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Kato et al. Hepatoma Res 2021;7:10 I http://dx.doi.org/10.20517/2394-5079.2020.129 Page 9 of 15

Postoperative complications
[17]
Postoperative complications were described according to the Clavien-Dindo (C-D) classification .
Major complications were defined as those with C-D grade ≥ IIIa. Complications at the surgical-site were
defined as those that might be related to technical failure requiring medical, radiological, or surgical
intervention, such as bile leak, fluid collection, and abscess formation on the liver resection plane. Systemic
complications were defined as those that induced cardiac, pulmonary, renal, or cerebral disorders.

We encountered several RLR and LLR cases complicated by severe acute kidney injury (AKI) and
intraoperative CO gas embolism with or without acute respiratory distress syndrome. As we suspected
2
that the AirSeal system (ConMed, Utica, NY, USA) for pneumoperitoneum was related to these events, we
abandoned this system in mid-2018. Thereafter, we created a rule stating that pneumoperitoneum must
be paused for 5-10 min every 2-3 h during surgery and that lung recruitment by manual ventilation with
positive end-expiratory pressure must be conducted during the paused phase.

Statistical analysis
Continuous data are expressed as median (range). Quantitative data and categorical data were compared
using the Kruskal-Wallis test and Pearson’s chi-square test, respectively. Cumulative overall survival
(OS) and disease-free survival (DFS) after surgery were analyzed by the Kaplan-Meier method; when
necessary, they were compared between groups using the log-rank test. P < 0.05 was considered statistically
significant. Statistical analyses were performed using JMP Pro software (v14.2.0; SAS Institute Inc., Cary,
NC, USA).

Study design
Medical records were searched and data were collected from the charts. The study was conducted with the
approval of the Institutional Regulation Board (approval number: HM19-064) and in accordance with the
Declaration of Helsinki (2000). Written informed consent was obtained from all patients.

RESULTS
Table 1 shows the characteristics of all 57 cases and compares the data of the AR (n = 23) and NAR (n =
34) groups. Patient age, sex distribution, and preoperative serum levels of TB, Alb, AST, ALT, and PT were
comparable between groups. Although all cases were Child-Pugh class A, the more precisely estimated liver
functional reserve, as judged by the serum PC and ICGR15, was significantly better in the AR group than
in the NAR group. The rate of (histologically proven) liver cirrhosis was significantly higher in the NAR
group than in the AR group (68 vs. 35%; P = 0.01). Tumor size was significantly greater in the AR group
than in the NAR group (2.5 cm vs. 1.8 cm; P = 0.002), and the tumor number per case was comparable in
both groups (n = 1). Difficult tumor locations (S-I, S-VII, or S-VIII), recurrent tumors, and serum levels of
alpha-fetoprotein (AFP) and des-gamma-carboxy prothrombin were comparable between groups. These
results suggest that patients who underwent AR had a significantly better hepatic functional reserve than
those who underwent NAR, and that larger tumors tended to be resected by AR. Tumor stages were I or II
for 51 of the 57 cases (89%); when the AR and NAR groups were compared, tumor stages were significantly
higher in the AR group (P = 0.03).

Short-term results of RLR for HCC
Intraoperative data
Table 2 shows the short-term outcomes of the 57 HCC cases who underwent RLR and a comparison
of the AR (n = 23) and NAR (n = 34) groups. The median total operative time, including that for robot
docking, laparoscopic adhesiolysis before docking, and other adjunctive non-hepatic procedures, was
612 min, and the median liver-specific console time (LSCT), which represented the console time only for
liver surgery, was 487 min. Total operative time (837 min vs. 445 min; P < 0.0001) and LSCT (703 min vs.