RU2850756C1 - Method for selecting technique of endoscopic retrograde choledocholitotripsy based on retrograde cholangiography data - Google Patents

Abstract

FIELD: medicine; surgery.

SUBSTANCE: can be used to select the technique of endoscopic retrograde choledocholithotomy based on the results of retrograde cholangiography (ERCP). The method consists of performing retrograde lithotripsy without lithotripsy or with preliminary intraductal lithotripsy. Based on the results of ERCP, the largest filling defect is determined and its transverse size (Ds) is measured. If DS<8 mm, lithoextraction is performed without lithotripsy; if DS>18 mm, lithoextraction with intraductal lithotripsy is performed. If DS is in the range from 8 mm to 18 mm inclusive, the clarity/unclarity of its contours is additionally assessed. If the contours of the filling defect are unclear, lithoextraction without lithotripsy is performed. If the contours are clear, the diameter of the duct lumen at the level of the filling defect with the maximum size (D2) and the diameter of the choledochal lumen in its distal third 1 cm proximal to the sphincter of Oddi (D3) are additionally measured. Then the ratio DS/D3 and the ratio DS/D2 are found and the smoothness/roughness of the filling defect contour is assessed. After that, the cholangiographic lithoextraction index (y) is calculated using the specified mathematical formula. If the value of y≤3.78, lithoextraction is performed without lithotripsy; if y>3.78, lithoextraction is performed with preliminary intraductal lithotripsy.

EFFECT: ability to simultaneously remove concretions from the common bile duct regardless of their size and minimise the frequency of undesirable intraoperative outcomes.

1 cl, 8 dwg, 5 tbl, 5 ex

Description

Field of technology to which the invention relates

The method relates to the field of medicine, namely to endoscopy, and is intended for

determining indications for endoscopic treatment of patients with choledocholithiasis, namely, endoscopic retrograde choledocholithoextraction without lithotripsy or using preliminary intraductal lithotripsy (mechanical, laser, electrohydraulic) based on retrograde cholangiography data.

State of the art

Endoscopic transpapillary lithoextraction is the method of choice in the treatment of patients with choledocholithiasis [Ardasenov TB, Budzinsky SA, Pankov AG, Bachurin AN, Shapovaliants SG Features of surgical treatment of complex forms of choledocholithiasis. Annals of surgical hepatology. 2013; 18(1): 23-28. - EDN RABSEJ.]. Adequate access for stone extraction and the choice of the optimal method and instrument for lithoextraction are the main conditions for successful treatment. The implementation of these conditions directly depends on proper assessment of the bile duct diameter, filling defects and their relationships according to ERCP data, which is performed immediately before endoscopic papillosphincterotomy (EPST). In general, lithoextraction methods can be divided into two groups: lithoextraction without lithotripsy and lithoextraction with preliminary lithotripsy. Lithotripsy can be of two types: intraductal or extracorporeal. The claimed invention explores the possibility of using only intraductal lithotripsy as a preliminary step in lithoextraction to improve the effectiveness of choledocholithiasis treatment.

Within the context of the present description of the invention, lithoextraction without lithotripsy is understood to mean the successful one-stage removal of stones from the bile ducts using a Dormia basket and/or a lithoextraction balloon. As a rule, this situation occurs in 80-90% of cases [Manes G., Paspatis G., Aabakken L., Anderloni A., et al. Endoscopic management of common bile duct stones: European Society of Gastrointestinal Endoscopy (ESGE) guideline. Endoscopy. 2019 May; 51(5):472-491. https://doi.org/10.1055/a-0862-0346].

Lithoextraction using preliminary intraductal lithotripsy (mechanical, laser or electrohydraulic) is required when “complex” stones are detected that cannot be removed with a basket or balloon on the first attempt or without a high risk of damage to the walls of the bile ducts or duodenum. Cases of “complex” choledocholithiasis include stones larger than 10-15 mm, irregular barrel-shaped, discrepancy between the size of the stone and the distal third of the common bile duct, multiple stones, the position of the stone in the cystic duct or in the intrahepatic ducts, impaction of the stone, the presence of a stricture distal to the stone, conical narrowing of the distal third of the common bile duct, a short intrapancreatic segment or angulation of the common bile duct less than 135° [Manti M., Shah J., Papaefthymiou A., Facciorusso A. et al. Endoscopic Management of Difficult Biliary Stones: An Evergreen Issue. Medicina. 2024; 60(2): 340. https://doi.org/10.3390/medicina60020340; Dynko V.Yu., Gabriel S.A., Mamishev A.K., et al. Possibilities of oral transpapillary cholangioscopy in the treatment of complex choledocholithiasis. Innovative Medicine of Kuban. 2024; 9(4): 113-119. https://doi.org/10.35401/2541-9897-2024-9-4-113-119].

The simplest available method of intraductal fragmentation of stones is mechanical lithotripsy. Its overall effectiveness can reach 76-91%, and 50-70% on the first attempt, which requires repeated intervention in a large number of patients [Troncone E., Mossa M., De Vico P., Monteleone G., Del Vecchio Blanco G. Difficult biliary stones: a comprehensive review of new and old lithotripsy techniques. Medicina. 2022; 58(1): 120. https://doi.org/10.3390/medicina58010120]. The most significant predictors of failure of mechanical lithotripsy are impaction of the calculus, calculus size greater than 30 mm, and the ratio of the transverse diameter of the calculus to the diameter of the distal third of the common bile duct greater than 1 [Doshi B., Yasuda I., Ryozawa S., Lee G.H. Current endoscopic strategies for managing large bile duct stones. Digestive Endoscopy. 2018; 30: 59-66. https://doi.org/doi: 10.1111/den.13019].

The development of a direct intraductal visualization system (SpyGlass®, Boston Scientific Corp., USA) has enabled cholangioscopy-guided lithotripsy using laser or electrohydraulic methods. This lithotripsy is the most effective and allows for the avoidance of open surgical interventions on the bile ducts for virtually any size of intraductal calculus. Contraindications to SpyGlass®-guided lithotripsy are the same as general contraindications for any endoscopic transpapillary intervention: 1) a patient's condition caused by severe concomitant pathology that prevents the use of adequate sedation; 2) altered gastrointestinal anatomy that impedes access to the major duodenal papilla; 3) severe coagulopathy.

