- Email: [email protected]
Management of umbilical hernias in patients with ascites: development of a nomogram to predict mortality
The American Journal of Surgery (2015) 209, 302-307
Clinical Science
Management of umbilical hernias in patients with ascites: development of a nomogram to predict mortality Fady Saleh, M.D., M.P.H.a,b, Allan Okrainec, M.D., M.H.P.E.a,b, Sean P. Cleary, M.D., M.Sc., M.P.H.a,b, Timothy D. Jackson, M.D., M.P.H.a,b,* a
Division of General Surgery, University Health Network, Toronto, Ontario, Canada; bDepartment of Surgery, University of Toronto, Toronto, Ontario, Canada
KEYWORDS: Umbilical hernias; Ascites; Mortality; Nomogram
Abstract BACKGROUND: The objective of this study was to develop an easy-to-use nomogram to assist clinicians in predicting patient-specific mortality in this patient population. METHODS: American College of Surgeons National Surgical Quality Improvement Program participant use files were used from 2005 to 2011. Multivariable logistic regression was used to model 30-day postoperative mortality in patients with ascites who underwent umbilical hernia repair. RESULTS: A total of 688 patients with ascites undergoing umbilical hernia repair were included. There were 643 (94%) survivors and 45 (7%) mortalities. A total of 300 (44%) patients were classified as emergent cases. Using logistic regression to predict 30-day mortality, preoperative Model for End-Stage Liver Disease score, albumin, white blood cell count, and platelet count were found to be significant predictors (P , .05) of mortality and were included in our model. CONCLUSION: We propose a nomogram to enable clinicians to better estimate mortality in patients with ascites undergoing umbilical hernia repair. Ó 2015 Elsevier Inc. All rights reserved.
There were no relevant financial relationships or any sources of support in the form of grants, equipment, or drugs. Disclaimer: American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors. Presented at the Canadian Surgery Forum, Ottawa 2013. * Corresponding author. Toronto Western Hospital, University Health Network, 399 Bathurst St., 8 MP 322. Toronto, Ontario, Canada M5T 2S8. Tel.: 11-416-603-5599; fax: 11-416-603-6458. E-mail address: [email protected] Manuscript received March 14, 2014; revised manuscript April 11, 2014 0002-9610/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjsurg.2014.04.013
Patients with chronic liver disease who require surgery represent a significant clinical challenge to surgeons. It is estimated that approximately 10% of patients with cirrhosis will require a surgical procedure within the last 2 years of life.1 Furthermore, up to 20% of patients with decompensated liver disease and ascites will develop an umbilical hernia. These umbilical hernias have a tendency to become symptomatic, enlarge quickly, and will often require surgical intervention.2,3 While the increased risk of mortality in patients with chronic liver disease undergoing nonhepatic surgery has been well
F. Saleh et al.
Umbilical hernia and ascites nomogram
303
documented, estimates of the procedure-specific risk of mortality associated with umbilical hernia repair in this patient population remains largely undefined.4,5 There is a wide range of mortality rates reported in cirrhotic patients undergoing surgery, depending on the type of procedure, whether it was elective or emergent, and the degree of liver dysfunction.6,7 Specific estimates of mortality rates in patients with ascites undergoing umbilical hernia repair range from 0% to 30%.8 Existing studies typically consist of a low number of patients and thus make it hard to generalize to other patient populations. At present, no convenient or widely accepted model exists to help surgeons estimate risk of umbilical hernia repair in patients with ascites based on preoperative patient characteristics. The objective of this study was to develop a predictive model for mortality after umbilical hernia repair using a prospective database with a large cohort of cirrhotic patients. We present a nomogram that may be used by clinicians to help estimate risks and inform decision making.
Turcotte–Pugh classification and the Model for End-Stage Liver Disease (MELD) score. The Child–Turcotte–Pugh classification was originally developed in 1964 for patients undergoing portosystemic surgery and is often criticized as a predictive tool because of the subjectivity of the clinical components of encephalopathy and ascites.15,16 The MELD score was created initially at the Mayo Clinic, and later modified by the United Network of Organ Sharing, to predict 3-month survival after transjugular intrahepatic portosystemic shunts in patients awaiting liver transplant.17 The score can easily be calculated with online calculators (http://www.mayoclinic.org/meld/) using 3 laboratory values and has been shown to correlate well with postoperative mortality after nonhepatic surgery.6,15 As such, MELD score was chosen as our exposure of interest. MELD score is calculated by the formula:
Methods
using the United Network of Organ Sharing modifications assigning dialysis patients a creatinine of 4.0 mg/dL and giving any patient with a laboratory value less than one a value of 1. Our outcome of interest was 30-day mortality after umbilical hernia repair in cirrhotic patients with ascites.
Data source The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) is a prospective, multi-institutional, cohort study for collecting rich clinical data on patients undergoing surgical procedures in private sector hospitals across North America. Data are collected on preoperative, intraoperative, and postoperative variables, including 30-day outcomes. ACS NSQIP data methodology and verification have been described in detail.9–14 The study protocol was approved by our institutional Research Ethics Board.
Study subjects Patients aged 18 years or older with ascites as defined by ACS NSQIP during the years 2005 to 2011, who underwent umbilical hernia repair were eligible for inclusion in this study. Current Procedural Terminology codes for open umbilical hernia repairs are 49,585 and 49,587. The respective codes for laparoscopic ventral hernias are 49,652 and 49,653, and were only included if the International Classification of Diseases-9 code was consistent with a diagnosis of umbilical hernia. Ascites was defined in the dataset as patients with peritoneal fluid because of liver disease or malignancy diagnosed preoperatively. Exclusion criteria were defined a priori and included patients with disseminated cancers who may have had ascites from another cause not consistent with liver cirrhosis.
