According to the ‘2014 Korean Interns & Residents Survey,’ the average weekly working time of trainee doctors was 93 hours.1 ‘Act on the improvement of training conditions and status of medical residents’ was officially enacted on December 22, 2015, and was announced to the public through the ‘Statutes of the Republic of Korea.’2 Its main proposal was limiting resident work hours to 88 hours per week, including 8 hours for education purposes.3 To compensate for the residents' reduced working hours, hospitalist, physician assistant and nurse practitioner systems have been discussed. However, because of no established legal status (physician assistant and nurse practitioner),4 shortages of candidates (hospitalist) and the specialty of critical care, the application of these systems is not easy in the intensive care units (ICUs) of Korea.

Medical resources such as medical staff and equipment are concentrated in ICUs. Among the medical staff, medical residents are essentially needed to operate the ICU. However, there are not enough medical residents in reality, especially at regional hospitals.5 In addition, after restriction of residents' working hours according to the resident law, it has been more requested that substitutes for medical residents be placed in the ICU. Because of these reasons, Korean regional academic hospitals may be likely to face running ICUs without residents in the near future.

If there are no alternatives, an intensivist has no choice but to become actively involved and endure overwork from managing critically ill patients in the ICU. We compared the outcomes of two ICUs in a regional academic hospital: one was operated by a critical care specialist with residents, and the other was operated by a critical care specialist without residents. The primary outcome was overall ICU mortality. The secondary outcomes were length of stay in the ICU, extracorporeal membrane oxygenation (ECMO), continuous renal replacement therapy (CRRT), cardiopulmonary resuscitation (CPR), and advanced care planning decisions such as physician orders for life-sustaining treatment (POLST) before death.

During the study period, 1,700 patients were admitted to the EICU, and 743 patients were admitted to the MICU at Ulsan University Hospital. We excluded 1,819 patients (1,527 patients in EICU and 292 patients in MICU) who were admitted to two ICUs from the emergency room, outpatient department, other ICUs and sub-ICUs. We further excluded 310 patients (103 patients in EICU and 207 patients in MICU): those who were not hospitalized in the department of internal medicine (n = 107), those who were hospitalized in the cardiology department (n = 160), those who transferred to other ICUs (n = 36), those who were repeatedly admitted to each ICU (n = 17), and those who were under 18 years of age (n = 1) (Fig. 2).

Our study results suggested that intensivists' direct management without residents might be associated with a lower ICU mortality than that resulting from ICU residents' management under intensivist supervision at academic ICUs. In addition, intensivists' direct management was also found to be associated with lower CRRT application and CPR in the ICU and more advanced care planning decisions before death. One study suggested that the absence of emergency medicine residents did not affect the activity and quality of patient management in the academic emergency department.10 Another study reported that direct staff physician (instead of resident) management resulted in fewer laboratory tests ordered, fewer radiographs ordered, and shorter lengths of stays in the emergency department.11 However, these studies evaluated the effect of staff physician's direct management without residents in non-critically ill patients and over a short period of time, and there were no data evaluating the ICU outcomes according to intensivist physician's direct management at academic ICUs. Our present study is, to our knowledge, the first to assess such outcomes in the ICU over a relatively long period.

This investigation was performed with an intensivist crossover study design between the two ICUs. We initially did not intend to conceive this study design. Between the two ICUs, there was a higher workload associated with the absence of residents in the MICU, and two intensivists agreed to work at each ICU alternatively after a mutual consultation. Through this arrangement, we minimized the difference between the two intensivists in ability that might have influenced the ICU outcomes, and consequentially, this design is a strength of our study.

