Literature search and study characteristics

The systematic search process is depicted in Fig. 1. We identified 1,736 relevant articles through searches in PubMed (n = 1331), Embase (n = 885), Web of Science (n = 1387), and CNKI (n = 311). After removing duplicates, 2,584 titles and abstracts were screened, resulting in 13 full-text articles being included in the pooled analysis [21,22,23,24,25,26,27,28,29,30,31,32,33], involving 4,493 patients (630 Ultrasonic vs. 787 Clamp). The studies comprised 3 prospective cohort studies [23, 25, 27], 1 retrospective cohort study [33], 1 comparative study [21], and 7 randomized controlled trials [22, 24, 26, 29,30,31,32]. Table 1 provides details on study characteristics, evidence levels, and quality scores, with a median quality score of 6 (range 5–7). Eight studies were deemed high quality [22,23,24,25,26, 28, 32, 33]. Quality assessment details are in Supplementary Material S3.

Fig. 1

Flow diagram of the systematic search and selection process

Table 1 Baseline characteristics of include studies and methodological assessmentDemographic characteristics

No significant differences were found between the ultrasonic and clamp groups in terms of age (WMD: 0.78; 95% CI: -1.07, 2.62; p = 0.41), gender distribution (OR: 0.79; 95% CI: 0.60, 1.04; p = 0.10), BMI (WMD: -0.05; 95% CI: -1.39, 1.29; p = 0.94), cirrhosis prevalence (WMD: 1.05; 95% CI: 0.79, 1.41; p = 0.73), major hepatectomy rates (WMD: 1.08; 95% CI: 0.85, 1.38; p = 0.53), or malignancy rates (WMD: 1.01; 95% CI: 0.71, 1.45; p = 0.95) (Table 2).

Table 2 Demographics and clinical characteristics of included studiesIntraoperative outcomesOperating time

Nine studies including 928 patients (404 ultrasonic vs. 524 clamp) were analyzed for operating time [21,22,23, 25, 26, 28, 29, 31, 32], showing no significant difference between the groups (WMD: 2.28; 95% CI: -6.95, 11.50; p = 0.63) but with high heterogeneity (I2 = 88%, p < 0.00001)(Fig. 2A). A funnel plot suggested potential publication bias(Fig. 3A), though Egger’s test did not confirm this (p = 0.363). Sensitivity analysis indicated that excluding Amad (2019) [31] and Sun (2015) [25] resulted in shorter operating times in the clamp group (WMD: 33.52; 95% CI: 19.33, 47.72; p < 0.00001) with reduced heterogeneity (I2 = 39%, p = 0.13).

Fig. 2

Forest plots of operative outcomes: (A) operating time (B) blood loss (C) transfusion rate

Fig. 3

Funnel plots of operative outcomes: (A) operating time (B) blood loss (C) transfusion rate

Blood loss

Five studies [23, 26, 28, 29, 33] involving 456 patients (168 ultrasonic vs. 288 clamp) found significantly less blood loss in the ultrasonic group (WMD: -85.45; 95% CI: -154.20, -16.70; p = 0.01) with moderate heterogeneity (I2 = 50%, p = 0.09)(Fig. 2B). Funnel plot analysis indicated slight publication bias(Fig. 3B), but Egger’s test did not (p = 0.489).

Transfusion rate

Data from 9 studies, including 1,102 patients (494 ultrasonic vs. 608 clamp) [21,22,23,24,25, 27, 28, 31, 32], showed a significantly higher transfusion rate in the clamp group (OR: 0.67; 95% CI: 0.48, 0.94; p = 0.02)(Fig. 2C), with substantial heterogeneity (I2 = 75%, p = 0.0001). Neither Egger’s test (p = 0.828) nor visual inspection indicated significant publication bias(Fig. 3C). Sensitivity analysis suggested that excluding studies by Luca (2006) [21] and S-T-FAN (1996) [23] revealed a lower transfusion rate in the ultrasonic group (WMD: 0.42; 95% CI: 0.26, 0.69; p = 0.0006) with reduced heterogeneity (I2 = 15%, p = 0.31).

Sensitivity analysis

We performed one-way sensitivity analyses for operating time and transfusion rate to assess the impact of each study on the combined weighted mean difference (WMD) by sequentially removing individual studies. Sensitivity analysis indicated that removing the studies by Amad (2019) [31] and Sun (2015) [25] affected the WMD for operating time (Fig. 4A), while excluding Luca (2006) [21] and S-T-FAN (1996) [23] impacted the WMD for transfusion rate (Fig. 4B). Excluding Amad (2019) [31] and Sun (2015) [25] reduced the heterogeneity in operating time (I2 = 39%, p = 0.13), suggesting these studies contributed significantly to the heterogeneity. Similarly, removing Luca (2006) [21] and S-T-FAN (1996) [23] resolved the heterogeneity in transfusion rate (I2 = 15%, p = 0.31).

Fig. 4

Sensitivity analysis of (A) operating time (B) transfusion rate

Postoperative outcomesComplication rate

Data from 11 studies involving 1,195 patients (536 ultrasonic vs. 659 clamp) [21, 22, 24, 25, 27,28,29,30,31,32,33] showed a significantly lower complication rate in the ultrasonic group (OR: 0.67; 95% CI: 0.51, 0.89; p = 0.005) with moderate heterogeneity (I2 = 58%, p = 0.008)(Fig. 5A). Although visual inspection and Egger’s test did not detect significant publication bias (p = 0.628), high heterogeneity led to a sensitivity analysis(Fig. 6A). Excluding the study by Nanashima [28] revealed a lower complication rate for the ultrasonic group (WMD: 0.59; 95% CI: 0.44, 0.80; p = 0.0005) with reduced heterogeneity (I2 = 35%, p = 0.13).

Fig. 5

Forest plots of postoperative outcomes: (A) complication rate (B) bile leakage (C) postoperative bleeding (D) mortality

Fig. 6

Funnel plots of postoperative outcomes: (A) complication rate (B) bile leakage (C) postoperative bleeding (D) mortality

Bile leakage

Eleven studies with 1,320 patients (585 ultrasonic vs. 735 clamp) were analyzed for bile leakage [21, 23,24,25, 27,28,29,30,31,32,33], showing a significantly lower rate in the ultrasonic group (OR: 0.57; 95% CI: 0.35, 0.93; p = 0.03)(Fig. 5B). The heterogeneity was low (I2 = 11%, p = 0.34), and no significant publication bias was found (Egger’s test, p = 0.172)(Fig. 6B).

Subgroup analysis of bile leakage

Subgroup analysis revealed differences between ultrasonic devices. Comparison between Cavitron Ultrasonic Surgical Aspirator (CUSA) and Harmonic scalpel showed no significant difference in leakage rates compared to clamps. However, CUSA had a significantly lower bile leakage rate (OR: 0.34; 95% CI: 0.17, 0.71; p = 0.004) with no heterogeneity (I2 = 0%, p = 0.54) (Fig. 7A) or publication bias (Egger’s test, p = 0.167) (Fig. 7B), demonstrating CUSA's superior performance over clamps and Harmonic scalpel.

Fig. 7

Forest and funnel plot of bile leakage between CUSA and clamp

Postoperative bleeding

Seven studies [21, 23,