Why to Use
When used individually, blood pressure and heart rate may fail to predict accurately the severity of hypovolemia and shock in major trauma. When initiated inappropriately, massive transfusion of blood products can be associated with significant risk. Identifying patients who are likely to require massive transfusion can be difficult, and objective measures such as the shock index can help. The shock index has also been shown to be more sensitive than the ABC score for massive transfusion (Schroll 2018).
When to Use
The accuracy of the shock index for identifying trauma patients in need of massive blood transfusion has not yet been prospectively investigated.
Kamal Medlej, MD
The shock index was first proposed in the literature in 1967 by Allgöwer and Burri as a measure of shock severity. More recently, the shock index has been studied further with modern protocols.
In a retrospective study by Mutschler et al (2013), 21,853 patients were identified in a trauma registry. Each patient’s shock index value was calculated based on vital signs taken on arrival at the emergency department. The degree of shock was found to correlate with increasing shock index values. The need for blood products, fluids, and vasopressors was also found to increase with higher shock index values.
A retrospective study by Cannon et al (2009), performed at a single Level I trauma center, identified 2445 patients admitted over a 5-year period. Patients with a shock index value > 0.9 were found to have a significantly higher mortality rate (15.9%) when compared with patients with a normal shock index (6.3%)
In a retrospective registry study by Vandromme et al (2011), the authors identified 8111 patients with blunt trauma who were admitted at a single Level I trauma center over an 8-year period. The shock index value for each patient was calculated from recorded prehospital vital signs, and patients with a shock index value > 0.9 were found to have a 1.6-fold higher risk for massive transfusion.
In a retrospective study of 542 patients who underwent emergency intubation, Heffner et al (2013) identified a pre-intubation shock index value ≥ 0.9 to be independently associated with peri-intubation cardiac arrest.
A retrospective study of 2524 patients at a single center who were screened for severe sepsis found that a shock index value ≥ 0.7 performed as well as the SIRS (systemic inflammatory response syndrome) criteria in negative predictive value and was the most sensitive screening tool for hyperlactatemia and 28-day mortality (Berger 2013).
The Protocolized Care for Early Septic Shock (ProCESS) trial (a large, multicenter prospective randomized controlled trial that enrolled 1341 patients) compared 3 different protocols for re-suscitation of septic patients, including a protocol that used a shock index value ≥ 0.8 as a fluid resuscitation goal. The study found no significant difference in mortality between the 3 intervention groups (Yearly 2014).
Manuel Mutschler, MD
Why to Use
Early initiation of massive transfusion has been shown to improve survival in critical trauma patients. The ABC score reduces delay in determining need for massive transfusion in a trauma patient, while also providing consistency in appropriateness of transfusion by minimizing practice variations among clinicians.
When to Use
The ABC score should be used in trauma patients for whom massive transfusion is being considered.
Cullen Clark, MD
Activation of a massive transfusion protocol (MTP) triggers the release of packed red blood cells, platelets, and fresh frozen plasma at frequent intervals until the MTP is called off.
The original study (Nunez 2009) was a retrospective review performed at Vanderbilt University Medical Center using the institution’s trauma registry. The study population was derived from all trauma patients admitted to the hospital over the course of a year (n = 596). Patients included were Level I trauma activations transported directly from the scene who received any blood transfusion while admitted. The ABC score was created by the trauma faculty based on clinical experience, and logistic regression modeling was used to determine the odds ratio of requiring MTP for each parameter of the score.
Of the total cohort, 76 patients (12%) required massive transfusion in the first 24 hours. Based on the number of patients who received massive transfusion and were identified using the ABC score, researchers found the best cutoff to be a score ≥ 2, giving a sensitivity of 75% and specificity of 86%. Compared with the Trauma Associated Severe Hemorrhage scoring system and the McLaughlin score using the same dataset, the ABC score was shown to be the most accurate in predicting need for MTP.
The validation study (Cotton 2010) was a retrospective review using trauma databases from 3 institutions: Vanderbilt University Medical Center, Johns Hopkins Hospital, and Parkland Memorial Hospital. The inclusion and exclusion criteria were the same as the original study. The study population was again derived from trauma patients admitted to 1 of the 3 hospitals over the course of a year. The sample size of the study was 1604, including 586 patients from the original study. There was significant variation in demographics between the centers involved, but the massive transfusion rate in the first 24 hours of admission was similar for each hospital (approximately 15%). There was little variability between each institution’s cohort in the percentage of patients correctly classified as meeting the ABC score cutoff for MTP, among those who received massive transfusions. For each institution, sensitivity ranged from 76% to 90% and specificity ranged from 67% to 87%. Negative predictive value was 97% and positive predictive value was 55%.
The validation study also measured the accuracy of the ABC score at predicting need for massive transfusion in the first 6 hours of admission. Sensitivity was 87% and specificity was 82%, with slightly higher negative predictive value (98%) and lower positive predictive value (55%) compared to prediction of massive transfusion need in the first 24 hours.
The major limitation to both studies was their retrospective nature. A prospective trial is ongoing. The study shows a novel means of quickly predicting the need for massive transfusion based on objective measures. While there are good data showing that early activation of MTP improves survival rates in severely injured trauma patients, a prospective study will be necessary to determine whether utilization of the ABC score improves patient outcomes.
Bryan Cotton, MD
Christopher Pitotti, MD, FACEP; Jason David, MD
Ryan M. Knight, MD; Leslie V. Simon, DO
November 1, 2020
November 1, 2023   CME Information
4 AMA PRA Category 1 Credits™, 4 ACEP Category I Credits, 4 AAFP Prescribed Credits, 4 AOA Category 2-A or 2-B Credits. Specialty CME Credits: Included as part of the 4 credits, this CME activity is eligible for 4 Trauma CME credits