Obesity Surgery Mortality Risk Score (OS-MRS)
Obesity Surgery Mortality Risk Score for gastric bypass: 1 point each for BMI ≥ 50 kg/m², male sex, hypertension, pulmonary embolism risk factors and age ≥ 45 years. Class A (0–1), B (2–3), C (4–5). DeMaria 2007, validated in a multicentre cohort the same year.
Score interpretation
OS-MRS 0–1: 90-day mortality 0.31 % (derivation) / 0.2 % (multicentre validation).
→ Standard bariatric surgery pathway; laparoscopic Roux-en-Y gastric bypass or sleeve gastrectomy appropriate if NICE NG246 referral criteria (BMI ≥ 40, or 35–39.9 with a significant weight-related condition; expedited assessment for recent-onset type 2 diabetes at BMI ≥ 35, considered at 30–34.9) are met; standard anaesthetic assessment; preoperative: very low calorie diet (VLCD) for 2-4 weeks (liver shrinkage); VTE prophylaxis: LMWH plus pneumatic compression; post-operative: early mobilisation, bariatric diet programme, follow-up at 6 weeks, 6 months, 12 months then annually.
OS-MRS 2–3: 90-day mortality 1.90 % (derivation) / 1.1 % (multicentre validation).
→ Bariatric surgery at experienced high-volume centre with ICU capability; senior anaesthetic and surgical team; cardiology pre-assessment if age above 45 or multiple cardiovascular risk factors; sleep study if OSA suspected; echocardiogram if pulmonary hypertension concern; extended VLCD preoperatively; enhanced VTE prophylaxis; HDU admission planned post-operatively; ensure adequate preoperative optimisation (blood pressure control, diabetes management, smoking cessation at least 4-6 weeks); discuss risks vs benefits clearly with patient; ensure bariatric MDT decision.
OS-MRS 4–5: 90-day mortality 7.56 % (derivation) / 2.4 % (multicentre validation); careful risk-benefit discussion required.
→ Highest-volume bariatric centre with full ICU; senior consultant surgeon and anaesthetist only; comprehensive preoperative workup: cardiology, respiratory, haematology, psychology; right heart catheterisation if pulmonary hypertension suspected; consider two-stage approach (intragastric balloon or sleeve gastrectomy first to reduce BMI before gastric bypass); document detailed consent including mortality risk; bariatric MDT review with consultant physician; if intraoperative difficulty anticipated: early conversion to open; ICU admission post-operatively; extended VTE prophylaxis (28 days post-discharge); consider whether surgery is appropriate vs continued medical management.
Interpretation bands for the OS-MRS Bariatric Risk. Apply clinical judgement and local guidance.
References
- DeMaria EJ, Portenier D, Wolfe L. Obesity surgery mortality risk score: proposal for a clinically useful score to predict mortality risk in patients undergoing gastric bypass. Surg Obes Relat Dis. 2007;3(2):134–140.
- DeMaria EJ, et al. Validation of the obesity surgery mortality risk score in a multicenter study proves it stratifies mortality risk in patients undergoing gastric bypass for morbid obesity. Ann Surg. 2007;246(4):578–582.
- NICE NG246. Overweight and obesity management. 2025.
Related
Curated clinical cross-links plus same-class fallbacks.
- Protamine Sulphate (Heparin Reversal) · Heparin Reversal / Cardiac Surgery
- Semaglutide · GLP-1 Receptor Agonist
- Liraglutide · GLP-1 Receptor Agonist
- Tirzepatide · Dual GIP/GLP-1 Receptor Agonist — Type 2 Diabetes / Obesity
- Naltrexone with bupropion · Anti-obesity (combination)
- Recombinant Factor VIIa · Bypass Agent — Haemophilia with Inhibitors
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.