Despite the widespread introduction of intraductal lithotripsy methods into practice, to date there is no universal methodology for the endoscopic treatment of complex choledocholithiasis and clear indications for the use of intraductal lithotripsy have not been developed. Often, the choice of lithoextraction method is based on the so-called intuitive examination and generally accepted criteria for "complex" choledocholithiasis [Bang J.Y., Wilcox C.M., Navaneethan U. et al. Orlando Protocol for single-session ductal clearance of common bile duct stones at endosopic retrograde cholangiopancreatography. Digestive Endoscopy. 2023; 36(7): 825-833. https://doi.org/10.1111/den.14719].

The most dangerous consequences of incorrect analysis of cholangiogram data during endoscopic treatment of patients with choledocholithiasis are the impaction of the basket with the stone contained in it in the narrowest part of the common bile duct below the stone (the zone of the common bile duct ampulla or the presence of a stricture), as well as iatrogenic damage to the walls of the common bile duct or duodenum during attempts at forced traction. Such situations are highly likely to lead to conversion and/or complications in the long term [Rosenkranz L., Patel S.N., Endoscopic Retrograde Cholangiopancreatography for Stone Burden in the Bile and Pancreatic Ducts. Gastrointestinal Endoscopy Clinics of North America. 2012; 22(3): 435-450. https://doi.org/10.1016/j.giec.2012.05.007].

The prior art provides various criteria and indicators that indicate that preliminary intraductal lithotripsy may be necessary for lithoextraction. These include: the size and shape of the stone, namely, stones whose transverse diameter exceeds the diameter of the distal third of the common bile duct and which have a rectangular or round shape [Wongkanong C., Patumanond J., Ratanachu-ek T., Junrungsee S., Tantraworasin A. Common bile duct stone-related parameters and their potential prognostic values for stone extraction requiring endoscopic papillary large balloon dilation. JGH Open. 2023; 7(1): 16-23. https://doi.org/10.1002/jgh3.12845; ]; the presence of bile duct strictures, as well as the older age group [Wang Z., Yuan H., Lin K., Zhang Y., Xue Y., Liu P., Chen Z., Wu M. Artificial intelligence-empowered assessment of bile duct stone removal challenges. Expert Systems with Applications. 2024; 258: 125146. https://doi.org/10.1016/j.eswa.2024.125146.];

It is known from the prior art that for stones larger than 1 cm in diameter, in combination with other factors that complicate their capture by the basket (e.g., irregular shape or impaction of the stone in the narrowed distal third of the common bile duct), lithoextraction with preliminary intraductal lithotripsy is more effective than lithoextraction without lithotripsy. According to published study results, duct diameter did not affect the success of the operation when comparing lithoextraction without lithotripsy with lithoextraction with preliminary lithotripsy. [Buxbaum J, Sahakian A, Ko C, Jayaram P, Lane C, Yu CY, Kankotia R, Laine L. Andomized trial of cholangioscopy-guided laser lithotripsy versus conventional therapy for large bile duct stones (with videos). Gastrointest Endosc. 2018; 87(4): 1050-1060. https://doi.org/10.1016/j.gie.2017.08.021. Epub 2017 Sep 1. PMID: 28866457].

It is also known that if the stone size is >30 mm and the ratio of the stone diameter to the duct lumen diameter is >1, mechanical lithoextraction is not recommended [Lee S.H., Park J.K., Yoon W.J., Lee J.K., Ryu J.K., Kim Y-T., Yoon Y.B. How to predict the outcome of endoscopic mechanical lithotripsy in patients with difficult bile duct stones? Scandinavian Journal of Gastroenterology. 2007; 42: 1006-1010. https://doi.org/10.1080/00365520701204253].

According to the authors of the publication [Garg K.P., Tandon R.K., Ahuja V., Makharia G.K., Batra Y. Predictors of unsuccessful mechanical lithotripsy and endoscopic clearance of large bile duct stones. Gastrointestinal Endoscopy. 2004; 59(6): 601-605. https://doi.org/], the only reliably significant sign in which mechanical lithotripsy or lithoextraction without lithotripsy is not recommended is the impaction of a calculus in the lumen of the bile duct, which does not allow the lithoextraction basket to be positioned proximally from the calculus, or does not allow the basket to be opened so that its strings can grasp the calculus. According to the authors of the publication, the size of the calculus can be significant only if it is correlated with the diameter of the common bile duct.

Another known factor influencing treatment outcomes in patients with choledocholithiasis is the chemical composition of the stone: calcium bilirubinate stones are fragile enough to be fragmented with a standard Dormia basket, while large cholesterol stones can be very dense and require preliminary contact lithotripsy. [Trikudanathan G, Navaneethan U, Parsi MA. Endoscopic management of difficult common bile duct stones. World J Gastroenterol. 2013; 19(2): 165-173. https://doi.org/10.3748/wjg.v19.i2.165. PMID: 23345939].

The closest to the declared technical solution is the method for selecting the lithoextraction option presented in the Orlando protocol [Bang J.Y., Wilcox C.M., Navaneethan U. et al. Orlando Protocol for single-session ductal clearance of common bile duct stones at endosopic retrograde cholangiopancreatography. Digestive Endoscopy. 2023; 36(7): 825-833. https://doi.org/10.1111/den.14719]. According to this protocol, to decide on lithoextraction without lithotripsy or lithoextraction with preliminary lithotripsy, the stone-to-common bile duct ratio (the diameter of the maximum stone to the diameter of the common bile duct 1 cm below this stone) is taken into account. If the stone-to-choledoch ratio is <1, the authors recommend balloon and/or basket lithoextraction. If the stone-to-choledoch ratio is =1, lithoextraction with preliminary mechanical lithotripsy is recommended; if the stone-to-choledoch ratio is >1, lithoextraction using laser or electrohydraulic lithotripsy is recommended. Furthermore, the Orlando protocol defines the indication for wide-balloon dilation of the major duodenal papilla based on the ratio of the common bile duct diameter at its widest point to the common bile duct diameter 1 cm proximal to the ampulla: if the common bile duct diameter 1 cm proximal to the ampulla is less than 2/3 of the duct diameter at its widest point, the authors consider wide-balloon dilation of the papilla necessary before lithoextraction. However, this method does not take into account the ratio of the diameter of the calculus to the narrowest section of the common bile duct, as well as the diameter of the section of the duct where the calculus is located, and does not take into account the radiographic characteristics of the contours of the filling defect, which reduces the effectiveness of endoscopic treatment of patients with choledocholithiasis.

