Use of an impedance threshold device improves short-term outcomes following out-of-hospital cardiac arrest.

INTRODUCTION: An impedance threshold device (ITD) has been developed for the treatment of cardiac arrest to augment circulation to the heart and brain during cardiopulmonary resuscitation (CPR). The ITD has ventilation timing lights that flash at 12 min(-1) to discourage excessive ventilation rates.

HYPOTHESIS: Implementation of the ITD during conventional manual CPR in a large emergency medical services (EMS) system (Staffordshire, UK) is safe, feasible and will improve short-term survival.

METHODS: ITD use was implemented by the Staffordshire Ambulance Trust, which treats 1600 cardiac arrests per year with 90 advanced life support (ALS) units and an average response time of 6.3 min. During training, rescuers learned to use the ventilation timing lights to discourage hyperventilation. Rescuers applied the device after tracheal intubation. They were trained to allow the chest to recoil fully after each compression. Prospective ITD use in adults receiving conventional manual CPR for non-traumatic cardiac arrest was compared to matched historical controls receiving conventional manual CPR without inspiratory impedance. All received similar ALS care. The primary endpoint was admission to the emergency department (ED) alive following cardiac arrest. Chi-square, Fisher's exact and Kolmogorov-Smirnov tests were used for statistical analyses.

RESULTS: Survival (alive upon ED admission) in all patients receiving an ITD (61/181 [34%]) improved by 50% compared to historical controls (180/808 [22%]) (P<0.01). Survival in patients presenting in asystole tripled in the group receiving an ITD (26/76 [34%]) compared with historical controls (39/351 [11%]) (P=0.001). There were no significant adverse events.

CONCLUSIONS: The ITD was used safely and effectively in a large, diverse EMS system and markedly improved short-term survival for adult patients in non-traumatic cardiac arrest.