Exposures and outcome A number of scoring systems to classify the degree of liver disease exist, the 2 most widely used being the Child–
MELD 53:78!ðbilirubin; mg=dLÞ111:2!1nðINRÞ 19:57!1nðcreatinine; mg=dLÞ16:43
Statistical analysis Summary statistics were used to define the study population. Univariate analyses using the chi-square test statistic was performed to compare categorical variables and the t test to compare continuous variables. Multivariable logistic regression with 30-day mortality as the binary dependent variable was performed using backward elimination (P , .05 was used as our cutoff). We modeled independent continuous variables in both linear format and as fractional polynomials. Potential clinical confounders considered for our model included sex, age, American Society of Anesthesiologists classification, current dialysis, smoking status, type of anesthetic (general vs nongeneral), blood pressure status (hypertensive or normotensive), presence of pre-existing infection, drinking status, diabetes, presence of varices, emergency versus nonemergent surgery, and whether the hernia was incarcerated. Laboratory values considered were serum international normalized ratio, sodium, creatinine, bilirubin, albumin, white blood cell count (WBC), and platelet count. All laboratory values were modeled as continuous variables but platelets, WBC count, and serum sodium were modeled as categorical variables using clinically relevant categories. The natural logarithm was used for all continuous variables to reduce the effects of extreme values. All laboratory values were the last set of blood work closest to the operation. A number of variables had missing data (see legend, Table 1) totaling 10% or less with the exception of the MELD score, which is a composite score and thus had the highest amount of missing data at 17%. A total of 20% of patients were thus eliminated in our multivariable model. A sensitivity analysis
304 Table 1
The American Journal of Surgery, Vol 209, No 2, February 2015 Baseline characteristics Survivors
n 5 688 Mean age (6SD) Male Smoker Hypertensive ASA classification 1 or 2 3 4 or 5 Dialysis CAD CHF COPD Alcohol use* General anesthetic Diabetic Varices Pre-exiting infection† Emergent Bowel resection Incarceration Laparoscopic Mean sodium, mmol/L (6SD) Mean albumin, g/dL (6SD) Mean platelets, !109/L (6SD) Mean creatinine, mg/dL (6SD) Mean INR (6SD) Mean bilirubin, mg/dL (6SD) Mean WBC, !109/L (6SD) MELD score
Nonsurvivors
643 56.8 480 239 321
(93.5) (11.1) (75.0) (37.2) (49.9)
45 58.7 36 18 24
(6.5) (10.7) (80.0) (40.0) (53.3)
48 386 209 28 52 10 52 44 604 123 121 113 273 28 325 34 135.2 3.1 146.7 1.3 1.4 1.9 6.9 13.9
(7.5) (60.0) (32.5) (4.4) (8.1) (1.6) (8.1) (7.5) (93.9) (19.1) (18.8) (17.6) (42.5) (4.4) (50.5) (5.3) (4.7) (.7) (93.3) (1.2) (.4) (1.6) (3.6) (4.9)
1 17 27 4 4 3 6 7 44 13 9 18 27 3 27 4 133.9 2.6 128.6 1.9 1.6 3.4 8.3 19.3
(2.2) (37.8) (60.0) (8.9) (11.1) (6.7) (13.3) (17.5) (97.8) (28.9) (20.0) (40.0) (60.0) (6.7) (60.0) (8.9) (7.3) (.7) (107.0) (1.7) (.5) (3.1) (4.6) (5.5)
P value N/A .253 .452 .704 .658 .001
.163 .477 .015 .221 .026 .287 .112 .845 ,.001 .022 .470 .220 .307 .095 ,.001 .2238 .003 .002 ,.001 .011 ,.001
Data are expressed as n (%) or mean (6SD). Note: Some variables contain missing values: EtOH: 9%, sodium: 2%, creatinine: 2.5%, albumin: 11%, bilirubin: 10%, platelets: 4%, INR 9%, MELD: 17%. Bold P-values denote statistically significant differences. ASA 5 American Society of Anesthesiologists; CAD 5 coronary artery disease; CHF 5 congestive heart failure; COPD 5 chronic obstructive pulmonary disease; INR 5 international normalized ratio; MELD 5 model for end-stage liver disease; N/A 5 not applicable; SD 5 standard deviation; WBC 5 white blood cell count. *2 drinks/day in the 2 weeks before admission. † One or more of pneumonia, pre-existing open/infected wound infection, sepsis, and/or septic shock.
was performed excluding all laparoscopic repairs to help examine for potential selection bias. Multicollinearity was examined for using variance inflation factors and tolerance. Lack-of-fit was examined using the Hosmer–Lemeshow test and a c-statistic was generated to examine the models’ predictive ability. Statistical significance was set at P values less than .05. All statistical analyses were performed using Stata/IC version 12.1 (Statacorp, College Station, TX).
Results A total of 688 patients were included for analysis: 643 (94%) survivors and 45 (7%) nonsurvivors who died within 30 days postoperatively. The characteristics of the study population are presented in Table 1. Generally, patients who died had higher proportions of comorbid conditions but few of these differences tested as significant, the exceptions being
American Society of Anesthesiologist class, drinking status, known congestive heart failure, the presence of pre-existing infection, and the proportion of emergent cases. Baseline blood work, however, differed substantially, with nonsurvivors having a lower mean albumin, 2.6 (standard deviation [SD] 6. 8) vs 3.1 g/dL (SD 6 .7) (P , .001); a higher mean creatinine, 1.9 (SD 6 1.7) vs 1.33 mg/dL (SD 6 1.2) (P 5 .003); a higher mean international normalized ratio, 1.6 (SD 6 .5) vs 1.4 (SD 6 .4) (P 5.002); a higher mean bilirubin, 3.4 (SD 6 3.1) vs 1.9 mg/dL (SD 6 1.6) (P , .001); and a higher mean WBC, 8.3 (SD 6 4.6) vs 6.9 (SD 6 3.6) (P 5 .011). The MELD score was consequently higher in the nonsurvivor group with a mean of 19.3 (SD 6 5.5) compared with 13.9 (SD 6 4.9) (P ,.0001). The distribution of the MELD score among patients is displayed in Fig. 1. Approximately 60% of patients had a MELD score of greater than or equal to 12, while fewer patients (13%) had MELD scores greater than 20.