ICU outcomes are influenced by many factors, such as ICU staff, equipment, ICU operation methods, and so on. Among these factors, the ICU staff is composed of residents, fellows, intensivists, nurses, respiratory care practitioners, pharmacists and nutritionists.7 In most academic hospitals, ICUs are usually operated by residents under the supervision of a fellow, attending staff or intensivist. Although one large study reported that patients managed by intensivists had a higher mortality than patients who were not,12 most studies have suggested that high-intensity critical care specialist staffing is associated with improved ICU outcomes.813141516 Furthermore, some authors have asserted that a 24-hour intensivist presence in the ICU would improve diagnostic and therapeutic efficiency, particularly for high-risk patients.171819

Considering the above studies and our results, ICU intensivist staffing might be associated with favorable ICU outcomes, and more active direct intervention of an ICU intensivist without residents was associated with much better ICU outcomes than indirect management through residents. We thought the better MICU outcomes resulted from the intensivists' specialty, rapid decision making, appropriate management, skilled procedures and responsibility, although the doctor-to-bed ratio of the EICU was higher than that of the MICU during the daytime (3:20 vs. 1:12) in our study. In addition, direct management by an intensivist might lead to patient, family and caregiver satisfaction by providing high-quality care in the ICU.20

However, there are several practical problems associated with an intensivist's direct management of the ICU. First, the number of intensivists is not enough to cover all ICUs. There has continued to be a nationwide shortage of intensivists. We expect the shortage of intensivist to continue in the future because the population is aging, which will lead to an increase in the burden of acute and chronic illnesses and the need for critical care services.2122 It is therefore necessary to provide institutional strategies for increasing the intensivist volume and decreasing prolonged, ineffective and harmful critical care for effective intensivist care.2223 Second, recruitment of intensivists is difficult because of the difficult working conditions, such as overwork, night duties, conflict with colleagues and continual exposure to stressful situations.24 In our study, intensivists were also overworked during the MICU duty period. Their average weekly work time was approximately 90 hours (day duty time: 55 hours/week [11 hours/day × 5 days/week]; shift overlap & preview times: 5 hours/week [0.5 hours/day × 2 × 5 days/week]; night duty time: approximately 20 hours/week [intensivist’s night duty was every 5–6 days, weekday night duty time: 13 hours and weekend night duty time: 24 hours], emergency call, research, education of trainees and so on). Specific interventions to prevent or treat burnout syndromes are needed, such as limiting the maximum number of days worked consecutively, actively increasing the number of physician assistants, suitable economic rewards, stress reduction training, relaxation techniques, and other measures.2224 Third, there were concerns about rising medical costs because of the substitution of intensivists for residents. Considering the public benefits of medical treatment and the relationship of the health insurance system, we thought that financial and social policy support was required from not only the hospital itself but also the government to solve this problem.2526

Our study had several limitations. First, it was a retrospective observational study. Selection bias might have occurred, and some of the patients' data were incomplete. However, we tried to minimize the differences between the two ICUs by carefully selecting and enrolling the study patients. Second, our investigation was conducted as an outcome evaluation of ICU patients from general wards at a single tertiary referral center, and although we recruited as many patients as possible, the sample size was not large enough. Selection bias cannot be excluded, and larger-scale multicenter studies are required to obtain more accurate and reliable results. Third, the two ICUs had different ICU bed capacities (EICU vs. MICU, 20 beds vs. 12 beds, respectively), main medical teams during the day (1 intensivist & 2 residents vs. 1 intensivist, respectively), and patient compositions (mainly from the emergency room vs. general wards, respectively). Consequently, the study results should be interpreted with caution. Fourth, our study patients had a high overall ICU mortality, which we believe is because of the high frequency of poor prognosis factors, such as malignancies, immunosuppression, and high APACHE II scores. The study protocol, which stipulated that only patients transferred to the ICU because of management failure from general wards were enrolled, is also likely to have contributed to the high ICU mortality. Fifth, our study revealed the superiority of intensivist’s direct management to ICU patients in terms of ICU outcomes. However, we could not provide solutions for the intensivists' direct management-related problems. Further financial and social policy support is required, and our retrospective data on direct management by intensivists may represent a major starting point for a randomized controlled study.

Intensivists play a central role in critical care medicine. In our study, intensivists' direct management without residents was associated with significantly better overall ICU mortality, CRRT application, CPR, and advance care planning decisions before death than indirect management through medical residents. Our findings suggest that larger prospective randomized trials on intensivists' direct management of ICU patients are warranted. Furthermore, we believe that additional approaches to establishing the proper environment for active work by intensivists are needed.