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Nota et al. Mini-invasive Surg 2020;4:74 I http://dx.doi.org/10.20517/2574-1225.2020.57 Page 3 of 9

We adhered to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE)
[8]
Statement . Eleven of the minor resections of the posterosuperior liver segments have been described
[9]
previously within a multi-institutional cohort study . The overall initial experience at our centre has been
published previously, including surgical outcomes of the first eighteen procedures [3,10] .

Definitions
[11]
Liver segments were defined using Couinaud’s classification . Segments 2, 3, 4B, 5 and 6 were classified
as anterolateral segments; segments 1, 4A, 7 and 8 were classified as posterosuperior segments. Minor
liver resection was defined as the resection of three or less segments, while major liver resection was
defined as the resection of four or more segments. A wedge resection was counted as a half segment .
[12]
En-bloc resections of the adrenal gland or diaphragm and cholecystectomies were not considered
concomitant procedures. Operative time was defined as time from first incision until wound closure.
Postoperative complications were scored using the Clavien-Dindo (CD) grading system for postoperative
[13]
complications . Major complications were defined as CD grade III or higher. Bile leak was defined using
[14]
the International Study Group of Liver Surgery definition and grading system . Complications were
scored during index admission. If a patient was readmitted within ten days after discharge, this readmission
was still considered index admission. Conversion was defined as a laparotomy made for any reason other
than for specimen extraction. Resections were considered radical (R0) if no tumour cells were present in
the transection surface and within 1 mm of the transection surface. Resections were considered irradical
[15]
(R1) if tumour cells were present in the transection surface or within 1 mm of the transection surface . If
multiple tumours were resected, the closest margin determined the R status.

Data collection
The baseline patient characteristics collected were the year of surgery, age, sex, body mass index, American
Society of Anesthesiologists score, previous abdominal surgery, and indication for resection. Data on
details of the operation collected included the resection performed, concomitant procedures, operative
time, console time, parenchymal transection time, estimated blood loss, conversion, placement of surgical
drain, use of Pringle manoeuvre, duration of inflow occlusion, epidural analgesia, number of stapler loads
used per procedure, type of robotic system, definitive histopathological diagnosis, margin status, and
tumour size. Postoperative outcomes were CD grade III or higher complications, bile leakage, unplanned
ICU admission, relaparotomy, percutaneous or endoscopic catheter drainage, length of hospital stay,
readmission, 30-day mortality, 90-day mortality and trocar herniation during 1-year follow-up.

Comparison with conventional laparoscopic approach
Additionally, to put our results into perspective and to compare outcomes of our series of robotic liver
resections to conventional laparoscopy, we have provided an overview of the outcomes of all laparoscopic
liver resections performed in the Netherlands between 2011 and 2016. Data were extracted from the Dutch
nationwide LAELIVE database on minimally invasive liver surgery (published in part).
[16]
Statistical analysis
Data with a normal distribution were reported as mean with standard deviation (SD). Data with a skewed
distribution were reported as median with interquartile range (IQR). Missing values were reported for each
parameter.

Ethical approval
The Medical Ethics Review Committee approved the study protocol with a waiver for informed consent.

Parenchymal transection technique
In the majority of procedures, parenchymal transection began with ultrasound for delineation of the
oncological margin. Either a laparoscopic ultrasound probe was used or a robotic ‘drop-in’ probe (both: