More than 300,000 Americans experience out-of-hospital cardiac arrest annually, with overall survival rates averaging less than 5%. Low survival rates persist, in part, because manual chest compressions and ventilation, termed standard cardiopulmonary resuscitation (S-CPR), is an inherently inefficient process, providing less than 25% of normal blood flow to the heart and the brain. Hemodynamics are often compromised further by poor S-CPR techniques, especially inadequate chest compression and incomplete chest recoil. Active Compression Decompression CPR (ACD-CPR) is performed with a hand-held device that is attached to the patient's chest, and also includes a handle containing a metronome and force gauge to guide proper compression rate, depth and complete chest wall recoil. The impedance threshold device (ITD) is designed for rapid connection to an airway adjunct (e.g. facemask or endotracheal tube) and allows for positive pressure ventilation, while also impeding passive inspiratory gas exchange during chest wall decompression. Prior studies have shown that the combination of ACD-CPR + ITD enhances refilling of the heart after each compression by augmenting negative intrathoracic pressure during the decompression phase of CPR, resulting in improved cardiac and cerebral perfusion. The intrathoracic pressure regulator (ITPR) is a next generation inspiratory impedance therapy. The ITPR uses a regulated external vacuum source to lower the negative intrathoracic pressure and is therefore less dependent on the quality of CPR (e.g., completeness of chest wall recoil). The ITPR generates a pre-set continuous and controlled expiratory phase negative intrathoracic pressure that is interrupted only when positive pressure ventilation is needed to maintain oxygenation and provide gas exchange.

The purpose of the study is to compare the early safety and hemodynamic effects of S-CPR, ACD- CPR + ITD, and S-CPR + ITPR in patients with out-of-hospital cardiac arrest.

Initial Inclusion Criteria:

• Subject is initially presumed or known to be 18 years of age or older;
• Subject presents with presumed non-traumatic, out-of-hospital cardiac arrest AND is a candidate for resuscitation attempt. [NOTE: the cardiac arrest may be witnessed OR unwitnessed];
• Subject has a secured cuffed advanced airway [e.g., endotracheal tube, Combitube, King airway].

Final Inclusion Criteria:

• Subject in whom femoral arterial access was successfully established;
• Subject remained in cardiac arrest (undergoing CPR) at the time of hemodynamic data acquisition;
• Subject in whom at least 5 minutes of continuous hemodynamic data were able to be collected, OR if ROSC occurs before 5 minutes, at least 2 minutes of hemodynamic data were able to be collected.

Initial Exclusion Criteria:

• Subject has known pre-existing DNR orders in place prior to this cardiac arrest;
• Subject has signs of obvious clinical death or conditions that preclude the use of CPR;
• Subject's family or legal guardians request that the subject not be entered in the study at the time of arrest;
• Subject has recent sternotomy, with wound not appearing completely healed (if date of sternotomy is unknown) or less than six months (if date of sternotomy is known);
• Subject has a stoma, tracheotomy, or tracheostomy prior to arrest;
• Subject is known or suspected to be pregnant;
• Subject is known/suspected to be a prisoner.

Final Exclusion Criteria:

• Subject in whom < 2 minutes of hemodynamic data were acquired while receiving CPR;
• Subject in whom an arterial pressure catheter was not placed or arterial pressure was not able to be successfully monitored;
• Subject is subsequently found to have had a traumatic arrest;
• Subject was in asystole at time of initial arrest AND remained in asystole during resuscitation effort AND arrest was unwitnessed or unknown if witnessed.