Open Access

Factors affecting operating time in laparoscopic anterior resection of rectal cancer

World Journal of Surgical Oncology201412:44

https://doi.org/10.1186/1477-7819-12-44

Received: 7 November 2013

Accepted: 10 February 2014

Published: 25 February 2014

Abstract

Background

The objective of this study is to clarify the relationship between demographic and surgical factors and operating time, and thus operative difficulty, in patients undergoing laparoscopic anterior resection for mid-low rectal cancer, since different studies have derived different results.

Methods

The records of patients with mid-low rectal cancer who underwent laparoscopic anterior resection were retrospectively studied. Demographic data, tumor characteristics, and pelvimetry measurements were collected and analyzed with respect to operating time, using correlation coefficient analysis, principle component analysis, and linear regression.

Results

A total of 14 patients (10 males, 4 females; 65.50 ± 7.12 years of age) were included. Demographic and tumor characteristics not correlated with operating time. Body mass index (BMI) (P = 0.001); interacetabular distance (IA) (P = 0.001); anatomical transverse distance (IP) (P = 0.008); interischial distance (IS) (P = 0.002); intertuberous distance (IT) (P = 0.005); distance between the coccyx and symphysis (CoSy) (P = 0.013); and the angle of the lower border of the symphysis pubis, upper border of symphysis pubis, and sacral promontory (angle 5) (P = 0.004) were significantly associated with operating time. The equation was:

operating time = 0.653 × BMI + 0.818 × angle 5 - 0.404 × IA - 0.380 × IP - 0.512 × IS - 0.405 × IT - 0.570 × CoSy + 330.8 .

Conclusions

Transverse diameters of the pelvis, BMI, angle 5, and CoSy played the most important role in affecting operating time. The equation can be a very useful tool for preoperative assessment.

Keywords

PelvimetryLaparoscopic surgeryRectal cancer

Background

Laparoscopic anterior resection for mid-low rectal cancer (LRC) has now been widely accepted for its safety and for less blood loss and trauma than conventional open surgery, and the outcome of laparoscopic surgery has been demonstrated to be equivalent to that of open surgery [1, 2]. However, LRC procedures need to be done within the pelvis, which leads to inherent technical operative difficulties.

Preoperative assessment of potential operative difficulties is quite important in preparation for LRC. For analyzing the factors affecting operative difficulty, operating time is typically chosen as the primary measure of difficulty as it is objective, and is well suited to a relatively small sample size in which some operative complications may not occur [36], and pelvimetry and tumor characteristics are expected to be reasonable. Some factors that have been shown to be associated with operative time and hence difficulty are high body mass index (BMI), narrow pelvic outlet, tumors closer to the anal verge, tumor T stage, previous abdominal surgery, and preoperative radiotherapy [3, 4, 69].

However, results derived from different studies are not identical [6, 8, 10, 11], leading to difficulty in preoperative assessment. This may be because of sampling error, different techniques of measurement, or different definitions of difficulties and subgroups of independent variables. The purpose of this study was to further clarify the relationship between demographic and surgical factors and operating time, and thus operative difficulty, in patients undergoing LRC.

Methods

Patients and pelvimetry

Since LRC involves only the laparoscopic techniques and no stoma is required, it is suitable for assessing the relationship between operating time and affecting factors. A retrospective correlational study was performed in LRC patients. Due to the retrospective nature of the study, informed consent was waived. The study was approved by the Ethics Committee of our hospital.

Inclusion criteria were:
  1. 1)

    received LRC by one of two colorectal specialists (Professors H.Z. Qiu and Y. Xiao, who have each been performing laparoscopic operations for approximately 150 cases per year for more than 6 years) at our center from July 2012 to December 2012;

     
  2. 2)

    rectal adenocarcinoma confirmed by colonoscopy before surgery; and

     
  3. 3)

    distance of the tumor from anal verge ≤10 cm.

     
Exclusion criteria were:
  1. 1)

    distance of the tumor from anal verge >10 cm;

     
  2. 2)

    emergency surgery;

     
  3. 3)

    total mesorectal excision was not performed; or

     
  4. 4)

    other procedure was performed in addition to LRC, such as laparoscopic cholecystectomy.

