- Email: [email protected]
What predicts gastroenterologists' and surgeons' diagnosis and management of common bile duct stones?
What predicts gastroenterologists' and surgeons' diagnosis and management of common bile duct stones? Judy A. Shea, PhD, David A. Asch, MD, MBA, Romaine F. Johnson, BA, Rudolf N. Staroscik, MD Peter F. Malet, MD, Bonnie J. Pollack, MD, John R. Clarke, MD, Paul E. Green, PhD J. Sanford Schwartz, MD, Sankey V. Williams, MD Philadelphia, Pennsylvania
Background: Because the literature suggests numerous indicators of common bile duct stones, we undertook a systematic assessment of physicians' judgments of the clinical utility of eight indicators: patient age, history of jaundice, history of pancreatitis, levels of serum alanine aminotransferase, alkaline phosphatase, amylase, and total bilirubin, and common bile duct diameter on ultrasonography. Methods: Random samples of 1500 gastroenterologists and 1500 surgeons were sent a survey asking them to indicate the importance of each potential indicator of common bile duct stones, the likelihood of common bile duct stones for each of nine clinical vignettes, and whether they would order a preoperative ERCP. An abbreviated survey was sent to nonrespondents. Results: Although there was substantial variation in the importances assigned to each indicator, the most important indicators were serum total bilirubin and diameter of common bile duct on ultrasound. The best predictors of the decision to order an ERCP were perceived likelihood of stones and specialty. The average threshold for ordering an ERCP was 37%. Respondents did not differ from nonrespondents in the perceived importance of the eight indicators. Conclusions: The substantial variation among gastroenterologists and surgeons regarding the optimal approach to common bile duct stones has clinical implications. Patients will receive varying recommendations for care, depending on whom they see. (Gastrointest Endosc 1997;46:40-7.)
Laparoscopic cholecystectomy, first performed in France in 1987, was introduced in the United States in 1988. Several case series suggest that laparoscopic cholecystectomy is associated with lower mortality and morbidity, shortened hospital stays, and Received July 23, 1996. For revision December 4, 1996. Accepted January 28, 1997. From the Divisions of General Internal Medicine and Gastroenterology-Department of Medicine, the Department of Surgery, the Wharton School, and the Leonard Davis Institute of Health Economics, University of Pennsylvania; the Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine; The Veteran's Affairs Medical Center; and the Department of Surgery, Allegheny University, Philadelphia, Pennsylvania. This work was supported by a grant from the Agency for Health Care Policy and Research (HS06481). Reprint requests: Judy A. Shea, PhD, General Internal Medicine, University of Pennsylvania, Ralston House 318, 3615 Chestnut St., Philadelphia, PA 19104-2676. 37/1/80768 46
GASTROINTESTINAL ENDOSCOPY
earlier return to activities, 1-13 compared to open cholecystectomy. However, one disadvantage is that there is a higher incidence of retained common bile duct stones in laparoscopic cholecystectomy compared to open cholecystectomy, 14-2° most likely because the duct is no longer accessible for direct observation and palpation. In response to concerns about retained stones (as well as safety issues), many surgeons recommend performing an intraoperative cholangiogram in almost all patients. 21-23 More recently, many experts agree that it is unnecessary and too expensive to perform intraoperative cholangiogram on all patients, 19' 24, 25 especially if one uses fluorocholangiography. 26 Instead, one should select patients for assessment given their likelihood of common bile duct stones as suggested by various preoperative indicators. Several clinical indicators have been proposed to help identify patients at risk for common bile duct VOLUME 46, NO. 1, 1997
Gastroenterologists' and surgeons' management of common bile duct stones
J Shea, D Asch, R Johnson, et al.
Table 1. Levels of attributes Age (y) History of jaundice History of pancreatitis Serum alanine aminotransferase (U/L) Serum alkaline phosphatase (U/L) Serum amylase (U/L) Serum total bilirubin (mg/dL) Common bile duct diameter on ultrasound (mm)
Patient #15
25, 50, 75 Yes, no Yes, no 24, 82, 160 90, 180, 320 100, 250, 550 1.0, 2.5, 4.5 4, 8, 12
stones, including history of jaundice, 27' 2s hyperbilirubinemia, 2'~-32 dilated bile ducts on ultrasound,29, 30, 32-3~ elevated levels of amylase and alkaline phosphatase, 2s-3°' 38 pancreatitis,2% 2s, 3o, 33, 35 and advanced age. 3°' 32, 34 A recent meta-analysis of 10 potential indicators of common bile duct stones found t h a t most indicators had high specificities (i.e., probabilities t h a t a person without common bile duct stones will not have a particular indicator), but poor sensitivities (i.e., probabilities t h a t a person with common bile duct stones will have a particular indicator). Patients with common bile duct stones seen on ultrasound, preoperative jaundice, and cholangitis were at least 10 times as likely to have common bile duct stones compared to patients lacking the same indicator. Other indicators, especially alkaline phosphatase level, pancreatitis, cholecystitis, and hyperamylasemia, were not useful in predicting common bile duct stones. 37 Because the literature suggested m a n y potentially useful indicators of common bile duct stones, some of which were not borne out by the metaanalysis, we surveyed random samples of practicing gastroenterolo~[sts and surgeons and asked them to (1) indicate the relative importance of each of eight indicators in diagnosing common bile duct stones, and (2) estimate the likelihood of common bile duct stones for sets of patient vignettes in which the patients varied in the level of each indicator, and indicate w h e t h e r they would order a preoperative ERCP. Our pu~:pose was to provide a systematic assessment of physicians' j u d g m e n t s of the clinical utility of the indicators, to describe variation in their judgments, and to explore how these j u d g m e n t s are used clinically. MATERIALS AND METHODS Subjects We randomly selected 1500 gastroenterologists and 1500 surgeons from the American Medical Association (AMA) Physician Masterfile. The Masterfile is the most comprehensive set; of physician information in the United States and includes physicians who are not members of VOLUME 46, NO. 1, 1997
Age
25 years
History of jaundice
NO
History of pancreatitis
Yes
Serum Alanine Aminotransferase
2~ U/L
Serum Alkaline
Phosphatase
320 U/L
Serum Amylase
250 U/L
Serum Total Bilirubin
1,0 mg/dL
Common bile duct diameter
12 mm
Figure 1, Sample patient vignette. the AMA. We specified that sample physicians be in practice in the United States, not retired, and not in training.
Instrument The survey instrument had three parts. In the first part we asked respondents to indicate the importance of each of eight potential indicators of common bile duct stones (listed in the first column of Table 1) by dividing 100 points among them. In the second part, we asked respondents to evaluate several hypothetical clinical scenarios, estimate the likelihood of stones for each case, and indicate whether they would order a preoperative ERCP. We specified that the patients were scheduled for elective laparoscopic cholecystectomy for symptomatic gallstones, were otherwise healthy, and had no known malignancies or other disease processes. Because the cases were hypothetical there was no known or true probability of stones for the vignettes. The vignettes were constructed by combining each of the eight indicators at various levels, as shown in Table 1. There were 2916 possible vignettes, given the number of indicators and levels we chose. Using a main effects orthogonal design, 3s we were able to test the importance of each indicator by limiting the set to 27 vignettes. To reduce respondent burden further, we randomly allocated subjects into three groups, so that each subject received only 9 of these 27 vignettes. A sample vignette is shown in Figure 1. Each vignette was printed on a separate card. We asked subjects to sort the cards from least likely to represent a patient with common bile duct stone to most likely. Then we asked them (1) to provide an estimate for the likelihood of stones for each vignette, and (2) to indicate whether they would order a preoperative ERCP for the patient. We provided subjects with a table of normal laboratory values. In the third part of the questionnaire we asked respondents to provide professional and demographic information, including their type of practice and the volume of patients they treat with gallstone-related problems.
