OBJECTIVES : Chile has transitioned from a bottom-up costing strategy towards DRGs. Many public providers are still reporting difficulties implementing this new system and concerns surrounding the costing method and its impact on resources.

METHODS : A cost-study for bariatric surgery was carried-out from the public perspective using two methodologies, for the same public provider. The first method consisted in a bottom-up costing based on an exhaustive analysis of pre-operative, intra-operative, and follow-up periods, complemented with a panel of experts. The investigators identified a homogenous payment basis, cost drivers (devices, length of stay, drugs, complications, medical care), and vectorial variables: price, quantity, expenditure, and risk for the horizon of one-year in cost matrices. The second methodology was based on DRGs. The public provider's DRG data was retrieved (IR-DRGs, DRG-weight, DRG base-price, length of hospitalization, outliers, etc.) to estimate the cost distribution. Univariate sensitivity analysis was performed on variables identified as most relevant (price): gastroduodenoscopy (+58%), basic (+187%), and Intensive Care Unit (+192%) bed days. For this method two scenarios were identified (average and conservative).

RESULTS : The bottom-up strategy identified an average cost of USD$ S3,508, and USD$ 3,827 (+9.10%), following the sensitivity analysis. The DRG average cost was estimated as USD$ 5,891 and USD$ 4,865 (-17,41%) in a conservative scenario. The difference between bottom-up average cost and DRG average cost was USD$ 2,382 (1.68 times). In the sensitivity analysis, the difference between the bottom-up and DRG average costs was USD$ 2,063 (1.54 times), and USD$ 1,038 (1.27 times) against a conservative DRG cost. The comparison of all costs results in a difference of USD$ 892 (1.23 times).

CONCLUSIONS : DRGs allocates more resources to bariatric surgery in all tested scenarios. The work based on cost matrices contributed to providers identifying financially sustainable resource use and helped them transition from bundled payments based on bottom-up costing to DRGs.