Impact of impedance threshold devices on cardiopulmonary resuscitation: A systematic review and meta-analysis of randomized controlled studies

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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.

Data Source:

MedCentral, CENTRAL, PubMed, and conference proceedings were searched (updated March 27, 2007). Authors and external experts were contacted.

Study Selections:

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.

Data Extraction:

A total of 833 patients from five high quality randomized studies were included in the analysis.

Data Synthesis:

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%]).


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.

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