     
Preoperative data, including demographic characteristics, history of preoperative neoadjuvant chemoradiotherapy (NACR), history of lower abdominal surgery, BMI, and distance of the tumor from the anal verge (Td), were reviewed from the patients’ medical records. Postoperative pathological results were used to provide a precise description of the tumors (diameter and T stage). Abdominopelvic computed tomographic (CT) images were imported into Materialise’s Interactive Medical Image Control System (Mimics, version 10.01, Materialise, Belgium) [12]. Pelvimetry, as previous described [3, 5], was measured twice via Mimics by one of our team (J. Yao), who was blinded to the clinical and histological outcomes of the cases studied. The mean of those data were calculated for further analysis. Operating time (opT) was collected from the medical records. This study was approved by the Ethic Committee of Peking Union Medical College. The pelvic variables measured are shown in Table 1 and Figure 1.
Table 1

Measurements of the pelvimetry and visceral fat area

Measurement

Definition

Transverse measurements

 

Interacetabular distance (IA)

Distance between the most inner points of right and left femoral heads

Anatomical transverse distance (IP)

Distance between the most outer points of right and left iliopectineal lines

Interischial distance (IS)

Distance between the right and left ischial spines

Intertuberous distance (IT)

Distance between the most inner points of right and left ischial tuberosities

Sagittal measurements

 

Pubis to promontory (SyPr)

Distance from the upper border of symphysis pubis to sacral promontory

Sacrum to promontory (S3Pr)

Distance from the middle point of the third sacrum to sacral promontory

Sacrum to coccyx (S3Co)

Distance from the middle point of the third sacrum to the tip of the coccyx

Promontory to coccyx (PrCo)

Distance from the sacral promontory to the tip of coccyx

Sacral depth (ScDep)

Distance from the deepest point of sacrum to the promontory-coccyx line

Pubis to coccyx (CoSy)

Distance from the lower border of symphysis pubis to the tip of coccyx

Length of symphysis pubis (SyLn)

Length of symphysis pubis

Angles

 

Angle 1

The angle of the upper border of symphysis pubis to sacral promontory to the middle point of the third sacrum

Angle 2

The angle of sacral promontory to the middle point of the third sacrum to the tip of coccyx

Angle 3

The angle of the middle point of the third sacrum to the tip of coccyx to the lower border of symphysis pubis

Angle 4

The angle of the tip of coccyx to the lower border of symphysis pubis to the upper border of symphysis pubis

Angle 5

The angle of the lower border of symphysis pubis to the upper border of symphysis pubis to the sacral promontory

Visceral fat area (VFA)

The area of visceral adipose tissue at the single level of the umbilicus

Figure 1

Pelvimetry using Materialise’s Interactive Medical Image Control System. A) Anterior-posterior transparent view of the pelvis; IP, anatomical transverse distance; IS, interischial distance; IA, interacetabular distance; IT, intertuberous distance. B) Superior-inferior transparent view of the pelvis. IP, anatomical transverse distance; IS, interischial distance; IA, interacetabular distance; IT, intertuberous distance. C) Lateral transparent view of the pelvis. Pr, promontory; S3, the middle point of the third sacrum; Co, coccyx; SyU, the upper border of symphysis pubis; SyL, the lower border of symphysis pubis; 1, angle 1; 2, angle 2; 3, angle 3; 4, angle 4; 5, angle 5. D) The purple shows the area of visceral adipose tissue at the single level of the umbilicus.

Statistical analysis

Statistical analyses were performed using SPSS Statistics 17.0 software (SPSS Inc., Chicago, IL, USA). Descriptive analyses were used to characterize the study population. Normally distributed data were examined using the Shapiro-Wilk test. For continuous data with a normal distribution, Pearson’s correlation coefficient was used to determine the relationships between factors and operating time; otherwise Spearman’s ranking correlation coefficient was applied. Univariate analysis was used to assess the relationship between gender, tumor T stage, history of lower abdominal surgery, and NACR with operating time. Linear regression with collinearity diagnostics was performed for data correlated with operating time. If collinearity existed, principle components analysis was applied to further explore the internal relationship between factors and operating time. A P value of less than 0.05 was considered significant.

