Study selection
Figure 1 shows a flow diagram of study selection. The electronic searches identified 111 literatures, and 80 reports were clearly not relevant after the first screening. The full text of 21 studies was retrieved for further in-depth consideration, and 15 studies were excluded for the several reasons. Finally, 6 RCTs[18-23] were included in this meta-analysis. References cited in published original and review papers were examined, and no further studies were found.
Characteristics of included RCTs
The characteristics of RCTs included in this present meta-analysis are presented in Table 1. Of these included studies, one were performed in India[23], the resting five in China[18-22]. The combined sample size across the 6 included studies was 277 participants, with 142 ALI patients with omega-3 fatty acids treatment and 135 patients without omega-3 fatty acids treatment. The patient samples in the included studies were variable with a range of 34 to 61. For study results, one study didn’t support the use of omega-3 fatty acids in ARDS patients, whereas the other studies all favored the the use of omega-3 fatty acids for the treatment of ALI.
Methodological quality of the included studies
Figure 2 and 3 show the quality assessment of the studies in this present meta-analysis. All 6 included studies were randomized, but only two RCTs[21, 23] specified the method of randomization. All the RCTs did not reference whether any allocation concealment process was used. 4 RCTs[20-23] reported the design on blinding patients, personnel and outcome assessors. No other significant biases amongst the included RCTs were found. Intention to treat (ITT) was performed for all patients.
Outcomes
The changes of PaO2 Three RCTs[19, 20, 22] reported the changes of PaO2 for ALI patients with or without omega-3 fatty acids treatment, the pooled data from the three RCTs revealed that the omega-3 fatty acids treatments significantly improve the PaO2 in ALI patients (MD =13.82, 95% CI 8.55– 19.09, P < 0.001, I2 = 0%; Figure 4).
The changes of PaO2/FiO2 Five RCTs[18-22] reported the changes of PaO2/FiO2 for ALI patients with or without omega-3 fatty acids treatment, the pooled data from the five RCTs revealed that the omega-3 fatty acids treatments significantly improve the PaO2/FiO2 in ALI patients (MD =33.47, 95% CI 24.22– 42.72, P < 0.001, I2 = 0%; Figure 5).
The changes of total protein (TP) Three RCTs[18, 21, 22] reported the changes of TP for ALI patients with or without omega-3 fatty acids treatment, the pooled data from the three RCTs revealed that the omega-3 fatty acids treatments significantly increase the TP in ALI patients (MD =2.02, 95% CI 0.43– 3.62, P=0.01, I2 = 30%; Figure 6).
The duration of mechanical ventilation (MV) Three RCTs[21-23] reported the duration of MV for ALI patients with or without omega-3 fatty acids treatment, the pooled data from the three RCTs revealed that the omega-3 fatty acids treatments significantly reduced the duration of MV in ALI patients (MD =-1.72, 95% CI -2.84– -0.60, P=0.003, I2 = 0%; Figure 7).
The length of ICU stay Three RCTs[21-23] reported the length of ICU stay for ALI patients with or without omega-3 fatty acids treatment, the pooled data from the three RCTs revealed that the omega-3 fatty acids treatments significantly reduced the length of ICU stay in ALI patients (MD =-1.29, 95% CI -2.14– -0.43, P=0.003, I2 = 59%; Figure 8).
Subgroup and sensitivity analyses
No subgroup analyses were performed in our study because the heterogeneity among included RCTs in the synthesized results remained small. We attempted to evaluate publication bias by using a funnel plot if 10 or more RCTs[24]. However, the number of included RCTs were only six, we could not evaluate publication bias by using a funnel plot. Sensitivity analyses, which investigate the influence of one study on the overall risk estimate by removing one study in each turn, suggested that the overall risk estimates were not substantially changed by any single study.