Background

Traumatic brain injury (TBI) is a major cause of morbidity and mortality, and is the leading cause of death in people aged 15–45 years [1]. Tagliaferri et al. [2] reported that TBI accounted for the majority of trauma deaths in Europe. It is generally agreed that patients with TBI should be treated without unnecessary delay to avoid secondary brain insults. Some studies have shown that trauma patients admitted during the night shift or on weekends have worse outcomes than those admitted during the day shift or on weekdays: Egol et al. [3] reported that patients admitted between midnight and 6 a.m. had a significantly higher risk for in-hospital mortality, and another study showed that TBI patients admitted at night had a significantly longer interval between hospital admission and surgery [4]. Other studies, however, found no significant effect of time of admission [5, 6], and one study reported lower mortality of trauma patients admitted on weekends [7].

There are two key factors that may influence outcomes of patients who are admitted during the night or on holidays: due to reduced staffing, fewer physicians, nurses, and technicians may be available, which might cause some delay of treatment, and fatigue may become a problem, as almost all physicians work 24-h shifts. The goal of this study was to analyze the effects of the time of hospital admission on outcomes in a sample of patients with severe TBI that had been collected prospectively over the past 10 years. Our hypothesis was that patients who were admitted during the night shift or on holidays/weekends would have higher rates of hospital death and unfavorable long-term outcome compared with patients who arrived on weekdays.

Patients and methods

Between 2001 and 2012, the International Neurotrauma Research Organization (INRO, a nongovernmental research organization, founded in 1999; based in Vienna, Austria) coordinated two projects that focused on Austrian patients with TBI. Both projects were purely observational and enrolled pediatric as well as geriatric patients, TBI patients with multiple trauma, and patients with low Glasgow Coma Scale (GCS) scores. The first project analyzed epidemiology and hospital treatment of patients with severe TBI as well as the effects of guideline-based treatment [8]. This project started in March 2002; five centers enrolled 400 patients until June 2005. The second project focused on prehospital and early hospital management of patients with moderate and severe TBI. It started in March 2009; 16 centers enrolled 777 patients until April 2012. Both projects were done with approval of the local ethical committees. Due to the purely observational design of the projects, informed consent of the patients was not mandatory; however, all patients who recovered sufficiently to consent gave written permission to use their data for scientific purposes.

The data were collected in 17 Austrian centers. Of these centers, 13 were “high-volume” centers: 4 free-standing trauma hospitals, 2 University departments of Traumatology, and 7 large trauma departments in tertiary hospitals. The four remaining centers were “low-volume” centers; they included three trauma departments in regional hospitals and one smaller trauma hospital. All centers were able to provide state-of-the-art patient management. The number of patients enrolled by these centers (median: 50, interquartile range (IQR): 29-101, range: 12–163) varied considerably, as 4 “high volume” centers participated in both projects, and some centers joined the second project with just few months remaining for patient inclusion. Using the prognostic International Mission for Prognosis and Analysis of Clinical Trials in TBI (IMPACT) core model [9], the observed vs. expected mortality ratio was < 1 for 16 of 17 centers (median: 0.85, IQR: 0.67–0.95, range: 0.59–1.09)—this confirms that the centers provided high-quality treatment.

Treatment in the field was provided by emergency physicians. All patients had rapid examination including documentation of vital signs (GCS score, pupillary status, blood pressure, heart rate, and oxygen saturation). Rapid sequence intubation facilitated by hypnotics and relaxants, ventilation, treatment of hemorrhage, and fluid resuscitation were done as appropriate. After admission, each patient was examined by a trauma team (anesthesiologists, trauma surgeons, and/or neurosurgeons, radiologists, nurses), and a computed tomography (CT) scan was done. The patients then underwent surgery as appropriate and/or were admitted to the intensive care unit (ICU). Neurosurgery was provided by neurosurgeons (6 centers) or by trauma surgeons (11 centers) who had the option of consulting neurosurgeons for more difficult cases. In a previous study, we have shown that the specialty of the surgeon had no impact on outcomes of the patients [10]. Intensive care was provided by anesthesiologists in cooperation with neurosurgeons or trauma surgeons.

A database developed by INRO was used to collect data. Basic demographic data of the patient, cause and location of trauma, prehospital status and treatment, mechanism and severity of trauma (Abbreviated Injury Score [AIS], Injury Severity Score [ISS]), results of CT scans, results of laboratory testing, and data on surgical procedures and outcomes were recorded prospectively. Prehospital data were documented by paramedics, and were then transferred into the databases. CT scans were interpreted by neurosurgeons, trauma surgeons, and radiologists, and the summarized findings were entered into the CT page of the database. This CT page collected detailed data on basal cisterns, midline shift, and main findings. Data on duration of various treatments, complications, and outcomes were collected at discharge from the ICU and at hospital discharge. Information on status and location was recorded at 6 months after injury. This was done by phone calls to the patients and/or their relatives; in some cases, the Glasgow Outcome Scale (GOS) score was recorded at patients’ follow-up visits to the centers. In all centers, data were collected by local investigators; data quality was monitored by the INRO project manager (Alexandra Brazinova). Missing or implausible data were reported to local investigators who then submitted missing or corrected values. Personal data protection was observed, and the identifiers were kept separately from the data.