Thus, published sources mention various factors influencing the choice of a specific endoscopic treatment method for patients with choledocholithiasis. However, no uniform thresholds have been established for the definition of "complex" choledocholithiasis, which would indicate a transition from lithoextraction without lithotripsy to the use of intraductal lithotripsy. Furthermore, no prior art sources have been identified that describe an intraoperative X-ray endoscopic method for selecting treatment tactics for patients with choledocholithiasis based on a set of parameters (factors) including the ratio of the transverse diameter of the largest filling defect to the transverse diameter of the distal third of the common bile duct, the ratio of the transverse diameter of the largest filling defect to the transverse diameter of the bile duct at the level of the calculus, the clarity/indistinctness of its contours, the coefficient of the presence of smooth or uneven contours of the filling defect (0.4 or 0), as well as a coefficient (0; 0.5 or 1) adjusted for the size of the largest filling defect. It was this set of parameters that demonstrated a statistically significant result in choosing a specific lithoextraction method in the endoscopic treatment of patients with choledocholithiasis.

The technical problem solved by the claimed invention is is to overcome the shortcomings inherent in known analogues and to optimize the choice of technique for performing lithoextraction (without lithotripsy or with preliminary intraductal lithotripsy) based on data from endoscopic retrograde cholangiography in patients with choledocholithiasis.

Disclosure of invention

The technical result achieved by the claimed invention is the identification, among the entire population of patients with choledocholithiasis, of patients who require choledocholithoextraction using preliminary intraductal lithotripsy, aimed at the complete one-stage removal of stones from the common bile duct, regardless of their size, while minimizing the frequency of undesirable intraoperative outcomes (wedging of the basket, injury to the wall of the common bile duct or the wall of the duodenum, damage to endoscopic instrumentation).

The technical result is achieved by selecting a technique for endoscopic treatment of patients with choledocholithiasis, consisting of performing retrograde lithoextraction without lithotripsy (using a basket and/or balloon) or with preliminary intraductal lithotripsy (mechanical, laser or electrohydraulic). The method includes performing endoscopic retrograde cholangiography (ERCP), identifying the largest filling defect (calculus), measuring its transverse size ("transverse diameter") (D _S ); if the obtained value D _S <8 mm, it is recommended to perform lithoextraction without lithotripsy; if D _S > 18 mm, it is recommended to perform lithoextraction with intraductal lithotripsy; if D _S is in the range from 8 mm to 18 mm inclusive, the clarity/fuzzyness of its contours is additionally assessed: if the contours of the filling defect are unclear, it is recommended to perform lithoextraction without lithotripsy; if the contours are clear, the diameter of the duct lumen at the level of the filling defect with the maximum size (D ₂ ), the diameter of the lumen of the common bile duct in its distal third (1 cm proximal to the sphincter of Oddi) (D ₃ ) are additionally measured, the ratio D _S /D ₃ is found, and the ratio D _S /D ₂ , the evenness/unevenness of the contour of the filling defect is assessed, after which the cholangiographic index of lithoextraction (y) is calculated using the formula:

, Where

the coefficient k ₁ is assigned the value “1” if the contours of the filling defect are uneven, the value “0” if the contours of the filling defect are smooth,

the coefficient k ₂ is assigned the value "0", ; value "0.5" - if ; value "1" - if

If the cholangiographic index of lithoextraction is y ≤ 3.78, it is recommended to perform lithoextraction without lithotripsy; if y > 3.78, it is recommended to perform lithoextraction with preliminary intraductal lithotripsy.

The set of parameters, based on the results of which a decision is made on the choice of lithoextraction technique, includes not only the measurement of the transverse diameter of the largest filling defect and the determination of its relationship with the lumen of the common bile duct at different levels, but also the radiographic characteristics of the contours of the filling defects - clarity/fuzzyness, evenness/unevenness, which in the study were statistically significantly correlated with the choice of the technique of endoscopic retrograde choledocholithoextraction.

Many researchers note that the harder a large calculus is, the more difficult it is to extract it from the lithotomy. However, estimating the calculus's hardness based on its appearance is only possible using a direct intraductal visualization system, and most lithotomy procedures do not require this system. Therefore, intraductal visualization of the bile ducts is limited in its application, unlike retrograde cholangiography. The literature contains references to a relationship between the density of calculi, primarily urinary calculi, and the contours of their filling defects. For example, [Alyaev Yu.G., Kuzmicheva G.M., Kolesnikova M., Ryazanov V.V., Rudenko V.I., Melnikov D., Levko A. Study of the composition of urinary stones in vivo using modern information technologies. Doctor, 2009, No. 1. [19-22] noted that low-density gallstones (472 HU) of heterogeneous structure had unclear contours and were fragmented by extracorporeal shock wave lithotripsy on the first attempt in 90-100% of cases, while stones of medium (903 HU) and high density (more than 1240 HU) had clear contours and required repeat extracorporeal shock wave lithotripsy sessions in 30-60% of cases. However, the published reports do not mention a relationship between gallstone hardness and the nature of their contours as determined by retrograde cholangiography. In our study, based on the results of which a set of parameters for selecting a lithoextraction method was developed, unclear and uneven contours of the filling defect were statistically significantly associated with the endoscopic lithoextraction technique without lithotripsy, while clear and smooth contours were associated with the endoscopic lithoextraction technique, including the preliminary use of intraductal lithotripsy.

The method is based on the assessment and analysis of data from direct retrograde contrast of the bile ducts and is intended as an auxiliary tool in the operating surgeon's decision-making regarding further lithoextraction technique: lithoextraction without lithotripsy (using only a basket and/or balloon) or lithoextraction using intraductal lithotripsy (mechanical, laser or electrohydraulic).

Brief description of the drawings

The invention is explained with illustrative material.

Figure 1 schematically shows the image of the contrasted bile ducts, gallbladder and duodenum. The following positions are indicated on the figure: 1 - right lobar duct, 2 - left lobar duct, 3 - common hepatic duct hepaticocholedochus, 4 - common bile duct, 5 - cystic duct, 6 - gallbladder, 7 - filling defect (calculus), 8 - duodenum, Ds - transverse diameter of the largest filling defect, D1 - diameter of the duct above the largest filling defect, D2 - diameter of the common bile duct at the level of the largest filling defect, D3 - diameter of the distal third of the common bile duct (1 cm proximal to the sphincter of Oddi).