Mailing strategy In November 1994 we mailed each subject a packet including an introductory cover letter, the card set, a GASTROINTESTINAL ENDOSCOPY
41
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Gastroenterologists" and surgeons' management of common bile duct stones
Table 2. Demographic and practice characteristics of respondents Total (N = 624)
Gastroenterologists (N = 350)
Year born [mean (SD)] 1948 (10.0) Male (%) 96 Year graduated from medical school 1975 (10.4) [mean (SD)] Board certified (%) 90 Primary hospital is university 69 affiliated (%) Practice setting (%) Solo practice 30 Single-specialty group 39 Multispecialty group 18 Other 13 Preferred strategy for diagnosing CBD stones (%) Preoperative ERCP 67 IOC 24 Other 9 Monthly volume of patients with GB-related problems (%) <10 30 10-19 35 20+ 36 Patients evaluated for CBD stones (%) 0%-10% 40 11%-40% 29 >40% 31 Perform ERCP (%) -Perform laparoscopic -cholecystectomy (%)
Surgeons (N = 274)
1950 (8.6) 96 1976 (9.0)
1946 (11.1) 96 1972 (11.2)
93 67
86 73
23 44 21 12
39 32 15 14
81 10 9
48 42 11
23 34 43
38 36 26
35 33 32 68 --
47 22 31 -92
IOC, I n t r a o p e r a t i v e cholangiogram; CBD, common bile duct; GB, gall bladder.
s u r v e y a n s w e r form w i t h d e t a i l e d instructions, a s t a m p e d r e t u r n envelope, a n d a c a r d to be m a i l e d u n d e r s e p a r a t e cover i n d i c a t i n g if t h e y d e s i r e d to receive a s u m m a r y of t h e project. E a c h q u e s t i o n n a i r e was coded w i t h a u n i q u e identifying n u m b e r so t h a t r e s p o n s e s could be tracked. W e m a i l e d a second p a c k e t to n o n r e s p o n d e r s a p p r o x i m a t e l y 4 w e e k s after t h e first mailing. In o r d e r to identify a n y n o n r e s p o n d e n t bias, we comp a r e d t h e r e s p o n s e s of those who completed the i n i t i a l s u r v e y w i t h t h e r e s p o n s e s of those who did not. To do this, we s e n t a n a b b r e v i a t e d questionnaire, composed only of p a r t s 1 a n d 3 of t h e i n s t r u m e n t (omitting t h e card sorting exercise) to a 25% r a n d o m s a m p l e of t h e n o n r e s p o n d e n t s . We t h e n c o m p a r e d t h e r e s p o n s e s to common e l e m e n t s of t h e survey.
Analysis We u s e d two different m e t h o d s to a s s e s s which clinical indicators were m o s t i m p o r t a n t to t h e r e s p o n d e n t s . F i r s t , we c a l c u l a t e d m e a n i m p o r t a n c e r a t i n g s a s s i g n e d b y res p o n d e n t s to each indicator. W i t h i n subjects t h e points a s s i g n e d to each i n d i c a t o r were converted to r a n k s a n d differences in r a n k s were a s s e s s e d w i t h t h e Wilcoxon R a n k S u m a n d D u n c a n ' s Multiple Range Tests. Second, we u s e d h y b r i d conjoint analysis, a tool developed in t h e field of m a r k e t i n g , 39-al to calculate derived i m p o r t a n c e s for each indicator. This t e c h n i q u e uses t h e e x p r e s s e d 42
GASTROINTESTINAL ENDOSCOPY
i m p o r t a n c e s from P a r t 1 of the q u e s t i o n n a i r e a n d t h e likelihoods a s s i g n e d to t h e i n d i v i d u a l v i g n e t t e s from P a r t 2 to derive i m p o r t a n c e r a t i n g s for each clinical indicator. I n essence, h y b r i d conjoint a n a l y s i s corrects w h a t respondents s a y is i m p o r t a n t (i.e., t h e e x p r e s s e d importances) w i t h how t h e y a c t u a l l y b e h a v e (i.e., t h e a s s i g n e d likelihoods for t h e nine vignettes). Differences b e t w e e n gastroenterologists' a n d surgeons' m e a n i m p o r t a n c e r a t i n g s a r e c o m p a r e d w i t h S t u d e n t s t tests. Between-subject v a r i a b i l i t y in t h e i m p o r t a n c e s assigned to each indicator is s u m m a r i z e d w i t h h i s t o g r a m s . Between-subject v a r i a b i l i t y in t h e e s t i m a t e s of t h e likelihood of stones for each of t h e 27 scenarios is described w i t h box plots. We u s e d t h r e e s e p a r a t e m e t h o d s to s t u d y decisions to obtain a n ERCP. F i r s t , we e x a m i n e d t h e r e l a t i o n s h i p b e t w e e n t h e m e a n perceived likelihood of common bile duct stones for each vignette a n d t h e proportion of respond e n t s i n d i c a t i n g t h e y would order a p r e o p e r a t i v e ERCP. Second, we developed full-model a n d stepwise o r d i n a r y l e a s t s q u a r e s regressions to predict t h e decision to o r d e r a n E R C P as a function of likelihood of stones a n d selected d e m o g r a p h i c a n d practice c h a r a c t e r i s t i c s of t h e respondents: age, p e r c e n t a g e of t i m e in i n p a t i e n t activities, a v e r a g e n u m b e r of p a t i e n t s seen p e r m o n t h w i t h g a l l b l a d d e r - r e l a t e d problems, e s t i m a t e d p e r c e n t a g e of pat i e n t s w i t h b i l i a r y disease e v a l u a t e d for common bile duct VOLUME 46, NO. 1, 1997
Gastroenterologists" and surgeons' management of common bile duct stones
J Shea, D Asch, R Johnson, et al.
Table 3. Summary of analyses exploring importance of clinical indicators Descriptive statistics Common bile duct diameter on ultrasound Serum total bilirubin Serum alkaline phosphatase History of jaundice History of pancreatitis Serum amylase Serum alanine aminotransferase Age
Mean
(SD)*
20.9 20.1 14.4 14.1 10.2 9.7 6.2 4.5
Hybrid conjoint analysis Mean
(SD)
(12.8)t
23.2
(12.1)
(10.8 )t (8.1)$ (9.0)$ (6.3)§ (6.0)§ (5.2) I] (4.5)~
17.9 15.1 11.4 8.6 9.4 7,7 6,8
(7.4) (7.9) (9.0) (5.7) (6.2) (5.9) (5.8)
*Differences among rankings significant (p < 0.0001) by Wilcoxon Rank Sum Test. ?,$,§, J],~Groups with similar rankings identified with Duncan's Multiple Range Test.
stones, specialty, the performance of ERCP (for gastroenterologists) or laparoscopic cholecystectomy (for surgeons), type of primary hospital (university or universityaffiliated hospital vs other type), practice setting (dummy variables for solo practice, single-specialty group practice, and multispecialty group practice), and total volume of patients per month. Third, we determined thresholds for ordering an ERCP, using each subject's expressed likelihoods of stones and the corresponding decisions whether to order the test. The threshold was defined as the midpoint between the lowest probability of stones for which an ERCP was ordered and the highest probability of stones for which an ERCP was not ordered. Respondents who were inconsistent in their pattern of responses, or who indicated they would always or never order an ERCP were eliminated from this analysis. To adjust for multiple comparisons, we set significance levels at p < .005.
