The results of the present study indicate that in our hospital, which is open 7 days a week, patients who received surgical care on weekends had higher 30-day mortality than those who received surgical care on weekdays; however, this association was only significant in the case of emergency surgery. The number of emergency surgeries performed on weekends accounted for one-fourth of the total number of emergency cases; this ratio is similar to that reported around the world in previous studies[9,19]. Overall, mortality for emergency surgery (30‰) was not high compared with previous studies, but the adjusted OR (2.7) was higher[9,10]. However, a difference was seen in the adjusted OR between surgeries on the day of hospitalization and after. In research examining the weekend effect in regard to surgeries for common diseases on the day of hospitalization, increased postoperative complications, longer lengths of stay and higher hospital charges were observed, but not inpatient mortality[20]. In addition, circumstantial evidence that the weekend effect is mitigated by improved staffing of doctors and nurses as well as ensuring the continuity of care, has been presented[21–24]. Thus, in outpatient clinics, carrying out examinations on weekends is considered to help provide, at least in part, the continuity of care for patients admitted as acute medical emergencies.
The disparity in mortality between weekday and weekend emergency surgery after the day of hospitalization remains an issue that will require consideration of future countermeasures. There are several possible explanations for this disparity. First, patients who underwent surgery on weekends were in a worse condition than those who underwent surgery on weekdays. It is therefore possible that we may not have adjusted for differences in severity-of-illness adequately. Several cases in which surgery was performed multiple times because of the need for reoperation or the deterioration of the patient’s condition during the hospitalization period. These types of surgical patients have often been excluded from past studies. Of the 416 emergency surgeries from the day after admission, 75 (57 on weekdays, 18 on weekends) were second and subsequent surgeries; six (3 on weekdays, 3 on weekends) of the 14 deaths that occurred within 30 days were the result of second and subsequent surgeries. Second, the results depend on differences in care, as mentioned in previous studies. Even though our hospital’s outpatient clinic is open and carries out elective surgeries on weekends, patients visiting certain departments such as cardiovascular surgery or neurosurgery, which do not routinely perform elective surgery on weekends, may be more vulnerable because these surgeries tend to be performed by ad hoc teams with weekend nursing staff, who are less familiar with operating theatres and the surgeries carried out by these departments[25]. Further study is needed to gain a better understanding of the patient-, preoperative-, anaesthetic-, surgical- and postoperative-related underlying mechanism that lead to worse outcomes for those undergoing emergency surgery on the weekend.
On the other hand, when elective surgery was conducted on the weekend, no association was apparent, which differs from the results of past studies[14,25,26]. Also, in this study, weekend patients were younger with a lower ASA class; such patients tended to have fewer comorbidities and a longer waiting time in England[14], and to be older with more comorbidities (especially cancer) in Canada[26]. Compared with previous similar reports from England (4.5%) and Canada (0.76%), our hospital conducted elective surgery more frequently on weekends (18%)[14,26]. The department with the highest number of surgeries on weekends was digestive surgery, followed by orthopaedics, otolaryngology, dentistry and plastic surgery. The departments of digestive surgery and orthopaedics conducted both elective and emergency surgeries, while the three remaining departments carried out elective surgery mostly on weekends. The imbalance of the population and surgical characteristics may reflect a clinical selection bias, wherein weekend surgery was targeted for patients at lower risk.
Both the U.K. study, which compared elective and non-elective admissions, and the U.S. study, which compared elective and non-elective surgical patients, reported that the elective setting had a higher risk for 30-day mortality than the non-elective setting[25,27]. On the other hand, in the present study, the weekend effect was observed for only emergency surgeries, and elective surgeries were safe to perform. In the U.K., the implementation of a 7-day service programme did not result in improved clinical outcomes[28,29]. In the present study, whether 7-day service including elective surgery is a beneficial approach for mitigating the weekend effect on emergency surgery remains unclear.
Although the cause of the weekend effect could not be identified in the present study, health administrators and policy makers who are considering restructuring the hospital workweek or weekend elective surgeries should consider the results of this study and related research findings carefully to help cope with the increased demand for such services due to the aging population and improve system efficiency. The 5-day workweek model is a long-standing tradition of medical culture, and converting to a 7-day model is not something that can be done easily. In our hospital, the implementation of weekend elective surgery as a 7-day service is premised on reforms in the way doctors work, and in practice, not all departments can make the proper adjustments. In the U.S., patients undergoing moderate-to-high risk surgery on the weekend have a clinically significantly increased risk of death and major complications compared with patients undergoing similar surgery on weekdays[25]. Therefore, it is important to select medical departments, procedure type and patients in consideration of patient safety.