F. Saleh et al.
Umbilical hernia and ascites nomogram
Using multivariable logistic regression to predict 30-day mortality, we found only MELD score, albumin, WBC, and platelet count to be significant predictors of mortality. All variables were continuous and expressed in their logarithmic form, except for platelet count, which was modeled as a binary variable (greater or less than 150 ! 109/L). Polynomial expressions of these independent variables offered no advantage over their linear form. Other variables listed in Table 1 were examined for potential predictive value. Interestingly, clinical variables that demonstrated significance at a univariate analysis for increased mortality fell out of the model when looked at in conjunction with other variables in a multivariate analysis. There was no evidence of multicollinearity in our model and there was no evidence of lack-of-fit (P 5 .154). The model’s c-statistic was .82 demonstrating that the model accurately describes mortality in patients within the ACS NSQIP database. Our sensitivity analysis excluding 38 laparoscopic cases did not alter our findings. The probability of death was derived from the logistic regression model and is expressed by the following formula:
305
Figure 2
Probability of death versus MELD score.
albumin level (holding WBC and platelet count at their mean value), with the lower albumin levels showing higher mortality rates. Table 2 displays a nomogram we developed for clinicians from our predictive model to help estimate postoper-
expð0:15!MELD11:45!Platelets11:06!lnðWBCÞ22:80!lnðAlbuminÞ24:62Þ Pr Death 5 11expð0:15!MELD11:45!Platelets11:06!lnðWBCÞ22:80!lnðAlbuminÞ24:62Þ
Fig. 2 displays the predicted probability from the multivariate model of mortality within 30 days postoperatively given a specific MELD score. The probabilities are displayed at mean albumin, WBC, and platelet count. Mortality begins to increase at a MELD score of 12. As is expected, the 95% confidence intervals are narrowest at the lower values of the MELD score where most of the data reside, and increases substantially toward the higher scores where data become sparse and extrapolation has more uncertainty. Fig. 3 demonstrates the relationship between mortality and MELD score at varying levels of
Figure 1
Distribution of MELD scores.
ative mortality in patients undergoing umbilical hernia repair in the setting of ascites, for both elective and emergent patients. It is noteworthy that while the model does very well in predicting mortality in both emergent and nonemergent cases, the model does perform better for elective and nonemergent cases (c-statistic .87 compared with .76 for emergency surgery patients). Using a web-based calculator, the clinician can determine a patient’s MELD score and using the patient’s blood work can determine the mortality risk at an individual level using Table 2. While each estimate of the nomogram is associated with a 95% confidence interval, these were omitted as the table would be virtually nonusable were they included. The nomogram is
Figure 3 score.
Probability of death using albumin (g/dL) over MELD
306
The American Journal of Surgery, Vol 209, No 2, February 2015
Table 2
Nomogram to predict mortality
MELD score WBC , 10.0 Platelet . 150
Platelet , 150
WBC . 10.0 Platelet . 150
Platelet , 150
6
9
12
15
18
.2 .4 .5 .9 1.7 3.6 1.0 1.5 2.3 3.7 6.7 13.9
.4 .5 .8 1.4 2.6 5.5 1.6 2.3 3.5 5.7 10.1 20.0
.6 .9 1.3 2.1 3.9 8.4 2.5 3.5 5.3 8.6 14.9 28.1
.9 1.3 2.0 3.3 6.0 12.5 3.8 5.4 8.1 12.7 21.4 37.8
1.4 2.0 3.1 5.0 9.0 18.2 5.8 8.2 12.0 18.5 29.8 48.7
1.1 1.5 2.3 3.8 6.9 14.2 4.4 6.2 9.2 14.5 24.0 41.4
1.6 2.4 3.6 5.8 10.3 20.5 6.6 9.3 13.7 20.9 33.0 52.4
2.5 3.6 5.5 8.8 15.2 28.6 10.0 13.8 19.8 29.1 43.4 63.2
3.9 5.5 8.3 13.0 21.9 38.5 14.7 20.0 27.8 39.1 54.5 72.8
5.9 8.3 12.3 18.9 30.3 49.3 21.2 28.0 37.5 50.0 65.1 80.6
an approximation as laboratory values in the table are converted to categories for ease of use. As an example, a patient presenting with a MELD score of 18, an albumin of 3.0, a WBC of 12.0, and a platelet count of 100 would have a predicted 30-day mortality of 12%.
