REVIEW

Systematic Review of Obesity Surgery Mortality Risk Score—Preoperative Risk Stratification in Bariatric Surgery

Harun Thomas & Sanjay Agrawal

Published online: 26 April 2012# Springer Science+Business Media, LLC 2012

Abstract Bariatric surgery is the best long term treatmentfor morbid obesity. However, it carries risks of considerablemorbidity and potential mortality. There is no publishedreview on pre-operative identification of high-risk patientsin bariatric surgery. This systematic review analyses obesitysurgery mortality risk score (OS-MRS) as a tool for pre-operative prediction of mortality risk in bariatric surgery.Medline and Embase was systematically searched using themedical subjects headings (MeSH) terms ‘bariatric surgery’and ‘mortality’ with further free text search and cross refer-ences. Studies that described OS-MRS to predict mortalityrisk after bariatric surgery were included in this review. Sixstudies evaluated 9,382 patients to assess the validity of OS-MRS to predict the mortality risk after bariatric surgery.Patient's age ranged from 19 to 67 years, and the body massindex ranged from 30 to 84. There were 83 deaths amongthe 9,382 patients (0.88 %) with individual studies reportinga mortality range from 0 % to 1.49 %. There were 13 deathsamong 4,912 (0.26 %) class A patients, 55 deaths among4,124 (1.33 %) class B patients and 15 deaths among 346

(4.34 %) class C patients. Mortality in classes A, B and Cwas significantly different from each of the other two classes(P<0.05, χ2). This systematic review confirms that OS-MRS stratifies the mortality risk in the three-risk classifica-tion subgroups of patients. The OS-MRS can be used forpre-operative identification of high-risk patients undergoingprimary Roux-en-Y gastric bypass surgery.

Keywords Bariatric surgery . Obesity surgery . Obesitysurgery mortality risk score . OS-MRS . Roux-en-Y gastricbypass . Laparoscopic gastric bypass . Morbid obesity .

Systematic review

Introduction

The incidence of morbid obesity has risen considerably inthe western world in the last few decades [1, 2]. The UK hasnot been exempted, with 1.3 % of men and 3.5 % of womenreported as morbidly obese in 2009 (http://www.ic.nhs.uk/statistics-and-data-collections/health-and-lifestyles-related-surveys/health-survey-for-england/health-survey-for-england–2009-trend-tables). The UK National Bariatric Sur-gery register recorded 7,045 bariatric procedures for thefinancial year 2009 and 2010 (www.augis.org/clinical_audits/clinical_audits_nbsr.htm). Bariatric surgery is the bestlong-term treatment for morbid obesity [3, 4]. It resolvesmanyof the obesity-related co-morbidities, including hypertension,sleep apnoea, hyperlipidaemia and type 2 diabetes [5]. How-ever, this elective surgery carries risks for considerable mor-bidity and potential mortality. A large meta-analysis of>22,000 patients reported the mortality rate for gastric bypassat 0.5 % [4], with different studies publishing a mortalityrange of 0 % to 1.5 % [6–11]. Reliable pre-operative identifi-cation of high-risk patients before bariatric surgery can aid in

The paper has been presented as an oral presentation in the ThirdAnnual Scientific Meeting of the British Obesity and MetabolicSurgery Society (BOMSS) on 20th January, 2012 in Bristol, UK andaccepted for oral presentation in the Fifth Congress of the InternationalFederation for the Surgery and Metabolic Disorders European Chapter(IFSO-EC) between 26th and 28th April, 2012 in Barcelona, Spain.

H. Thomas : S. AgrawalBariatric Surgery Unit,Homerton University Hospital,Homerton Row,London E9 6SR, UK

S. Agrawal (*)9, Stonehall Avenue,Ilford IG1 3SH Essex, UKe-mail: sanju_agrawal@hotmail.com

OBES SURG (2012) 22:1135–1140DOI 10.1007/s11695-012-0663-7

better counselling about the choice of operation, preoperativeoptimization of therapy for co-morbidity and enhanced vigi-lance in the peri-operative period [7].