Figure 2 schematically depicts the types of filling defect contours during ERCP. The following positions are indicated: 9 – duodenoscope, 10 – common bile duct, 11 – filling defect with clear, even contours, 12 – filling defect with unclear contours, 13 – filling defect with uneven contours, 14 – catheter.

Figure 3 shows a histogram of the distribution of lithoextractions by type depending on the transverse diameter of the maximum filling defect.

Figure 4 shows a histogram of the frequency of occurrence of evenness/unevenness of contours depending on the type of lithoextraction.

Figure 5 shows a histogram of the frequency of use of intraductal lithotripsy depending on the diameter of the filling defect in a group of patients with filling defects of 8-18 mm with clear contours.

Figure 6 shows a histogram of the distribution of weights of observations (WoE) depending on the filling defect diameters, grouped into seven groups. WoE > 0 indicates a higher frequency of use of lithoextractions with lithotripsy, WoE < 0 indicates a higher frequency of use of standard lithoextractions.

Figure 7 shows a histogram of the distribution of observation weights depending on the diameters of the filling defect, combined into three groups.

Figure 8 shows an algorithm for determining the method of lithoextraction based on endoscopic retrograde cholangiography data.

Implementation of the invention

The development of the claimed method was preceded by clinical, laboratory and radiation studies of patients treated at the N.V. Sklifosovsky Research Institute for Emergency Medicine from 2018 to 2024 (N = 776). Inclusion criteria for the study: 1) diagnosis of "gallbladder disease complicated by choledocholithiasis"; 2) age over 18 years; 3) performed endoscopic retrograde choledocholithoextraction during the period of this hospitalization. Exclusion criteria from the study: 1) malignant neoplasms of the liver, bile ducts or pancreas that caused compression of the bile ducts; 2) history of reconstructive surgeries on the bile ducts; 3) lack of visualization of filling defects according to retrograde cholangiography.

At one of the stages of the method development, when determining the treatment tactics for patients with identified filling defects of 8-18 mm in diameter, cases of retrograde choledocholithoextraction were excluded from the specified sample, in which retrograde cholangiograms and/or their descriptive picture in the operation protocol were absent, including measurements of the diameter of the common bile duct in the areas under study, the transverse diameter of the maximum filling defect, and a description of the contours (clear/fuzzy, smooth/uneven) of this defect (N=249).

To characterize and analyze the relationship between the common bile duct diameter and the filling defect, the following parameters were analyzed: the largest transverse dimension (or hereinafter referred to as the transverse diameter) of the largest filling defect - calculus (D _S ), the diameter of the common bile duct proximal to the largest filling defect (D ₁ ), the diameter of the common bile duct at the level of the largest filling defect (D ₂ ), the diameter of the common bile duct at the level of the distal third - approximately 1 cm above the level of the sphincter of Oddi (D ₃ ). These measurements are schematically shown in Fig. 1. In addition to the listed parameters, the contours of the filling defect were also examined, including clarity or fuzziness, evenness or unevenness of the contours.

Within the context of the present invention, the clarity or fuzziness of a contour is understood to mean the presence of a sharp or blurred (erased) line at the boundary of two media (in this case, the calculus and the surrounding fluid), respectively. A filling defect is considered "clear" if the sharp contour line in the image occupies 50% or more of the filling defect perimeter; otherwise, the filling defect is considered "fuzzy." Smooth contours of a filling defect are considered to be smooth. An uneven contour is considered to be the presence of relatively small (no more than 0.5-2 mm) protrusions and depressions in the perimeter profile, with an average pitch typically no greater than 2-3 times the height of the irregularities. A graphical representation of the characteristics of the described filling defect contours is schematically shown in Fig. 2.

In developing the claimed method, a comparative statistical analysis was performed between a group of patients with and without lithotripsy based on the following parameters: gender, age, history of cholecystectomy and/or endoscopic intervention on the bile ducts, duration of the exacerbation period, liver enzyme levels upon admission (total bilirubin, direct bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), D _S , D ₁ , D ₂ , D ₃ , D _S /D ₂ , D _S /D ₃ ratios, number and shape of filling defects, nature of the contours of the maximum filling defect, nature of the extracted material (sludge and/or stones), presence of parapapillary diverticulum, adenoma of the major papilla.

Of the listed parameters, a statistically significant difference in values between the groups was revealed only for a number of radiological characteristics of the filling defect and the common bile duct (except for _D3 ), which are presented in Table 1.

Table 1. Comparison of retrograde cholangiogram parameters in the standard lithoextraction group and in the lithotripsy group (N=527) Lithoextraction with lithotripsy (N=78) Lithoextraction without lithotripsy (N=449) p-value 95% CI D1, mm 18.4 13.6 2.73⋅10 ^-8 * -6.4; -3.25 D2, mm 16.8 11.65 3.9⋅10 ^-14 * -6.3; -4 D3, mm 7.24 7.81 0.2041 -1.4; 0.3 D1/D3 2.54 2.03 1.16⋅10 ^-6 * -0.7; -0.3 Ds, mm 14.19 9.05 2.2⋅10 ^-16 * - Filling defect contours clear 66 (85%) 526 (99.8%) 2.81⋅10 ^-8 * - fuzzy 12 (15%) 1 (0.2%) even 56 (71.8%) 250 (55.7%) 0.0078* - uneven 22 (28.2%) 199 (44.3%) Ds/D2 0.91 0.81 2.5⋅10 ^-6 * -0.1; -0.06 Ds/D3 2.13 1.45 8.64⋅10 ^-12 * -0.9; -0.5 * - the difference in values is statistically significant, 95%CI – 95% confidence interval.

Next, based on the identified reliable factors, the stages of the method were developed.

1. Estimating the transverse diameter of the largest filling defect. The first step is to identify the largest filling defect and measure its transverse dimension, selecting the largest of the measured values for subsequent calculations. This parameter is defined as the "transverse diameter D _S ."

The following results were obtained as a result of a comparative analysis of the number of lithoextractions without lithotripsy and lithoextractions with preliminary lithotripsy depending on the diameter of the maximum filling defect. Table 2 shows that in patients with a transverse filling defect diameter <8 mm, lithotripsy was not performed in any of 213 cases, with filling defects of 8-18 mm, lithotripsy was used in 57 of 348 cases (16.4%), and in patients with filling defects >18 mm, lithotripsy was used in 21 of 23 cases (91.3%). All differences in the resulting groups were statistically significant according to the Pearson χ ² test. For clarity, Figure 3 shows a histogram of the frequency of lithotripsy depending on the filling defect diameter.

