The majority of in-hospital deaths after major trauma occurred during the initial ICU treatment period. This study showed that a relevant group (17.1%) of all non-surviving patients initially admitted to the ICU were discharged from ICU at least once and treated outside the ICU for more than one day.
Multiple studies focussed on in-hospital mortality after discharge from the ICU (18-22) Pearse et al. performed a prospective observational study on mortality after surgery in Europe (9) In emergency surgery, they found a mortality rate of 11.1 % of all patients initially discharged alive from ICU to normal ward. They concluded that ICU resources were not allocated to patients at greatest risk of death. A variety of factors influencing readmission rate have been identified. Several studies showed a relationship between daytime and weekday of discharge from ICU and outcome. They confirmed that unplanned discharges from the ICU during night-time and on weekends were independent risk factors for readmission to the ICU and increased mortality (18, 23, 24). Others confirmed older age, severity of illness on the day of admission to the ICU and day of discharge from the ICU as well as comorbidities as independent risk factors (8, 25-27). We did not compare surviving and non-surviving patients after ICU-discharge but non-survivors with or without initial discharge from ICU. Non-survivors after initial ICU discharge were older, less severely injured and the severity of comorbidities as measured by the American Association of Anaesthesiologists Classification (ASA)(28) were higher. Interestingly, the injury pattern and the course in the ICU differed in several points: While the percentage of blunt trauma and isolated head injury did not differ relevantly, the proportion of trauma patients without head injury was much higher in non-survivors discharged from the ICU. Percentage of patients after low fall was higher in non-survivors discharged from ICU. Regarding the ICU treatment period one hypothesis could be that patients dying after ICU discharge underwent less intensive care as they were less severely injured. They may have been underestimated by the treating physicians and were discharged from the ICU prematurely. However, the mean length of stay on the ICU long (mean days on ICU: 4) as well as the days with ventilatory support (mean days ventilated: 5.8). Low fall is a known surrogate marker for frailty, predicting long-term mortality in older trauma patients (29).
In general, fatalities after the initial discharge from the ICU may be explained by either a limitation of life-sustaining intensive care treatment with palliative care outside the ICU due to a living will or by patients who were discharged from the ICU after initial recovery but suffered a late fatal complication.
The causes of mortality of these patients remained unclear. A documented living will to limit sustaining therapy was present in 60 % of patients who died after discharge from the ICU. However, we couldn’t state that all of these patients actually underwent palliative care and were discharged from the ICU due to therapy limitation. A living will was also present in 46 % of non-survivors who died during their initial ICU stay. Consequently, a living will to limit life-sustaining treatment did not per se lead to an ICU discharge in this setting. The ICU stay was also rather long so that we cannot assume that there was a significant number of short (e.g. 24 hours) ICU try-outs for the very old critically ill patients with consecutive withdrawal of intensive care treatment in those patients with failing recovery.
After initial recovery late complications like sepsis (19.5 %) and thromboembolic complications (10.4 %) resulted in death of the patient. Assumed causes of death differed to typical reasons for early mortality, i.e. bleeding, head injury and organ failure in 23.4 % of cases. We can only assume which other causes of death occurred as the registry data gives no more detailed information regarding the parameter “assumed cause of death”. However it appears logical that all late deaths after ICU discharge were due to a potentially occult complication.
Surprisingly, we found relevant differences between trauma centers of different care levels. About 5% of our study population was treated in a local level 3 trauma center, 24 % in a regional level 2 trauma center, and the vast majority in a supra-regional or level 1 trauma center. The percentage of non-survivors after initial ICU discharge was highest in level 3 centers and lowest in level 1 centers (Table 2). Although it seems intuitive that fewer late fatal complications occur in experienced trauma centers, previous studies focusing on the relationship between center volume and complication rates were inconclusive. Several studies found a correlation between high volume and improved outcome, especially in high-risk surgical and trauma patients (30-32) However, other studies found no association between institution or surgeon volume and survival.(33-35) Bell et al.(36) investigated the relationship between trauma center volume and in-hospital outcome and showed that higher hospital volumes were associated with decreased likelihood of mortality but not for complication or FTR.
We cannot conclude from our data that our findings were related to differences in availability of ICU beds, other recourses or higher rates of failure to rescue (FTR). Different institutions may have different limitations in resources and, for example, comfort care in the high-dependency unit in one hospital may be equivalent to staying in the ICU for comfort care in another hospital.
Although our study identified a cohort of FTR patients, we could not measure and compare FTR rates. Firstly, we did not know whether patients that died during their initial stay in the ICU suffered from complications or what the influence on mortality might have been. Secondly, we did not know complication rates of surviving patients to show the rate of survived complications.
FTR rates are considered as a quality indicator superior to complication or mortality rates as they are more associated with institutional factors.(37-40) The rate was based on elective surgical populations and reclassified deaths not caused by adverse events. Holena et al.(37) demonstrated that this approach lacks validity in trauma because patients often die as a direct consequence of injury without any adverse events. They also argued that another common approach to simply exclude deaths without recorded adverse events reduces the reliability of the FTR rate. They proposed to include all deaths but excluding those with an expected mortality >50%. Though the limit is still under discussion and yet to set definitely.
Moore et al (38) performed a systematic review on complication rates as a trauma care performance indicator. Only three complications (pneumonia, pulmonary embolism and deep vein thrombosis) were recommended to evaluate acute trauma care hospitals. A recent study by Chung et al. (39) showed that 33% of all major complications in trauma patients occurred on normal surgical wards.
Rauf et al.(41) observed that the time distribution of in-hospital mortality in severely injured patients shows a constant decrease. About 61 % of all deaths occur within the first 48 h after admission. Mean time to death was about 6.5 days with a median of two days.
This might suggest to focus on the initial hours and days after trauma in terms of quality improvement. However, we believe that our study identified a relevant field of potential improvement to decrease mortality rates even further.
Therefore we propose the mortality rate of patients after initial discharge from ICU as a reliable quality indicator for trauma care. Its calculation and extraction from registries is simple and independent from definition and measurement of adverse events.
Limitations
This study has several limitations: It is a retrospective study of a registry and therefore there is potential for bias or residual confounding from factors we did not measure. We only have information on acute care hospital outcome without any follow-up data on discharged patients. Furthermore, we did not discriminate between patients that died on the normal ward on those readmitted to ICU. We also cannot give information on patients treated less than 2 days outside the ICU. Our study protocol included these patients in the group of patients that died within first ICU course. We cannot give detailed information whether and how a living will to limit life-sustaining therapy contributed to the observed mortality rate. The registry does not discriminate between “the patient did not want any more intensive care medicine though intensivists recommended” and “therapy was limited due to grave prognosis”. Furthermore, there are patients who are discharged from ICU (“terminal discharge”) due to poor prognosis, and patients who die before this terminal discharge can be planned. We included patients from Germany, as differences in health systems, i.e. limited ICU resources or cultural differences i.e. handling of living will statements might have influenced our results.
However, the strength of this study is the large study population with detailed patient characteristics representing most severely injured patient in one representative developed country and health system.