Emergency Medicine

Resuscitation Outcomes Consortium (ROC) - Prehospital Resuscitation IMpedance valve and Early vs Delayed analysis (PRIMED)


Prehospital Resuscitation IMpedance valve and Early vs Delayed analysis (ROC PRIMED) Trial

Cardiac arrest is the sudden, abrupt loss of heart function. Death usually occurs within minutes unless cardiopulmonary resuscitation (CPR), rapid defibrillation, and paramedic interventions are available. CPR consists of pumping on the patient's chest and delivering breaths to produce some circulation until the heart can be restarted. When the chest is compressed, oxygen-rich blood is pumped forward. When the chest is released, oxygen-poor blood is brought back to the heart and lungs where it can be restored with oxygen before being pushed out to the body with another compression. Both actions -- pushing oxygen-rich blood forward and bringing oxygen-poor blood back to the heart and lungs -- are important. CPR however produces only about 30% of normal circulation. Methods to improve the circulation produced by CPR may lead to better survival.

Impedance Threshold Device (ITD)

One experimental device, called an impedance threshold device or ITD, is being studied in this clinical trial. The ITD is a device smaller than your fist that attaches to the end of the breathing bag used by EMTs and paramedics. The ITD works to bring more oxygen-poor blood back to the heart so that ultimately more oxygen-rich blood is available to be pushed forward.

Cardiopulmonary Resuscitation (CPR)

The timing of the CPR compressions is also being studied in this trial. Some evidence indicates that the period right before the heart is shocked may be especially important for the heart to have the best chance to regain its own natural heart beat. Experts have long believed that the first priority when trying to restart the heart was to shock the abnormal heart rhythm. More recently however some evidence has indicated that CPR should be the priority before delivering the shock. The research indicates that delaying the shock a few minutes to provide CPR may actually help the heart. The CPR seems to prime the heart pump so that after a few minutes of CPR the shock is more likely to produce a natural heartbeat than if the heart was shocked right away.

A study is planned involving the Emergency Medical Services of Portland and Multnomah County to evaluate whether either of these strategies -- the ITD or priming the heart with CPR before the shock -- will improve survival following cardiac arrest. The study is entitled ROC-PRIMED (Resuscitation Outcomes Consortium Prehospital Resuscitation using an Impedance threshold device and Early versus Delayed rhythm analysis), is supported by the National Institute of Health and will involve 10 communities from across the United States and Canada. Portland and greater Multnomah County are one of the 10 communities. Although these approaches appear promising and safe, they are yet to be proven to save lives.

Potential Risks & Benefits Associated with Use of the ITD

In earlier studies involving 922 patients, 16% survived to hospital admission without the ITD, and 23% survived with the ITD. No adverse events were reported. So it appears that the ITD has significant benefits, and that any possible serious side effects are infrequent (probably less than 1 out of every 1000 patients or so).

The reason this study is being conducted is that we do not know about the long-term effects of the ITD. In the long term, the ITD could be helpful, harmful, or have no effect on how long, after hospitalization, someone survives following a cardiac arrest. Similarly, the ITD could make a person's quality of life following a cardiac arrest better, worse, or have no effect. The main concern about quality-of-life is whether patients would suffer brain damage that impairs their ability to think, take care of themselves, or interact with other people.

If negative effects on either length of life or quality of life begin to show up, the study will be ended.

Potential Risks & Benefits of Differing Lengths of CPR

In different communities, CPR may be done for as little as 30 seconds and as long as three minutes before a cardiac arrest patient is given an electrical shock to restart the heart. But we don't really know which of these may be better. The only way to tell is to compare the two delays scientifically. The potential benefits of this part of the study would be knowing which approach is better in helping cardiac arrest patients to survive. There appear to be no significant risks to the systematic administration of CPR for a set length of time. Different communities already use different approaches with no apparent ill effects.

Note: This study was completed on November 6, 2009
For more information about the completion of the study,
please read the official OHSU press release and the NIH press release here     

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