Guidelines continue to stress the importance of airway, breathing, and circulation as the basic tenets of initial response to a CA. While this approach has merit in out-of-hospital arrests, it is an anathema in hospitalized patients. Valuable time is often lost trying to ascertain the presence or absence of respirations or pulse. Earle et al. designed a very creative way to gauge the operating characteristics of the carotid pulse check. Providers were asked to assess randomized patients who were to undergo open-heart surgery; some of the patients were already on cardiopulmonary bypass (“true negatives” with no spontaneous pulse) and the remainder were not (“true positives” with a pulse). With a median time of over 30 seconds, care providers could only accurately determine pulselessness 65% of the time (90% sensitivity and 55% specificity).22 Given that this study occurred in a very controlled environment without the drama of a real CA, it is likely that these data would even be worse in the chaos of resuscitation.
First Effective Stratagem: If an unresponsive adult inpatient clinically appears to be suffering a cardiopulmonary arrest, treatment (activation of a “code team” and application of CPR) should be initiated immediately without performing a pulse check.
CPR Physiology and Impact
CPR is a critical bridge to defibrillation but is not an end unto itself. The physiology that occurs during CPR is remarkably complex, and our current understanding is incomplete. Kouwenhoven posited that chest compressions result in a functional equivalent to open cardiac massage (2). In this “cardiac pump model,” the physiology is similar to a surgeon’s hands squeezing the non-beating heart: artificial systole from the down stroke of a compression compresses the heart against the spinal column forcing blood from the ventricles and forcing closure of the mitral and tricuspid valves. During artificial diastole, reversing pressure gradients result in closure of the aortic and pulmonic valves resulting in bi-ventricular filling of blood and perfusion of the coronary arteries.
An alternative model, the “thoracic pump model,” looks at the entire thoracic cavity as a pump with functional “valves” at the thoracic inlet preventing back-flow from the intrathoracic veins into the extrathoracic veins (23). The intrathoracic pressure rapidly increases during artificial systole leading to antegrade flow of blood from vessels under relatively higher pressure (the aorta and the pulmonary vasculature) to blood vessels under relatively lower pressure (the carotid arteries). The elevated intrathoracic pressure collapses the comparably weak vena cava, and, combined with tricuspid valve closure, prevents simultaneous retrograde venous flow. With three of the cardiac valves open during artificial systole, the heart is relegated to the role of a passive conduit for blood rather than providing any meaningful pumping action. During artificial diastole, intrathoracic pressure drops to near zero resulting in transient back flow of blood from the carotid arteries toward the heart. This induces aortic valve closure and generates only meager coronary artery perfusion.
Subsequent work by Paradis et al. shows that, in essence, both “pump” models have equal validity, and one or the other physiology dominates in any given patient (24). Regardless of which type of physiology occurs during resuscitation, neither provides physiologically sufficient circulation to maintain organ viability for long. When performed ideally, chest compressions during actual resuscitations in humans yield systolic blood pressures of only 60–80mmHg; and blood flow of less than one third the normal cardiac output, less than 10–15% of normal cerebral blood flow, and less than 1–5% of normal coronary artery blood flow (25).
Such subphysiologic circulation leaves little latitude for improper technique. Yet, care providers rarely perform chest compressions properly, erring towards too shallow a compression depth 62.6% of the time and too slow a compression rate 71.9% of the time on actual resuscitations―errors that increase in frequency the longer it has been since the caregiver was trained (26,27). Observational data on the quality of CPR suggest that these are not just esoteric technical deviations, but that compared with those in whom CPR is correctly performed, 14-day survival was almost 75% lower in those on whom CPR was incorrectly performed (16% vs. 4%)(28).