Recently, various risk factors have been integrated to proposedifferent scoring systems like obesity surgery mortality risk score(OS-MRS) [8], Longitudinal Assessment of Bariatric Surgery(LABS) [12] consortium risk stratification system, metabolicacuity score [13] and a nomogram for predicting surgical com-plications in bariatric surgery [14]. The OS-MRS was the firstscoring system for risk assessment and stratification in bariatricsurgery and is the only system validated independently by mul-tiple centres [6, 7, 9–11] throughout the world. The OS-MRSassigns 1 point to each of the following five preoperative varia-bles: age ≥45 years, male gender, body mass index (BMI)≥50 kg/m2, hypertension and known risk factors for pulmonaryembolism or ‘PE risk’ (previous thromboembolism, presence ofinferior vena cava filter placement, a history of right heart failureor pulmonary hypertension and obesity hypoventilation syn-drome). Patients with score 0 to 1 are classified as class ‘A’(lowest) risk group, score 2 to 3 as class ‘B’ (intermediate) riskgroup and score 4 to 5 as class ‘C’ (high) risk group. In thissystematic review, we analyse OS-MRS as a tool for predictingmortality risk in bariatric surgery.

Materials and Methods

All articles published in English after 2000 on mortality riskstratification for bariatric surgerywere considered. A systematicsearch in Medline and Embase was performed up to first ofSeptember 2011 using the medical subject's headings (MeSH)terms ‘bariatric surgery’ and ‘mortality’. Cross references andfree text searches combining the keywords ‘bariatric surgery’,‘scoring’, ‘mortality risk’, ‘risk score’ and ‘gastric bypass’wereperformed (Fig. 1). Two independent assessors (HT and SA)evaluated the abstracts to select the studies for this review. Anydifference of opinion was resolved by mutual discussion. Allstudies that used OS-MRS to stratify patients pre-operatively topredict mortality risk after bariatric surgery were included inthis review. Data was collected by the two reviewers usingspecific data collection forms. Data collected included totalnumber of patients in each study, age range, BMI, surgicalprocedure, end points, number of patients in each OSMRSgroup and the mortality in each OSMRS sub-group. The abovedata was expressed as total, percentage and in descriptive termsas applicable. Chi-square test (χ2) was used to assess thesignificance of differences between the three groups.

Results

An advanced PubMed search combining the MeSH terms‘bariatric surgery’ AND ‘mortality’ yielded 210 abstracts. A

MeSH term search in Embase provided 834 abstracts. Fur-ther cross references and free text searches using the key-words ‘bariatric surgery’, ‘scoring’, ‘mortality risk’, ‘riskscore’ and ‘gastric bypass’ provided 615 abstracts (Fig. 1).From the above searches, duplicates were removed, and 966titles were screened. Nine hundred forty titles were found tobe unrelated to mortality risk assessment in bariatric surgery.The remaining 26 abstracts were screened and 14 full textarticles assessed for eligibility. Six articles (Table 1) wereselected for this review. We excluded eight articles whichdescribed scoring systems other than OS-MRS and articleswhich did not propose a scoring system but analysed the riskfactors for mortality after bariatric surgery.

Six studies (Table 1) have reported on 9,382 patients toevaluate the validity of OS-MRS to predict the mortality riskafter bariatric surgery. Nine thousand two hundred sevenpatients (98.1 %) underwent gastric bypass (open/laparo-scopic), 141 patients (1.5 %) underwent laparoscopic ad-justable gastric band (LAGB), 30 patients (0.32 %)underwent laparoscopic sleeve gastrectomy (LSG) and 4patients (0.04 %) underwent biliopancreatic diversion/du-odenal switch (BPD/DS). Patient's age ranged from 19 to67 years, and the BMI ranged from 30 to 84. All studiesincluded mortality as the main end point. Sarela et al. [7]used a composite endpoint of adverse events consisting ofany one or more of mortality, re-intervention, re-admissionto any hospital, pulmonary embolism or blood transfusion.Dimitrios et al. [10] and Agrawal [11] included peri-operative (30-day) complications as an end point along withmortality.

