Cardiac Arrest Bundle of Care Trial

Out of hospital cardiac arrest (OOHCA) is the sudden cessation of effective cardiovascular circulation in the pre hospital setting. This is sadly a common occurrence within the UK with approximately 60,000 OOHCAs per year. In 30,000 of these, resuscitation is attempted by the ambulance service. Survival remains poor (2-12%) within the UK and even the best performing regions still lag someway behind exemplar global systems (Seattle 21%, Norway 25%). There are a plethora of reasons for variation in outcome, not limited to the availability of community defibrillators, the education and ability of bystanders to provide effective CPR, the response times of the emergency medical personnel, the training of emergency services personnel and their individual exposure to cardiac arrest, the availability of primary percutaneous coronary intervention, and even the availability of extracorporeal resuscitation.

Despite poor outcomes from OOHCA for decades, there exists promising data from animal and cadaver studies that new technological devices could improve the currently poor blood flow generated by chest compressions during CPR, particularly cerebral blood flow. The current standard of care for patients with an OOHCA includes manual CPR delivered at a rate of 100-120 compressions per minute with a depth of 5 cm (maximum 6 cm). In turn, periodic inflation of the lungs using positive pressure ventilation to maintain oxygenation is mandated during CPR. Animal data have shown that blood flow to the heart and brain using this method is approximately 15-30% of normal. Conventional CPR is therefore unphysiological by definition, with intracerebral pressures being too high in the compression phase and intrathoracic pressure being too high in the release phase for adequate blood flow to the brain and heart respectively. Mechanisms and tools to improve this have been available for some time but using them synergistically to achieve improved cerebral and coronary blood flow is a relatively recent advance.

It is now possible to mimic a more physiologically normal situation by combining 3 pieces of technology. These may lead to better organ perfusion during CPR and therefore better rates of survival. The 3 devices in question do this in different complementary ways, in turn;

1. Head up position- gradated elevation of the head after CPR has been initiated, improves cerebral blood flow during CPR. This has been studied predominantly in porcine models. HUP-CPR enhances venous return, and reduces intracranial pressure during the decompression phase of CPR. This results in improved cerebral perfusion pressure and improves cerebral blood flow.
2. Active compression/decompression CPR uses a device with a suction cup placed on the thorax that via active decompression generates a negative intrathoracic pressure on each upward stroke, meaning that venous return to the heart improves during each cycle of CPR, allowing more blood to then be pumped to the brain on the next compressive cycle.
3. Combined with an impedance threshold device which works by limiting air entry into the lungs during chest recoil between chest compressions thereby enhancing the lower intrathoracic pressure achieved by active decompression, as described above.

The first retrospective study examining the combination of active compression decompression CPR with an ITD and HUP-CPR in humans was published in 2022, concluding that rapid initiation of bundle of care-CPR was associated with a higher likelihood of survival to hospital discharge after OHCA when compared with conventional CPR. 9. The first prospective human study using this triple bundle approach is currently ongoing in France.