RESULTS Ninety of the 3000 surveys were r e t u r n e d by the ]post office as undeliverable. Of the remaining 2910, 1324 were returned for a response rate of 21%. To test for nonrespondent bias, 580 of the nonrespondents were randomly selected to receive the abbreviated survey. Of these, 30 were undeliverable and 174 were returned. Respondents to the full survey did not differ from respondents to the abbreviated ins t r u m e n t in their feelings about the importance of seven of the eight potential clinical indicators. The only attribute on which there was a significant difference (history of pancreatitis) had a m e a n of 10.0 (SD = 6.5) for respondents and 12.4 (SD = 8.4) for nonrespondents (F(1,755) -- 17.03, p < .001). Characteristics of the 624 respondents to the full survey are summarized in Table 2. Most of the following analyses presented are limited to the subset of 482 respondents who completed three parts of the i n s t r u m e n t without error (e.g., no missing data, importance points assigned to the eight indicators VOLUME 46, NO. 1, 1997
summed to 100). Results are the same when atl surveys are analyzed.
Importance of clinical indicators Table 3 reports results of the task in which respondents were instructed to divide 100 points among the eight indicators, assigning larger numbers of points to more important indicators. Common bile duct diameter on ultrasound and serum total bilirubin received the highest mean ratings, suggesting they have the greatest perceived importance in the diagnosis of common bile duct stones. History of jaundice and serum alkaline phosphatase receive the next highest rankings. Next in importance are history ofpancreatitis and serum amylase, followed by serum alanine aminotransferase and age. Table 3 also reports the results of the hybrid conjoint analysis. Though there are small shifts in the rank order of some indicators, compared to the original means, in general, this analysis provides similar results: how physicians allocated points among the eight indicators was consistent with how they used the indicators in predicting likelihood of stones. Figure 2 reports the mean expressed importances for gastroenterologists and surgeons for each of the eight clinical indicators. There are small but significant differences between the two groups (p < .005) for five of the eight indicators. However, the importance of serum total bilirubin and common bile duct diameter on ultrasound is maintained for both groups.
Variation in importance of indicators and perceived likelihood of stones Although these two methods yielded similar results regarding aggregate ratings of the clinical indicators, there was great variation in the ratings GASTROINTESTINAL ENDOSCOPY 43
J Shea, D Asch, R Johnson, et al.
Gastroenterologists' and surgeons' management of common bile duct stones
100
25
BIlE 20
(3 rr l.U
15 10
"0 5
0 0
age
Fix jaundice*
Hx panc
aat*
alk phos*
amylase
bilirubin*
CBDon US"
Figure 2. Expressed importances for gastroenterologists and surgeons. *p < .0001 with Students t test; Hxjaundice, history of jaundice; Hx panc, history of pancreatitis; aat, serum alanine aminotransferase; alk phos, serum alkaline phosphatase; bflirubin, serum total bilirubin; CBD on US, common bile duct diameter on ultrasonography.
at the level of the individual physician (i.e., betweensubject variability). All attributes received ratings of 0, and for some (e.g., age, pancreatitis), a sizable proportion of respondents thought t h a t it was not at all important. Conversely, several attributes received 30 or more of the 100 available points from numerous respondents (e.g., total bilirubin, common bile duct diameter on ultrasound). Physicians revealed similar variation in assigning likelihoods of common bile duct stones for each of the 27 vignettes. Not only did the cases in aggregate portray a broad range in the perceived likelihood of common bile duct stones, but within most cases estimates ranged from 0 to 100 and the interquartile range (i.e., the middle 50% of responses) extended more t h a n 30 points, showing wide variation in the perceived likelihood of stones. Ordering an E R C P
Figure 3 describes the relationship between m e a n likelihood of stones and proportion of respondents who would order an ERCP for each of the 27 cases. As might be expected, the relationship is strong. The correlation between the m e a n likelihood of stones and the proportion ordering an ERCP is .62 for the total group, .66 for gastroenterologists, and .56 for surgeons. The regression based on likelihoods and practice characteristics explained 43% of the variation in the decision to order an ERCP. As expected, the best predictor was the perceived likelihood of stones (38.8%), followed by specialty (4.2%). No other variable explained more t h a n 0.2% of the variation. Despite the importance of the likelihood of stones in predicting the decision to order an ERCP, there was also great variation in physicians' thresholds for this decision. Three h u n d r e d and three respondents 44
GASTROINTESTINAL ENDOSCOPY
•
80 60 II
40
I!
.I
20 0
I
0
5O
" !
100
Likelihood of Stone Figure 3. Relationship between mean likelihood of stones and proportion ordering an ERCP.
revealed a single point at which their decision changed from 'q(es, order an ERCP" to "No, do not order an ERCP." One h u n d r e d sixty-seven of the respondents (36%) were omitted from this analysis because there was more t h a n one point where the decision changed from yes to no (n = 98, 21%); because they would always order an ERCP (n = 38, 8%; 82% gastroenterologists); or because they would never order an ERCP (n = 31, 7%; 94% surgeons). The m e a n threshold was 37.5% (SD = 18.0), meaning t h a t they would order an ERCP if the likelihood of a common bile duct stone was above this level, but not otherwise. But even among these subjects who were most internally consistent, the range in threshold was 2.5% to 82.5%. The m e a n threshold for ordering an ERCP was significantly lower for gastroenterologists (mean = 34.8, SD = 15.9) t h a n for surgeons (mean = 41.6, SD = 20.1), p = .0012.