Table 2. Comparative statistical analysis of lithoextraction methods depending on the diameter of filling defects in patients Analyzed parameters Number of lithoextractions p-value ( χ ² ) With lithotripsy Without lithotripsy total Filling defect diameter <8 mm 0 213 213 <1⋅10 ^-10 * 8-18 mm 57 234 291 >18 mm 21 2 23 total 78 449 527 * - the difference in values is statistically significant

Based on the results of the study, standard lithoextraction is recommended for patients with _DS <8 mm at this stage, while preliminary lithotripsy is recommended for patients with _DS >18 mm. For patients with _DS between 8 and 18 mm, inclusive, additional parameters determined in the next stage of the study must be considered before deciding on further action.

2. Assessment of the clarity/fuzzyness of the contours of the filling defect.

When analyzing the X-ray characteristics of the contours of maximum filling defects, ranging from 8 to 18 mm inclusive (N=291), 29 patients had filling defects that were fuzzy. Of these, only one (3.4%) underwent intraductal lithotripsy. Table 3 shows that this parameter had a statistically significant difference between patients with and without lithotripsy. Based on this observation, it was concluded that filling defects with fuzzy contours in the 8-18 mm diameter range do not require lithotripsy. Given the statistical significance (p-value 0.021), this parameter was included in the reliable set of features for decision-making regarding the use of lithoextraction methods.

Table 3. Comparative analysis of filling defect contours between patients without lithotripsy and with lithotripsy in the group with a stone size of 8-18 mm (N=291) with lithotripsy without lithotripsy total p-value ( χ ² ) clear contours 56 (21.4%) 206 (78.6%) 262 0.021* fuzzy contours 1 (3.4%) 28 (96.6%) 29 * - statistically significant difference

Therefore, for patients with a filling defect diameter of 8-18 mm and unclear filling defect margins, lithoextraction without prior lithotripsy is recommended. In cases with clear margins, the cholangiographic index of the calculus ( y ) must be calculated to decide on further action.

3. Determination of the cholangiographic index of the stone ( y ) for a group of patients with filling defects of 8-18 mm with clear contours.

In the third stage, to identify factors significantly influencing the choice of lithoextraction method, a comparative statistical analysis of all previously reviewed retrograde cholangiogram parameters (except for the clarity/indistinctness of the contours) and biochemical markers of liver function was performed in patients with a largest filling defect diameter ranging from 8 to 18 mm inclusive with clear margins. The results of the comparison are presented in Table 4. Compared with the previous analysis using the same criteria for the entire sample (Table 1), in this group of patients, D1 no longer showed a statistically significant difference, while D3 was significant. Preoperative levels of total bilirubin, its direct fraction, ALT, and AST were slightly higher in patients who underwent lithotripsy, but did not demonstrate a significant difference.

All statistically significant indicators are included in a comprehensive assessment to make an optimal decision on the choice of lithoextraction technique based on the determination of the cholangiographic index of the calculus ( y ) using the following formula:

, Where

y – cholangiographic index of the calculus,

D _S - transverse diameter of the maximum filling defect,

D ₂ - diameter of the duct lumen at the level of the maximum filling defect,

D ₃ - the diameter of the lumen of the common bile duct in the lower third (1 cm proximal to the sphincter of Oddi),

coefficientk ₁ assign the value “1” if the contours of the filling defect are uneven, the value “0” if the contours of the filling defect are smooth,

the coefficient k ₂ is assigned the value “0” if 8≤ D _S ≤10.5, the value “0.5” if 10.5<D _S <14, the value “1” if 14≤ D _S ≤18.

The result of the cholangiographic index of the calculus ( y ) equation is a numerical value reflecting the probability of using lithotripsy, which has a linear relationship: the higher the obtained value, the higher the probability of the need for intraductal lithotripsy. The cutoff value is 3.78. If the cholangiographic index of the calculus ( y ) ≤ 3.78, lithoextraction without lithotripsy is recommended; if the cholangiographic index of the calculus ( y ) > 3.78, preliminary intraductal lithotripsy is recommended for calculus extraction.

The cholangiographic calculus index equation contains four parameters:

1) Parameter D _S /D ₃ . When choosing the lithoextraction method, the ratio of the diameter of the maximum filling defect D _S to the diameter of the narrowest section of the common bile duct D ₃ is taken into account, measured distally from the calculus in the visually narrowest part of the common bile duct (intraduodenal portion or stricture, if present), where there is the greatest risk of damage to the duct wall or wedging of the lithoextraction basket with the captured calculus during traction attempts. The conducted statistical analysis confirmed the fact that the D _S /D ₃ ratio has the highest degree of significance (p-value 1.1⋅10 ^-10 ) among other reliable indicators (Table 4).

2) Parameter D_S/D₂. When choosing a lithoextraction method, this parameter is taken into account. It reflects the extent to which the filling defect occupies the duct lumen at the level where the lithoextractor will need to be inserted between the calculus and the duct wall. This is important because the smaller the free space for manipulation, the greater the likelihood of failure when attempting to insert the instrument above the calculus to capture it. If this is impossible (the calculus is tightly adherent to the inner walls of the common bile duct, in other words, there is calculus impaction), laser or electrohydraulic lithotripsy is usually the endoscopic treatment of choice. It is worth noting that in this case, we are not referring to calculus impaction within the ampulla of the common bile duct, which typically resolves after dissection of the muscular layer of the major duodenal papilla, but rather at a higher level. The importance of parameter D_S/D₂is shown with a fairly high degree of reliability (p-value 2.1⋅10^-4), which exceeds the degree of reliability of the value of isolated D₂(p-value 0.044). For this parameter, a factor of "2" was applied to equalize the values based on the results of the regression analysis.

3) Coefficientk ₁ This coefficient reflects the presence or absence of irregularities in the contours of the maximum filling defect. The histogram in Fig. 4 shows that patients with smooth filling defect contours required lithotripsy almost 30% more often than patients with irregular filling defect contours. The difference between these two radiographic contour characteristics, according to Fisher's exact test, was statistically significant (Table 4). Therefore, the parameterk ₁ , meeting the following conditions:k= 0 - with a smooth contour of the maximum filling defect,k= 1 - for an uneven contour of the maximum filling defect. Coefficientkis subtrahendable and is applied with a multiplier of 0.4. The optimal value of the multiplier was calculated by applying logistic regression to the current sample data set.

