Shock Index - A Better Vital Sign in Trauma

The gist:  Don't rely on a trauma patient's normal vital signs to assume they're hemodynamically stable. Rather, use the shock index (HR/SBP) to predict a patient's need for massive transfusion.

The Shock Index (SI) is Heart Rate divided by Systolic Blood Pressure (HR/SBP)

• Heart rate and blood pressure are often poor predictors of a patient's perfusion status.  Patients notoriously crash, even if they never really become hypotensive or tachycardic (especially in the elderly!).  In trauma patients, a better assessment of a patient's vital signs is the SI.

Normal SI = 0.5-0.7

• SI > 0.9 then approach the patient as though they are actively bleeding 
• SI increases more than 0.3 at any point in care (prehospital to ED), then treat this as though the patient is actively exsanguinating 
• Don't rule out bleeding if SI is within normal limits
• Elderly patient multiply their age by the SI (Age x SI)

The Vandromme, et al paper in the Journal of Trauma in 2011 posited that the following holds true...

• SI > 0.9  predicts twice the risk of massive transfusion
• SI > 1.1 predicts four times the risk of massive transfusion
• SI > 1.3 predicts nine times the risk of massive transfusion!

So, in trauma patients who come in with normal appearing vital signs, calculate the SI (and hopefully get a lactate and base deficit) before determining the patient is stable. 

References:
Paladino L, Subramanian RA, Nabors S, Sinert R.  The utility of shock index in differentiating major from minor injury. Eur J Emerg Med. 2011 Apr;18(2):94-8.

Vandromme, Griffin, Kerby, McGwin, Rue, Weinber Identifying Risk for Massive Transfusion in the Relatively Normotensive Patient: Utility of the Prehospital Shock Index. J Trauma. 2011 Feb;70(2):384-8; discussion 388-90.