The impact of severe traumatic brain injury on a novel base deficit- based classification of hypovolemic shock

The TraumaRegister DGU®, founded in 1993, is the official trauma registry of the German Trauma Society. Details of this registry have been published in extenso elsewhere [5, 8, 9, 20]. To date, datasets from approximately > 450 hospitals have been entered into the database. The TraumaRegister DGU® captures all severe trauma patients, who are either admitted to the hospital via the emergency department (ED) with subsequent admission to an intensive care unit (ICU)/intermediate care unit (IMC) or reach the hospital with vital signs and die prior to ICU/IMC admission. The TraumaRegister DGU® is approved by the review board of the German Trauma Society (DGU) and is in compliance with the institutional requirements of its members. Furthermore, all data analyses have been approved by the review board of the “Sektion NIS” of the German Trauma Society.

Datasets of multiple injured patients entered into the TraumaRegister DGU® between 2002 and 2011 were analyzed. Inclusion criteria were age ≥ 16 years, primary admission, and complete datasets for base deficit upon admission blood gas analysis in the emergency department. Severe traumatic brain injury was defined by an AIS_head ≥ 3 (abbreviated injury scale) as previously described [21‐23]. Based on these criteria, 10,201 patients with severe TBI could be identified and were classified into four strata of worsening BD according to the recently proposed classification of hypovolemic shock (Table 1) [9]. Assessments included demographics, injury patterns and vital signs as present upon ED arrival. Additionally, therapeutic interventions such as administration of blood products, intravenous fluids and vasopressors were analyzed. The assessment of mortality was performed by analyzing the overall in-hospital mortality. Massive transfusion (MT) was defined by the administration of ≥ 10 blood products between ED arrival and ICU admission. Coagulopathy was defined by a Quick’s value ≤ 70%, which is equivalent to an international normalized ratio (INR) of approximately 1.3 [22, 24]. For the evaluation of the applicability of the novel BD-based classification in the context of severe TBI, patients with an AIS_head ≥ 3 were classified according to their BD at ED admission and compared to both, an unselected cohort of all trauma patients derived from the TraumaRegister DGU® as well as to patients without a significant TBI (no TBI). Subsequently, transfusion requirements within the different cohorts were assessed.

Data are shown as mean ± standard deviation (SD) for continuous variables or percentages (%) for categorical variables. GCS is displayed as median and interquartile ranges (IQR). For continuous variables, normal distribution was excluded using the Shapiro-Wilk test. To detect differences between the four groups of worsening BD a Kruskal-Wallis test was performed. Categorical variables were analyzed accordingly with the Chi-square test. For all statistical analyses, a probability of less than 0.05 was considered to be statistically significant. All data were analyzed using IBM SPSS (IBM SPSS 19, Chicago, USA).

A total of 23,496 patients from the TraumaRegister DGU® were identified for further analysis. Out of these, 10,201 (43.4%) patients presented with severe TBI defined by an AIS_head ≥ 3. General demographics and trauma mechanism for the four classes of hypovolemic shock are shown in Table 2. Worsening of BD category was associated with an increased injury severity score (ISS 25.8 ± 11.9 in class I to 41.6 ± 17.0 in class IV). Through the classes I to IV, this was paralleled by an increased incidence of sepsis (7.5% to 14.1%) and multiple organ failure (18% to 44.4). Overall in-hospital mortality increased from 15.9% in class I patients to 61.4% in class IV patients (Table 3). No relevant tachycardia was observed in any group and a substantial hypotension was found in class IV patients only. Patients with a BD > 10.0 mmol/l (class IV) were coagulopathic (Table 4) and presented with significantly decreased haemoglobin levels (9.4 ± 3.2 g/dl) and platelet counts (177 ± 93 tsd/μl) compared to class I patients (haemoglobin 12.6 ± 2.3 g/dl; platelet counts 208 ± 72 tsd/μl).

Fluid resuscitation and transfusion requirement in correlation to increasing BD category are demonstrated in Table 5. Patients of class I received 1.5 ± 6 blood units, whereas class IV patients received 15.1 ± 22 blood units until ICU admission. The average transfusion ratio between packed red blood cells (pRBC’s) and fresh frozen plasma (FFP’s) was almost 1:1 within all groups. Likewise, observed and predicted transfusion requirements were concordant as the number of blood products transfused paralleled increased TASH (Trauma-Associated Severe Hemorrhage) scores.

In multiply injured patients with TBI, an increase in BD category was associated with a progressively increasing transfusion requirement (Figure 1). The percentage of patients who received ≥ 1 blood unit during early ED resuscitation increased from 14% in class I to 64% in class IV (Figure 1A), while simultaneously massive transfusion rates increased stepwise from 5% in class I to 42% in class IV (Figure 1B). However, substantial and clinical relevant differences between patients who sustained TBI and the general trauma population were not observed within the four classes of hypovolemic shock based on BD. Similar results were seen when multiply injured patients with TBI were compared to a cohort of severely injured patients without TBI (Figure 1A and B). Only in group IV, patients without TBI had a slightly higher overall transfusion requirement. However, the clinical relevance of this finding remains questionable.