4) Coefficient k ₂ . This coefficient is a correction for the transverse diameter of the largest filling defect (D _S ). Unlike D ₂ and D ₃ , which are generally associated with the presence and size of the calculus, D _S is an independent parameter. A comparative analysis revealed a linear relationship between the frequency of lithotripsy and the filling defect diameter, which is shown by the trend line in Fig. 5.

Therefore _{, to determine the coefficient k2} , which depends on the transverse diameter of the largest filling defect (Ds), the weights of evidence (WoE) were analyzed, calculating the information value. This analysis allowed us to identify threshold values for the common bile duct diameter, which divided the dataset into groups corresponding to a linear increase in the likelihood of lithotripsy.

During the initial analysis, the results of measurements of all transverse diameters of maximum filling defects were combined into seven groups (8-8.5 mm, 9-9.5 mm, 10 mm, 11 mm, 12-13.5 mm, 14-14.5 mm, 15-18 mm). For each group of calculus diameter values, the WoE parameter was determined using the formula:

where WoE is the weight of observations (Weight of Evidence), LT is lithotripsy.

A positive WoE value corresponded to a high relative number of lithotripsies performed in the study group of patients, therefore, the probability of using lithotripsy was high. A negative WoE value corresponded to a low relative number of lithotripsies performed in the study group of patients, therefore, the probability of using lithotripsy was low. Figure 6 shows a histogram displaying the weight of observations depending on the above-mentioned groups. As can be seen, lithotripsy was practically not used in patients with filling defects up to 10 mm and, accordingly, there is no linear increase corresponding to the risk of using this technique. Starting with the groups of patients with filling defects of 11 mm, a more frequent use of intraductal stone fragmentation is noted; however, the WoE in patients in the groups with filling defects of 11 and 12-13.5 mm is almost the same, after which it increases sharply. The information index for all values of observation weights was 0.595.

Because the weight of observations must maintain a linear increase, a larger breakdown of filling defect transverse diameter measurements was used for further analysis. These diameters were divided into three groups: 8 to 10.5 mm, 10.5 to 14.0 mm, and 14.5 to 18 mm. An information index was determined for each group, characterizing the degree to which this division by filling defect diameter corresponded to the selected treatment method. The information index was determined using the following formula:

where IV is the information index, LT is lithotripsy, WoE is the weight of observations

The result of the equation is a value that displays 5 degrees of conformity:

1) <0.02 - does not correspond, 2) 0.02-0.1 - corresponds weakly, 3) 0.1-0.3 - corresponds moderately, 4) 0.3-0.5 - corresponds strongly, 5) > 0.5 - corresponds very strongly.

As a result of the calculations, the final observation weights had a linear relationship, and the information index was 0.575 for all three groups of filling defect diameters. Figure 7 shows the distribution of groups according to WoE values and the linear trend line.

Thus, the risk of lithotripsy increased linearly with increasing stone diameter, starting at 10.5 mm, and sharply increased above 14 mm. These values (10.5 mm and 14 mm) were used as thresholds, and the following coefficients, obtained through regression analysis, were introduced into the equation, taking into account the linear increase in the probability of lithotripsy:

1) 0, if 8≤Ds≤10.5 mm,

2) 0.5, if 10.5<Ds<14 mm,

3) 1, if 14≤Ds≤18 mm.

To verify the developed method To determine the method of lithoextraction based on endoscopic retrograde cholangiography data, the sensitivity, specificity, overall accuracy, negative and positive predictive value were calculated using the available data set of 776 patients with choledocholithiasis and endoscopic lithoextraction. These indicators were determined both for the method as a whole and separately for the presented equation of the cholangiographic calculus index (y) for a group of patients with a filling defect diameter of 8-18 mm with clear contours. The results are presented in Table 5, which shows that the sensitivity of the cholangiographic calculus index equation and the method as a whole are almost comparable (82.1% vs. 85.0%), while the specificity and accuracy of the latter are, on average, 11% higher.

Table 5. Verification of the lithotripsy index method and equation Sensitivity Specificity Accuracy PPC OPC Equations of cholangiographic index of calculus ¹ 82.1% 82.0% 82.0% 55.4% 94.4% Method for selecting a lithoextraction method based on ERCG data ² 85.0% 94.0% 93.0% 61.8% 98.2% Note . PPV – positive predictive value, NPV – negative predictive value, ERCG – endoscopic retrograde cholangiography, ¹ – sample with filling defects of 8-18 mm with clear contours (N=262), ² – entire sample (N=776).

The claimed method is carried out as follows .

When a filling defect is detected in a patient based on retrograde cholangiography data, the first step is to measure the transverse diameter of the filling defect (the largest one, if there are several). If the filling defect diameter is less than 8 mm, the treatment method of choice is lithoextraction without lithotripsy (using a lithoextraction basket and/or balloon), which can be performed using known prior art means and methods (see, for example, European and American guidelines [Manes G, Paspatis G, Aabakken L, Anderloni A, et al. Endoscopic management of common bile duct stones: European Society of Gastrointestinal Endoscopy (ESGE) guideline. Endoscopy. 2019 May; 51(5):472–491. https://doi.org/10.1055/a-0862-0346; Buxbaum J.L., Fehmi S.A., Sultan S. et al. ASGE guideline on the role of endoscopy in the evaluation and management of choledocholithiasis. Gastrointestinal Endoscopy, 89(6), 1075-1105. https://doi.org/10.1016/j.gie.2018.10.001]. For filling defects greater than 18 mm in diameter, the treatment method is lithoextraction with intraductal lithotripsy. Intraductal lithotripsy can be mechanical, laser, or electrohydraulic, the procedure for which is also described in detail in the European and American guidelines. For filling defects ranging in size from 8 to 18 mm inclusive, additional parameters are taken into account when choosing the endoscopic lithoextraction tactics. Initially, the clarity/indistinctness of the filling defect contours is assessed in accordance with the above definitions of these concepts. In the presence of unclear defects, lithoextraction without lithotripsy is selected. In the case of clear defects, the cholangiographic index of the calculus is calculated to make a further decision on lithoextraction methods. To calculate this index, the diameter of the largest filling defect, the common bile duct diameter at the level of the largest filling defect, and the common bile duct diameter in the distal third are measured, and the smoothness/unevenness of the contours of the largest filling defect are assessed. The resulting measurements and estimates are then inserted into the proposed formula. The equation is compared with a cutoff value of 3.78: if the equation result is ≤3.78, the stone is removed without intraductal lithotripsy; if it is >3.78, preliminary intraductal lithotripsy is used.

