title: Impact of impedance threshold devices on cardiopulmonary resuscitation: a systematic review and meta-analysis of randomized controlled studies.
abstract: OBJECTIVE
  Vital organ hypoperfusion significantly contributes to the dismal survival rates observed with manual cardiopulmonary resuscitation after cardiac arrest. The impedance threshold device is a valve which reduces air entry into lungs during chest recoil between chest compressions, producing a potentially beneficial decrease in intrathoracic pressure and thus increasing venous return to the heart. This review provides an update on the impedance threshold device and underlines its effect on short-term survival.
  
  
  METHODS
  MedCentral, CENTRAL, PubMed, and conference proceedings were searched (updated March 27, 2007). Authors and external experts were contacted.
  
  
  METHODS
  Three unblinded reviewers selected randomized trials using an impedance threshold device in cardiopulmonary resuscitation of nontraumatic out-of-hospital cardiac arrests. Four reviewers independently abstracted patient, treatment and outcome data.
  
  
  METHODS
  A total of 833 patients from five high quality randomized studies were included in the analysis.
  
  
  RESULTS
  Pooled estimates showed that the impedance threshold device consistently and significantly improved return to spontaneous circulation (202/438 [46%] for impedance threshold device group vs. 159/445 [36%] for control, relative risk [RR] = 1.29 [1.10-1.51], p = .002), early survival (139/428 [32%] vs. 97/433 [22%], RR = 1.45 [1.16-1.80], p = .0009) and favorable neurologic outcome (39/307 [13%] vs. 18/293 [6%], RR = 2.35 [1.30-4.24], p = .004) with no effect on favorable neurologic outcome in survivors (39/60 [65%] vs. 18/44 [41%]) nor an improved survival at the longest available follow up (35/428 [8.2%] vs. 24/433 [5.5%]).
  
  
  CONCLUSIONS
  This meta-analysis of randomized controlled studies suggests that the impedance threshold device improves early outcome in patients with out-of-hospital cardiac arrest undergoing cardiopulmonary resuscitation.
authors.affiliation: Department of Anesthesia and Intensive Care, Università Vita-Salute San Raffaele, and Istituto Scientifico San Raffaele, Milan, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Cabrini
authors.forename: Paolo
authors.initials: P
authors.lastname: Beccaria
authors.forename: Giovanni
authors.initials: G
authors.lastname: Landoni
authors.forename: Giuseppe G L
authors.initials: GG
authors.lastname: Biondi-Zoccai
authors.forename: Imad
authors.initials: I
authors.lastname: Sheiban
authors.forename: Marta
authors.initials: M
authors.lastname: Cristofolini
authors.forename: Oliviero
authors.initials: O
authors.lastname: Fochi
authors.forename: Giulia
authors.initials: G
authors.lastname: Maj
authors.forename: Alberto
authors.initials: A
authors.lastname: Zangrillo
mesh_terms: D016887:Cardiopulmonary Resuscitation / Q000295:instrumentation*; D017097:Electric Impedance; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D016032:Randomized Controlled Trials as Topic