A retrospective cohort study identifying risk factors and using CLOC score as a prediction tool for conversion in laparoscopic cholecystectomy: insights from a Malaysian tertiary hospital

Introduction

Over the last 2 decades, laparoscopic cholecystectomy (LC) has been the gold standard for the treatment of symptomatic gallstone disease. Compared to open cholecystectomy (OC), LC holds numerous advantages such as a reduction in post-operative pain, better cosmetic outcomes, faster functional recovery time, and decreased length of hospitalization (1).

Current literature suggests that 1–15% of patients who undergo LC are converted to OC (2). Common indications for conversion include failure to demonstrate the critical view of safety, or the presence of intraoperative complications such as bowel perforation, uncontrolled bleeding, and bile duct injury (3).

As converted cases are often associated with increased morbidity, higher complication rates, and longer hospital stays, the identification of risk factors of conversion to open is important to prevent negative outcomes. A meta-analysis done in 2016 showed that age above 60 or 65 years old, male gender, a contracted gallbladder, a thickened gallbladder wall (more than 4–5 mm), and acute cholecystitis were preoperative risk factors for the conversion of LC to open surgery (4). In another study, a preoperative risk score known as the Conversion from Laparoscopic to Open Cholecystectomy (CLOC) score was developed to predict the CLOC (3). However, there remains a scarcity of data on the risk factors and prediction scores within the Malaysian population. Hence, our study intended to address this gap by focusing on the local population.

The primary aim of this study was to identify the pre-operative patient-related factors that increase the risk of conversion of LC to OC. The secondary aim of this study was to determine the cut-off of CLOC score which was applicable to our local population. We present this article in accordance with the STROBE reporting checklist (available at https://asj.amegroups.com/article/view/10.21037/asj-24-41/rc).

Methods

Study design

This was a single-centre retrospective observational study using the data collected from January 2021 to December 2021 in the surgical unit of Hospital Sultanah Aminah, Johor Bahru, Malaysia—the state tertiary hospital. Data was collected and recorded into the predefined proforma. In year 2021, the unit surgeons performed 130 cholecystectomies. However, only patients who underwent cholecystectomy laparoscopically were included.

In our clinical practice, the decision to convert from LC to OC was based on the progression of laparoscopic dissection. Conversion is considered when the surgeon encountered significant difficulty and was unable to make progress in dissecting the Calot’s triangle. This decision prioritized patient safety and minimized the risk of complications. The time required to reach this decision varied depending on the complexity of the case and the intraoperative findings, typically ranging from 15 minutes to 1 hour.

Pre-operative variables including patient demographics, body mass index (BMI), comorbidities and American Society of Anaesthesiologists score, admission type, diagnosis, previous interventions such as endoscopic retrograde cholangiopancreatography (ERCP), imaging findings, clinical parameters (temperature, blood pressure, pulse rate), and blood investigations (full blood examination, renal profile, and liver function tests) were obtained. Operative data and perioperative outcomes including duration of surgery, the requirement of open conversion, morbidities, and mortality were recorded. Duration of surgery was calculated from the time (minutes) of skin incision to the end of skin closure.

Pericholecystic fluid was defined as any fluid collection adjacent to the gallbladder wall that was detected radiologically, identified either via ultrasound or computed tomography, without the volume quantification (5,6). Gallbladder wall thickening was defined as a thickness of ≥4 mm, corresponding to the established criteria in the literature due to its association with increased risks of acute cholecystitis and surgical complications (7,8).

CLOC score was calculated for each case (Table 1) (3)

Postoperative complications were identified at the discretion of the surgeon or clinician during clinical rounds and documented in the case notes. If any patient was readmitted within a one-month period, complications related to the cholecystectomy surgery will be recorded. Additionally, complications were graded according to the Clavien-Dindo classification. Based on prospective data tracking by hospital staff, there were no recorded mortalities.

Patient selection, inclusion, and exclusion criteria

We included patients aged 18 years old and above who were operated initially as LC, If the pathology was cancer or oncologic cases, they were excluded. Patients with incomplete data were excluded from the analysis. We evaluated the applicability of the CLOC risk scoring system in the local context and identified individual preoperative risk factors that were associated with an increased open conversion rate. We also compared the outcomes between successful laparoscopy versus conversion arm.

