ICU mortality indicates the severity of disease, healthcare quality, and the efficacy of interventions. The severity scores are tools to predict the risk of mortality in the ICU, and the APACHE II score is frequently used for this purpose. However, studies validating the score in Colombia are limited. There is uncertainty about the precision and discrimination capacity of the APACHE II score in a population that varies from the original, with varying diseases, and in a different timeline. The investigators determined to evaluate: 1. Evaluate the rate of mortality in the ICU by type of disease and type of admission. 2. The factors associated with mortality. 3. Validate the performance of the APACHE II score as a predictor of mortality.

Introduction Mortality serves as an indicator of healthcare quality in the intensive care unit. The APACHE II score is a practical tool for predicting mortality, though its application varies. Studies validating the APACHE II score in Colombia are limited. This study aimed to evaluate the performance of the Acute Physiology and Chronic Health Evaluation (APACHE) II score as a predictor of mortality in the intensive care unit of a hospital in Villavicencio, Colombia.

Methodology Design: In this single-center, retrospective cohort, consecutive cases were observed from admission to discharge from the ICU. The demographic characteristics, diagnosis type, admission origin, and APACHE II score were systematically calculated on a database, and the cases were divided into two populations for comparison based on the outcome.

Setting: The study was performed in the ICU of Hospital Departamental de Villavicencio, a reference institution for the Orinoco region. It has 350 beds, four adult polyvalent critical care units with 40 beds, and the only oncology unit in the zone.

Patients: Critically ill patients admitted from January 2022 to June 2025 were included.

Sample: The study included all patients in the discharge database and used no sampling method.

Inclusions: All adult patients older than 18 years admitted during the study period were included.

Exclusions: The analysis excluded patients admitted as intermediate care (low therapeutic intervention with a TISS [Therapeutic Intervention Scoring System]-28 score below 20 points).

Data collection: The information of all patients admitted to the ICU was systematically collected from the clinical chart on discharge and uploaded to an electronic database in a standardized online format. The severity score was calculated within the first 24 hours of admission. Demographic characteristics, insurance, diagnosis information, APACHE II score, TISS-28 score, mechanical ventilation duration, and outcome were recorded. The outcomes evaluated were mortality (early or late), ICU length of stay, and mechanical ventilation duration.

Analysis plan: The investigators used Jamovi 2.6.44 program for the analysis, and Prism 10.6.1 or Wizard 1.9.49 for the graphics. Categorical variables are presented as frequencies and proportions; continuous variables are presented as their central tendency and dispersion, after verifying normality. The Chi-square test was selected to compare categorical variables, and the t-test or the Mann-Whitney test to compare quantitative variables. A value of p < 0.01 was chosen as statistical significance. A logistic regression analysis was performed to confirm the effect of APACHE II score on the outcome. Observed mortality rate (early or late [more than 48 hours) was compared with the expected rate (standardized or SMR). The discrimination of the score was determined by the area under the curve (AUC) of the receiver operating characteristic (ROC), with a closer value to 1 for diagnosis and type of admission.

Ethical aspects: The hospital research committee previously approved the database analysis and waived informed consent, as the study was classified as low-risk research in accordance with national regulations. The project was registered on the platform ClinicalTrials.gov in accordance with the Helsinki Declaration, including observational trials.](streamdown:incomplete-link)

Inclusion Criteria:

• All adult patients older than 18 admitted to the intensive care unit during the study period.

Exclusion Criteria:

• Patients admitted for intermediate care (low therapeutic intervention with a TISS [Therapeutic Intervention Scoring System] - 28 score below 20 points). Patients derived to other institutions.

Adult critically ill patients with a high need of support and intervention in the intensive care unit.

The data contains sensitive information from patients.