Obesity Surgery Mortality Risk Score (OS-MRS)
Validated risk score predicting 90-day mortality following bariatric surgery. Five risk factors: BMI above 50, male sex, hypertension, known risk factors for pulmonary embolism, and age above 45 years. Score 0-5; class A (0-1) = low risk (0.31% mortality); class B (2-3) = intermediate (1.9%); class C (4-5) = high risk (7.56%). From DeMaria et al. 2007.
Score interpretation
OS-MRS 0-1 -- low risk; 90-day mortality approximately 0.31%
→ Standard bariatric surgery pathway; laparoscopic Roux-en-Y gastric bypass or sleeve gastrectomy appropriate if NICE TA1 criteria met (BMI above 40, or above 35 with comorbidities, or above 30 with T2DM not controlled by medications); 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 -- intermediate risk; 90-day mortality approximately 1.9%
→ 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 -- high risk; 90-day mortality approximately 7.56%; 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 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; discussion 583-584.
- NICE TA1. Obesity: guidance on the prevention and management of obesity. NICE. 2006 (updated 2023).
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.