Based on the reported patient population of 2,326 in the Annual Hospital Report 2021, the power estimate required a minimum of 341 patients to achieve a representative sample of 95% confidence level and 0.05 margin of error (9).

Statistical analysis

Data were analysed with Statistical Package for Social Sciences (SPSS, version 26). Patients who underwent complete LC were compared to patients who required conversion to OC. The associations between these 2 groups were analysed with a chi-square test and t-test to identify the predictive factor for the CLOC. Results were presented with odds ratio (OR) and 95% confidence interval (CI). P value <0.05 was considered statistically significant.

We assessed the normality of the demographic factors, blood investigations, and imaging findings using the Kolmogorov-Smirnov test. Categorical variables were presented as frequencies and percentages. Continuous variables were summarized as mean with standard deviation (SD) for normally distributed data or median with interquartile range (IQR) for non-normally distributed data.

Missing data were handled using pairwise deletion to allow the inclusion of all available cases while maintaining the integrity of the analyses.

Logistic regression analysis was performed to identify the independent predictors of open conversion. Adjusted ORs with 95% CIs were analysed to assess the strength of the association.

Receiver operating characteristic (ROC) analysis was performed to determine the cut-off value of the CLOC score in predicting the need for open conversion. Sensitivity and specificity were determined by the calculation of Youden’s index. An area under the curve (AUC) of 0.5 suggested no discrimination, 0.7–0.8 suggested acceptable, 0.8–0.9 indicated excellent while >0.9 implied an outstanding prediction model (10).

Based on CLOC scores, patients were divided into 2 groups: CLOC ≤6 and CLOC >6. This cut-off value of 6 followed the UK study which derived and validated the CLOC score (3).

Ethical considerations

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the Medical Research & Ethics Committee (MREC) Malaysia (NMRR ID-24-02278-6MU), and individual consent for this retrospective analysis was waived.

Results

Subject characteristics/demographics

All patients’ demographic factors, vital signs, blood investigations, and imaging findings followed a normal distribution except for pulse rate (PR), bilirubin level, and ALT level. Accordingly, we reported PR, bilirubin level, and ALT level using median and IQR while other parameters using mean ± SD.

Amongst the 72 patients included in this study, 60 (83.3%) patients underwent elective, and 12 (16.7%) patients underwent emergency LC. The majority of the patients were female (72.2%), and Malay (70.8%), with a mean age of 46.18 years old. Ten (13.9%) of patients had diabetes mellitus, 22 (30.6%) had hypertension and 6 (8.3%) were smokers (Table 1).

For vital signs on admission, the mean temperature, systolic blood pressure, and diastolic blood pressure were 37 ℃ and 130.39/79.95 mmHg respectively. The median PR was 84 beats/min (Table 1).

Seventeen patients (23.6%) were converted to OC. Several causes of conversion included:

• Dense adhesions and fibrosis;
  • At the Calot’s triangle: 6 cases;
  • With omentum: 2 cases.
• Distorted anatomy;
  • Densely contracted gallbladder: 2 cases;
  • Largely distended gallbladder: 2 cases;
  • Cirrhotic liver with fibrosis: 2 cases;
  • Gallbladder embedded into liver: 1 case.
• Intraoperative causes.
  • Bleeding from right hepatic artery dissection: 1 case;
  • Bile spillage during surgery and unable to identify: 1 case.

Comparisons were made between 2 groups (laparoscopic vs. open conversion). Admission history, settings, comorbidities, and ethnicity were not associated with a higher risk of open conversion (Table 1).

There was no association between the two groups in regard to vitals, and blood investigations (Tables 1,2).

Based on pre-op imaging, most patients had impacted gallstone (23.6%), followed by thickened gallbladder wall (20.8%), pericholecystic fluid (12.5%), pancreatitis (9.7%) and contracted gallbladder (6.9%). Only 11 (15.3%) patients had pre-op ERCP (Table 3).

The mean for the largest size of the stone and common bile duct diameter was 13.88 and 6.41 mm respectively. The mean differences between the two groups were not statistically significant (Table 4).

