ies^\[[@R14],[@R16]--[@R23]\]^ that were included in the systematic review and meta-analysis. No randomized control trial was included, the quality of the studies included in the meta-analysis was assessed by the NOS scale. Overall, an average medium quality (5 out of 9 stars) was achieved in all studies (range 5--6). Table [2](#T2){ref-type="table"} illustrated the effect of preoperative cholangitis on patients with hilar cholangiocarcinoma.

![Search flow diagram.](medi-97-e12025-g001){#F1}

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Characteristics of included studies.

![](medi-97-e12025-g002)

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The characteristics of preoperative cholangitis-related outcomes of included studies.

![](medi-97-e12025-g003)

3.1. Primary outcomes: morbidity and mortality
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Postoperative morbidity was identified in 7 studies^\[[@R14],[@R16],[@R18],[@R19],[@R21]--[@R23]\]^ (n = 638 patients) in total. The RR and 95% CI for each study and the pooled RR are shown in Figure [2](#F2){ref-type="fig"}. In <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5671862/figure/F2/the> fixed effects model (RR = 1.15; 95% CI = 1.00--1.32), heterogeneity testing revealed *I*^2^ = 79% and revealed a significant difference in the incidence of overall complications in favor of the no-cholangitis (*P = *.04).

![Forest plot for morbidity (cholangitis vs noncholangitis).](medi-97-e12025-g004){#F2}

Six out of the 7 studies^\[[@R14],[@R16]--[@R18],[@R22],[@R23]\]^ provided the data (n = 491 patients) on the incidence of mortality. The RR and 95% CI for each study and the pooled RR are shown in Figure [3](#F3){ref-type="fig"}. The overall summary estimated RR was 2.29 (95% CI: 1.48--3.52; *P* = .0002). Heterogeneity testing revealed *I*^2^ = 60% and the *P* value for heterogeneity is .06, when analyzed using a fixed-effect model.

![Forest plot for mortality (cholangitis vs noncholangitis).](medi-97-e12025-g005){#F3}

3.2. Secondary outcomes: the incidence of hepatic failure, infection and sepsis
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