title: Use of respiratory impedance in prehospital care of hypotensive patients associated with hemorrhage and trauma: a case series.
abstract: BACKGROUND
  The respiratory pump can be optimized to enhance circulation in patients with hypotension by having patients spontaneously breathe through a low level of inspiratory resistance. This can be achieved with an impedance threshold device (ITD) designed to provide 7 cm H2O resistance during spontaneous inspiration with minimal resistance during expiration. Little is known about the effects of harnessing this physiological concept to increase blood pressure (BP) in the prehospital setting of care for patients with hypotension caused by blood loss or trauma. In this case series, we report on the feasibility, effectiveness, and safety of rapidly deploying the ITD by first responders to treat hypotension secondary to blood loss and trauma in the urban setting by emergency medical services personnel.
  
  
  METHODS
  Hemodynamic data from hypotensive patients (pretreatment systolic BP [SBP] <100 mm Hg) from 3 U.S. cities where the ITD is deployed were evaluated. The primary end point was maximum change in SBP and diastolic BP (DBP) from before to during ITD use in patients with hypotension secondary to documented blood loss or trauma. Secondary end points were device tolerance, whether the patient felt "better," change in heart rate, O2 saturation, and adverse events.
  
  
  RESULTS
  Of the 255 hypotensive patients treated, there were 26 categorized with blood loss and 13 with trauma. In this 39-patient subgroup, the SBP and DBP (mean ± SD) increased from 79 ± 14 mm Hg and 48 ± 12 mm Hg before ITD placement to 110 ± 17 mm Hg and 66 ± 14 mm Hg after ITD placement (p < 0.001). Breathing through the ITD resulted in no reported adverse events, was well tolerated, and resulted in feeling "better" in more than 85% of the patients.
  
  
  CONCLUSIONS
  Use of an ITD by emergency medical services personnel on hypotensive spontaneously breathing patients secondary to blood loss and trauma increased SBP and DBP and was feasible, well tolerated, and not associated with adverse effects (e.g., increased bleeding).
authors: Tactical Combat Casualty Care Research Program, United States Army Institute of Surgical Research, Fort Sam Houston, Texas 78234, USA. victor.convertino@amedd.army.mil
authors: Victor A
authors: VA
authors: Convertino
authors: Brent
authors: B
authors: Parquette
authors: John
authors: J
authors: Zeihr
authors: Kevin
authors: K
authors: Traynor
authors: Daryn
authors: D
authors: Baia
authors: Mark
authors: M
authors: Baumblatt
authors: Levon
authors: L
authors: Vartanian
authors: Mithun
authors: M
authors: Suresh
authors: Anja
authors: A
authors: Metzger
authors: Robert T
authors: RT
authors: Gerhardt
authors: Keith G
authors: KG
authors: Lurie
authors: David
authors: D
authors: Lindstrom
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure; D004632:Emergency Medical Services / Q000379:methods*; D005260:Female; D006339:Heart Rate; D006470:Hemorrhage / Q000150:complications / Q000628:therapy*; D006801:Humans; D007022:Hypotension / Q000209:etiology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000295:instrumentation / Q000379:methods*; D014947:Wounds and Injuries / Q000150:complications / Q000628:therapy*; D055815:Young Adult