DISCUSSION The purpose of this study was to determine w h a t gastroenterologists and general surgeons t h i n k are the important clinical indicators of common bile duct stones, and how they use this information in deciding whether to perform a preoperative ERCP. The results of this study support several m a i n conclusions. First, most physicians, whether they are gastroenterologists or surgeons, believe t h a t the diameter of the common bile duct visualized on ultrasound and the serum total bilirubin are the most important indicators of common bile duct stones. Serum alkaline phosphatase is also thought to be important, but much less so. In contrast, patient age, serum alanine aminotransferase, and serum amylase are considered relatively unimportant. VOLUME 46, NO. 1, 1997
Gastroenterologists' and surgeons" management of common bile duct stones
Second, despite the general concordance, there is extreme variability in the degree of importance individual physicians place on specific clinical indicators. This finding is striking, because it implies that physicians do not agree on what simple and routine clinical indicators mean. This finding might be explained because it is not clear from the clinical literature which indicators are most useful, particularly since the advent of laparoscopic cholecystectomy has made the question more relevant. And a small amounl~ of the variability is attributable to differences between gastroenterologists and surgeons, who m a y see subgroups of patients with different underlying base rates of common bile duct stones. Whatever the reason, the implication of this variability is that as different physicians place weight on different indicators, patients m a y receive inconsistent t r e a t m e n t recommendations. Third, the degree of variability is also evident in physicians' predictions of the likelihood of common bile duct stones in response to clinical vignettes. For each vignette, our physicians varied greatly in their estimates for Lhe probability of a common bile duct stone. In the typical cases, half of the physicians varied in their estimates by approximately 30%. Fourth, the variability is probably clinically important. We found that, on average, our subjects wanted to obtain preoperative ERCP for patients whose likelihood of a common bile duct stone was greater than 37% and forego an ERCP otherwise. However, a 37% threshold crosses the range of predictions of the likelihood of a common bile duct stone in every clinical vignette, and often crosses the interquartile range, or middle 50% of responses. This result suggests the variability has the potential to affect the decision to order an E R C P in every presented case, even though they represent a wide range of likelihoods of common bile duct stones. This study has several limitations. Given the low response rate, we might be concerned that those who did not respond were different from those who did, and that our results are therefore not generalizable to the wider population of gastroenterologists and surgeons. Although nonrespondent bias becomes more likely with lower response rates, there is no direct connection between the response rate to a survey and the presence of this bias. In fact, when we resurveyed a random sample of our original nonrespondents, the responses we obtained were no different from those achieved with the main study. Nonrespondent bias would have to be extreme to alter our conclusions. Although not every subject responded to the abbreviated survey to nonrespondents, the similar findings make significant nonrespondent bias unlikely. VOLUME 46, NO. l, 1997
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Second, we used hypothetical vignettes and other tools that represent abstractions from actual clinical settings. Also, we specified that the patients were scheduled for elective laparoscopic cholecystectomy for symptomatic gallstones, were otherwise healthy, and had no known malignancies or other disease processes. The serum chemistries were for one point in time and we did not address if they were rising or falling. Real clinical cases provide richer sets of information that m a y make the clinical exercise easier. Nevertheless, we suspect that m a n y clinicians try to simplify the complexity of real clinical cases by relying on a few heuristics based on many of the clinical indicators we investigated. In focusing on these indicators, it is possible we have reduced the noise of actual bedside decision making. If this is so, our format might have made the task even easier. Third, we chose to focus only on preoperative E R C P as the procedure to investigate potential common bile duct stones. This should not have affected our results pertaining to the importance of the individual indicators, nor to the estimates of the likelihoods of stones for each of the vignettes. However, preferences for alternative diagnostic and therapeutic strategies, such as postoperative ERCP and laparoscopic common bile duct explorations for stones discovered during an intraoperative cholangiogram, m a y have influenced decisions for each vignette regarding when to do an ERCP. We doubt this is a major problem because preoperative ERCP remains the most prevalent strategy for detecting common bile duct stones (it was preferred by over two thirds of our respondents). Nevertheless, some of the variation we observed could be attributable to respondents who preferred other methods, or whose preference of method depended on the perceived likelihood of stones. It might also be related to other factors such as the (perceived) skills of the local endoscopist or surgeon at their respective procedures. Overall, these results suggest there is substantial confusion or disagreement among gastroenterologists and surgeons regarding the optimal approach to potential common bile duct stones. To a large extent, this variability reflects the lack of consensus observed in the literature for diagnosis of common bile duct stones per se. 27-35 It also mirrors the wide variation in practice patterns that has been observed for m a n y common medical conditions and p r o c e d u r e s Y -46 Whether the differences within and between groups reflect varying interpretations of the literature or are based on personal experience and accumulated clinical wisdom, two outcomes are certain. First, patients will likely receive varying GASTROINTESTINAL ENDOSCOPY
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Gastroenterologists" and surgeons' management of common bile duct stones
recommendations for care, depending on whom they see. Second, many preoperative ERCPs will be ordered, even when the likelihood of stones is quite low. Because the decision to look for common bile duct stones is not without complications and costs, these results suggest that future work is needed to identify the most useful clinical indicators to guide these decisions, in combination with optimal clinical approaches for removal of stones. ACKNOWLEDGMENTS
We are grateful for the assistance of Paul-Andr6 Abboud, Marlon Fisher, Wim Haentjens, Greg Helmstetter, Juliet Wilder, and John V. White. REFERENCES 1. Schlumpf R, Klotz HP, Wehrli H, Herzog U. A nation's experience in laparoscopic cholecystectomy. Surg Endosc 1994;8:35-41. 2. Stoker ME, Vose J, O'Mara P, Maini BS. Laparoscopic cholecystectomy: a clinical and financial analysis of 280 operations. Arch Surg 1992;127:589-95. 3. Baird DR, Wilson JP, Mason EM, Duncan TD, Evans JS, Luke JP, et al. An early review of 800 laparoscopic cholecystectomies at a university-affiliated community teaching hospital. Am Surg 1992;58:206-10. 4. Hardy KJ, Miller H, Fletcher DR, Jones RM, Shulkes A, McNeil JJ. An evaluation of laparoscopic versus open cholecystectomy. Med J Aust 1994;160:58-62. 5. Phillips EH, Carroll BJ, Fallas MJ, Pearlstein AR. Comparison of laparoscopic cholecystectomy in obese and non-obese patients. Am Surg 1994;60:316-20. 6. Soper NJ, Stockmann PT, Dunnegan DL, Ashley SW. Laparoscopic cholecystectomy: the new 'gold standard'. Arch Surg 1992;127:917-23. 7. Spaw AT, Reddick EJ, Olsen DO. Laparoscopic laser cholecystectomy: analysis of 500 procedures. Surg Laparoscop Endosc 1991;1:2-7. 8. McMahen A, Russell IT, Baxter JN, Ross S, Anderson JR, Morran CG, et al. Laparoscopic versus minilaparotomy cholecystectomy: a randomised trial. Lancet 1994;343:135-8. 9. Orlando R, Russell JC, Lynch J, Mattie A. Laparoscopic cholecystectomy: a statewide experience. Arch Surg 1993;128: 494-9. 10. Larson GM, Vitale GC, Casey J, Evans JS, Gilliam G, Heuser L, et al. Multipractice analysis of laparoscopic cholecystectomy in 1983 patients. Am J Surg 1992;163:221-6. 11. The Southern Surgeons Club. A prospective analysis of 1518 laparoscopic cholecystectomies. New Engl J Med 1991;324: 1073-8. 12. Wherry DC, Rob CG, Morohn MR, Rich NM. An external audit of laparoscopic cholecystectomy performed in medical treatment facilities of the department of defense. Ann Surg 1994;5:626-34. 13. Shea JA, Healey MJ, Berlin JA, Clarke JR, Malet PF, Staroscik RN, et al. Mortality and complications associated with laparoscopic cholecystectomy: a recta-analysis. Ann Surg 1996;224:609-20. 14. Dunn D, Nair R, Fowler S, McCley R. Laparoscopic cholecystectomy in England and Wales: results of an audit by The Royal College of Surgeons of England. Ann R Cell Surg Engl 1994;76:269-75. 15. Phillips EH. Routine versus selective intraoperative cholangiography. Am J Surg 1993;165:505-7. 16. Donohue J-l-I,Farnell MB, Grant CS, van Heerden JA, Wahlstrom HE, Sarr MG, et al. Laparoscopic cholecystectomy: early Mayo experience. Mayo Clin Proc 1992;67:449-55. 17. Cox MR, Wilson TG, Jeans PL, Padbury RT, Toouli J. 46 G A S T R O I N T E S T I N A L E N D O S C O P Y