Results

A total of 14 patients (10 males, 4 females) with a mean age of 65.50 ± 7.12 years were included in this retrospective study (Table 2). No patient had a history of a previous abdominal surgery. One patient was stage Tis, One patient was stage T1, three patients were stage T2, eight patients were stage T3 and one patient was stage T4. The mean opT of LRC was 171.43 ± 48.18 minutes [see Additional file 1: Table S1].
Table 2

Statistical results of factors affecting operating time

Variables (unit)

Description mean ± SD (minimal, maximal) or median (interquartile range)

Correlation with operating time

  

r or F

P

Operating time (min)

171.43 ± 48.18 (100, 260)

-

-

Age (years old)

65.50 ± 7.12 (54, 76)

0.174

0.553

Gendera

-

3.102

0.138

NACRa

-

0.937

0.377

BMIb

22.88 (21.94, 24.57)

0.779

0.001

VFA (cm2)

106.83 ± 47.19 (4.52, 162.07)

0.296

0.304

diameter of tumor (cm)

2.91 ± 1.32 (1, 5)

-0.225

0.439

T stage of tumora

-

0.736

0.606

Td (cm)b

8.00 (6.75, 10.0)

-0.328

0.252

IA (mm)

128.76 ± 12.22 (111.36, 158.92)

-0.771

0.001

IS (mm)

104.65 ± 15.47 (84.55, 131.36)

-0.760

0.002

IT (mm)

101.24 ± 17.89 (79.71, 134.63)

-0.704

0.005

IP (mm)

133.97 ± 16.30 (113.21, 170.18)

-0.676

0.008

SyPr (mm)

120.74 ± 12.78 (99.47, 145.94)

0.066

0.822

S3Pr (mm)

82.54 ± 9.61 (63.77, 99.28)

-0.063

0.831

S3Co (mm)

69.12 ± 8.94 (56.11, 87.20)

0.494

0.072

PrCo (mm)

137.82 ± 14.24 (117.77, 175.47)

0.304

0.291

ScDep (mm)

32.99 ± 4.54 (22.16, 41.45)

0.077

0.793

CoSy (mm)

103.99 ± 11.33 (86.17, 121.51)

-0.646

0.013

SyLn (mm)

40.27 ± 4.80 (30.73, 47.50)

-0.032

0.913

Angle 1 (°)

84.86 ± 12.16 (62.99, 109.48)

-0.430

0.125

Angle 2 (°)

130.78 ± 8.47 (111.80, 142.61)

0.137

0.640

Angle 3 (°)

92.22 ± 6.46 (77.98, 103.87)

0.146

0.619

Angle 4 (°)

131.79 ± 7.96 (117.39, 146.16)

-0.504

0.066

Angle 5 (°)

100.17 ± 9.99 (84.11, 123.25)

0.716

0.004

aUnivariate analysis was applied.

bSpearman’s ranking correlation coefficient was applied. For the rest of the variables, Pearson’s correlation coefficient was applied.

BMI: body mass index; CoSy: distance from the lower border of symphysis pubis to the tip of coccyx; IA: interacetabular distance; IP: anatomical transverse distance; IS: interischial distance; IT: intertuberous distance; NACR: neoadjuvant chemoradiotherapy; PrCo: distance from the sacral promontory to the tip of coccyx; ScDep: distance from the deepest point of sacrum to the promontory-coccyx line; SyLn: Length of symphysis pubis; SyPr: distance from the upper border of symphysis pubis to sacral promontory; S3Co: distance from the middle point of the third sacrum to the tip of the coccyx; S3Pr: distance from the middle point of the third sacrum to sacral promontory; Td: tumor distance from the anal verge; VFA: visceral fat area.

Table 2 shows the correlations that were found between BMI, IA, IP, IS, IT, CoSy, and angle 5 with opT, while other factors including age, gender, NACR, VFA, tumor diameter, tumor T stage, Td, SyPr, S3Pr, S3Co, PrCo, ScDep, SyLn, angle 1, angle 2, angle 3, and angle 4, were not correlated with operating time.

Linear regression with collinearity diagnostics showed collinearity existed within the correlated factors (eigenvalue = 0.008, condition index = 25.322). Dimension reduction using principle component analysis was applied after the variables were standardized (Z-score). If more than 85% of the variance can be explained by several components (principle components), the principle components can be regarded as the major factors, while the other components can be ignored. Principle component analysis showed that 89.06% of the total variance could be explained by two principle components [see Additional file 2: Table S2], so two principle components (Z1 and Z2) were calculated, and linear regression analysis was applied:
Z - score opT = - 0.342 × Z 1 + 0.097 × Z 2 .
After return operation, the final equation could be obtained as:
opT = 0.653 × BMI + 0.818 × angle 5 - 0.404 × IA - 0.380 × IP - 0.512 × IS - 0.405 × IT - 0.570 × CoSy + 330.8 .

