Aim: This study investigates the impact of admission timing on intensive care unit (ICU) outcomes for patients transferred from internal medicine wards to the ICU at a tertiary university hospital.

Study Design: A retrospective cohort study was conducted in a nine-bed medical ICU at a hospital from January 2020 to November 2022. Patients ≥18 years old admitted from internal medicine wards were included. Statistical analyses compared outcomes based on admission timing and ICU mortality.

Results: Of 316 patients, 59% were admitted during off-hours, with an overall ICU mortality of 56%. No difference in mortality was found between office-hour and off-hour admissions (52% vs 59%, p=0.17). There were no differences in the length of ICU stay (5[3-11] days vs. 5[3-12] days, p=0.72), invasive (60% vs. 61%, p=0.47), or non-invasive mechanical ventilation (17% vs. 16%, p=0.44) requirement, intermittent (30% vs. 30%, p=0.54) or continuous renal replacement therapy (22% vs 26%, p=0.24) requirement, and nosocomial infection (49% vs 52%, p=0.35) rate based on admission timing. Independent mortality risk factors included invasive mechanical ventilation requirement (OR: 3.33 [95% CI: 1.49-7.29], p<0.01), the presence of circulatory shock (OR: 2.02 [95% CI: 1.29-2.89], p<0.01) and solid cancer (OR: 1.98 [95% CI: 1.22-3.19], p<0.01), and APACHE II score (OR: 1.08 [95% CI: 1.01-1.16] p=0.04).

Conclusion: Unlike some previous studies, we found no difference in ICU mortality between office-hour and off-hour admissions in patients admitted from internal medicine wards. This finding suggests that equal staffing distribution throughout the day may prevent adverse effects of out-of-hours admissions, supporting better organization in specialized ICUs.