primary outcomes
In-hospital mortality
Data from five trials indicated that FC as a treatment for emergency haemorrhagic events may result in a slight increase in in-hospital mortality (RR 1.21, 95% CI: 0.49–3.00, p = 0.68). However, due to the moderate weight of high risk of bias and low number of events, the certainty of this evidence is very low. Statistical heterogeneity was also observed (Tau2 = 0.68; I2 = 54%). In order to address this heterogeneity in in-hospital mortality, a sensitivity analysis was conducted (Supplementary Figure 2a.). When considering the high risk of bias, the risk ratio for in-hospital mortality was 1.21 (95% CI: 0.49–3.00, p = 0.68). Further details on risk of bias can be found in Supplementary Figure 5.
Secondary outcomes
RBC Transfusion in the first 24 h
The results from six clinical trials suggest that FC does not significantly reduce the need for RBC transfusion within the first 24 h after admission (MD 0.00 units lower in the FC group, 95% CI: -0.99–0.98, p = 0.99). However, the certainty of this evidence is very low due to moderate weight of high risk of bias, low number of events, and high levels of heterogeneity (Tau2 = 1.02; I2 = 77%). A sensitivity analysis was conducted with the removal of the high risk of bias study, resulting in a MD of 0.03 units for RBC transfusion in the first 24 hours (95% CI: -0.55–0.62, p = 0.001) (Supplementary Figure 2b). Subgroup analyses were also performed for each type of haemorrhage. Further details on risk of bias can be found in Supplementary Figure 5.
FFP Transfusion in the first 24 h
The results from five clinical trials suggest that FC may increase the need for FFP transfusion in the first 24 h after admission (MD 2.61 units higher in the FC group, 95% CI: 0.07–5.16, p = 0.04). The certainty of this evidence is low due to the low number of events. Statistical heterogeneity was also observed (Tau2 = 3.43; I2 = 71%) (see Figure 2c). A sensitivity analysis was conducted with the removal of the high risk of bias study, resulting in a mean difference of 1.21 units for FFP transfusion (95% CI: 0.76–1.67, p < 0.01) (see Supplementary figure 2c). Subgroup analyses were also performed for each type of haemorrhage.
PC transfusion in the first 24 h
The results of the study suggest that FC may result in a large increase in PC transfusion within the first 24 h after admission (MD 0.46 units higher in the FC group, 95% CI: 0.17–0.76, p = 0.002). The certainty of this evidence is moderate due to the moderate number of events. No statistical heterogeneity was observed (Tau2 = 0.00; I2 = 0%) (Figure 2d). Further details on risk of bias can be found in Supplementary Figure 5.
Blood loss within first 24 h after admission
The results of a clinical trial suggest that FC may result in little to no difference in blood loss within the first 24 h. The mean blood loss within the first 24 h was 392.88 mL (MD 171 mL lower in the FC group, 95% CI: -400.35–58.35, p= 0.14). The risk of bias was low due to the low number of events. Heterogeneity was not applicable (see Supplementary Figure 1a). Further details on risk of bias can be found in Supplementary Figure 5.
Thrombotic events
The results from five clinical trials suggest that FC may result in little to no difference in thrombotic events. The risk ratio was 0.71 (95% CI: 0.32–1.58, p = 0.4) with very low level of certainty due to the moderate weight of high risk of bias and low number of events. No statistical heterogeneity was observed (Tau2 = 0.00; I2 = 0%) (see Supplementary Figure 1b). Further details on Risk of bias can be found in Supplementary Figure 5.
Multiple organ failure
The results from two clinical trials suggest that FC may result in a slight reduction in the risk of multiple organ failure. The risk ratio was 0.54 (95% CI: 0.18–1.56, p=0.25) with a low risk of bias due to the moderate weight of high risk of bias and low number of events. Statistical heterogeneity was observed (Tau2 = 0.40; I2 = 57%) (see Supplementary Figure 1c). Further details on the risk of bias can be found in Supplementary Figure 5.
Length of ICU stay
The results from one clinical trial suggest that FC may result in little to no difference in the length of ICU stay. The mean length of ICU stay was lower in the FC group (MD, -2.22 days lower, 95% CI: -4.96–0.52, p = 0.11) with a very low risk of bias due to the moderate weight of high risk of bias and low number of events. Statistical heterogeneity was not applicable (see Supplementary Figure 1d). Further details on risk of bias can be found in Supplementary Figure 5.
Length of hospital stay
The results of two clinical trials suggest that FC may result in a slight reduction in the length of hospital day. The mean length of hospital stay was lower in the FC group (MD, -1.08 days lower, 95% CI: -3.35–1.19, p = 0.35) with a very low risk of bias due to the moderate weight of high risk of bias and low number of events. Statistical heterogeneity was not observed (Tau2 = 3.11; I2 = 50%) (see Supplementary Figure 1e). Further details on risk of bias can be found in Supplementary Figure 5.
Subgroup analysis: Trauma setting
The results of the study indicate that the risk ratio for in-hospital mortality was 1.08 (95% CI: 0.64–1.84, p = 0.77). The MD in RBC transfusion was – 0.35 units (95% CI: -0.76-0.05, p = 0.02). The MD in FFP transfusion was 1.24 units (95% CI: 0.79–1.69, p < 0.01). The mean difference of PC transfusion in the first 24 hours was 0.46 units (95% CI: 0.17–0.76, p = 0.002). The RR for the thrombotic events was 0.67 (95% CI: 0.30–1.51, p = 0.33) (Supplementary figure 3a-e).
Subgroup analysis: Obstetrics setting
In-hospital mortality was not analysed as the included RCTs reported no death. The MD of RBC transfusion was – 0.09 (95% CI: -0.87–-0.69, p = 0.82). The MD of the FFP transfusion was not estimable due to no demand of FFP in the included trial. The risk ratio of the thrombotic events was 0.96 (95% CI: 0.06–16.21, p = 0.98) (see Supplementary figure 4a-b).