Minimizing the risk of bile duct injury at laparoscopic cholecystectomy. World J Surg 1994;18:422-6. 18. Horvath KD. Strategies for prevention of laparoscopic common bile duct injuries. Surg Endosc 1993;7:439-44. 19. Barkun JS, Fried GM, Barkun AN, Sigman HH, Hinchey EJ, Garzon J, et al. Cholecystectomy with operative cholangiography. Implications for common bile duct injury and retained common bile duct stones. Ann Surg 1993;218:371-7. 20. Ferguson CM, Rattner DW, Warshaw AL. Bile duct injury in laparoscopic cholecystectomy. Surg Laparosc Endosc 1992;2: 1-7. 21. Panton ON, Nagy AG, Scudamore CH, Panton RJ. Laparoscopic cholecystectomy: a continuing plea for routine cholangiography. Surg Laparosc Endosc 1995;5:43-9. 22. Phillips EH. Routine versus selective cholangiography. Am J Surg 1993;164:505-7. 23. Morgenstern L, McGrath MF, Carroll BJ, Paz-Partlow M, Berci G. Continuing hazards of the learning curve in laparoscopic cholecystectomy. Am Surg 1995;61:914-8. 24. Lorimer JW, Fairfull-Smith RJ. Intraoperative cholangiography is not essential to avoid duct injuries during laparoscopic cholecystectomy. Am J Surg 1995;169:344-7. 25. Soper NJ, Dunnegan DL. Routine versus selective intraoperative cholangiography during laparoscopic cholecystectomy. World J Surg 1993;17:686-8. 26. Jones DB, Dunnegan DL, Soper NJ. Results of a change to routine fluorocholangiography during laparoscopic cholecystectomy. Surgery 1995;118:693-701. 27. Sharma AK, Cherry R, Fielding JWL. A randomised trail of selective or routine on-table cholangiography. Ann R Cell Surg Engl 1993;75:245-8. 28. Leitman IM, Fisher MI, McKinley MJ, Rothman R, Ward RJ, Reiner DS, et al. The evaluation and management of known or suspected stones on the common bile duct in the era of minimal access surgery. Surg Gynecol, Obstet 1993;176:52733. 29. Graham SM, Flowers JL, Scott TR, Bailey RW, Scovill WA, Zucker KA, et al. Laparoscopic cholecystectomy and common bile duct stones. The utility of planned perioperative endoscopic retrograde cholangiography and sphincterotomy: experience with 63 patients. Ann Surg 1993;218:61-7. 30. Barkun AN, Barkun JS, Fried GM, Ghitulescu G, Steinmetz O, Pham C, et al. Useful predictors of bile duct stones in patients undergoing laparoscopic cholecystectomy. Ann Surg 1994;220:32-9. 31. Wilson TG, Hall JC, Watts JM. Is operative cholangiography always necessary? Br J Surg 1986;73:637-40. 32. Hauer-Jensen M, Karesen R, Nygaard K, Solheim K, Amlie EJ, Havig O, et al. Prospective randomized study of routine intraoperative cholangiography during open cholecystectomy: long-term follow-up and multivariate analysis of predictors of choledocholithiasis. Surgery 1993;113:31823. 33. Widdison AL, Longstaff AJ, Armstrong CP. Combined laparoscopic and endoscopic treatment of gallstones and bile duct stones: a prospective study. Br J Surg 1994;81:595-7. 34. Huguier M, Bornet P, Charpak Y, Houry S, Chastang C. Selective contraindications based on multivariate analysis for operative cholangiography in biliary lithiasis. Surg Gynecol Obstet 1991;172:470-4. 35. Mills JL, Beck DE, Harford FJ. Routine operative cholangiography. Surg Gynecol Obstet 1985;161:343-5. 36. Neuhaus H, Feussner H, Ungeheuer A, Hoffman W, Siewart JR, Classen M. Prospective evaluation of the use of endoscopic retrograde cholangiography prior to laparoscopic cholecystectomy. Endoscopy 1992;24:745-9. 37. Abboud PC, Malet PF, Berlin JA, Staroscik R, Cabana MD, Clarke JR, et al. Predictors of common bile duct stones prior to cholecystectomy: a recta-analysis. Gastrointest Endosc 1996;44:450-7. 38. Addelman S. Orthogonal main-effect plans for asymmetrical factorial experiments. Technometrics 1962;4:21-46. VOLUME 46, NO. 1, 1997
Gastroenterologists' and surgeons' management of common bile duct stones
39. Green PE, Krieger AM, Carroll JD. Conjoint analysis and multidimensional scaling: a complementary approach. Journal of Advertising Research 1987;October/November: 21-7. 40. Green PE, Sr!mivasan V. Conjoint analysis in marketing: new developments with implications for research and practice. Journal of Marketing 1990;54:3-19. 41. Green PE, I@ieger AM. Individualized hybrid models for conjoint analysis. Management Science 1996;42:850-67. 42. Deyo RA. Promises and limitations of the Patient Outcomes Research Teams: the low back pain example. Proc Assoc Am Physicians 1995;107:324-8. 43. Mort EA. Clinical decision making in the face of scientific uncertainty: hormone replacement therapy as an example. J Fam Pract 1996;42:147-51.
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44. Weiner JP, Parente SE, Garnick GW, Fowles J, Lawthers AG, Palmer RH. Variation in office-based quality: a claimsbased profile of care provided to Medicare patients with diabetes. JAMA 1995;273:1503-8. 45. Roark R, Petrofski J, Berson E, Berman S. Practice variations among pediatricians and family physicians in the management of otitis media. Arch Pediatr Adolesc Med 1995;149: 839-44. 46. Winkenwerder W, Levy BD, Eisenberg JM, Williams SV, Young MJ, Hershey JC. Variation in physicians' decisionmaking thresholds in management of a sexually transmitted disease. J Gen Int Med 1993;8:369-73.
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47
Background: Because the literature suggests numerous indicators of common bile duct stones, we undertook a systematic assessment of physicians' judgments of the clinical utility of eight indicators: patient age, history of jaundice, history of pancreatitis, levels of serum alanine aminotransferase, alkaline phosphatase, amylase, and total bilirubin, and common bile duct diameter on ultrasonography. Methods: Random samples of 1500 gastroenterologists and 1500 surgeons were sent a survey asking them to indicate the importance of each potential indicator of common bile duct stones, the likelihood of common bile duct stones for each of nine clinical vignettes, and whether they would order a preoperative ERCP. An abbreviated survey was sent to nonrespondents. Results: Although there was substantial variation in the importances assigned to each indicator, the most important indicators were serum total bilirubin and diameter of common bile duct on ultrasound. The best predictors of the decision to order an ERCP were perceived likelihood of stones and specialty. The average threshold for ordering an ERCP was 37%. Respondents did not differ from nonrespondents in the perceived importance of the eight indicators. Conclusions: The substantial variation among gastroenterologists and surgeons regarding the optimal approach to common bile duct stones has clinical implications. Patients will receive varying recommendations for care, depending on whom they see. (Gastrointest Endosc 1997;46:40-7.)
Laparoscopic cholecystectomy, first performed in France in 1987, was introduced in the United States in 1988. Several case series suggest that laparoscopic cholecystectomy is associated with lower mortality and morbidity, shortened hospital stays, and Received July 23, 1996. For revision December 4, 1996. Accepted January 28, 1997. From the Divisions of General Internal Medicine and Gastroenterology-Department of Medicine, the Department of Surgery, the Wharton School, and the Leonard Davis Institute of Health Economics, University of Pennsylvania; the Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine; The Veteran's Affairs Medical Center; and the Department of Surgery, Allegheny University, Philadelphia, Pennsylvania. This work was supported by a grant from the Agency for Health Care Policy and Research (HS06481). Reprint requests: Judy A. Shea, PhD, General Internal Medicine, University of Pennsylvania, Ralston House 318, 3615 Chestnut St., Philadelphia, PA 19104-2676. 37/1/80768 46
GASTROINTESTINAL ENDOSCOPY
earlier return to activities, 1-13 compared to open cholecystectomy. However, one disadvantage is that there is a higher incidence of retained common bile duct stones in laparoscopic cholecystectomy compared to open cholecystectomy, 14-2° most likely because the duct is no longer accessible for direct observation and palpation. In response to concerns about retained stones (as well as safety issues), many surgeons recommend performing an intraoperative cholangiogram in almost all patients. 21-23 More recently, many experts agree that it is unnecessary and too expensive to perform intraoperative cholangiogram on all patients, 19' 24, 25 especially if one uses fluorocholangiography. 26 Instead, one should select patients for assessment given their likelihood of common bile duct stones as suggested by various preoperative indicators. Several clinical indicators have been proposed to help identify patients at risk for common bile duct VOLUME 46, NO. 1, 1997
Gastroenterologists' and surgeons' management of common bile duct stones
J Shea, D Asch, R Johnson, et al.
