Introduction
The early recognition and management of hypovolemic shock in multiply injured patients are still among the most challenging tasks in the acute assessment and treatment of trauma patients. For the initial evaluation of circulatory depletion, the American College of Surgeons has defined in its training program 'Advanced Trauma Life Support' (ATLS) four classes of hypovolemic shock. This classification is based upon an estimated blood loss in percent together with corresponding vital signs [
1,
2]. For each class, ATLS allocates therapeutic recommendations (for example, the administration of intravenous fluids and blood products) [
1]. Recently, the clinically validity of the ATLS classification of hypovolemic shock has been questioned by two analyses independently from each other on two large-scale trauma databases: the TARN (Trauma Audit and Research Network) registry and the TraumaRegister DGU
®, which had consisted of more than 140,000 trauma patients. According to both analyses, ATLS seems (a) to overestimate the degree of tachycardia associated with hypotension and (b) to underestimate mental disability in the presence of hypovolemic shock [
3‐
5].
These observations and conclusions prompted us to develop an alternative approach for the early assessment of hypovolemic shock in the emergency department (ED). Several studies have already identified worsening base deficit (BD) as an indicator for increased transfusion requirement [
6,
7]. Furthermore, BD has been associated with increased mortality, intensive care unit (ICU) and in-hospital lengths of stay, and a higher incidence of shock-related complications such as acute respiratory distress syndrome, renal failure, hemocoagulative disorders, and multiorgan failure (MOF) [
6‐
9]. Monitoring of BD has also been suggested as an indicator and monitoring parameter for the success of resuscitation efforts [
7,
10,
11]. In times of point-of-care testing (POCT), BD can be assessed in a fast and easy manner and therefore is available within minutes after admission to the ED. The aim of this study was to introduce and validate a four-class BD-based classification of hypovolemic shock on datasets of severely injured patients derived from the TraumaRegister DGU
® database.
Discussion
The aim of this study was to introduce and validate a new BD-based classification of hypovolemic shock for the initial assessment of trauma patients. This analysis was conducted on a cohort of not less than 16,305 severely injured patients derived from the TraumaRegister DGU® database.
The early assessment of hypovolemic shock and the prediction of transfusion requirements in multiply injured patients are still among the most challenging tasks in the initial management of trauma patients. One approach comprises the initial evaluation of vital signs as suggested by ATLS in its classification of hypovolemic shock by using combinations of HR, SBP, and GCS score. However, recent analyses on data of multiply injured patients derived from the TraumaRegister DGU
® and the TARN database indicated that the current ATLS classification of hypovolemic shock displays substantial deficits in allocating trauma patients into the corresponding classes [
3,
4]. Furthermore, the role of vital signs alone in the initial assessment of hypovolemic shock is still debated [
3,
15‐
18]. Paladino and colleagues [
19] recently assessed the additional use of metabolic parameters (for example, BD as a sensitive indicator of blood loss by measuring tissue perfusion) to traditional triage vital signs to distinguish major from minor trauma. In their retrospective single-center analysis, abnormal vital signs alone had a sensitivity of 40.9% for identifying major injury, but when abnormal metabolic parameters were added, the detection of major trauma increased significantly to a sensitivity of 76.4% [
19].
In the present study, we propose a new classification based upon BD, a parameter that indicates the presence of hypovolemic shock and identifies patients who are at risk to require blood product transfusions. In times of POCT, BD is available within minutes after ED admission. As early as 2005, Rixen and Siegel [
9] suggested the evaluation of BD as a more useful approach to quantify the extent of hypovolemic shock than the estimation of blood loss, the extent of volume resuscitation, or vital signs such as HR and SBP. Additionally, these authors proclaimed that BD may be superior to the measurement of lactate levels.
The diagnostic use and prognostic value of BD are well documented. Out of 10 clinical and 20 laboratory parameters assessed, changes of BD have been proven to be the best predictor of blood volume change in a canine model of hemorrhagic shock [
20]. On the basis of 1,810 multiply injured trauma patients derived from the TraumaRegister DGU
® database, potential predictors for transfusion requirements, including BD and lactate, have been identified via logistic regression. Seven variables could be identified to independently predict MT: gender (male), SBP, HR, hemoglobin, relevant injuries to the abdomen and extremities (Abbreviated Injury Scale score of at least 3), and BD, but not lactate [
21,
22]. Furthermore, our group has recently compared six scoring systems to predict the risk of ongoing hemorrhage and MT, including the TASH, Prince of Wales Hospital/Rainer (PWH/Rainer), Larson, Vandromme, Schreiber, and ABC (assessment of blood consumption) scores. The TASH and PWH/Rainer scores showed the highest overall accuracy in predicting ongoing hemorrhage and MT. Interestingly, both scores include BD as a laboratory surrogate for hypoperfusion. In contrast, only one scoring system (that is, the Vandromme score) comprises lactate [
23]. Similarly, several mortality scores (for example, the Emergency Trauma Score (EMTRAS) [
24] and BIG score [
25]) use BD as the laboratory surrogate for shock. In the present study, worsening BD paralleled worsening lactate. However, the use of Ringer's lactate in the initial fluid resuscitation as well as the presence of ketoacidosis in patients with diabetes may influence lactate levels and can falsify the initial assessment [
9,
26]. The present study did not intend to address the question of whether BD or lactate may be superior in risk-stratifying trauma patients, and therefore this question remains unanswered. However, the data derived from the TraumaRegister DGU
® database suggest that BD may be more accurate in detecting shock and blood loss as compared with lactate. Therefore, the proposed classification here is based on BD upon ED admission.