Comments Using a multivariate analysis, we were able to model 30day mortality after umbilical hernia repairs in patients with ascites and chronic liver disease. Predictors that entered into the multivariate model included MELD score, albumin, WBC, and platelet count (P ,.05). This model showed no evidence of lack-of-fit (P 5 .154) and had a c-statistic of .82 indicating that the model predicted mortality very well. Using this information, we created a nomogram for use by clinicians to help predict postoperative mortality (Table 2). Our mortality rate overall was 6%, which is comparable with other case series in the literature.4,8,18 Emergency repairs were associated with an approximately doubled mortality, 9% vs 5% (P 5.033). This is consistent with other studies, which have found that emergency repairs tend to be associated with higher morbidity and mortality.19–21 Modeling mortality in cirrhotic patients undergoing surgery was previously addressed by Northup et al.6 They looked at 140 patients who underwent nontransplant
21
24
27
30
33
36
2.2 3.1 4.7 7.7 13.4 25.7 8.7 12.2 17.6 26.2 39.8 59.6
3.4 4.8 7.2 11.4 19.4 35.0 12.9 17.7 24.9 35.6 50.8 69.7
5.1 7.3 10.8 16.7 27.3 45.6 18.8 25.1 34.1 46.3 61.6 78.2
7.8 10.9 15.8 23.9 36.9 56.7 26.5 34.4 44.6 57.3 71.5 84.8
11.6 16.0 22.7 32.8 47.7 67.1 36.0 44.9 55.7 67.6 79.6 89.7
17.0 22.9 31.4 43.2 58.7 76.0 46.7 56.0 66.2 76.5 85.9 93.1
Albumin (g/dL) 4.0 3.5 3.0 2.5 2.0 1.5 4.0 3.5 3.0 2.5 2.0 1.5
8.9 12.4 17.9 26.7 40.4 603 29.5 37.8 48.3 60.9 74.4 86.6
13.2 18.1 25.4 36.2 51.4 70.3 39.4 48.6 59.3 70.8 81.9 91.0
19.2 25.6 34.7 46.9 62.2 78.6 50.4 59.6 69.4 79.1 87.6 94.0
27.0 34.9 45.3 57.9 72.0 85.2 61.3 69.7 78.0 85.5 91.7 96.1
36.6 45.6 56.3 68.2 80.0 89.9 71.1 78.2 84.6 90.2 94.5 97.5
47.3 56.6 66.7 77.0 86.2 93.3 79.3 84.8 89.6 93.5 96.4 98.4
4.0 3.5 3.0 2.5 2.0 1.5 4.0 3.5 3.0 2.5 2.0 1.5
operations to develop their predictive model, and performed a subgroup analysis on their abdominal procedures (totaling 67 patients in all). They provide their predicted probability of mortality, which as a rule-of-thumb averages to 1% per MELD score below a MELD score of 20, and 2% thereafter. Their grouping of heterogeneous operations (eg, both major and minor abdominal surgery) grossly overestimates mortality in patients undergoing a lesser operation such as umbilical hernia repair (see Fig. 1 in comparison). We feel we are able to provide a more accurate individualized prediction in a well-defined population undergoing a specific surgery. Cho et al22 previously explored outcomes of umbilical hernia repairs in patients with ascites using the same dataset from the ACS NSQIP. However, they did not specifically model mortality but rather identified risk factors for death. In their multivariate analysis, they found age greater than 65, MELD score greater than 15, preoperative sepsis, and albumin less than 3.0 g/dL as significant predictors for mortality. While this study also identified MELD score and albumin level as important predictors of mortality, our model did differ in that we also identified WBC and platelet count as important predictors of adverse outcome. Differences in predictors between the 2 studies are likely attributable to the fact that this study has 3 more years of patient accrual, had different model selection criteria, and Cho et al focused on clinically relevant dichotomous variables that give clinicians a general sense of high risk patients. Our study is
F. Saleh et al.
Umbilical hernia and ascites nomogram
novel in that we provide an individualized assessment tool to help clinicians more accurately predict mortality. There are a number of important limitations to this study. First, the dataset does not allow one to distinguish high volume from low volume liver centers, which may be a factor influencing outcome. Second, and related to the previous point, the dataset does not provide any information on the nature of the preoperative and postoperative patient management. Finally, patients who die beyond 30 days would not be captured in our study, although we feel most would. Using a multivariate analysis, we were able to develop an easy-to-use nomogram to help surgeons estimate postoperative risk of mortality in patients with ascites undergoing umbilical hernia repair. This tool may be applied to help better inform the decision-making process and facilitate patient discussion when faced with this challenging clinical scenario. High quality outcomes data from the ACS NSQIP allow for the development of clinical predictive models to better define patient-specific surgical risk and represents an additional opportunity to improve surgical care. Further study is needed to validate our model prospectively.
References 1. Rice HE, O’Keefe GE, Helton WS, et al. Morbid prognostic features in patients with chronic liver failure undergoing nonhepatic surgery. Arch Surg 1997;132:880–4; discussion, 884–5. 2. Ammar SA. Management of complicated umbilical hernias in cirrhotic patients using permanent mesh: randomized clinical trial. Hernia 2010; 14:35–8. 3. Belli G, D’Agostino A, Fantini C, et al. Laparoscopic incisional and umbilical hernia repair in cirrhotic patients. Surg Laparosc Endosc Percutan Tech 2006;16:330–3. 4. Ziser A, Plevak DJ, Wiesner RH, et al. Morbidity and mortality in cirrhotic patients undergoing anesthesia and surgery. Anesthesiology 1999;90:42–53. 5. Leonetti JP, Aranha GV, Wilkinson WA, et al. Umbilical herniorrhaphy in cirrhotic patients. Arch Surg 1984;119:442–5. 6. Northup PG, Wanamaker RC, Lee VD, et al. Model for End-Stage Liver Disease (MELD) predicts nontransplant surgical mortality in patients with cirrhosis. Ann Surg 2005;242:244–51.
