NEJM: Using an impedance device during CPR does not improve survival
Use of an impedance threshold device (ITD) has been shown to enhance cardiac output during cardiopulmonary resuscitation (CPR); however, a study published Sept. 1 in the New England Journal of Medicine showed that use of these devices may not improve survival among patients with out-of-hospital cardiac arrest who received standard CPR.

“One proposed strategy to augment cardiac output during CPR is the use of an impedance threshold device (ITD),” Tom P. Aufderheide, MD, of the Medical College of Wisconsin in Milwaukee, and colleagues wrote. “The ITD is designed to enhance venous return and cardiac output during CPR by increasing the degree of negative intrathoracic pressure."

To compare the use of an active ITD with a sham ITD in patients with out-of-hospital cardiac arrest who underwent CPR, the researchers enrolled 8,718 patients; 4,345 were randomly assigned to treatment with a sham ITD and 4,373 to an active device. The patients underwent care at 10 centers in the U.S. and Canada that participate in the Resuscitation Outcomes Consortium (ROC).

The primary outcome used was survival to hospital discharge with satisfactory function. The researchers reported that 260 patients in the sham-ITD group and 254 patients in the active-ITD group met the primary outcome. The researchers concluded that there were no significant differences between the two groups in terms of adverse events.

“[T]his large effectiveness trial did not confirm a survival advantage with the use of an active ITD during standard CPR in patients with nontraumatic, out-of-hospital cardiac arrest,” the authors wrote. Aufderheide and colleagues speculated that one reason for the lackluster results could have been due to the fact that the ITD may not generate physiological effects in terms of hemodynamics. Additionally, some EMS systems did not recreate the physiological effects seen in previous studies, the researchers said.

“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,” the authors wrote. “For these reasons, the ROC investigators implemented comprehensive training, retraining, electronic monitoring of the CPR process and follow-up quality-assurance monitoring.

“Use of the active ITD did not significantly improve survival with satisfactory function,” the authors concluded. The authors noted that there were several limitations during the trial. Limitiations included unmeasured factors such as hemodynamics, intrathoracic pressure, ventilation rate and duration and the effects of ITD use during gasping and spontaneous ventilation.