Table 1. Levels of attributes Age (y) History of jaundice History of pancreatitis Serum alanine aminotransferase (U/L) Serum alkaline phosphatase (U/L) Serum amylase (U/L) Serum total bilirubin (mg/dL) Common bile duct diameter on ultrasound (mm)
Patient #15
25, 50, 75 Yes, no Yes, no 24, 82, 160 90, 180, 320 100, 250, 550 1.0, 2.5, 4.5 4, 8, 12
stones, including history of jaundice, 27' 2s hyperbilirubinemia, 2'~-32 dilated bile ducts on ultrasound,29, 30, 32-3~ elevated levels of amylase and alkaline phosphatase, 2s-3°' 38 pancreatitis,2% 2s, 3o, 33, 35 and advanced age. 3°' 32, 34 A recent meta-analysis of 10 potential indicators of common bile duct stones found t h a t most indicators had high specificities (i.e., probabilities t h a t a person without common bile duct stones will not have a particular indicator), but poor sensitivities (i.e., probabilities t h a t a person with common bile duct stones will have a particular indicator). Patients with common bile duct stones seen on ultrasound, preoperative jaundice, and cholangitis were at least 10 times as likely to have common bile duct stones compared to patients lacking the same indicator. Other indicators, especially alkaline phosphatase level, pancreatitis, cholecystitis, and hyperamylasemia, were not useful in predicting common bile duct stones. 37 Because the literature suggested m a n y potentially useful indicators of common bile duct stones, some of which were not borne out by the metaanalysis, we surveyed random samples of practicing gastroenterolo~[sts and surgeons and asked them to (1) indicate the relative importance of each of eight indicators in diagnosing common bile duct stones, and (2) estimate the likelihood of common bile duct stones for sets of patient vignettes in which the patients varied in the level of each indicator, and indicate w h e t h e r they would order a preoperative ERCP. Our pu~:pose was to provide a systematic assessment of physicians' j u d g m e n t s of the clinical utility of the indicators, to describe variation in their judgments, and to explore how these j u d g m e n t s are used clinically. MATERIALS AND METHODS Subjects We randomly selected 1500 gastroenterologists and 1500 surgeons from the American Medical Association (AMA) Physician Masterfile. The Masterfile is the most comprehensive set; of physician information in the United States and includes physicians who are not members of VOLUME 46, NO. 1, 1997
Age
25 years
History of jaundice
NO
History of pancreatitis
Yes
Serum Alanine Aminotransferase
2~ U/L
Serum Alkaline
Phosphatase
320 U/L
Serum Amylase
250 U/L
Serum Total Bilirubin
1,0 mg/dL
Common bile duct diameter
12 mm
Figure 1, Sample patient vignette. the AMA. We specified that sample physicians be in practice in the United States, not retired, and not in training.
Instrument The survey instrument had three parts. In the first part we asked respondents to indicate the importance of each of eight potential indicators of common bile duct stones (listed in the first column of Table 1) by dividing 100 points among them. In the second part, we asked respondents to evaluate several hypothetical clinical scenarios, estimate the likelihood of stones for each case, and indicate whether they would order a preoperative ERCP. We specified that the patients were scheduled for elective laparoscopic cholecystectomy for symptomatic gallstones, were otherwise healthy, and had no known malignancies or other disease processes. Because the cases were hypothetical there was no known or true probability of stones for the vignettes. The vignettes were constructed by combining each of the eight indicators at various levels, as shown in Table 1. There were 2916 possible vignettes, given the number of indicators and levels we chose. Using a main effects orthogonal design, 3s we were able to test the importance of each indicator by limiting the set to 27 vignettes. To reduce respondent burden further, we randomly allocated subjects into three groups, so that each subject received only 9 of these 27 vignettes. A sample vignette is shown in Figure 1. Each vignette was printed on a separate card. We asked subjects to sort the cards from least likely to represent a patient with common bile duct stone to most likely. Then we asked them (1) to provide an estimate for the likelihood of stones for each vignette, and (2) to indicate whether they would order a preoperative ERCP for the patient. We provided subjects with a table of normal laboratory values. In the third part of the questionnaire we asked respondents to provide professional and demographic information, including their type of practice and the volume of patients they treat with gallstone-related problems.
Mailing strategy In November 1994 we mailed each subject a packet including an introductory cover letter, the card set, a GASTROINTESTINAL ENDOSCOPY
41
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Gastroenterologists" and surgeons' management of common bile duct stones
Table 2. Demographic and practice characteristics of respondents Total (N = 624)
Gastroenterologists (N = 350)
Year born [mean (SD)] 1948 (10.0) Male (%) 96 Year graduated from medical school 1975 (10.4) [mean (SD)] Board certified (%) 90 Primary hospital is university 69 affiliated (%) Practice setting (%) Solo practice 30 Single-specialty group 39 Multispecialty group 18 Other 13 Preferred strategy for diagnosing CBD stones (%) Preoperative ERCP 67 IOC 24 Other 9 Monthly volume of patients with GB-related problems (%) <10 30 10-19 35 20+ 36 Patients evaluated for CBD stones (%) 0%-10% 40 11%-40% 29 >40% 31 Perform ERCP (%) -Perform laparoscopic -cholecystectomy (%)
Surgeons (N = 274)
1950 (8.6) 96 1976 (9.0)
1946 (11.1) 96 1972 (11.2)
93 67
86 73
23 44 21 12
39 32 15 14
81 10 9
48 42 11
23 34 43
38 36 26
35 33 32 68 --
47 22 31 -92
IOC, I n t r a o p e r a t i v e cholangiogram; CBD, common bile duct; GB, gall bladder.
s u r v e y a n s w e r form w i t h d e t a i l e d instructions, a s t a m p e d r e t u r n envelope, a n d a c a r d to be m a i l e d u n d e r s e p a r a t e cover i n d i c a t i n g if t h e y d e s i r e d to receive a s u m m a r y of t h e project. E a c h q u e s t i o n n a i r e was coded w i t h a u n i q u e identifying n u m b e r so t h a t r e s p o n s e s could be tracked. W e m a i l e d a second p a c k e t to n o n r e s p o n d e r s a p p r o x i m a t e l y 4 w e e k s after t h e first mailing. In o r d e r to identify a n y n o n r e s p o n d e n t bias, we comp a r e d t h e r e s p o n s e s of those who completed the i n i t i a l s u r v e y w i t h t h e r e s p o n s e s of those who did not. To do this, we s e n t a n a b b r e v i a t e d questionnaire, composed only of p a r t s 1 a n d 3 of t h e i n s t r u m e n t (omitting t h e card sorting exercise) to a 25% r a n d o m s a m p l e of t h e n o n r e s p o n d e n t s . We t h e n c o m p a r e d t h e r e s p o n s e s to common e l e m e n t s of t h e survey.
