A large number of studies have analyzed the association of weekend admissions with significantly higher in-hospital mortality rates compared with weekday admissions (“weekend effect”) in a wide range of patient populations, diseases, health care providers, and health systems.1,2 Major health policy interventions have been proposed and implemented to avoid the weekend effect,3 but these have been highly controversial. The debate about the existence of the “weekend effect” and its causes remains open. Some researchers have questioned the existence of a weekend effect,4 while others have highlighted the uncertainty about its causes,5 attributing the excess mortality to the greater severity of patients admitted at weekends or to structural and managerial aspects of the centers.6 Others have proposed an extended weekend effect describing an excess of mortality also on Mondays and Fridays.7

The existence of a weekend effect on various aspects of health care quality, including mortality, has also been demonstrated in the Spanish National Health System (SNHS).8,9 Heart failure (HF) is one of the main causes of hospital admissions in the SNHS, with high in-hospital mortality rates, 30-day readmissions, and prolonged hospital stays.10 In patients with HF, excess mortality has been described in weekend admissions, attributed to the greater severity of these patients11 or to the reduced hospital staffing at weekends.12

Although there are local exceptions, on weekends and holidays (nonworking days [NWD]) nursing staff are halved, consultants are only on call for emergencies, there are no ward rounds and no imaging, and pathology departments are only used for emergencies.13 The aim of this study was to analyze whether nonelective admissions of patients with HF on NWD and the length of reduced care on admission were associated with higher in-hospital mortality. Secondary objectives were to analyze the association of NWD with length of stay and the likelihood of 30-day readmission for circulatory diseases.

After exclusions (figure 1 of the supplementary data), 235 281 episodes of nonelective HF admissions were selected, with a mean age of 80.8±10.6 years and 53.4% were female. Crude in-hospital mortality was 11.1%, median length of stay was 6.9 [IQR, 4.1:10.8] days, and 10.2% of the patients were readmitted for circulatory diseases within 30 days of discharge. A total of 73 202 (31.1%) episodes were admitted on NWD, 26 117 episodes (11.1%) corresponded to the 1-day group; 38 424 (16.3%) to 2 days; 4421 (1.9%) to 3 days; and 4240 (1.8%) to 4 or more days of NWD after admission. There were no clinically relevant differences in the patient profile according to the duration of NWD (table 1 and table 2), although NWD patients were slightly older (81.2±10.4 vs 80.5±10.7; P < .001), more likely to be women (54.3% vs 52.8%; P < .001), and with a slightly higher presence of cognitive decline (12% vs 11.3%; P < .001), cardiorespiratory failure (excluding cardiogenic shock) (31.3% vs 29.4%; P < .001), acute myocardial infarction (0.7% vs 0.6%; P < .001), and renal failure (44.8% vs 44.1%; P=.003). The crude mortality rate was 10.7% for patients admitted on weekdays and 11.7% for patients admitted on NWD (P < .001). The crude mortality rates for 1, 2, 3 or more NWD on admission were 12%, 12.2%, 12.5%, and 12.8%, respectively (P < .001).

The prognostic variables included in the risk adjustment model for in-hospital mortality are shown in table 3 of the supplementary data. The adjustment model had an AUROC of 0.69 (95%CI, 0.69-0.70) and fair calibration (figure 2 of the supplementary data). When NWD periods were included in the in-hospital mortality model, compared with a weekday admission, 1 day of NWD increased an 11% the odds of in-hospital death (OR, 1.11; 95%CI, 1.07-1.16); 2 days by 13% (OR, 1.13; 95%CI, 1.09-1.17); 3 days by 16% (OR, 1.16; 95%CI, 1.05-1.27); and ≥4 days by 20% (OR, 1.20; 95%CI, 1.09-1.32) (table 3). Although the differences between the NWD groups were not statistically significant, there was a statistically significant association between a linear increase in NWD and higher risk-adjusted in-hospital mortality (chi-square trend P=.0002).

The crude rate of 30-day cardiovascular readmission increased with the duration of NWD, from 10% when admission occurred on a weekday to 11.4% when the period of NWD exceeded ≥4 days. The prognostic variables included in the risk adjustment model for 30-day cardiovascular readmissions are shown in table 4 of the supplementary data. The adjustment model had poor discrimination (AUROC, 0.58) and good calibration (figure 3 of the supplementary data). When the NWD period was incorporated into the model for 30-day in-hospital readmissions, compared with a weekday admission, 1 day of NWD increased the risk of 30-day readmission by 11% (OR, 1.10; 95%CI, 1.05-1.16); 2 days by 7% (OR, 1.07; 95%CI, 1. 03-1.11); 3 days by 9% (OR, 1.09; 95%CI, 0.98-1.22); and 4 or more days by 16% (OR, 1.16; 95%CI, 1.04-1.3) (P < .001), although the differences between the NWD groups were not statistically significant. There was no competing effect of mortality on readmissions.

