Introduction:
Currently, patient risk stratification plays a central role in the daily practice of anaesthesiologists. Obesity Surgery Mortality Risk Score (OS-MRS) was developed and validated to predict mortality at 90 days for patients submitted to bariatric surgery. The score ranges from 0 to 5, with 1 point attributed per each of 5 factors According to this, patients are classified as Class A (OS-MRS=0-1), B (OS-MRS=2-3) or C (OS-MRS=4-5), with expected mortality of 0,26%, 1,33% or 4,34%, respectively. The present study aimed to show if OS-MRS is a good score for the prediction of hospital length of stay following bariatric surgery in a tertiary hospital.

Methods:
After approval by the institutional review board, the clinical processes of 393 patients submitted to gastric bypass surgery between January 2010 and May 2015 in a tertiary hospital, in Portugal, were accessed. Clinical and demographic data, such as age, gender, American Society of Anaesthesiology (ASA) Physical Status Classification, weight, height, OS-MRS, surgery time, intraoperative and immediate postoperative analgesia, hospital length of stay and 90 days outcome were collected. The statistical analysis was performed using SPSS® version 23 – Kruskal-Wallis with Dunn post hoc test (p<0,05) was used to compare groups based on OS-MRS (Classes A, B and C).

Results:
A total of 393 (82,2% female) patients, with average age of 43,91 years old (±10,59), were included in the study. ASA 2 – 21,2%; ASA 3 – 78,4%. Average Body Mass Index (BMI) was 44,20 Kg/m2 (±6,36) and duration of surgery 132,52 minutes (±40,23).
168 patients were classified as OS-MRS Class A, 184 as class B and 41 as Class C, with average hospital length of stay, in days, of 3,2 (±1), 3,5 (±1,2) and 3,8 (±1,3), respectively. The difference between Class A and Class C was statistically significant (p<0,05).

Conclusion:
It seems to be a positive relation between OS-MRS classification and hospital length of stay, with patients classified with higher classes spending more time in the hospital.

The usefulness of OS-MRS in the prediction of hospital length of stay - a retrospective audit in a tertiary hospital