All patients who had severe TBI (defined as AIS “head” > 2 and/or enrollment GCS score < 9) were selected for this analysis. Patients with unsurvivable injuries (AIS “head” = 6) and those who had been transferred from another hospital were excluded. Data on trauma mechanism, trauma severity, CT findings, treatment, and outcomes were retrieved for each patient. The IMPACT core model [9] was used to estimate the probabilities of hospital death and unfavorable long-term outcome. This model has been validated for our patient sample. To describe long-term outcomes, the GOS [11] was used. “Favorable outcome” was defined as a GOS score of 5 or 4; “unfavorable outcome” was defined as a GOS score of 3 or less at 6 months after trauma.

Based on the time of arrival at the center, patients were assigned to group “regular service” (arrival at workdays from 7 a.m. to 7 p.m.) or to group “on-call service” (arrival at any other time). In the centers that participated in the TBI projects, minimum in-house staffing during “on-call service” included two surgeons, one anesthesiologist, one radiologist, two surgical nurses, one anesthesia nurse, one radiology technician, and one to two paramedic assistants. Depending on the size of the center, other surgical specialists would be available either from in-house departments, or from other hospitals. During “regular service,” the teams could be considerably larger. Physicians usually worked 24-h shifts, and all others worked 12-h shifts.

Demographic data, clinical status, treatment, and outcomes of these two groups were compared. In addition, demographic and treatment data were analyzed, and rates of mortality and unfavorable outcomes were calculated for the following groups:

  • admission between midnight and 6 a.m. vs. admission between 6 a.m. and midnight,

  • admission on workdays vs. admission on holidays/weekends (including the nights),

  • admission between 7 a.m. and 7 p.m. (day) vs. admission between 7 p.m. and 7 a.m. (night),

  • admission during the night (7 p.m. to 7 a.m.) vs. admission on workdays (7 a.m. to 7 p.m.) vs. admission on holidays/weekends (7 a.m. to 7 p.m.).

Statistical analysis

Our sample was large enough (power = 0.83) to detect a small effect (d = 0.2) at a significance level of 0.05. Two-tailed t-test (for comparisons of mean values), Fisher’s exact test, and chi-square test (for analysis of 2 × N contingency tables) were done as appropriate to identify differences between the groups. To check for associations with outcomes, we constructed logistic regression models for hospital death and unfavorable long-term outcome, where the effects of time of admission on outcomes were corrected for age, GCS scores, and ISS. Data are presented as means with standard deviations, or as proportions. A P-value of < 0.05 was considered statistically significant.

Results

Of the 1,177 patients in the database, 202 patients had been transferred from another hospital, 74 had an unsurvivable injury (AIS “head” = 6), and 49 had only moderate TBI (AIS “head” < 3 and GCS score > 8 at enrollment). This left 852 patients with severe TBI for analysis. Of these, 413 arrived on a workday between 7 a.m. and 7 p.m. (“regular service” group), and 439 arrived at another time (holiday, weekend, night; “on-call service” group).

Demographic data, data on status, and data on trauma severity are given in Table 1. “On-call” patients were significantly younger. Patients aged between 15 and 34 years were significantly more likely to be admitted during “on-call service” (Fig. 1); patients from all other age groups were more likely to be admitted during “regular service.” “On-call” patients had a significantly higher rate of alcohol intoxication (Table 1) and had different trauma mechanisms (fewer falls, more motor vehicle accidents, and more motorbike accidents). Trauma severity was comparable; AIS “head,” ISS, GCS score, rates of hypoxia and hypotension, and pupillary reactivity were not different. The probabilities of death and unfavorable outcome were almost identical.

Fig. 1
figure 1

Percentages of cases admitted during “regular service” and “on-call service” vs. age groups (years)

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Table 1 Demographics, prehospital status, and trauma severity
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With regard to treatment (Table 2), the rate of helicopter transport was significantly lower in “on-call” patients because Austrian rescue helicopters usually do not fly missions after dark. All other treatment variables were not different. The intervals between admission and CT scan and between admission and start of neurosurgery (if required) were comparable. There were no differences regarding CT scan findings (Table 2). The causes of death (Table 2) were not different. Hospital mortality and rate of patients with unfavorable outcome at 6 months were lower in the “on-call” group, but this difference was not significant.