Fig. 8 shows the algorithm for selecting a lithoextraction method with an integrated LT index.

Clinical example 1 (filling defect with a diameter of less than 8 mm).

Patient V., 54 years old. Two days before admission to the hospital, he noted the onset of pain in the upper abdomen, yellowing of the sclera and skin, itching, and darkening of the urine. The patient has no history of surgery on the gallbladder or bile ducts. On physical examination, the sclera and skin are icteric, and there is abdominal tenderness upon palpation in the upper sections. Blood biochemistry: ALT - 243 U/L, AST - 264 U/L, total bilirubin 60.1 μmol/L. According to ultrasound, the common bile duct is dilated to 1.0 cm, with a calculus up to 0.8 cm in diameter in the lumen. The patient is indicated for endoscopic choledocholithoextraction. Intraoperatively, retrograde contrast enhancement of the bile ducts revealed four oval-shaped filling defects in the common bile duct. The largest of these had a transverse diameter (D _S ) of 6 mm. The duct lumen at the level of the largest filling defect (D ₂ ) was 8 mm, and in the distal third of the common bile duct (D ₃ ) it was 5 mm. According to the proposed method, standard lithoextraction without lithotripsy is recommended for patients with filling defects of this diameter (<8 mm). After evaluating the retrograde cholangiograms, a typical 1.2 cm long EPST was performed; there was no bleeding. During exploration of the common bile duct with a Dormia basket, four stones and a small amount of sludge were removed. The surgery time was 35 minutes. No postoperative complications were identified.

Clinical example 2 (Ds range 8-18 mm, contours are unclear).

Patient L., 72, was admitted to the emergency department complaining of persistent, aching pain in the right upper quadrant. His medical history revealed that he had undergone a laparoscopic cholecystectomy six months prior to admission; no bile duct procedures had been performed. Two days prior to admission, the patient underwent an outpatient MR cholangiography, the results of which confirmed choledocholithiasis. Physical examination revealed subicteric sclera and skin, and abdominal tenderness to palpation in the right upper quadrant. With choledocholithiasis suspected, the patient was hospitalized for further evaluation and treatment. A biochemical blood test revealed a slight increase in some liver enzymes: ALT 48.1 U/L (normal range up to 45), U/L, GGT - 71.7 U/L (normal range up to 55), an increase in total bilirubin to 28.63 μmol/L (normal range up to 21), alkaline phosphatase 148.1 (normal range up to 120). AST is not elevated - 30.9 U/L. According to ultrasound examination, the common bile duct is up to 16 mm in diameter, with a calculus located in its lumen. The patient was admitted to the operating room for endoscopic lithoextraction. Retrograde contrast revealed an oval-shaped filling defect with a transverse diameter (D _S ) of 16.5 mm, the lumen of the duct at the level of the filling defect (D ₂ ) is 19 mm, and in the distal third of the common bile duct (D ₃ ) - 5 mm. The filling defect's contours were assessed as unclear and uneven along most of its perimeter. During exploration of the common bile duct using a Dormia basket and a lithoextraction balloon, an oval-shaped, soft stone measuring 16 x 1.5 cm and a large amount of sludge were removed without any technical difficulties. The biliary tree was debrided with 60 ml of sterile saline until clear water was achieved. The surgery lasted 35 minutes. No postoperative complications were observed in the patients following lithoextraction.

Thus, despite the fact that the transverse diameter of the filling defect was quite large in this case, the calculus was removed using a standard Dormia lithoextraction basket without prolonging the procedure time (35 minutes) or causing postoperative complications. This lithoextraction method was chosen because, despite the large size of the calculus, the radiographic evaluation revealed unclear contours of the filling defect. The unclear contours of the defect in this case indicated the relatively soft consistency of the calculus. This was confirmed by direct visualization after removal into the duodenum: a soft calculus and a large amount of sludge were removed. In this case, the use of our proposed method eliminated the use of lithotripsy, which would have been an obvious option given the large calculus and the narrow distal third of the common bile duct.

Clinical example 3 (D _S in the range of 8-18 mm, clear contours, cholangiographic index of the calculus ≤3.78).

Patient I., 35, reported pain in the right hypochondrium the day before admission. Her medical history revealed that she had undergone endoscopic choledocholithotomy 4 months prior to this visit. Physical examination revealed abdominal tenderness in the right hypochondrium, and normal-colored sclera and skin. Biochemical analysis revealed total bilirubin 11.5 μmol/L, AST 66.42 U/L, ALT 119 U/L, alkaline phosphatase 267.71 U/L, and GGT 165.75 U/L. According to ultrasound data, the common bile duct is dilated along its entire length to 0.9 cm. A calculus with a clear acoustic shadow measuring 1.3 x 0.8 cm is localized in the lumen at the level of the head of the pancreas. The patient is indicated for endoscopic lithoextraction. Intraoperatively, retrograde contrast of the bile ducts revealed one round filling defect with a transverse diameter (D _S ) of 16 mm, the lumen of the duct at its filling level (D ₂ ) is 20 mm, and in the distal third of the common bile duct (D ₃ ) is 20 mm. The contours of the filling defect are assessed as clear and smooth. In this case, a calculus is present, which, according to the European guidelines (ESGE), can be assessed as "complex" due to its size and theoretically require preliminary lithotripsy. According to the proposed method, a patient with such a filling defect (16 mm in diameter, clearly delineated) falls into the category of patients requiring determination of the cholangiographic index of the calculus ( y ). In this case, y, according to the previously described formula, equals 16/20 + 2 * 16/20 - 0 + 1 = 3.4. This value is less than the cutoff value (3.78) and does not require lithotripsy. During exploration of the common bile duct using a lithoextraction balloon and a Dormia basket, a 1.5 cm diameter calculus and a moderate amount of sludge were removed without technical difficulties. The procedure took 70 minutes, and no postoperative complications were observed. Thus, by using this method in the presence of a large filling defect with clear contours, which, according to the literature, falls under the definition of “complex” choledocholithiasis due to its large size and requires lithotripsy, we were able to avoid the use of intraductal crushing of the stone, which lengthens and increases the cost of the procedure.

Clinical example 4 (D _S in the range of 8-18 mm, clear contours, cholangiographic index of the calculus >3.78).

