title: Use of an impedance threshold device in spontaneously breathing patients with hypotension secondary to trauma: an observational cohort feasibility study.
abstract: BACKGROUND
  An impedance threshold device (ITD) intended for use in the spontaneously breathing patient has been shown to raise blood pressure in hypotensive patients. This device has not been evaluated in patients with hypotension secondary to trauma. This study focused on changes in key vital signs when the ITD was added to the paramedic treatment protocol for hypotensive patients with prehospital traumatic injury.
  
  
  METHODS
  A 6-month prospective nonrandomized observational cohort study was conducted of 200 spontaneously breathing symptomatic adult patients with prehospital hypotension due to multiple causes; the patients of primary interest experienced a traumatic injury. Upon determination of hypotension (systolic blood pressure of approximately ≤90 mm Hg), standard therapy was initiated by application of the mask-style ITD. Vital signs were documented every 2 minutes to 5 minutes after intervention. A change in mean arterial pressure (MAP) with ITD use was the primary study endpoint.
  
  
  RESULTS
  Of the 200 hypotensive subjects treated, 29 (3 were excluded because of incomplete data sets and 3 patients treated with the ITD were excluded because their blood pressure did not meet inclusion criterion) were hypotensive secondary to trauma. Their MAP increased from 60 mm Hg (SD, 11 mm Hg; 95% confidence interval [CI], 8.17-15.432) to 78 mm Hg (16 mm Hg; 95% CI, 12.43-23.46) (p = 0.001), without significant change in mean heart rate. Approximately 75% of the patients reported moderate to easy tolerance. Similar increases in MAP were observed in the nontraumatic patients, from 60 mm Hg (10 mm Hg; 95% CI, 9.4-11.5) to 70 (15; 95% CI, 13.4-16.7) (p = 0.0001).
  
  
  CONCLUSIONS
  In this observational cohort study of patients with hypotension secondary to trauma, the ITD was well tolerated, and MAP as well as systolic and diastolic blood pressure were improved. The patients were not overresuscitated with this intervention. On the basis of these findings, additional studies in patients with hypotension secondary to traumatic injury should be performed to better define the need and benefit of additional fluid resuscitation when the ITD is used.
  
  
  METHODS
  Therapeutic study, level IV.
authors.affiliation: From the Department of Emergency Health Sciences (D.W., J.L., C.M.), University of Texas Health Science Center at San Antonio; San Antonio Fire Department (D.W., S.W., M.H., C.M.), San Antonio; United States Army Institute for Surgical Research (V.A.C.), Fort Sam Houston; and Southwest Texas Regional Advisory Council for Trauma (S.W.), San Antonio, Texas.
authors.forename: David
authors.initials: D
authors.lastname: Wampler
authors.forename: Victor A
authors.initials: VA
authors.lastname: Convertino
authors.forename: Shannon
authors.initials: S
authors.lastname: Weeks
authors.forename: Michael
authors.initials: M
authors.lastname: Hernandez
authors.forename: Jacob
authors.initials: J
authors.lastname: Larrumbide
authors.forename: Craig
authors.initials: C
authors.lastname: Manifold
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D001794:Blood Pressure / Q000502:physiology; D017097:Electric Impedance / Q000627:therapeutic use; D004632:Emergency Medical Services / Q000379:methods; D005240:Feasibility Studies; D006339:Heart Rate / Q000502:physiology; D007022:Hypotension / Q000209:etiology / Q000503:physiopathology / Q000628:therapy; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000295:instrumentation / Q000379:methods; D056152:Respiratory Rate / Q000502:physiology; D055986:Vital Signs / Q000502:physiology; D014947:Wounds and Injuries / Q000150:complications / Q000503:physiopathology / Q000628:therapy