There were 83 deaths among the 9,382 patients (0.88 %)with individual series reporting a mortality range from 0 %to 1.49 %. Table 2 groups data from each study into riskclassification groups A, B and C and shows the combinedcalculated mortality for each group. There were 13 deathsamong 4,912 (0.26 %) class A patients, 55 deaths among4,124 (1.33 %) class B patients and 15 deaths among 346(4.34 %) class C patients. Mortality in classes A, B and Cwas significantly different from each of the other two classes(P<0.05, χ2). Mortality of class B and class C was fivefoldand 17-fold greater compared to class A. The highest riskgroup (class C) comprised only 3.7 % of the study popula-tion but showed 18 % of all mortality (15 out of 83 deaths).Class A had 52.4 % of the study population and 15.7 % (13out of 83) of deaths, while class B had 43.9 % of the studypopulation and 66.3 % (55 out of 83) of deaths.

Discussion

The OS-MRS was originally developed by DeMaria etal. [8] in 2007 from a large single institution experiencein the USA with 2,075 cases of primary RYGB

1136 OBES SURG (2012) 22:1135–1140

procedures based upon multivariate analysis of preoper-ative factors contributing to mortality. It comprised ofthe following five significant independent preoperativevariables: age ≥45 years, male gender, BMI ≥50 kg/m2,hypertension and known risk factors for pulmonary em-bolism or ‘PE risk’. The mortality odds ratio (OR) for

BMI ≥50 kg/m2 (3.600) was highest, whereas malegender (2.795), hypertension (2.783) and PE risk(2.623) were lower and similar [8]. Age ≥45 years hadthe lowest OR for mortality (1.642) [8]. The OS-MRSwas subsequently validated in a US multi-centre study[6] with 4,431 patients that had not participated in the

Records from databases

MeSH search

(Medline = 210,

Embase = 834)

Additional records identified through cross references and free text searches

n=615

Records screened after duplicates removed n= 966

Abstracts screened n=26 Records excluded n= 12

Full-text articles assessed for eligibility n= 14

Studies included

in qualitative synthesis n= 6

Articles excluded n= 8

(scoring systems other than OSMRS and articles mentioning risk factors without a proposed

scoring system)

Quantitative synthesis

(meta-analysis)

not performed

Iden

tifi

cati

onSc

reen

ing

Elig

ibili

tyIn

clud

ed

Fig. 1 Flow chart of articlesidentified, included andexcluded

Table 1 Summary of studies using OS-MRS in bariatric surgery

Study/year Number Age in years(mean/median)

BMI(mean/median)

Procedure End point

DeMaria et al. [8], 2007 2,075 NM NM Gastric bypass(open/laparoscopic)

Mortality

DeMaria et al. [6], 2007 4,431 NM NM Gastric bypass(open/laparoscopic)

Mortality

Efthimiou et al. [9], 2009 2,121 39.7±9.9 50.7±8.6 Open gastric bypass,1,254 (59 %); LRYGB,867 (41 %)

Mortality

Dimitrios et al. [10], 2010 300 44.2±10.4 50±6.7 LRYGB Mortality, peri-operative(30-day) complications

Sarela et al. [7], 2011 381 34 (19–67) 46 (30–84) LAGB, 141 (37 %); LRYGB,206 (54 %); LSG, 30 (8 %);BPD/DS, 4 (1 %)

Composite end pointa

of adverse events(includes mortality)

Agrawal [11], 2011 74 45.1 (25–66) 47.7 (36–57) LRYGB Mortality, peri-operative(30-day) complications

Total 9,382

OS-MRS obesity surgery mortality risk score, BMI body mass index, NM not mentioned, LRYGB laparoscopic Roux-en-Y gastric bypass, LAGBlaparoscopic adjustable gastric band, LSG laparoscopic sleeve gastrectomy, BPD/DS biliopancreatic diversion/duodenal switcha Any one or more of re-intervention, blood transfusion, re-admission to hospital, pulmonary embolism or mortality

OBES SURG (2012) 22:1135–1140 1137

original development of the scoring system. Since then,the OS-MRS has been applied in the Canadian [9] andthe UK [7, 11] populations.