307 7. Suman A, Carey WD. Assessing the risk of surgery in patients with liver disease. Cleve Clin J Med 2006;73:398–404. 8. McKay A, Dixon E, Bathe O, et al. Umbilical hernia repair in the presence of cirrhosis and ascites: results of a survey and review of the literature. Hernia 2009;13:461–8. 9. Khuri SF, Henderson WG, Daley J, et al. The patient safety in surgery study: background, study design, and patient populations. J Am Coll Surg 2007;204:1089–102. 10. Khuri SF, Daley J, Henderson W, et al. Risk adjustment of the postoperative mortality rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:315–27. 11. Daley J, Khuri SF, Henderson W, et al. Risk adjustment of the postoperative morbidity rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:328–40. 12. Daley J, Forbes MG, Young GJ, et al. Validating risk-adjusted surgical outcomes: site visit assessment of process and structure. National VA Surgical Risk Study. J Am Coll Surg 1997;185:341–51. 13. Khuri SF, Henderson WG, Daley J, et al. Successful implementation of the Department of Veterans Affairs’ National Surgical Quality Improvement Program in the private sector: the Patient Safety in Surgery study. Ann Surg 2008;248:329–36. 14. Shiloach M, Frencher Jr SK, Steeger JE, et al. Toward robust information: data quality and inter-rater reliability in the American College of Surgeons National Surgical Quality Improvement Program. J Am Coll Surg 2010;210:6–16. 15. Farnsworth N, Fagan SP, Berger DH, et al. Child-Turcotte-Pugh versus MELD score as a predictor of outcome after elective and emergent surgery in cirrhotic patients. Am J Surg 2004;188:580–3. 16. Cattau EL Jr , Benjamin SB, Knuff TE, et al. The accuracy of the physical examination in the diagnosis of suspected ascites. JAMA 1982; 247:1164–6. 17. Malinchoc M, Kamath PS, Gordon FD, et al. A model to predict poor survival in patients undergoing transjugular intrahepatic portosystemic shunts. Hepatology 2000;31:864–71. 18. Eker HH, van Ramshorst GH, de Goede B, et al. A prospective study on elective umbilical hernia repair in patients with liver cirrhosis and ascites. Surgery 2011;150:542–6. 19. Gray SH, Vick CC, Graham LA, et al. Umbilical herniorrhaphy in cirrhosis: improved outcomes with elective repair. J Gastrointest Surg 2008;12:675–81. 20. Marsman HA, Heisterkamp J, Kazemier G. Re: management in patients with liver cirrhosis and an umbilical hernia. Surgery 2008;143:695. 21. Choi SB, Hong KD, Lee JS, et al. Management of umbilical hernia complicated with liver cirrhosis: an advocate of early and elective herniorrhaphy. Dig Liver Dis 2011;43:991–5. 22. Cho SW, Bhayani N, Newell P, et al. Umbilical hernia repair in patients with signs of portal hypertension: surgical outcome and predictors of mortality. Arch Surg 2012;147:864–9.
Clinical Science
Management of umbilical hernias in patients with ascites: development of a nomogram to predict mortality Fady Saleh, M.D., M.P.H.a,b, Allan Okrainec, M.D., M.H.P.E.a,b, Sean P. Cleary, M.D., M.Sc., M.P.H.a,b, Timothy D. Jackson, M.D., M.P.H.a,b,* a
Division of General Surgery, University Health Network, Toronto, Ontario, Canada; bDepartment of Surgery, University of Toronto, Toronto, Ontario, Canada
KEYWORDS: Umbilical hernias; Ascites; Mortality; Nomogram
Abstract BACKGROUND: The objective of this study was to develop an easy-to-use nomogram to assist clinicians in predicting patient-specific mortality in this patient population. METHODS: American College of Surgeons National Surgical Quality Improvement Program participant use files were used from 2005 to 2011. Multivariable logistic regression was used to model 30-day postoperative mortality in patients with ascites who underwent umbilical hernia repair. RESULTS: A total of 688 patients with ascites undergoing umbilical hernia repair were included. There were 643 (94%) survivors and 45 (7%) mortalities. A total of 300 (44%) patients were classified as emergent cases. Using logistic regression to predict 30-day mortality, preoperative Model for End-Stage Liver Disease score, albumin, white blood cell count, and platelet count were found to be significant predictors (P , .05) of mortality and were included in our model. CONCLUSION: We propose a nomogram to enable clinicians to better estimate mortality in patients with ascites undergoing umbilical hernia repair. Ó 2015 Elsevier Inc. All rights reserved.
There were no relevant financial relationships or any sources of support in the form of grants, equipment, or drugs. Disclaimer: American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors. Presented at the Canadian Surgery Forum, Ottawa 2013. * Corresponding author. Toronto Western Hospital, University Health Network, 399 Bathurst St., 8 MP 322. Toronto, Ontario, Canada M5T 2S8. Tel.: 11-416-603-5599; fax: 11-416-603-6458. E-mail address: [email protected] Manuscript received March 14, 2014; revised manuscript April 11, 2014 0002-9610/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjsurg.2014.04.013
Patients with chronic liver disease who require surgery represent a significant clinical challenge to surgeons. It is estimated that approximately 10% of patients with cirrhosis will require a surgical procedure within the last 2 years of life.1 Furthermore, up to 20% of patients with decompensated liver disease and ascites will develop an umbilical hernia. These umbilical hernias have a tendency to become symptomatic, enlarge quickly, and will often require surgical intervention.2,3 While the increased risk of mortality in patients with chronic liver disease undergoing nonhepatic surgery has been well
F. Saleh et al.
Umbilical hernia and ascites nomogram
303
documented, estimates of the procedure-specific risk of mortality associated with umbilical hernia repair in this patient population remains largely undefined.4,5 There is a wide range of mortality rates reported in cirrhotic patients undergoing surgery, depending on the type of procedure, whether it was elective or emergent, and the degree of liver dysfunction.6,7 Specific estimates of mortality rates in patients with ascites undergoing umbilical hernia repair range from 0% to 30%.8 Existing studies typically consist of a low number of patients and thus make it hard to generalize to other patient populations. At present, no convenient or widely accepted model exists to help surgeons estimate risk of umbilical hernia repair in patients with ascites based on preoperative patient characteristics. The objective of this study was to develop a predictive model for mortality after umbilical hernia repair using a prospective database with a large cohort of cirrhotic patients. We present a nomogram that may be used by clinicians to help estimate risks and inform decision making.