After propensity score matching, patients with HF admitted on an NWD had higher in-hospital mortality than patients with HF admitted on weekdays (OR, 1.11; average treatment effect, 12.2% vs 11.1%; P < .001).

The length of stay of patients with 1 or more NWD was shorter than that of patients admitted on working days (6; IQR, 3:12 vs 7; IQR, 4:11; P < .001).

The main findings of this study were as follows: a) there was an association between patients with HF admitted to SNHS hospitals during periods of NWD with an increased risk of in-hospital mortality and 30-day readmission for circulatory diseases; and b) the increased risk of in-hospital mortality tended to be greater as the period of NWD became longer (figure 1).

Figure 1.

Central illustration. Cumulative effect of 'nonworking' days. Methodology and results. 95%CI, 95% confidence interval; ATT, average treatment effect; MBDS, Minimum Basic Data Set; NWD, nonworking days; OR, odds ratio; PSM, propensity score matching; SNHS, Spanish National Health System; WD, working days.

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Previous studies have reported an association of admission on weekend days with excess in-hospital mortality in patients admitted for decompensated HF.11,12,21–23 To our knowledge, this study is the first to analyze the association between the duration of NWD on admission and outcomes (in-hospital mortality, 30-day readmissions) in decompensated patients with HF. Despite the described association between weekend admission and greater patient severity,11 our study found slight clinical, but statistically significant differences in the profile of patients according to the duration of NWD groups, with patients with HF admitted on NWD being slightly more severe. However, the differences in in-hospital mortality between the 2 groups remained after risk adjustment (logistic regression model and propensity score matching).

A plausible explanation for the findings of this study is the potential gap in care that may be associated with reduced staffing on weekends and holidays.1 Aldridge et al.24 found no association between specialist intensity and admission mortality in acute hospital trusts in England, but reduced nursing staffing on weekends may be associated with mortality. Zapatero et al.13 reported an association between higher ratios of patients per registered nurse and risk-standardized in-hospital mortality for selected causes, although these authors did not find this association specifically for in-hospital mortality due to HF. Amigo et al.25 also found an association between weekend admissions and short-term mortality from selected causes in Spanish hospitals (Catalonia), with a stronger effect for HF admissions. The ratio of patients to registered nurses is high in acute general hospitals of the SNHS (9.9±0.7, weekday morning shift in internal medicine wards),13 and higher mortality rates and lower quality of care have been described when nursing workload increases.26 Walker et al.27 found no association between excess mortality rates during weekend admissions and hospital workload, but these authors used a proxy for workload due to lack of information on staffing information. Continuity of care during weekends in hospitals of the SNHS is generally addressed by on-duty teams, which are called when a nurse detects worsening in the clinical situation; weekend rounds are infrequent, and the implementation of early warning systems is low.13,28 In-hospital avoidable deaths have been described when patient deterioration goes undetected or communication between staff is inadequate.6,29 Clinical management may also be related to the weekend effect in hospitals of the SNHS, and it has been reported that adherence to clinical practice guidelines may vary throughout the day.30

Although there were no statistically significant differences in risk-adjusted mortality between the NWD groups, we found a statistically significant trend for in-hospital risk-adjusted mortality in patients with HF to increase with the length of NWD. Excess mortality was 20% for NWD of 4 or more days and 11% for NWD of 1 day. A cumulative negative effect of the “weekend effect” can be expected if the contributing weekend conditions remain unchanged, as is the case in the hospitals of the SNHS in relation to reduced staffing, low implementation of early warning systems, and multidisciplinary round wards.

The association between the reported NWD effect of weekends and holidays on patients with HF in the SNHS hospitals indicates the need for research into other diseases with specific risk adjustment models and analysis of the underlying probable causes: staffing and hospital workload, adherence to clinical practice guidelines, and other organizational causes such as the functioning of the primary health care level on weekends and holidays.

We found an association between nonelective hospital admissions for decompensated HF on an NWD day and higher in-hospital mortality and a higher likelihood of 30-day readmission for circulatory diseases in acute general hospitals of the SNHS. The excess of mortality is likely not explained by differences in severity. In this study, the “weekend effect” tended to increase with more prolonged NWDs.

This work was supported by an unrestricted grant from the Fundación Interhospitalaria de Investigación Cardiovascular (Madrid, Spain).

This study was based on anonymized administrative data and did not require the approval of an ethics committee or informed consent.

Artificial intelligence was not used in this study.

All authors meet the characteristics defined by the International Committee of Medical Journal Editors.

The authors have no relevant relationships to disclose that could affect the content of this article.