Tuesday, May 14, 2013

AutoPulse -- Sometimes a Life Saver

The AutoPulse is an automated, portable, battery-powered cardiopulmonary resuscitation device created by Revivant and subsequently purchased and currently manufactured by ZOLL Medical Corporation. It is a chest compression device composed of a constricting band and half backboard that is intended to be used as an adjunct to CPR during advanced cardiac life support by professional health care providers. The
AutoPulse uses a distributing band to deliver the chest compressions. In literature it is also known as LDB-CPR (Load Distributing Band-CPR).

The AutoPulse measures chest size and resistance before it delivers the unique combination of thoracic and cardiac chest compressions. The compression depth and force varies per patient. The chest displacement equals a 20% reduction in the anterior-posterior chest depth. The physiological duty cycle is 50%, and it runs in a 30:2 or continuous compression mode, which is user-selectable, at a rate of 80 compressions-per-minute.

Device Operation
The patient's head, shoulders and upper back lay upon the base unit, with the controls for the AutoPulse beside the patient's left ear. It can be augmented for cervical spinal support. The unit contains the control computer, the rechargeable battery, and the motors that operate the LifeBand. The LifeBand is an adjustable strap that covers the entire rib cage. When the patient (who must be disrobed) is strapped in and the start button is pressed, the LifeBand pulls tight around the chest, determines the patient's chest size and resistance, and proceeds to rhythmically constrict the entire rib cage, pumping the heart at a rate of 80 compressions per minute. The LifeBand can be placed over defibrillation pads but must be temporarily loosened to use standard paddle defibrillators and repositioned after the shock has been delivered. The LifeBand is disposable, and designed to be used on a single patient for sanitary reasons.

Studies and Clinical Trials
The gold standard for resuscitation research is survival to hospital discharge. Although common sense suggests that short-term and intermediate outcomes like return of spontaneous circulation (ROSC) or survival to hospital admission are promising, experienced scientists know that anything less than a neurologically intact survivor walking out of the hospital is ultimately irrelevant.


Several animal studies have shown that automated CPR machines are more effective at providing circulatory support than manual CPR. One study showed that use of the AutoPulse produced blood flow to the heart and brain that was comparable to pre-arrest levels. In another study, an adapted AutoPulse was shown to be highly effective in support of cardiac arrest in animals, whereas manual CPR was tenuous in its effectiveness. Pigs were used in the study, and were left in cardiac arrest for eight minutes to simulate average ambulance response time. 73% of the pigs that were put into the AutoPulse were revived, and 88% of the surviving pigs showed no neurological damage. None of the pigs that received manual CPR survived.

The device has shown less promise with human research. Although some studies showed improved coronary perfusion pressure and more spontaneous return of circulation with the AutoPulse, one large, multi-centered, randomized clinical trial was canceled early by the International Review Board (IRB) when it was determined that patients who received manual CPR were more likely to walk out of the hospital, suggesting that enthusiasm for the device "is premature, given that the effectiveness of the device likely depends on still-to-be-defined factors independent of the mechanical capabilities of the device."

Criticism
The AutoPulse has received a fair amount of criticism surrounding its battery life, bulk, and studies suggesting poor survival to hospital discharge. The most notable case of such issues can be found in the news reports of the resuscitation of Prince Frisco after he and his companion were caught in an avalanche. In that case, the AutoPulse batteries failed after only 9 and 15 minutes. Others have criticized the high cost and non-reimbursable nature of the disposable AutoPulse LifeBand.

Studies have also failed to show an increase in survival to hospital discharge. During the ASPIRE trial (the first multi-centered, randomized trial with large enrollment), the survival to hospital discharge rates decreased from 9.9% with manual CPR to approximately 5%. Because of these findings, the ethics review board terminated the study. However, some researchers question the validity of the ASPIRE protocol. The CIRC study results additionally indicate that the AutoPulse increases the time before first defibrillation and decrease the average compressions per minute in comparison with manual CPR. Overall, the study shows no improvement over high quality manual CPR.


Several cases have been reported where the AutoPulse has caused additional injury to patients receiving compressions from the device.


Some departments and agencies have begun discontinuing the use of the AutoPulse, citing battery and reliability issues.

http://en.wikipedia.org/wiki/AutoPulse

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