Robert C. Hyzy - Evidence-Based Critical Care

Emergency Medicine, University of Michigan Hospital, Ann Arbor, MI, USA

Ronny M. Otero

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It is currently estimated that over 300,000 out-of-hospital cardiac (OHCA) arrests occur in the United States. Over half of OHCA cases are managed by EMS systems [].

Early effective chest compressions and attention to basic life support components are part of high quality CPR. Various organizations have revisited each of the components of cardiac arrest resuscitation over the last couple of years and thus the elements of high-quality CPR are ever-evolving []. Rapid activation of the Chain of Survival and meticulous attention to early defibrillation and chest compressions may lead to greater overall trends in survival.

A 68 year-old male was playing cards at a casino when suddenly he clutched his chest and became unresponsive. Casino security arrived within less than a minute and applied an automated external defibrillator (AED). AED displayed an audio prompt that no shock was advised. Bystander cardiopulmonary resuscitation (CPR) was begun within another 10 s. Paramedics arrived and provided two-rescuer CPR with a compression rate of 110 compressions/minute. In the ambulance rescuers used a mechanical compression device to administer continuous chest compressions at a rate of 110 and depth of 2.5 inches with manual ventilation using a bag mask valve. This support was continued until their arrival at the hospital in approximately 9 min. Patient was not intubated in the field. During CPR there was no evidence of an organized cardiac rhythm. Patient had received a total of 3 doses of epinephrine totaling 3 mg via humeral intra-osseous line. Upon arrival in the emergency department endotracheal intubation was performed without incident and capnography displayed a good waveform with an ETCO2 of 15 mm Hg. On arrival emergency physicians administered another dose of epinephrine while continuing CPR. At this point the team leader paused and solicited ideas from the team about possible etiologies for persistent pulseless electrical activity (PEA).

Components of high quality CPR include minimizing interruptions of chest compressions with a chest compression fraction of >60 %, correct chest compression rate and depth. Recommended chest compression rates are greater than 100 and a depth of 50 mm with allowance for chest recoil between compression and minimizing ventilations to no more than 1012 breaths/minute []. How well chest compressions are meeting the goal of providing circulatory flow to the brain and vital systems is often difficult to ascertain.

Of the readily available parameters capnography and arterial blood pressure monitoring are the most easily applied measurements to provide feedback of the quality of chest compressions. Close attention to the physiologic response to chest compressions is desirable, as studies indicate that even healthcare professionals have poor recall and variable quality when performing chest compressions [].

Capnography has long-been seen as a potential surrogate for blood flow through heart and the pulmonary circulation [].

Achieving a higher blood pressure during CPR makes intuitive sense, as thoracic compression and thus, cardiac output will be the driving force behind improving cerebral and systemic perfusion. However, the hemodynamics of cardiac arrest is complex and patient-specific factors may be responsible for the variable responses to chest compressions, vasopressors and ventilation. One of the main determinants of successful resuscitation is the coronary perfusion pressure (CPP), which is the difference between the right atrial pressure (or CVP) and aortic pressure during diastole (relaxation phase of chest compression). In the arrested patient there is a delay until there is a complete cessation of flow through the cardiac chambers and by 1 min there is no flow to the coronary arteries. In a human study a CPP < 15 mm Hg was associated with not achieving ROSC []. When the ability to monitor CPP is unavailable a strategy to assess the efficacy of chest compressions may depend upon capnography and diastolic pressure.

Lastly, emerging technology, which provides instantaneous feedback about the quality of chest compressions is now available. This CPR-sensing feedback (FB) system often utilizes accelerometers to detect rate and depth of compressions while delivering audio cues to the rescuer. Currently available CPR-FB systems include the Phillips Q-CPR , Zoll Real CPR Help and Physio-Control compression metronome and Code Stat []. It is not known at this time whether utilizing these CPR-FB systems improves outcomes.