Analysis We u s e d two different m e t h o d s to a s s e s s which clinical indicators were m o s t i m p o r t a n t to t h e r e s p o n d e n t s . F i r s t , we c a l c u l a t e d m e a n i m p o r t a n c e r a t i n g s a s s i g n e d b y res p o n d e n t s to each indicator. W i t h i n subjects t h e points a s s i g n e d to each i n d i c a t o r were converted to r a n k s a n d differences in r a n k s were a s s e s s e d w i t h t h e Wilcoxon R a n k S u m a n d D u n c a n ' s Multiple Range Tests. Second, we u s e d h y b r i d conjoint analysis, a tool developed in t h e field of m a r k e t i n g , 39-al to calculate derived i m p o r t a n c e s for each indicator. This t e c h n i q u e uses t h e e x p r e s s e d 42
GASTROINTESTINAL ENDOSCOPY
i m p o r t a n c e s from P a r t 1 of the q u e s t i o n n a i r e a n d t h e likelihoods a s s i g n e d to t h e i n d i v i d u a l v i g n e t t e s from P a r t 2 to derive i m p o r t a n c e r a t i n g s for each clinical indicator. I n essence, h y b r i d conjoint a n a l y s i s corrects w h a t respondents s a y is i m p o r t a n t (i.e., t h e e x p r e s s e d importances) w i t h how t h e y a c t u a l l y b e h a v e (i.e., t h e a s s i g n e d likelihoods for t h e nine vignettes). Differences b e t w e e n gastroenterologists' a n d surgeons' m e a n i m p o r t a n c e r a t i n g s a r e c o m p a r e d w i t h S t u d e n t s t tests. Between-subject v a r i a b i l i t y in t h e i m p o r t a n c e s assigned to each indicator is s u m m a r i z e d w i t h h i s t o g r a m s . Between-subject v a r i a b i l i t y in t h e e s t i m a t e s of t h e likelihood of stones for each of t h e 27 scenarios is described w i t h box plots. We u s e d t h r e e s e p a r a t e m e t h o d s to s t u d y decisions to obtain a n ERCP. F i r s t , we e x a m i n e d t h e r e l a t i o n s h i p b e t w e e n t h e m e a n perceived likelihood of common bile duct stones for each vignette a n d t h e proportion of respond e n t s i n d i c a t i n g t h e y would order a p r e o p e r a t i v e ERCP. Second, we developed full-model a n d stepwise o r d i n a r y l e a s t s q u a r e s regressions to predict t h e decision to o r d e r a n E R C P as a function of likelihood of stones a n d selected d e m o g r a p h i c a n d practice c h a r a c t e r i s t i c s of t h e respondents: age, p e r c e n t a g e of t i m e in i n p a t i e n t activities, a v e r a g e n u m b e r of p a t i e n t s seen p e r m o n t h w i t h g a l l b l a d d e r - r e l a t e d problems, e s t i m a t e d p e r c e n t a g e of pat i e n t s w i t h b i l i a r y disease e v a l u a t e d for common bile duct VOLUME 46, NO. 1, 1997
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Table 3. Summary of analyses exploring importance of clinical indicators Descriptive statistics Common bile duct diameter on ultrasound Serum total bilirubin Serum alkaline phosphatase History of jaundice History of pancreatitis Serum amylase Serum alanine aminotransferase Age
Mean
(SD)*
20.9 20.1 14.4 14.1 10.2 9.7 6.2 4.5
Hybrid conjoint analysis Mean
(SD)
(12.8)t
23.2
(12.1)
(10.8 )t (8.1)$ (9.0)$ (6.3)§ (6.0)§ (5.2) I] (4.5)~
17.9 15.1 11.4 8.6 9.4 7,7 6,8
(7.4) (7.9) (9.0) (5.7) (6.2) (5.9) (5.8)
*Differences among rankings significant (p < 0.0001) by Wilcoxon Rank Sum Test. ?,$,§, J],~Groups with similar rankings identified with Duncan's Multiple Range Test.
stones, specialty, the performance of ERCP (for gastroenterologists) or laparoscopic cholecystectomy (for surgeons), type of primary hospital (university or universityaffiliated hospital vs other type), practice setting (dummy variables for solo practice, single-specialty group practice, and multispecialty group practice), and total volume of patients per month. Third, we determined thresholds for ordering an ERCP, using each subject's expressed likelihoods of stones and the corresponding decisions whether to order the test. The threshold was defined as the midpoint between the lowest probability of stones for which an ERCP was ordered and the highest probability of stones for which an ERCP was not ordered. Respondents who were inconsistent in their pattern of responses, or who indicated they would always or never order an ERCP were eliminated from this analysis. To adjust for multiple comparisons, we set significance levels at p < .005.
RESULTS Ninety of the 3000 surveys were r e t u r n e d by the ]post office as undeliverable. Of the remaining 2910, 1324 were returned for a response rate of 21%. To test for nonrespondent bias, 580 of the nonrespondents were randomly selected to receive the abbreviated survey. Of these, 30 were undeliverable and 174 were returned. Respondents to the full survey did not differ from respondents to the abbreviated ins t r u m e n t in their feelings about the importance of seven of the eight potential clinical indicators. The only attribute on which there was a significant difference (history of pancreatitis) had a m e a n of 10.0 (SD = 6.5) for respondents and 12.4 (SD = 8.4) for nonrespondents (F(1,755) -- 17.03, p < .001). Characteristics of the 624 respondents to the full survey are summarized in Table 2. Most of the following analyses presented are limited to the subset of 482 respondents who completed three parts of the i n s t r u m e n t without error (e.g., no missing data, importance points assigned to the eight indicators VOLUME 46, NO. 1, 1997
summed to 100). Results are the same when atl surveys are analyzed.
Importance of clinical indicators Table 3 reports results of the task in which respondents were instructed to divide 100 points among the eight indicators, assigning larger numbers of points to more important indicators. Common bile duct diameter on ultrasound and serum total bilirubin received the highest mean ratings, suggesting they have the greatest perceived importance in the diagnosis of common bile duct stones. History of jaundice and serum alkaline phosphatase receive the next highest rankings. Next in importance are history ofpancreatitis and serum amylase, followed by serum alanine aminotransferase and age. Table 3 also reports the results of the hybrid conjoint analysis. Though there are small shifts in the rank order of some indicators, compared to the original means, in general, this analysis provides similar results: how physicians allocated points among the eight indicators was consistent with how they used the indicators in predicting likelihood of stones. Figure 2 reports the mean expressed importances for gastroenterologists and surgeons for each of the eight clinical indicators. There are small but significant differences between the two groups (p < .005) for five of the eight indicators. However, the importance of serum total bilirubin and common bile duct diameter on ultrasound is maintained for both groups.
Variation in importance of indicators and perceived likelihood of stones Although these two methods yielded similar results regarding aggregate ratings of the clinical indicators, there was great variation in the ratings GASTROINTESTINAL ENDOSCOPY 43
J Shea, D Asch, R Johnson, et al.
