Impedance Threshold Device Study Results

October 10, 2011

The Resuscitation Outcomes Consortium Study about the Impedance Threshold Device was published in the New England Journal of Medicine (click here to link to article).  This study was conducted in 10 regions of the US and Canada, including Western Pennsylvania.  Research subjects were patients with cardiac arrest who were treeated by paramedics in participating services.  The demographics of the subjects enrolled were representative of the region served by each paramedic service.  A total of 8,718 subjects were involved in this trial, making it one of the largest tests of a medical device ever performed.

For this study, paramedics applied an impedance threshold device (ITD) to the bag used to provide oxygen to patients who were receving CPR. The ITD is a small tube with a valve that is designed to decrease the pressure inside the lungs during chest compressions.  This decreased pressure helps blood return to the heart, which was hypothesized to promote the blood flow generated by chest compressions.  Several small studies have demonstrated improved blood pressures in patients where an ITD was used.  However, this study examined whether patients recovered to a good functional status at the time of hospital discharge.

In order to determine the effect of the ITD, paramedics in this study sometimes used a real ITD, and other times they used a "sham" ITD.  The sham ITD looked the same, but lacked any internal valve that would alter pressure in the chest.  A total of 4,373 subjects were treated with a real ITD and 4,345 subjects were treated with a sham ITD.  Survival to hospital discharge with good neurological status was the same whether a real ITD (5.8%) or sham ITD (6.0%) was used.  No subgroup of patients seemed to have any different outcomes related to the ITD.

This study concluded that using an ITD with standard CPR does not improve survival or funtional recovery.