Discussion

Factors affecting the operating time of LRC have drawn attention in recent years, and a great deal of effort has been given to validating the relationship between factors and operating time [3, 6, 8, 10, 11, 13, 14]. Tumor diameter, BMI, operator experience, tumor distance from the anal verge, tumor depth, pelvic outlet, gender, and VFA have been demonstrated to be related to operating time [6, 8, 10, 11]. However, different studies have provided different conclusions, leading to confusion, and no discussions on how the various factors correlate with each other and the operating time were presented. This might be because of different definitions of subgroups and difficulties, or sampling error. In this study, we focused on the establishment of a more precise description of the relationship between factors and operating time. According to previous studies and our own experience, we assumed that pelvimetry, in addition to demographic characteristics, was quite important in LRC. Two-dimensional magnetic resonance imaging (MRI) and X-ray images have been used to measure pelvimetry [3, 4]; however, if the patient is not positioned symmetrically, deviation of the measurements will result. In order to describe the pelvis more precisely, three-dimensional measurements were adopted using Mimics in this study (Figure 1).

The equation we obtained showed the internal relationship between the various factors studied. Based on the equation, BMI, angle 5, transverse diameters of the pelvis, and CoSy were related to operating time. However none of the factors was the dependent factor affecting operating time. Thus, the frame of the pelvis should be considered as a whole. BMI and angle 5 have positive effects on operating time, while transverse diameters (IA, IP, IS and IT) and CoSy have negative effects on opT. According to the coefficients in the equation, a wider pelvis, especially with a ‘bigger’ pelvic floor, could reduce the difficulty of the operation, while increased angle 5 may increase the operating time for the step of anterior dissection, which needs further verification via step-by-step timing. Besides the anatomical factors, BMI, which could reflect the soft tissue volume in the pelvis, was also very important in affecting operating time.

This equation can be used as a very useful tool for preoperative assessment of patients undergoing LRC. If calculated or predicted operating time is more than a given time, the technique might not be suitable for junior specialists without extensive training. Further research should be performed to identify the given time.

Advantages and limitations

The advantage is that we used three-dimensional measurements to obtain pelvimetry data, which is much more accurate than that of two-dimensional measurements. We described the relationship between factors and operating time more accurate by the equation, which provides the internal relationship among the factors. The small number of patients is the major limitation of the study. In addition, the timings for different steps of the procedure were not been recorded, which lead to step-by-step analysis of the procedures impossible. We recognized the limitations of the retrospective study; nevertheless, we believe that this study provides important information for further research.

Conclusions

No demographic datum and any measurement of pelvimetry could not be identified as an independent predictor for operating time in our study. Instead, transverse diameters of the pelvis, BMI, angle 5, and CoSy played the most important role in affecting operating time. The equation reveals the internal relationship among the factors, and it can be a very useful tool for preoperative assessment.

Abbreviations

BMI: 

body mass index

CoSy: 

distance from the lower border of symphysis pubis to the tip of coccyx

CT: 

computed tomography

IA: 

interacetabular distance

IP: 

anatomical transverse distance

IS: 

interischial distance

IT: 

intertuberous distance

LRC: 

Laparoscopic anterior resection for mid-low rectal cancer

Mimics: 

Materialise’s Interactive Medical Image Control System

MRI: 

magnetic resonance imaging

NACR: 

neoadjuvant chemoradiotherapy

PrCo: 

distance from the sacral promontory to the tip of coccyx

ScDep: 

distance from the deepest point of sacrum to the promontory-coccyx line

SyLn: 

Length of symphysis pubis

SyPr: 

distance from the upper border of symphysis pubis to sacral promontory

S3Co: 

distance from the middle point of the third sacrum to the tip of the coccyx

S3Pr: 

distance from the middle point of the third sacrum to sacral promontory

Td: 

tumor distance from the anal verge

VFA: 

visceral fat area.

Declarations

Authors’ Affiliations

(1)
Department of General Surgery, Peking Union Medical College Hospital (PUMCH), Chinese Academy of Medical Sciences and Peking Union Medical College (CAMS & PUMC)
(2)
School of Biological Science and Medical Engineering, Beihang University
(3)
Department of Radiology, Peking Union Medical College Hospital (PUMCH), Chinese Academy of Medical Sciences and Peking Union Medical College (CAMS & PUMC)

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Copyright

© Wang et al.; licensee BioMed Central Ltd. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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