Table 2 Treatment, computed tomography scan findings, and outcomes
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Table 3 gives an overview of the rates of hospital deaths and unfavorable outcome at 6 months for groups with different admission times. Patients who arrived between midnight and 6 a.m. had lower hospital mortality, and had a significantly lower rate of unfavorable outcome. The same pattern was found for patients who arrived during the night shift vs. during the day shift. No significant differences were found for all other comparisons. For all comparisons, patients who arrived during the night shift or during holidays/weekends were significantly younger, were more likely to test positive for blood alcohol, and had different trauma mechanisms.

Table 3 Comparison of rates of death and unfavorable outcome for different admission times
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The multivariate analysis (Table 4) showed that only age, ISS, and first GCS score were significantly associated with outcomes; after correction for these factors, alcohol intoxication had no significant effect.

Table 4 Multivariate analysis
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Discussion

This study presents an analysis of the effects of the time of hospital admission for Austrian patients with severe TBI who had direct transport to the participating centers and had survivable injuries. We choose to compare “on-call service” to “regular service” in detail because the influence of both reduced staffing and fatigue was expected to be found in the “on-call” patients. However, we found that “on-call” service was adequate because the time of admission had no significant effect on hospital mortality and on the rate of unfavorable outcome at 6 months after trauma. The guidelines of the Austrian Society of Traumatology state that all departments admitting severe trauma cases must have at least one full trauma team available 24/7 to care for these patients. Thus, limitation of service during “on-call” times does not affect treatment of severe cases (but may affect patients with minor injuries, e.g., by longer intervals between admission and treatment). This study also found no effects of fatigue. Our hypothesis has been proven wrong.

This study confirms previous findings from Guly et al. [6]: this British group used data from Trauma Audit and Research Network (3 years, 40,866 cases) and reported that 31.1 % of trauma patients with an ISS > 15 who were admitted “out of hours” died, compared with 33.5 % of patients who were admitted inside “working hours.” Similar results have been reported by Carmody et al. [5]: this group from California reviewed 8,015 consecutive trauma admissions (3 years) and found that mortality of trauma patients admitted at night was significantly lower than that of patients admitted during the day (10.1 vs. 13.1 %). They performed different comparisons (e.g., morning vs. night for all patients, for blunt trauma, for penetrating trauma, weekday vs. weekend, and weeknight vs. weekend night) and found no significant differences in ISS-matched mortality rates. A recent study by Carr et al. [7] used data from the Pennsylvania trauma system (5 years, 90,461 cases) and reported that patients who arrived on weeknights were more likely to die than patients who arrived on weekdays (unadjusted mortality: 7.5 vs. 6.6 %). In the adjusted analysis, there was no significant difference in mortality between weekday and weeknight admissions, and patients who arrived on weekends were less likely to die than those who arrived on weekdays (odds ratio (OR): 0.89; 95 % confidence interval (CI): 0.81–0.97). None of these three articles reported data on staffing.

Other authors reported different results. Egol et al. [3] used 2002–2006 data from the US National Trauma Data Bank and analyzed outcomes of 601,388 patients aged > 18 years. They found that cases admitted between midnight and 6 a.m. were significantly more likely to die (OR: 1.18; 95 % CI: 1.12–1.25, adjusted analysis). This pattern was found in all trauma centers, but was weakest at level 1 trauma centers and strongest at level 3 and 4 trauma centers. This article did not report data on staffing.

All studies discussed so far included all trauma patients, while our study included only patients with severe TBI. There is only one study that also focused on TBI patients [4]; it showed that patients who arrived between 6 p.m. and 8 a.m. had significantly longer intervals between admission and start of neurosurgery; no data on staffing were given. In our study, however, there were no differences regarding the intervals admission to CT scan and admission to neurosurgery.

What are the possible reasons for the small outcome differences observed in our study? The differences in mortality and unfavorable outcome were most pronounced in all analyses that included periods after 7 p.m. No differences were observed for patients who were admitted during weekends or holidays between 7 a.m. and 7 p.m. There were no differences in treatment, and only age and rate of alcohol intoxication were significantly different. Age is one of the most important factors influencing outcomes after TBI as demonstrated in the large study done by Hukkelhoven et al. [12] and by a number of other studies. The significant effect of age has been confirmed by our results. In addition to the factor “age,” it seems possible that “alcohol intoxication” may be responsible for the small difference in outcomes. There is evidence that alcohol intoxication may be beneficial for patients with moderate and severe TBI [13, 14]. Suggested mechanisms for this beneficial effect include a reduction of the neuroinflammatory response to TBI [15] and a decrease in pneumonia rate after TBI [16].

Conclusions

The study analyzed hospital mortality and long-term outcome of patients admitted either during workdays (regular service) or during holidays/weekends and nights (“on-call service”). “On-call” patients were younger and were more likely to have positive blood alcohol levels. There were no differences in trauma severity or treatment. Timing of hospital admission had no effect on outcomes, although mortality and rate of unfavorable outcomes were insignificantly lower in “on-call” patients.