Gastroenterologists' and surgeons' management of common bile duct stones
100
25
BIlE 20
(3 rr l.U
15 10
"0 5
0 0
age
Fix jaundice*
Hx panc
aat*
alk phos*
amylase
bilirubin*
CBDon US"
Figure 2. Expressed importances for gastroenterologists and surgeons. *p < .0001 with Students t test; Hxjaundice, history of jaundice; Hx panc, history of pancreatitis; aat, serum alanine aminotransferase; alk phos, serum alkaline phosphatase; bflirubin, serum total bilirubin; CBD on US, common bile duct diameter on ultrasonography.
at the level of the individual physician (i.e., betweensubject variability). All attributes received ratings of 0, and for some (e.g., age, pancreatitis), a sizable proportion of respondents thought t h a t it was not at all important. Conversely, several attributes received 30 or more of the 100 available points from numerous respondents (e.g., total bilirubin, common bile duct diameter on ultrasound). Physicians revealed similar variation in assigning likelihoods of common bile duct stones for each of the 27 vignettes. Not only did the cases in aggregate portray a broad range in the perceived likelihood of common bile duct stones, but within most cases estimates ranged from 0 to 100 and the interquartile range (i.e., the middle 50% of responses) extended more t h a n 30 points, showing wide variation in the perceived likelihood of stones. Ordering an E R C P
Figure 3 describes the relationship between m e a n likelihood of stones and proportion of respondents who would order an ERCP for each of the 27 cases. As might be expected, the relationship is strong. The correlation between the m e a n likelihood of stones and the proportion ordering an ERCP is .62 for the total group, .66 for gastroenterologists, and .56 for surgeons. The regression based on likelihoods and practice characteristics explained 43% of the variation in the decision to order an ERCP. As expected, the best predictor was the perceived likelihood of stones (38.8%), followed by specialty (4.2%). No other variable explained more t h a n 0.2% of the variation. Despite the importance of the likelihood of stones in predicting the decision to order an ERCP, there was also great variation in physicians' thresholds for this decision. Three h u n d r e d and three respondents 44
GASTROINTESTINAL ENDOSCOPY
•
80 60 II
40
I!
.I
20 0
I
0
5O
" !
100
Likelihood of Stone Figure 3. Relationship between mean likelihood of stones and proportion ordering an ERCP.
revealed a single point at which their decision changed from 'q(es, order an ERCP" to "No, do not order an ERCP." One h u n d r e d sixty-seven of the respondents (36%) were omitted from this analysis because there was more t h a n one point where the decision changed from yes to no (n = 98, 21%); because they would always order an ERCP (n = 38, 8%; 82% gastroenterologists); or because they would never order an ERCP (n = 31, 7%; 94% surgeons). The m e a n threshold was 37.5% (SD = 18.0), meaning t h a t they would order an ERCP if the likelihood of a common bile duct stone was above this level, but not otherwise. But even among these subjects who were most internally consistent, the range in threshold was 2.5% to 82.5%. The m e a n threshold for ordering an ERCP was significantly lower for gastroenterologists (mean = 34.8, SD = 15.9) t h a n for surgeons (mean = 41.6, SD = 20.1), p = .0012.
DISCUSSION The purpose of this study was to determine w h a t gastroenterologists and general surgeons t h i n k are the important clinical indicators of common bile duct stones, and how they use this information in deciding whether to perform a preoperative ERCP. The results of this study support several m a i n conclusions. First, most physicians, whether they are gastroenterologists or surgeons, believe t h a t the diameter of the common bile duct visualized on ultrasound and the serum total bilirubin are the most important indicators of common bile duct stones. Serum alkaline phosphatase is also thought to be important, but much less so. In contrast, patient age, serum alanine aminotransferase, and serum amylase are considered relatively unimportant. VOLUME 46, NO. 1, 1997
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Second, despite the general concordance, there is extreme variability in the degree of importance individual physicians place on specific clinical indicators. This finding is striking, because it implies that physicians do not agree on what simple and routine clinical indicators mean. This finding might be explained because it is not clear from the clinical literature which indicators are most useful, particularly since the advent of laparoscopic cholecystectomy has made the question more relevant. And a small amounl~ of the variability is attributable to differences between gastroenterologists and surgeons, who m a y see subgroups of patients with different underlying base rates of common bile duct stones. Whatever the reason, the implication of this variability is that as different physicians place weight on different indicators, patients m a y receive inconsistent t r e a t m e n t recommendations. Third, the degree of variability is also evident in physicians' predictions of the likelihood of common bile duct stones in response to clinical vignettes. For each vignette, our physicians varied greatly in their estimates for Lhe probability of a common bile duct stone. In the typical cases, half of the physicians varied in their estimates by approximately 30%. Fourth, the variability is probably clinically important. We found that, on average, our subjects wanted to obtain preoperative ERCP for patients whose likelihood of a common bile duct stone was greater than 37% and forego an ERCP otherwise. However, a 37% threshold crosses the range of predictions of the likelihood of a common bile duct stone in every clinical vignette, and often crosses the interquartile range, or middle 50% of responses. This result suggests the variability has the potential to affect the decision to order an E R C P in every presented case, even though they represent a wide range of likelihoods of common bile duct stones. This study has several limitations. Given the low response rate, we might be concerned that those who did not respond were different from those who did, and that our results are therefore not generalizable to the wider population of gastroenterologists and surgeons. Although nonrespondent bias becomes more likely with lower response rates, there is no direct connection between the response rate to a survey and the presence of this bias. In fact, when we resurveyed a random sample of our original nonrespondents, the responses we obtained were no different from those achieved with the main study. Nonrespondent bias would have to be extreme to alter our conclusions. Although not every subject responded to the abbreviated survey to nonrespondents, the similar findings make significant nonrespondent bias unlikely. VOLUME 46, NO. l, 1997
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Second, we used hypothetical vignettes and other tools that represent abstractions from actual clinical settings. Also, we specified that the patients were scheduled for elective laparoscopic cholecystectomy for symptomatic gallstones, were otherwise healthy, and had no known malignancies or other disease processes. The serum chemistries were for one point in time and we did not address if they were rising or falling. Real clinical cases provide richer sets of information that m a y make the clinical exercise easier. Nevertheless, we suspect that m a n y clinicians try to simplify the complexity of real clinical cases by relying on a few heuristics based on many of the clinical indicators we investigated. In focusing on these indicators, it is possible we have reduced the noise of actual bedside decision making. If this is so, our format might have made the task even easier. Third, we chose to focus only on preoperative E R C P as the procedure to investigate potential common bile duct stones. This should not have affected our results pertaining to the importance of the individual indicators, nor to the estimates of the likelihoods of stones for each of the vignettes. However, preferences for alternative diagnostic and therapeutic strategies, such as postoperative ERCP and laparoscopic common bile duct explorations for stones discovered during an intraoperative cholangiogram, m a y have influenced decisions for each vignette regarding when to do an ERCP. We doubt this is a major problem because preoperative ERCP remains the most prevalent strategy for detecting common bile duct stones (it was preferred by over two thirds of our respondents). Nevertheless, some of the variation we observed could be attributable to respondents who preferred other methods, or whose preference of method depended on the perceived likelihood of stones. It might also be related to other factors such as the (perceived) skills of the local endoscopist or surgeon at their respective procedures. Overall, these results suggest there is substantial confusion or disagreement among gastroenterologists and surgeons regarding the optimal approach to potential common bile duct stones. To a large extent, this variability reflects the lack of consensus observed in the literature for diagnosis of common bile duct stones per se. 27-35 It also mirrors the wide variation in practice patterns that has been observed for m a n y common medical conditions and p r o c e d u r e s Y -46 Whether the differences within and between groups reflect varying interpretations of the literature or are based on personal experience and accumulated clinical wisdom, two outcomes are certain. First, patients will likely receive varying GASTROINTESTINAL ENDOSCOPY
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recommendations for care, depending on whom they see. Second, many preoperative ERCPs will be ordered, even when the likelihood of stones is quite low. Because the decision to look for common bile duct stones is not without complications and costs, these results suggest that future work is needed to identify the most useful clinical indicators to guide these decisions, in combination with optimal clinical approaches for removal of stones. ACKNOWLEDGMENTS
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