No Survival Benefit of an Impedance Threshold Device during Out-of-Hospital Cardiac Arrest

A randomized study of 8,718 patients with non-traumatic out-of-hospital cardiac arrest at 10 ROC sites in the U.S. and Canada found no difference in the discharge rates between the patients who received standard CPR by EMS providers with use of an active impedance threshold device (ITD) or a sham device placed within five minutes.¹

The purpose of the ITD is to enhance venous return and cardiac output during CPR by lowering intrathoracic pressure. The primary outcome was the rate of discharge from hospital with satisfactory neurological function as measured by the modified Rankin score. Discharge status did not differ significantly between the group of patients who received the active device and those that received the sham device (5.8% and 6.0%). The researchers found no significant differences in subgroup analyses between the two groups.

The study was funded by the government, and ITDs were supplied by the manufacturer. EMS personnel were trained in ITD function and proper use. The trial included a run-in phase where EMS personnel were required to provide evidence of acceptable performance to an internal monitoring committee before they were permitted to participate in the main trial.

All 10 sites halted enrollment in November 2009 when the Data and Safety Monitoring Board recommended termination because interim analysis showed that the findings were not likely to change with continuation of the study.

The researchers suggest that a possible explanation for the results is that the ITD may not generate the physiological effects that have been proposed. A second possible explanation is that delayed application of the ITD, failure to prevent airway leaks and suboptimal performance of CPR can interfere with the hemodynamic improvements that are associated with ITD use. However, the researchers noted that comprehensive training, monitoring and followup provided a high level of assurance that CPR was optimal during the study. “It is not likely that EMS systems would apply the ITD in a more operationally efficacious way than they were applied in this study,” they said in the report.

The researchers noted that neither intrathoracic pressure nor chest recoil was measured during the study.

Conclusion: Use of the ITD did not significantly improve survival with satisfactory function among patients with out-of-hospital cardiac arrest receiving standard CPR from EMS personnel.

Reference

1. Aufderheide TP, et al. A trial of an impedance threshold device in out-of-hospital cardiac arrest. N Engl J Med. 2011 Sep 1; 365:798. doi:10.1056/NEJMoa1010821