Caroline Helwick

October 15, 2012

October 15, 2012 (Washington, DC) — The prehospital shock index — a measurement obtained while the patient is en route to a trauma center — can predict the need for emergency blood transfusion, according to a study from investigators at the Shock Trauma and Anesthesiology Research Center (STAR) of the University of Maryland, in Baltimore.

The approach can be lifesaving, but its advantages go beyond this, according to Peter F. Hu, who presented the study at Anesthesiology 2012: American Society of Anesthesiologists (ASA) 2012 Annual Meeting.

"First, we want to save patients' lives," he said. "If we can better prepare our trauma centers, if we can predict early on the right type of blood we need, then we will not only save lives but also reduce anxiety for the medical team and save costs."

Hemorrhage is a leading cause of preventable trauma death. Acute resuscitation protocols increasingly advocate early transfusion of blood components at a 1:1:1 ratio of packed red blood cells, fresh frozen plasma, and platelets, but the latter products may require 30 minutes to prepare, even for emergency use, Hu explained.

"We need a method to enable earlier alert of the blood bank for an impending blood product requirement," he said.

Paramedics or other transport personnel could determine the shock index as soon as possible after the trauma, prior to the patient's arrival at the trauma center. With this half-hour or so head start, clinicians could better prepare for the patient's needs, including the need for blood products.

Shock Index Best Predictor

The investigators analyzed the trauma registry of all adult patients transferred directly to STAR by prehospital providers and transfused with uncrossmatched red blood cells (UnXRBC) immediately upon arrival between January 1, 2009, and December 31, 2010. Prehospital heart rate and systolic blood pressure were abstracted, and the shock index was calculated from these values (heart rate divided by systolic blood pressure). Using univariate logistic regression analysis, these factors were assessed as predictors of the need for UnXRBC transfusion.

During the study period, 282 of 8804 (3.2%) patients received UnXRBC upon arrival at the center. The shock index was significantly associated with emergency blood use (odds ratio, 27.5; 95% confidence interval [CI], 16.77 - 45.03; P < .001). For individuals aged 18 to 30 years, the predictive value was even stronger (odds ratio, 74.7; 95% CI, 31.20 - 178.21; P < .001), Hu reported.

In contrast, heart rate and systolic blood pressure were not independently associated with the need for blood transfusion.

The prehospital shock index was a better predictor for the clinician-assessed risk for massive hemorrhage and the need for emergent transfusion than either of its component values, the authors concluded.

They suggested that physiologic monitors could display the shock index and alert prehospital personnel, who in turn could convey this information to the trauma center, prompting earlier blood bank engagement than is now possible.

Approach Potentially Useful to the Military

The algorithm is highly applicable to the combat setting, said coinvestigator Colin F. MacKenzie, MD, also of STAR. In fact, he added, the study has been funded by the Department of Defense.

In the combat setting, where multiple casualties can be overwhelming and "a lot of blood can be needed on very short notice," he said, the index would be especially beneficial in giving a "heads up" to have fresh frozen plasma ready. Also it could help make "walking blood bank donors" available, which can require about 2 hours.

He added that this simple algorithm can be age-adjusted for further predictive value, ultimately reaching an 85% accuracy rate. "It's not perfect, but it's pretty good," Dr. MacKenzie noted.

The investigators are now conducting a prospective study to further test the shock index as a predictor of blood product need.

Leif Saager, MD, of the Department of Outcomes Research at the Cleveland Clinic in Ohio, moderated the session in which the results were presented. He commented, "This was a retrospective analysis, and the concept needs further study, but as a first look, I think this approach is promising and very relevant clinically.

"Blood transfusions save lives, but blood is a scarce resource," Dr. Saager noted. "We want to be ready for trauma patients, but on the other hand we cannot have large amounts of blood sitting ready."

Mr. Hu, Dr. MacKenzie, and Dr. Saager have disclosed no relevant financial relationships.

Anesthesiology 2012: American Society of Anesthesiologists (ASA) Annual Meeting. Abstract A649. Presented October 14, 2012.

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