Conference Coverage

Hypotension ‘dose’ drives mortality in traumatic brain injury


– The severity and duration of hypotension in traumatic brain injury patients during EMS transport to an emergency department has a tight and essentially linear relationship to their mortality rate during subsequent weeks of recovery, according to an analysis of more than 7,500 brain-injured patients.

For each doubling of the combined severity and duration of hypotension during the prehospital period, when systolic blood pressure was less than 90 mm Hg, patient mortality rose by 19%, Daniel W. Spaite, MD, reported at the American Heart Association scientific sessions.

However, the results do not address whether aggressive treatment of hypotension by EMS technicians in a patient with traumatic brain injury (TBI) leads to reduced mortality. That question is being assessed as part of the primary endpoint of the Excellence in Prehospital Injury Care-Traumatic Brain Injury (EPIC-TBI) study, which should have an answer by the end of 2017, said Dr. Spaite, professor of emergency medicine at the University of Arizona in Tuscon.

Dr. Daniel W. Spaite presenting at the AHA Scientific Sessions. Mitchel L. Zoler/Frontline Medical News

Dr. Daniel W. Spaite

Results from prior studies have clearly linked prehospital hypotension with worse survival in TBI patients. But until now, no appreciation existed that not all hypotensive episodes are equal, and that both the severity of hypotension and its duration incrementally contribute to mortality as the “dose” of hypotension a patient experiences increases. In large part, that’s because until now prehospital hypotension has been recorded simply as a dichotomous, yes/no condition.

The innovation introduced by Dr. Spaite and his associates in their analysis of the EPIC-TBI data was to drill down into each patient’s hypotensive event, made possible by the 16,711 patients enrolled in EPIC-TBI.

The calculation they performed was limited to patients with EMS records of at least two blood pressure measurements during prehospital transport. These data allowed them to use both the extent to which systolic blood pressure dropped below 90 mm Hg and the amount of time pressure was below this threshold to better define the total hypotension exposure each patient received.

This meant that a TBI patient with a systolic pressure of 80 mm Hg for 10 minutes had twice the hypotension exposure of both a patient with a pressure of 85 mm Hg for 10 minutes, and a patient with a pressure of 80 mm Hg for 5 minutes.

Their analysis also adjusted the relationship of this total hypotensive dose and subsequent mortality based on several baseline demographic and clinical variables, including age, sex, injury severity, trauma type, and head-region severity score. After adjustment, the researchers found a “strikingly linear relationship” between hypotension dose and mortality, Dr. Spaite said, although a clear dose-response relationship was also evident in the unadjusted data.

EPIC-TBI enrolled TBI patients age 10 years or older during 2007-2014 through participation by dozens of EMS providers throughout Arizona. For the current analysis, the researchers identified 7,521 patients from the total group who had at least two blood pressure measurements taken during their prehospital EMS care and also met other inclusion criteria.

The best way to manage hypotension in TBI patients during the prehospital period remains unclear. Simply raising blood pressure with fluid infusion may not necessarily help, because it could exacerbate a patient’s bleeding, Dr. Spaite noted during an interview.

The primary goal of EPIC-TBI is to assess the impact of the third edition of the traumatic brain injury guidelines released in 2007 by the Brain Trauma Foundation. (The fourth edition of these guidelines came out in August 2016.) The new finding by Dr. Spaite and his associates will allow the full EPIC-TBI analysis to correlate patient outcomes with the impact that acute, prehospital treatment had on the hypotension dose received by each patient, he noted.

“What’s remarkable is that the single, prehospital parameter of hypotension for just a few minutes during transport can have such a strong impact on survival, given all the other factors that can influence outcomes” in TBI patients once they reach a hospital and during the period they remain hospitalized, Dr. Spaite said.

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