Previous research showed that intensivist staffing in the ICU leads to a significant reduction in ICU and in-hospital mortality, and length of stay. [3–9] However, the Society of Critical Care Medicine guidelines do not recommend 24/7 intensivist staffing in the ICU in high-intensity ICU models  based on only one randomized cohort study performed in the medical ICU.  To date, there is lack of evidence about whether admission in the SICU during after-hours is safe.
In this study, we investigated whether SICU admission during after-hours is associated with in-hospital mortality compared with admission during work-hours among patients who underwent surgical treatment. We found that admission to the SICU during after-hours increased the in-hospital mortality (OR = 2.526; 95% CI = 1.010–6.320, p = 0.048; Table 3). Moreover, unplanned admissions, APACHE II score ≥ 25, need for ventilator support, and administration of inotropic drugs were also markedly higher in the after-hours group than in the work-hours group. These findings are important for the allocation and distribution of ICU resources, including intensivists.
Two systematic reviews reported that while patients admitted to an ICU over the weekend are at a higher risk of death, admission to the ICU during night hours did not appear to be associated with increased mortality. [16, 17] The authors inferred that lower level of staffing and intensity of care provided by many hospitals over the weekend might account for this finding. [5, 16, 17] In our study, “after-hours” was defined as the absence of the intensivists, and the results showed increased mortality in patients admitted to the SICU during after-hours. Although there was no change in the level of nurse staffing and intensity of care, and real-time consultation was provided by work-hour intensivists, absence of the intensivist might affect resolute decisions required during critical illness.
One recent study found that the out-of-office hours’ ICU admission after elective surgery was associated with significantly higher rates of postoperative complications, increased hospital length-of-stay, and increased inter-hospital transfers.  In our study, the subgroup analysis of patients admitted for planned surgery showed a higher median length of hospitalization in the after-hours group than in the work-hours group. This result might suggest that the cases with higher risk are referred to the SICU outside regular work-hours. Therefore, surgeons and anesthesiologists should plan surgeries of patients with higher risk towards the beginning of the surgical schedule for the day.
Despite the retrospective design and short period of the study, these findings might reflect the current status of most ICUs in Korea, considering that 82.3% of all ICUs are either in university teaching hospitals or in university-affiliated hospitals.  One of the main strengths of this study is that we specifically targeted surgical patients in conducting the research. Recently, O et al  reported a retrospective observational study of 10,708 postoperative patients showing an increased risk of 30-day mortality in the group without intensivist coverage. Compared to the previous studies performed in mixed or medical ICUs, [12, 14, 21–28] we only focused on postoperative SICU admissions. In our study, we included patients with unplanned admission including those who underwent emergency operations, those who developed postoperative sepsis, bleeding or other medical complications and we also included patients who had an elective postoperative status. The enrolled patients in this study represented the general population of patients who required intensive care postoperatively, and the results were consistent with those of previous studies. [18, 20, 29] Additionally, we performed subgroup analyses according to the causes of SICU admission to adjust for negative effects of unplanned admission on mortality.