Turcotte–Pugh classification and the Model for End-Stage Liver Disease (MELD) score. The Child–Turcotte–Pugh classification was originally developed in 1964 for patients undergoing portosystemic surgery and is often criticized as a predictive tool because of the subjectivity of the clinical components of encephalopathy and ascites.15,16 The MELD score was created initially at the Mayo Clinic, and later modified by the United Network of Organ Sharing, to predict 3-month survival after transjugular intrahepatic portosystemic shunts in patients awaiting liver transplant.17 The score can easily be calculated with online calculators (http://www.mayoclinic.org/meld/) using 3 laboratory values and has been shown to correlate well with postoperative mortality after nonhepatic surgery.6,15 As such, MELD score was chosen as our exposure of interest. MELD score is calculated by the formula:
Methods
using the United Network of Organ Sharing modifications assigning dialysis patients a creatinine of 4.0 mg/dL and giving any patient with a laboratory value less than one a value of 1. Our outcome of interest was 30-day mortality after umbilical hernia repair in cirrhotic patients with ascites.
Data source The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) is a prospective, multi-institutional, cohort study for collecting rich clinical data on patients undergoing surgical procedures in private sector hospitals across North America. Data are collected on preoperative, intraoperative, and postoperative variables, including 30-day outcomes. ACS NSQIP data methodology and verification have been described in detail.9–14 The study protocol was approved by our institutional Research Ethics Board.
Study subjects Patients aged 18 years or older with ascites as defined by ACS NSQIP during the years 2005 to 2011, who underwent umbilical hernia repair were eligible for inclusion in this study. Current Procedural Terminology codes for open umbilical hernia repairs are 49,585 and 49,587. The respective codes for laparoscopic ventral hernias are 49,652 and 49,653, and were only included if the International Classification of Diseases-9 code was consistent with a diagnosis of umbilical hernia. Ascites was defined in the dataset as patients with peritoneal fluid because of liver disease or malignancy diagnosed preoperatively. Exclusion criteria were defined a priori and included patients with disseminated cancers who may have had ascites from another cause not consistent with liver cirrhosis.
Exposures and outcome A number of scoring systems to classify the degree of liver disease exist, the 2 most widely used being the Child–
MELD 53:78!ðbilirubin; mg=dLÞ111:2!1nðINRÞ 19:57!1nðcreatinine; mg=dLÞ16:43
Statistical analysis Summary statistics were used to define the study population. Univariate analyses using the chi-square test statistic was performed to compare categorical variables and the t test to compare continuous variables. Multivariable logistic regression with 30-day mortality as the binary dependent variable was performed using backward elimination (P , .05 was used as our cutoff). We modeled independent continuous variables in both linear format and as fractional polynomials. Potential clinical confounders considered for our model included sex, age, American Society of Anesthesiologists classification, current dialysis, smoking status, type of anesthetic (general vs nongeneral), blood pressure status (hypertensive or normotensive), presence of pre-existing infection, drinking status, diabetes, presence of varices, emergency versus nonemergent surgery, and whether the hernia was incarcerated. Laboratory values considered were serum international normalized ratio, sodium, creatinine, bilirubin, albumin, white blood cell count (WBC), and platelet count. All laboratory values were modeled as continuous variables but platelets, WBC count, and serum sodium were modeled as categorical variables using clinically relevant categories. The natural logarithm was used for all continuous variables to reduce the effects of extreme values. All laboratory values were the last set of blood work closest to the operation. A number of variables had missing data (see legend, Table 1) totaling 10% or less with the exception of the MELD score, which is a composite score and thus had the highest amount of missing data at 17%. A total of 20% of patients were thus eliminated in our multivariable model. A sensitivity analysis
304 Table 1
The American Journal of Surgery, Vol 209, No 2, February 2015 Baseline characteristics Survivors
n 5 688 Mean age (6SD) Male Smoker Hypertensive ASA classification 1 or 2 3 4 or 5 Dialysis CAD CHF COPD Alcohol use* General anesthetic Diabetic Varices Pre-exiting infection† Emergent Bowel resection Incarceration Laparoscopic Mean sodium, mmol/L (6SD) Mean albumin, g/dL (6SD) Mean platelets, !109/L (6SD) Mean creatinine, mg/dL (6SD) Mean INR (6SD) Mean bilirubin, mg/dL (6SD) Mean WBC, !109/L (6SD) MELD score
Nonsurvivors
643 56.8 480 239 321
(93.5) (11.1) (75.0) (37.2) (49.9)
45 58.7 36 18 24
(6.5) (10.7) (80.0) (40.0) (53.3)
48 386 209 28 52 10 52 44 604 123 121 113 273 28 325 34 135.2 3.1 146.7 1.3 1.4 1.9 6.9 13.9
(7.5) (60.0) (32.5) (4.4) (8.1) (1.6) (8.1) (7.5) (93.9) (19.1) (18.8) (17.6) (42.5) (4.4) (50.5) (5.3) (4.7) (.7) (93.3) (1.2) (.4) (1.6) (3.6) (4.9)
1 17 27 4 4 3 6 7 44 13 9 18 27 3 27 4 133.9 2.6 128.6 1.9 1.6 3.4 8.3 19.3
(2.2) (37.8) (60.0) (8.9) (11.1) (6.7) (13.3) (17.5) (97.8) (28.9) (20.0) (40.0) (60.0) (6.7) (60.0) (8.9) (7.3) (.7) (107.0) (1.7) (.5) (3.1) (4.6) (5.5)
P value N/A .253 .452 .704 .658 .001
.163 .477 .015 .221 .026 .287 .112 .845 ,.001 .022 .470 .220 .307 .095 ,.001 .2238 .003 .002 ,.001 .011 ,.001
Data are expressed as n (%) or mean (6SD). Note: Some variables contain missing values: EtOH: 9%, sodium: 2%, creatinine: 2.5%, albumin: 11%, bilirubin: 10%, platelets: 4%, INR 9%, MELD: 17%. Bold P-values denote statistically significant differences. ASA 5 American Society of Anesthesiologists; CAD 5 coronary artery disease; CHF 5 congestive heart failure; COPD 5 chronic obstructive pulmonary disease; INR 5 international normalized ratio; MELD 5 model for end-stage liver disease; N/A 5 not applicable; SD 5 standard deviation; WBC 5 white blood cell count. *2 drinks/day in the 2 weeks before admission. † One or more of pneumonia, pre-existing open/infected wound infection, sepsis, and/or septic shock.