The majority of the patients (75%) had CLOC score ≤6. (Table 5)

The risk factors for laparoscopic conversion to open

A P value of 0.04 was observed for the association between male gender and conversion to open surgery, indicating statistical significance (P<0.05). The association between the presence of pericholecystic fluid and conversion to open surgery was statistically significant with a P value of 0.02 (P<0.05). A P value of 0.04 was observed for the association between thickened gallbladder wall and conversion to open surgery, indicating statistical significance (P<0.05). These suggested that male gender, presence of pericholecystic fluid, and thickened gallbladder walls were likely correlated with a higher risk of conversion to OC (Table 3).

A 4-fold increased risk for open conversion was observed when the CLOC score was >6, with a P value of 0.03, suggesting statistical significance (P<0.05) (Table 5).

Outcomes

The majority of the cases were primarily performed by gazetting surgeons (40.3%), followed by surgeons with experiences >5 years (31.9%), surgeons with experiences ≤5 years (22.2%), and consultants (5.6%). Among the open conversion cases, 29.4% were performed by gazetting surgeons. Surgeons’ experiences were not significantly associated with open conversion (P=0.18) (Table 6).

Operative duration for laparoscopic vs. laparoscopic converted open was 107.98 minutes (SD: 28.68) vs. 167.06 minutes (SD 62.00) (P<0.001) (Table 7).

There were 3 (4.2%) of bile leak, 2 (3.6%) in laparoscopic and 1 (5.8%) in LC converted to OC. There were no major bile duct injuries requiring reconstruction and no recorded mortality.

Emergency vs. elective cases

There were 12 cases of emergency surgery. The majority was male (83.3%) and Malay ethnicity (83.3%). The mean age of patients in the emergency group was significantly lower than the elective group, with a P value of 0.03 (P<0.05). Five (41.7%) required conversion to open surgery, which was higher than 12 (20.0%) in the elective group. A P value of 0.14 was observed, indicating that the correlation between the emergency group and open conversion was not statistically significant (P>0.05). Diabetes mellitus and hypertension were absent in the emergency group (Table 8).

There were no major differences for septic parameters. The median of the PRs in the emergency group were higher than the elective group but not statistically significant (i.e., P=0.07) (Table 8).

For blood investigations, ALT was significantly higher in the emergency group than the elective group, with a P value of 0.04 (P<0.05). Sodium level was significantly lower in the emergency group than in the elective group, with P<0.001 (P<0.05) (Table 9).

Based on imaging findings, the presence of an impacted gallstone was significantly more common in the emergency group than the elective groups, with a P value of 0.007 (P<0.05) (Table 10).

Correlation between emergency and open cases

Based on logistic regression, a P value of 0.20 was observed for the association between emergency and open surgery, adjusted for age, comorbidities, and imaging findings. This indicated that being an emergency case did not significantly predict the need for open surgery (P>0.05).

ROC curve analysis: determination of the cut-off value for CLOC score in determining intraoperative open conversion

The area under the ROC curve was 0.738 (95% CI, 0.598–0.878; P=0.003), indicating the acceptable accuracy of the CLOC score in predicting the risks of open conversion in our population. The determined cut-off was 5.5 marks, which achieved a sensitivity of 71% and specificity of 75% (Figure 1).

Figure 1 Receiver operating characteristic curve analysis: determination of the cut-off value for CLOC score in determining intraoperative open conversion. CLOC, Conversion from Laparoscopic to Open Cholecystectomy; AUC, area under the curve; CI, confidence interval.

Discussion

In the era of minimally invasive surgery (MIS), LC is the gold-standard surgical approach to gallbladder diseases (11,12). However, intraoperative conversion to open surgery was inevitable and needed in some cases to warrant patient safety (13). It remained a difficult decision for surgeons (14).

The overall conversion rate was 23.61% in our study, consisting of 12.7% of emergency cases. This conversion rate was within the range reported in the literature (i.e., 3% to 24%) (11). However, some institutional studies reported lower conversion rates (3,11,15-19).

The major cause of conversions in our study was dense adhesions and fibrosis at the Calot’s triangle. This was consistent with the literature and was attributed to severe inflammation, leading to difficult anatomical identification of structures at the Calot’s triangle (18). Conversion-to-open surgery was the common approach based on local practice in Malaysia.

Our study showed densely contracted and largely distended gallbladder causing an open conversion. These were considered difficult cholecystectomies in the literature and were proven associated with open conversion (20). Liver cirrhosis increases the bleeding risk and hence the risk of conversion.