Apart from OS-MRS, various other risk-stratificationsystems for bariatric surgery have been reported. The LABS[12] consortium study found that four risk factors (extremesof BMI, history of venous thromboembolism, obstructivesleep apnoea or inability to walk 200 ft.) are related tocomposite outcome of complications (re-intervention,thromboembolism or hospital stay >30 days) or mortality.The LABS consortium data [12] provide a continuous riskscale rather than stratifying patients into discrete classes asin OS-MRS. Metabolic acuity score (MAS) [13], which wasreported by Blackstone and Cortes, divided patients intofour groups and incorporated diabetes and a psychologicalclassification, in addition to factors included in earlier scor-ing systems. The end point was either major complications,re-admissions to hospital or re-operation [13]. Turner et al.[14] published a nomogram which gives different scores forvarious risk factors and predicts the 30-day postoperativemorbidity and mortality depending upon the total scoreobtained. The data was obtained from the NSQIP databaseidentifying 32,426 bariatric surgery patients. Unlike theprevious studies, low serum albumin was the strongestfactor in terms of producing a highly expected probabilityof mortality for a given patient, followed by BMI, age andfunctional dependence [14]. Gupta et al. [15] has proposed amorbidity risk calculator for bariatric surgery which requiresfurther validation.

The OS-MRS was originally applied to assess the riskof mortality for gastric bypass (open and laparoscopic)only. Sarela et al. [7] extended OS-MRS to all laparo-scopic bariatric operations and included a composite endpoint of non-fatal adverse events as well as mortality. Theincidence of the composite end point of adverse eventsbetween class A and class B patients (3.5 % and 5.8 %,respectively) was not significantly different [7]. Com-pared to an open approach, laparoscopic gastric bypassis associated with substantially lower risk of adverse

events [16]. This may be due to similar risk profiles forclass A and class B patients undergoing laparoscopicbariatric procedures. Sarela et al. [7] also demonstratedthat OS-MRS and type of the bariatric operation areindependently predictive of the risk of post-operative ad-verse events. In their study, on multivariate analysis,banding had a significantly low risk of adverse event,independent of the OS-MRS class. Similarly, in the LABSconsortium study [12], the type of operation (bandingversus bypass) was a significant predictive factor for therisk of an adverse event, independent of various patient-related risk factors. The number of patients with laparo-scopic sleeve gastrectomy is very small to draw any con-clusions about its role in relation to the OS-MRS, basedon this review.

The significantly higher mortality in OS-MRS class Cpatients (4.34 % in this review) compared with class Apatients could provide an argument that RYGB surgeryshould be avoided in class C patients. Class C patients,comprised of either older super-obese men with systemichypertension or older super-obese women with systemichypertension and higher than average PE risk, also repre-sent a high-risk group for early death from the effects ofmorbid obesity. Petersen et al. [17] prospectively identi-fied 105 class C patients and applied rigorous risk-reduction strategies to obtain zero mortality in this group.Group C patients may be the ones who may get themaximum benefit from a successful bariatric procedure.Hence, surgery should not be denied to these patientsunless further evidence emerges. One approach suggestedis the use of low-risk procedures like laparoscopic sleevegastrectomy or gastric band only, or by using staged/sequential approaches in which a low-risk operation isdone first to reduce weight and improve co-morbiditiesfollowed by subsequent revision to a more durable oreffective operation [18, 19]. Unfortunately, the lower-risk procedures like LAGB are overall less successful inweight loss and co-morbidity resolution, particularly inthe super-obese patient [20].

