title: Clinical evaluation of an inspiratory impedance threshold device during standard cardiopulmonary resuscitation in patients with out-of-hospital cardiac arrest.
abstract: OBJECTIVE
  To determine whether an impedance threshold device, designed to enhance circulation, would increase acute resuscitation rates for patients in cardiac arrest receiving conventional manual cardiopulmonary resuscitation.
  
  
  METHODS
  Prospective, randomized, double-blind, intention-to-treat.
  
  
  METHODS
  Out-of-hospital trial conducted in the Milwaukee, WI, emergency medical services system.
  
  
  METHODS
  Adults in cardiac arrest of presumed cardiac etiology.
  
  
  METHODS
  On arrival of advanced life support, patients were treated with standard cardiopulmonary resuscitation combined with either an active or a sham impedance threshold device.
  
  
  RESULTS
  We measured safety and efficacy of the impedance threshold device; the primary end point was intensive care unit admission. Statistical analyses performed included the chi-square test and multivariate regression analysis. One hundred sixteen patients were treated with a sham impedance threshold device, and 114 patients were treated with an active impedance threshold device. Overall intensive care unit admission rates were 17% with the sham device vs. 25% in the active impedance threshold device (p = .13; odds ratio, 1.64; 95% confidence interval, 0.87, 3.10). Patients in the subgroup presenting with pulseless electrical activity had intensive care unit admission and 24-hr survival rates of 20% and 12% in sham (n = 25) vs. 52% and 30% in active impedance threshold device groups (n = 27) (p = .018, odds ratio, 4.31; 95% confidence interval, 1.28, 14.5, and p = .12, odds ratio, 3.09; 95% confidence interval, 0.74, 13.0, respectively). A post hoc analysis of patients with pulseless electrical activity at any time during the cardiac arrest revealed that intensive care unit and 24-hr survival rates were 20% and 11% in the sham (n = 56) vs. 41% and 27% in the active impedance threshold device groups (n = 49) (p = .018, odds ratio, 2.82; 95% confidence interval, 1.19, 6.67, and p = .037, odds ratio, 3.01; 95% confidence interval, 1.07, 8.96, respectively). There were no statistically significant differences in outcomes for patients presenting in ventricular fibrillation and asystole. Adverse event and complication rates were also similar.
  
  
  CONCLUSIONS
  During this first clinical trial of the impedance threshold device during standard cardiopulmonary resuscitation, use of the new device more than doubled short-term survival rates in patients presenting with pulseless electrical activity. A larger clinical trial is underway to determine the potential longer term benefits of the impedance threshold device in cardiac arrest.
authors.affiliation: Department of Emergency Medicine, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: Tom P
authors.initials: TP
authors.lastname: Aufderheide
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Pirrallo
authors.forename: Terry A
authors.initials: TA
authors.lastname: Provo
authors.forename: Keith G
authors.initials: KG
authors.lastname: Lurie
mesh_terms: D000368:Aged; D016887:Cardiopulmonary Resuscitation / Q000009:adverse effects / Q000295:instrumentation* / Q000706:statistics & numerical data; D004311:Double-Blind Method; D004632:Emergency Medical Services / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D010343:Patient Admission / Q000706:statistics & numerical data; D011175:Positive-Pressure Respiration / Q000009:adverse effects / Q000295:instrumentation* / Q000706:statistics & numerical data; D011654:Pulmonary Edema / Q000209:etiology; D020127:Recovery of Function; D012044:Regression Analysis; D016019:Survival Analysis; D014839:Vomiting / Q000209:etiology; D014922:Wisconsin