Patient T., 54, developed the disease 5 days prior to admission, when he noted discomfort and pain in the upper abdomen, nausea, dry mouth and bitterness, icterus of the sclera and skin, and dark urine. His medical history revealed a history of gallstone disease for over 20 years and no previous surgery on the bile ducts or gallbladder. Physical examination revealed abdominal tenderness upon palpation in the upper abdomen, yellow skin and sclera, light-colored stool, and tea-colored urine. Blood chemistry revealed total bilirubin 278.9 μmol/L, ALT 478.5 U/L, AST 288.16 U/L, and alkaline phosphatase 836 U/L. An ultrasound examination of the abdominal organs revealed a dilation of the common bile duct to 9 mm, a homogeneous visible lumen, and a gas-shielded distal common bile duct in the transverse colon. A patient with severe mechanical jaundice and suspected choledocholithiasis underwent endoscopic lithoextraction. Intraoperatively, retrograde contrast of the bile ducts revealed one irregularly shaped filling defect with a transverse diameter (D _S ) of 12 mm. The duct lumen at its filling level (D ₂ ) was 12 mm, and in the distal third of the common bile duct (D ₃ ) it was 5 mm. The contours of the filling defect were assessed as clear and smooth. In this case, since the filling defect has a diameter of 12 mm (which is in the range of 8-18 mm) and clear contours, the cholangiographic calculus index equation must be used. According to the formula, y is equal to 12/5 + 2 * 12/12 - 0 + 0.5 = 4.9. This value exceeds the threshold (3.78), indicating the use of lithotripsy. To verify the validity of the proposed algorithm, the endoscopist first attempted to remove the calculus with a lithoextraction basket without intraductal fragmentation. However, when attempting to traction the captured calculus, sharp resistance of the basket was observed at the level of the common bile duct ampulla. This could lead to basket impaction or common bile duct injury with further attempts to remove the calculus. Therefore, the solution proposed by the algorithm was adopted: perform intraductal lithotripsy. Cholangioscopy with the SpyGlass system visualized a calculus with a smooth surface, approximately 1.2 cm in diameter, in the middle third of the common bile duct. Electrohydraulic lithotripsy was performed at a frequency of 30 Hz and medium power until stone fragments up to 0.3-0.4 cm in diameter formed. During exploration of the common bile duct using a Dormia basket, numerous small stone fragments were removed. The biliary tract was sanitized with sterile saline. Thus, despite the relatively small transverse size of the filling defect (12 mm), a comprehensive assessment of its relationship with the common bile duct lumen at two levels indicated a potentially complex form of choledocholithiasis. The use of lithotripsy in this case prevented wedging of the lithoextraction basket or damage to the walls of the common bile duct or duodenum.

Clinical example 5 (Ds >18 mm).

Patient D., 85 years old. Six months prior to this admission, percutaneous transhepatic gallbladder drainage was performed for cholelithiasis and acute cholecystitis. The day before admission, the patient noted increasing pain in the right upper quadrant and at the site of the drainage tube placement. Her medical history includes bile duct intervention for choledocholithiasis. Physical examination reveals abdominal tenderness in the right upper quadrant, normal-colored skin and sclera. A microcholecystostomy tube is leaking 250 ml of bile per day. Ultrasound data show that the common bile duct is dilated to 1.3 cm, with a calculus (an inclusion of increased echogenicity) located within the lumen, producing an acoustic shadow measuring 1.1 x 0.8 cm. According to antegrade cholecystocholangiography, the shadow of the common bile duct along its entire length, as well as the common hepatic duct at the level of the middle third, is non-homogeneous due to several irregularly shaped filling defects with clear contours, ranging in diameter from 0.5 cm to 1.9 cm. Blood biochemistry is unremarkable. The patient was recommended to perform lithoextraction and cholecystectomy. Laparoscopic cholecystectomy was performed first, then an endoscopic team was invited to the operating room. Retrograde contrast of the bile ducts revealed 4 rectangular filling defects of the common bile duct, the largest (D _S ) with a diameter of 20 mm, the lumen of the duct at its filling level (D ₂ ) is 20 mm, in the distal third of the common bile duct (D ₃ ) - 18 mm. Such a diameter of the common bile duct, according to the method, suggests performing lithotripsy regardless of any other factors. Cholangioscopy was performed using a guidewire using the SpyGlass system. Dilated extra- and intrahepatic bile ducts were visualized. Multiple stones with smooth, even contours were noted in the lumen of the common bile duct. Electrohydraulic lithotripsy of large stones was performed under endoscopic control at a pulse rate of 30 pulses and high power. Subsequently, lithoextraction of stone fragments and sludge was performed using a Dormia basket. The biliary tract was irrigated with 200 ml of sterile saline. The procedure lasted 130 minutes, and the postoperative period was uneventful.

Thus, despite the rather wide diameter of the distal third of the common bile duct, a decision was made to perform intraductal lithotripsy due to a large filling defect with clear contours, which made it possible to avoid basket wedging or iatrogenic damage.

Claims (5)

A method for selecting the technique of endoscopic retrograde choledocholithoextraction based on retrograde cholangiography (ERCP) data, consisting of performing retrograde lithoextraction without lithotripsy or with preliminary intraductal lithotripsy, including identifying the largest filling defect based on ERCP results, measuring its transverse size (D _S ); if the obtained value D _S <8 mm, lithoextraction is performed without lithotripsy; if D _S >18 mm, lithoextraction is performed with intraductal lithotripsy; if D _S is in the range from 8 mm to 18 mm inclusive, the clarity/fuzzyness of its contours is additionally assessed: if the contours of the filling defect are unclear, lithoextraction is performed without lithotripsy; if the contours are clear, the diameter of the duct lumen at the level of the filling defect with the maximum size (D ₂ ) is additionally measured, the diameter of the lumen of the common bile duct in its distal third at 1 cm proximal to the sphincter of Oddi (D ₃ ), the ratio D _S /D ₃ and the ratio D _S /D ₂ are found, the evenness/unevenness of the contour of the filling defect is assessed, after which the cholangiographic index of lithoextraction ( y ) is calculated using the formula: , where the coefficient k ₁ is assigned the value “1” if the contours of the filling defect are uneven, the value “0” if the contours of the filling defect are smooth, the coefficient k ₂ is assigned the value "0", ; value "0.5" - if ; value "1" - if when the cholangiographic index of lithoextraction is y ≤3.78, lithoextraction is performed without lithotripsy; when y >3.78, lithoextraction is performed with preliminary intraductal lithotripsy.