Absence of Weekend and Out-of-Hours Effects in Emergency Abdominal Surgery: A Retrospective Cohort Study

Technical Summary: Absence of Weekend and Out-of-Hours Effects in Emergency Abdominal Surgery

Problem Statement
The "weekend effect" is a well-documented phenomenon wherein patients undergoing medical procedures on weekends experience worse clinical outcomes compared to those treated on weekdays. While this effect has been observed in various conditions, including myocardial infarction, pulmonary embolism, and certain surgical emergencies, its presence and mechanisms in emergency abdominal surgery remain inconsistent across literature. Proposed causes for this disparity include reduced staffing levels, limited availability of experienced personnel and diagnostic services, and higher disease severity among weekend admissions. However, existing studies yield heterogeneous results, with some failing to demonstrate a weekend effect in specific surgical contexts. This study aims to clarify whether the timing of emergency abdominal surgery (weekends vs. weekdays, and out-of-hours vs. working hours) independently influences clinical outcomes and hospitalization costs.

Methodology
This research is a retrospective cohort study conducted at Yao Tokushukai General Hospital involving 125 consecutive patients who underwent emergency abdominal surgery between April 2022 and March 2024. The study utilized three distinct analytical approaches to evaluate timing effects:

1. Method 1 (Out-of-Hours Comparison): Compared weekend cases against weekday out-of-hours cases (5:00 p.m. to 8:30 a.m.) to isolate the effect of the day of the week independent of working hours. This included sub-analyses comparing Monday vs. Friday and early-week vs. late-week cases.
2. Method 2 (Working Hours Comparison): Compared weekend cases against weekday working hours (8:30 a.m. to 5:00 p.m.) to assess the impact of surgery timing relative to optimal staffing conditions.
3. Method 3 (Entire Weekday Comparison): Compared weekend cases against the entire weekday cohort (including both working and out-of-hours periods) to evaluate the overall weekend effect.

Data were extracted from electronic medical records, capturing demographic variables (age, sex, BMI), preoperative indices (PNI, ASA-PS, SII), perioperative factors (surgical approach, blood loss, operative time), and outcomes. The primary outcome was in-hospital mortality; secondary outcomes included postoperative length of stay, surgical site infection (SSI) rates, and total hospitalization costs. Statistical analyses employed the Mann–Whitney U test for continuous variables, chi-square or Fisher's exact tests for categorical variables, and univariate logistic regression for mortality associations.

Key Results
The study found no statistically significant differences between weekend and weekday groups across any of the three analytical methods.

• Patient Characteristics: No significant differences were observed in demographics, preoperative severity indices, or comorbidity burdens between groups.
• Operative Variables: Surgical approaches (60.0% laparoscopic, 40.0% open), operative times, and intraoperative blood loss were comparable.
• Clinical Outcomes: In-hospital mortality, postoperative length of stay, and SSI rates showed no significant variation based on surgery timing.
• Economic Outcomes: Total hospitalization costs, including surgical and ICU expenses, were comparable regardless of whether surgery occurred on weekends, weekday working hours, or weekday out-of-hours.

These findings remained consistent across all sub-analyses, including temporal comparisons of early-week versus late-week cases.

Significance and Claims
The authors conclude that in their specific institutional setting, there is no evidence of a weekend or out-of-hours effect in emergency abdominal surgery. The study posits that the absence of such an effect is likely attributable to a well-resourced healthcare system characterized by:

• Consistent Staffing: On-site availability of essential personnel, including board-certified surgeons, radiology technologists, and laboratory staff, during all hours.
• Standardized Postoperative Care: Strict adherence to nurse-to-patient ratios in Intensive Care Units (1:2) and High-Care Units (1:4), ensuring uniform postoperative management.
• Protocol Implementation: The use of Enhanced Recovery After Surgery (ERAS) protocols and standardized clinical pathways to minimize practice variability.

The paper suggests that when healthcare delivery systems are adequately structured with consistent resource availability, the timing of surgery may not independently influence outcomes. The authors further contextualize their findings with a literature review indicating that the presence of a weekend effect varies significantly by disease category and geographic region, with surgical studies showing a higher proportion of "no effect" findings compared to internal medicine. The study concludes that the weekend effect may disappear once a robust healthcare system is fully established, implying that disparities often stem from systemic resource allocation rather than the day of the week itself.

Limitations
The authors acknowledge several limitations, including the retrospective design which limits causal inference, the potential for residual confounding regarding patient severity, the single-center nature of the study which may affect generalizability, and a relatively small sample size that limits statistical power for subgroup analyses. Additionally, the study did not include a comparison with internal medicine populations.