Table 2 Number of deaths/number of patients (mortality as a percent) in the different OS-MRS risk classification groups A, B and C for each of thesix studies

Class DeMaria et al.[8], 2007

DeMaria et al.[6], 2007

Efthimiou et al.[9], 2009

Dimitrios et al.[10], 2010

Sarela et al.[7], 2011

Agrawal[11], 2011

Total

A 3/957 (0.31 %) 5/2,164 (0.23 %) 5/1,385 (0.36 %) 0/137 (0 %) 0/229 (0 %) 0/40 (0 %) 13/4,912 (0.26 %)*

B 19/999 (1.9 %) 25/2,142 (1.17 %) 10/671 (1.49 %) 1/144 (0.69 %) 0/137 (0 %) 0/31 (0 %) 55/4,124 (1.33 %)*

C 9/119 (7.56 %) 3/125 (2.4 %) 2/65 (3.08 %) 0/19 (0 %) 1/15 (6.67 %) 0/3 (0 %) 15/346 (4.34 %)*

Total 31/2,075 (1.49 %) 33/4,431 (0.74 %) 17/2,121 (0.80 %) 1/300 (0.33 %) 1/381 (0.26 %) 0/74 (0 %) 83/9,382 (0.88 %)

Compiled data from all six studies demonstrated that mortality was significantly different between each groups

OS-MRS obesity surgery mortality risk score

*P<0.05 by χ2

1138 OBES SURG (2012) 22:1135–1140

Out of the risk factors comprising the OS-MRS, thepreoperative risk reduction for a particular patient is limitedto reducing the preoperative BMI only. Whereas modifyingother risk factors may not be possible (e.g. male sex) oreffective, earlier intervention in younger healthier patientswould avoid the influence of advanced age and co-morbidities on mortality after surgery for morbid obesity[21]. A recent study by Adams et al. of more than 7,000bypass patients and an equal number of controls showed that1-year mortality was 0.52 % and 0.53 %, respectively [22].Therefore, surgical mortality should not exceed 0.5 % tomatch the effect at 12 months of not operating in thispopulation [22]. To achieve this low mortality, health policyorganizations and providers should fund bariatric surgerywhen they are younger and less obese and have fewerobesity-related co-morbidities, as the postoperative mortal-ity will be substantially lower at this stage.

The OS-MRS is attractive for its simplicity of applica-tion and interpretation by clinicians in their everydaypractice. All five predictive factors associated with in-creased mortality can be identified preoperatively. Apartfrom identifying high-risk patients, it can aid informedconsent discussions and guide surgical decision makingby estimating the risk of postoperative mortality afterbariatric surgery. Additionally, it also allows standardiza-tion of outcome comparisons between different bariatricunits throughout the world. This would mean justificationof mortality for bariatric units performing high-risk casesthat might appear high but is within accepted standardsafter risk stratification.

As with every other scoring system, there are limitationsof using the OS-MRS in bariatric surgery. Three of the sixstudies in this review looked at mortality as the only endpoint for OS-MRS. Though it has the advantage of being aneasily defined and definite end point for assessment of a‘bad outcome’, the frequency of mortality is low in bariatricsurgery making it a difficult end point for analysis fromstatistical standpoint [6]. However, it is reasonable to as-sume that the higher rate of mortality found with classes Band C of the OS-MRS correlates with a higher incidence ofcomplications, as has been shown in a recent study [7].

Another limitation is using this scoring system for revi-sional bariatric surgery. The OS-MRS was specificallydesigned for patients undergoing primary gastric bypasssurgery. The LABS study [12] convincingly shows that the30-day adverse outcomes are significantly higher after revi-sional bariatric procedures compared to primary bariatricoperations. It has been suggested that consideration shouldbe given for inclusion of a separate category in the OS-MRSto specify primary or revisional procedures [7].

Further studies are required to assess if OS-MRS can beimproved by altering the patient factors to better predictmortality and also predict the complications after bariatric

surgery. Non-patient-related factors like surgeon's experi-ence and bariatric surgery volume–outcome relation needto be factored in.

The limitation of this review is that only articles inEnglish obtained from the major databases are included.Further evidence may be available in the grey literatureand in other languages.

In conclusion, this systematic review confirms that theOS-MRS stratifies the mortality risk in the three risk classi-fication subgroups of patients. The OS-MRS can be used forpre-operative identification of high-risk patients undergoingprimary RYGB surgery.

Conflicts of interest Sanjay Agrawal and Harun Thomas have noconflicts of interest to declare regarding this article.

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