was performed excluding all laparoscopic repairs to help examine for potential selection bias. Multicollinearity was examined for using variance inflation factors and tolerance. Lack-of-fit was examined using the Hosmer–Lemeshow test and a c-statistic was generated to examine the models’ predictive ability. Statistical significance was set at P values less than .05. All statistical analyses were performed using Stata/IC version 12.1 (Statacorp, College Station, TX).
Results A total of 688 patients were included for analysis: 643 (94%) survivors and 45 (7%) nonsurvivors who died within 30 days postoperatively. The characteristics of the study population are presented in Table 1. Generally, patients who died had higher proportions of comorbid conditions but few of these differences tested as significant, the exceptions being
American Society of Anesthesiologist class, drinking status, known congestive heart failure, the presence of pre-existing infection, and the proportion of emergent cases. Baseline blood work, however, differed substantially, with nonsurvivors having a lower mean albumin, 2.6 (standard deviation [SD] 6. 8) vs 3.1 g/dL (SD 6 .7) (P , .001); a higher mean creatinine, 1.9 (SD 6 1.7) vs 1.33 mg/dL (SD 6 1.2) (P 5 .003); a higher mean international normalized ratio, 1.6 (SD 6 .5) vs 1.4 (SD 6 .4) (P 5.002); a higher mean bilirubin, 3.4 (SD 6 3.1) vs 1.9 mg/dL (SD 6 1.6) (P , .001); and a higher mean WBC, 8.3 (SD 6 4.6) vs 6.9 (SD 6 3.6) (P 5 .011). The MELD score was consequently higher in the nonsurvivor group with a mean of 19.3 (SD 6 5.5) compared with 13.9 (SD 6 4.9) (P ,.0001). The distribution of the MELD score among patients is displayed in Fig. 1. Approximately 60% of patients had a MELD score of greater than or equal to 12, while fewer patients (13%) had MELD scores greater than 20.
F. Saleh et al.
Umbilical hernia and ascites nomogram
Using multivariable logistic regression to predict 30-day mortality, we found only MELD score, albumin, WBC, and platelet count to be significant predictors of mortality. All variables were continuous and expressed in their logarithmic form, except for platelet count, which was modeled as a binary variable (greater or less than 150 ! 109/L). Polynomial expressions of these independent variables offered no advantage over their linear form. Other variables listed in Table 1 were examined for potential predictive value. Interestingly, clinical variables that demonstrated significance at a univariate analysis for increased mortality fell out of the model when looked at in conjunction with other variables in a multivariate analysis. There was no evidence of multicollinearity in our model and there was no evidence of lack-of-fit (P 5 .154). The model’s c-statistic was .82 demonstrating that the model accurately describes mortality in patients within the ACS NSQIP database. Our sensitivity analysis excluding 38 laparoscopic cases did not alter our findings. The probability of death was derived from the logistic regression model and is expressed by the following formula:
305
Figure 2
Probability of death versus MELD score.
albumin level (holding WBC and platelet count at their mean value), with the lower albumin levels showing higher mortality rates. Table 2 displays a nomogram we developed for clinicians from our predictive model to help estimate postoper-
expð0:15!MELD11:45!Platelets11:06!lnðWBCÞ22:80!lnðAlbuminÞ24:62Þ Pr Death 5 11expð0:15!MELD11:45!Platelets11:06!lnðWBCÞ22:80!lnðAlbuminÞ24:62Þ
Fig. 2 displays the predicted probability from the multivariate model of mortality within 30 days postoperatively given a specific MELD score. The probabilities are displayed at mean albumin, WBC, and platelet count. Mortality begins to increase at a MELD score of 12. As is expected, the 95% confidence intervals are narrowest at the lower values of the MELD score where most of the data reside, and increases substantially toward the higher scores where data become sparse and extrapolation has more uncertainty. Fig. 3 demonstrates the relationship between mortality and MELD score at varying levels of
Figure 1
Distribution of MELD scores.
ative mortality in patients undergoing umbilical hernia repair in the setting of ascites, for both elective and emergent patients. It is noteworthy that while the model does very well in predicting mortality in both emergent and nonemergent cases, the model does perform better for elective and nonemergent cases (c-statistic .87 compared with .76 for emergency surgery patients). Using a web-based calculator, the clinician can determine a patient’s MELD score and using the patient’s blood work can determine the mortality risk at an individual level using Table 2. While each estimate of the nomogram is associated with a 95% confidence interval, these were omitted as the table would be virtually nonusable were they included. The nomogram is
Figure 3 score.