There were 2 cases of intraoperative complications which were intraoperative bleeding and bile spillage in suspicion of bile duct injury. Both were considered the commonest intraoperative complications that led to conversion (12).

The conversion rate in emergency cases (42%) was about 2-times higher than the elective cases (20%). This was consistent with a study in England which reported a twofold higher conversion rate in emergency procedures compared to elective procedures (16). These differences emphasised that the open conversion of a LC was multifactorial and complex, involving patient factors, gallbladder pathology, and surgeon factors (12).

Our study revealed that male gender was a statistically significant risk factor for conversion, with a threefold increased risk for open conversion. The rate of conversion in males was 8/20 (40%) while in females was 9/52 (17.3%). This rate was concomitant to most studies which acknowledged male gender as an independent risk factor that might be caused by increased severity of gallstone disease experienced by men (11,12,18,21). Other patient factors such as advanced age, comorbidities (diabetes, hypertension) and haemoglobin level of <9 g/dL were reported as risk factors in some studies but their associations with open conversion were not significant in our study (2,11,22).

Based on the pre-operative imaging, the presence of pericholecystic fluid and thickened gallbladder significantly increased the rate of open conversion for 4.9 and 3.5 folds respectively. Pericholecystic fluid was a well-recognised risk factor in multiple research (23-25). It was expected to result in difficult surgery by complicating the dissection of Calot’s triangle, causing adhesions, and making the separation of the gallbladder from the liver bed challenging (26). Gallbladder wall thickness of ≥4 mm is another independent predictor of open conversion as it is also associated with difficult exposure of cystic duct during LC (17,27-29).

The current study showed that the level of experience of the primary surgeon was not a statistically significant factor leading to open conversion. Some studies identified the caseload of individual surgeons as a predictor of the conversion rate. This was true when trained senior surgeons with experience were able to manage difficult LC using the subtotal approach (12,16,20).

There were only 3 cases that had bile leaks or biloma due to minor bile duct injury. They were all managed conservatively with prolonged drain placement or percutaneous drainage. There was no bile duct injury requiring reoperation or reconstruction and no recorded mortality.

Our study adopted the UK Validated Risk Score to predict the CLOC. Based on the ROC curve analysis, the CLOC score was a good tool in predicting the risks of conversion in our populations, achieving an AUC of 0.74. The sensitivity and specificity were similar to the UK study (71% sensitivity and 75% specificity in our study vs. 77% sensitivity and 65% specificity in the UK study) (3). This risk score may assist in perioperative patient counselling and decision-making of the surgical approach (30).

There were a few limitations to the study. The study populations were relatively small and single-centred. The actual sample size (N=72) fell short of the initially calculated requirement of 341 patients due to challenges with manual data management and incomplete records in our tertiary hospital. This smaller sample size might have reduced the statistical power of the study to 75% and introduced a potential risk of bias. While this limitation affected the generalizability of the findings, the results nonetheless provided valuable insights and served as a foundation for future, larger-scale studies. We recommend future research in the country or regional collaboration to improve the validation.

Conclusions

LC is the cornerstone of the surgical approach to diseased gallbladder. To warrant patient safety and to prevent complications, the decision of open conversion is distinctively crucial. Our study revealed that the male gender was the only independent patient factor that increased the risk of conversion. The presence of pericholecystic fluid and thickened gallbladder wall were associated significantly with intraoperative conversion, asserting the importance of accurate pre-operative imaging and suggesting the necessity of reporting the risk of conversion in imaging reports. Although the operative duration was significantly longer in open conversion, no major bile duct injury nor mortality was reported. CLOC score was a reliable tool to be adopted in our populations, with a statistical cut-off of 5.5 (sensitivity 71%, specificity 75%). With the tools, patients would be risk-stratified and counselled accordingly before the surgery. In conclusion, future larger, randomised, and multi-centred research is recommended.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://asj.amegroups.com/article/view/10.21037/asj-24-41/rc

Data Sharing Statement: Available at https://asj.amegroups.com/article/view/10.21037/asj-24-41/dss

Peer Review File: Available at https://asj.amegroups.com/article/view/10.21037/asj-24-41/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://asj.amegroups.com/article/view/10.21037/asj-24-41/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Medical Research & Ethics Committee (MREC) Malaysia, NMRR (ID-24-02278-6MU), and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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