Review of: Guyette F, Gomez H, Suffoletto B, et al. Prehospital dynamic tissue oxygen saturation response predicts in-hospital lifesaving interventions in trauma patients. J Trauma Acute Care Surg. 2012;72(4):930–935.
This is an observational study from the University of Pittsburgh on predictive value of measuring tissue oxygen saturation (StO2) in trauma patients. The convenience sample included 150 patients who were transported by HEMS either from the scene or from another tertiary hospital. Investigators attempted to determine if tissue oxygen saturation could predict the need for a life-saving intervention (LSI) in the hospital—either emergent surgery or transfusion within 24 hours—based on a relationship between the desaturation and resaturation rates founded on a vascular occult test (VOT). They found desaturation was a better predictor for the need of an LSI in trauma patients.
Doc Wesley: There continues to be refinement in trauma triage to help EMS better identify those patients who are most in need of the care that a Level 1 Trauma Center can provide. We currently rely on a combination of physiologic, anatomic and mechanism-of-injury criteria to identify the Level 1 trauma patient. However, there will always be patients who fail to meet any of the criteria, and later be found to have a severe injury. For systems with a choice of hospital destination, this could result in the patient being transported to less-than-definitive care, only to be transferred once the severity of their injuries is recognized.
When the body is under stress from medical or traumatic causes, there are changes in the process of oxygen utilization. The technology utilized in this study measured this stress and determines whether the body is providing sufficient tissue perfusion. The test is easy to perform, and the technology has been in use for many years in the operating room.
The authors found that they were able to identify patients who had normal vital signs who ultimately required life-saving interventions, such as surgery and blood transfusions.
It’s important to recognize that this study was conducted in an air medical helicopter that had been summoned by EMS for a trauma patient, so there’s clearly some selection bias. However, I have to wonder how many patients transported by ground would have benefited by this technology. A finding of poor tissue perfusion would have led to air medical transport or ground transport to a Level 1 Center.
As the technology of tissue perfusion evolves, I’m confident that its application in EMS will only improve our care.
Medic Marshall: This is a technology that I’ve been passively following for a while and, quite frankly, I’m excited to see more research on it being published. Unlike the SpO2, which is just hemoglobin oxygenation, StO2 actually measures tissue oxygenation. This has great implications for EMS. Just as Dr. Wesley says, our current methods and tools available to triage trauma patients are based on some validated criteria. However, we still tend to miss a population of those patients who appear normal, but are actually decompensating in front of us.
However, I don’t think we need to all jump on the bandwagon quite yet. First, the study population is a convenience sample. Although not the best method, it definitely provides us with a picture of trauma patients transported by air. Secondly, the technology is still fairly new, and it’s not exactly clear what measurements we need to be monitoring. Although the study found no correlation between StO2 and other vital signs, it doesn’t necessarily mean there isn’t one. Again, this comes back to a small convenience sample and specific patient population.
Finally, we don’t know how using this technology is going to change our treatments in the field yet—if at all. You could make an argument that it may be the difference between a Level III trauma center and a Level I trauma center, but that’s only speculation.
At the end of the day, this study positively shows that measuring StO2 has some value and may help improve patient outcomes through earlier identification of shock states.
Objective: StO2 plus a vascular occlusion test is a noninvasive technology that targets indices of oxygen uptake and delivery. We hypothesize that prehospital tissue oximetric values and vascular occlusion test response can predict the need for in-hospital LSI.
Methods: We conducted a prospective, blinded observational study to evaluate StO2 slopes to predict the need for LSI. We calculated the DeO2 slope using Pearson’s coefficients of regression (r2) for the first 25% of descent and the ReO2 slope using the entire recovery interval. The primary outcome was LSI defined as the need for emergent operation or transfusion in the first 24 hours of hospitalization. The created multivariable logistic regression models using covariates of age, sex, vital signs, lactate and mental status.
Results: We assessed StO2 in a convenience sample of 150 trauma patients from April to November 2009. In-hospital mortality was 3% (95% confidence interval [CI], 1.1-7.6); 31% (95% CI, 24-39) were admitted to the intensive care unit, 6% (95% CI, 2.8-11.1) had an emergent operation, and 10% (95% CI, 5.7-15.9) required transfusion. Decreasing DeO2 was associated with a higher proportion of patients requiring LSL. In the multivariate model, the association between the need for LSI and DeO2, Glasgow Coma Scale, and age persists.
Conclusions: Prehospital DeO2 is associated with need for LSI in our trauma population. Further study of DeO2 is warranted to determine whether it can be used as an adjunct triage criterion or an endpoint for resuscitation.