Probability of death using albumin (g/dL) over MELD
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Table 2
Nomogram to predict mortality
MELD score WBC , 10.0 Platelet . 150
Platelet , 150
WBC . 10.0 Platelet . 150
Platelet , 150
6
9
12
15
18
.2 .4 .5 .9 1.7 3.6 1.0 1.5 2.3 3.7 6.7 13.9
.4 .5 .8 1.4 2.6 5.5 1.6 2.3 3.5 5.7 10.1 20.0
.6 .9 1.3 2.1 3.9 8.4 2.5 3.5 5.3 8.6 14.9 28.1
.9 1.3 2.0 3.3 6.0 12.5 3.8 5.4 8.1 12.7 21.4 37.8
1.4 2.0 3.1 5.0 9.0 18.2 5.8 8.2 12.0 18.5 29.8 48.7
1.1 1.5 2.3 3.8 6.9 14.2 4.4 6.2 9.2 14.5 24.0 41.4
1.6 2.4 3.6 5.8 10.3 20.5 6.6 9.3 13.7 20.9 33.0 52.4
2.5 3.6 5.5 8.8 15.2 28.6 10.0 13.8 19.8 29.1 43.4 63.2
3.9 5.5 8.3 13.0 21.9 38.5 14.7 20.0 27.8 39.1 54.5 72.8
5.9 8.3 12.3 18.9 30.3 49.3 21.2 28.0 37.5 50.0 65.1 80.6
an approximation as laboratory values in the table are converted to categories for ease of use. As an example, a patient presenting with a MELD score of 18, an albumin of 3.0, a WBC of 12.0, and a platelet count of 100 would have a predicted 30-day mortality of 12%.
Comments Using a multivariate analysis, we were able to model 30day mortality after umbilical hernia repairs in patients with ascites and chronic liver disease. Predictors that entered into the multivariate model included MELD score, albumin, WBC, and platelet count (P ,.05). This model showed no evidence of lack-of-fit (P 5 .154) and had a c-statistic of .82 indicating that the model predicted mortality very well. Using this information, we created a nomogram for use by clinicians to help predict postoperative mortality (Table 2). Our mortality rate overall was 6%, which is comparable with other case series in the literature.4,8,18 Emergency repairs were associated with an approximately doubled mortality, 9% vs 5% (P 5.033). This is consistent with other studies, which have found that emergency repairs tend to be associated with higher morbidity and mortality.19–21 Modeling mortality in cirrhotic patients undergoing surgery was previously addressed by Northup et al.6 They looked at 140 patients who underwent nontransplant
21
24
27
30
33
36
2.2 3.1 4.7 7.7 13.4 25.7 8.7 12.2 17.6 26.2 39.8 59.6
3.4 4.8 7.2 11.4 19.4 35.0 12.9 17.7 24.9 35.6 50.8 69.7
5.1 7.3 10.8 16.7 27.3 45.6 18.8 25.1 34.1 46.3 61.6 78.2
7.8 10.9 15.8 23.9 36.9 56.7 26.5 34.4 44.6 57.3 71.5 84.8
11.6 16.0 22.7 32.8 47.7 67.1 36.0 44.9 55.7 67.6 79.6 89.7
17.0 22.9 31.4 43.2 58.7 76.0 46.7 56.0 66.2 76.5 85.9 93.1
Albumin (g/dL) 4.0 3.5 3.0 2.5 2.0 1.5 4.0 3.5 3.0 2.5 2.0 1.5
8.9 12.4 17.9 26.7 40.4 603 29.5 37.8 48.3 60.9 74.4 86.6
13.2 18.1 25.4 36.2 51.4 70.3 39.4 48.6 59.3 70.8 81.9 91.0
19.2 25.6 34.7 46.9 62.2 78.6 50.4 59.6 69.4 79.1 87.6 94.0
27.0 34.9 45.3 57.9 72.0 85.2 61.3 69.7 78.0 85.5 91.7 96.1
36.6 45.6 56.3 68.2 80.0 89.9 71.1 78.2 84.6 90.2 94.5 97.5
47.3 56.6 66.7 77.0 86.2 93.3 79.3 84.8 89.6 93.5 96.4 98.4
4.0 3.5 3.0 2.5 2.0 1.5 4.0 3.5 3.0 2.5 2.0 1.5
operations to develop their predictive model, and performed a subgroup analysis on their abdominal procedures (totaling 67 patients in all). They provide their predicted probability of mortality, which as a rule-of-thumb averages to 1% per MELD score below a MELD score of 20, and 2% thereafter. Their grouping of heterogeneous operations (eg, both major and minor abdominal surgery) grossly overestimates mortality in patients undergoing a lesser operation such as umbilical hernia repair (see Fig. 1 in comparison). We feel we are able to provide a more accurate individualized prediction in a well-defined population undergoing a specific surgery. Cho et al22 previously explored outcomes of umbilical hernia repairs in patients with ascites using the same dataset from the ACS NSQIP. However, they did not specifically model mortality but rather identified risk factors for death. In their multivariate analysis, they found age greater than 65, MELD score greater than 15, preoperative sepsis, and albumin less than 3.0 g/dL as significant predictors for mortality. While this study also identified MELD score and albumin level as important predictors of mortality, our model did differ in that we also identified WBC and platelet count as important predictors of adverse outcome. Differences in predictors between the 2 studies are likely attributable to the fact that this study has 3 more years of patient accrual, had different model selection criteria, and Cho et al focused on clinically relevant dichotomous variables that give clinicians a general sense of high risk patients. Our study is
F. Saleh et al.
Umbilical hernia and ascites nomogram
novel in that we provide an individualized assessment tool to help clinicians more accurately predict mortality. There are a number of important limitations to this study. First, the dataset does not allow one to distinguish high volume from low volume liver centers, which may be a factor influencing outcome. Second, and related to the previous point, the dataset does not provide any information on the nature of the preoperative and postoperative patient management. Finally, patients who die beyond 30 days would not be captured in our study, although we feel most would. Using a multivariate analysis, we were able to develop an easy-to-use nomogram to help surgeons estimate postoperative risk of mortality in patients with ascites undergoing umbilical hernia repair. This tool may be applied to help better inform the decision-making process and facilitate patient discussion when faced with this challenging clinical scenario. High quality outcomes data from the ACS NSQIP allow for the development of clinical predictive models to better define patient-specific surgical risk and represents an additional opportunity to improve surgical care. Further study is needed to validate our model prospectively.
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