The present investigation revealed that increasing BD category reflected injury severity as demonstrated by an increasing injury severity score (ISS), new injury severity score (NISS), and RISC score and the incidence of MOF and sepsis. All of them are important factors influencing mortality and outcome of trauma patients. In our analysis, mortality rates rose from 7.4% to 51.5% with altered BD values. These observations are consistent with those of previous studies reporting an association between admission BD and mortality [
6,
7,
10,
11]. In a univariate logistic model, admission BD has been proven to be one of the best predictors for mortality, and a BD level of 6 mmol/L was identified as an important cutoff point for mortality [
7,
11]. Also, in pediatric and older trauma populations, BD has been shown to be an important indicator for injury severity and mortality [
27‐
30]. Interestingly, the use of alcohol and drugs did not impair the predictive accuracy of admission BD with respect to trauma outcome [
31].
In the present analysis, BD correlated with transfusion requirements, both in the overall amount of transfused blood units and in the percentage of patients who required any blood transfusion (≥ 1 blood unit). Furthermore, worsening BD paralleled increasing risk of ongoing hemorrhage as reflected by increasing TASH scores. The mean amount of blood products administered increased from 1.5 ± 5.9 to 20.3 ± 27.2 units with worsening BD category. These findings are consistent with those of a previous analysis demonstrating that worsening of BD was associated with an increased need for blood product transfusions [
6,
7,
32]. Through the groups I to IV, the increasing amounts of intravenous fluids and vasopressors administered indicate the presence of hemodynamic instability and validated the results previously reported by Rixen and colleagues [
7]. Laboratory findings such as decreases in hemoglobin levels and platelet counts and an impaired coagulation as reflected by a Quick's value of less than 70% were further interpreted as evidence for hypovolemic instability. Given these results, BD indicates the presence of hypovolemic shock related to hemostatic resuscitation need, transfusion requirements, laboratory findings, and mortality.
To the best of our knowledge, there is no gold standard to assess the presence of hypovolemic shock and to trigger therapeutic interventions. Thus, there is no option yet to test our novel approach against a gold standard. Therefore, the authors have decided to test against the current ATLS classification of hypovolemic shock given that this approach has been widely implemented in daily clinical routine as a standard protocol of care and for the initial assessment and treatment in trauma centers. Both the percentage of patients who had received at least one blood product and MTs were increased throughout the groups I to IV in both classifications. However, transfusion requirements were significantly higher when patients were classified by BD. Similar results were observed for mortality. Obviously, stratification by BD was associated with superior discrimination of trauma patients with respect to outcome and need for early blood products. In this context, ATLS seems to dramatically underestimate the need for blood product transfusion, particularly in group III and IV patients.
In summary, we suggest assessing patients in the ED on the basis of BD. Davis and colleagues [
6] have already proposed that, in patients with a BD of less than 6 mmol/L, blood typing should be sufficient but that patients with a BD of at least 6 mmol/L should undergo blood typing and cross-match. Given MT rates and the identification of patients who are in need of emergent transfusion, a BD of 6 mmol/L could also be suggested as a threshold. Table
4 displays our suggestion for a modified version of the current ATLS classification of hypovolemic shock based upon BD as a principal trigger for action. Following the ATLS paradigm of 'keep algorithms simple', specific recommendations are presented with regard to preparation and use of blood products. For class I and II patients, a careful observation should be sufficient unless clinical circumstances dictate otherwise. In class III patients, preparation for transfusion should be initiated. In class IV patients, in whom MT rates were more than 50%, the trauma leader should definitely be prepared for an MT (for example, by activation of an MT protocol and corresponding logistics).
Table 4
A new base deficit-based classification of hypovolemic shock
Shock | No shock | Mild | Moderate | Severe |
Base deficit at admission, mmol/L | ≤ 2 | > 2.0 to 6.0 | > 6.0 to 10.0 | > 10.0 |
Need for blood products | Watch | Consider | Act | Be prepared for massive transfusion |
The retrospective nature of this study and the modifications applied to the ATLS classification in order to conduct the present analysis are clear limitations of this study, and the authors are aware of this shortcoming. Although POCT can provide BD within minutes after ED admission, not every ED is equipped with this technology. However, ATLS claims that the knowledge and skills taught are easily adapted to all venues of trauma care. This implies that every ED worldwide as well as pre-hospital systems (Pre-hospital Trauma Life Support) use similar principles and assessment tools as suggested by ATLS. However, this study may be a first step toward a 'modified ATLS classification of hypovolemic shock' with improved clinical applicability. Further validation on other trauma databases and in prospective studies is needed, especially on cohorts including higher numbers of penetrating injuries. In the absence of POCT, future research is needed to develop alternative approaches (for example, modified and clinically adopted combinations of vital signs), which can be used as an equivalent to BD in the initial assessment of hypovolemic shock. Hereby, the basic and underlying ATLS concept focusing on its intentionally simple applicability, independent of venue, technical prerequisites, and time scales, would be preserved.
Competing interests
The authors declare that they have no competing interests. This is an unfunded study.
Authors' contributions
MMu contributed to study design, acquisition and interpretation of data, and drafting of the manuscript. UN and BB contributed to analysis and interpretation of data and to revision of the manuscript. TB, AW, TF, and TP contributed to study design and to revision of the manuscript. MMae contributed to study conception and design, acquisition of data, analysis and interpretation of data, and revision of the manuscript. All authors read and approved the final manuscript.