Cardiopulmonary Resuscitation and Emergent Cardiac Care «Part I»

Cardiopulmonary Resuscitation and Emergent Cardiac Care «Part I»
M. Sherif Mokhtar, MD
Professor of Cardiology,
Professor of Critical Care Medicine - Cairo University
The complexity of cardiac arrest has led to the generation of a theory for its study, which divides cardiac arrest from VF into three phases.
Although the existence of those three phases is not scientifically proven, they are widely used as a basis for research. Specific treatments targeting the pathophysiology of each phase increases the chances for a meaningful recovery[1].
The first phase, the electrical, lasts about 4 minutes after the initial collapse, and is characterized by a high degree of responsiveness to early defibrillation. The second phase, the circulatory, lasts from 4-10 minutes, depending on the surrounding temperature and conditions. Good quality CPR, with emphasis given to improve delivery of oxygenated blood to the brain and the heart before defibrillation, is of paramount importance, and techniques that increase circulation have been shown to improve outcomes. The third phase, the metabolic, usually starts after 10 minutes.
Current treatments are poor, and late efforts generally target the metabolic effects of prolonged ischemia. Survival is inversely related to the time of untreated cardiac arrest. Most of the victims
of cardiac arrest get professional assistance during the second phase of cardiac arrest, namely the circulatory phase. This is one of the reasons that the current guidelines have placed extra emphasis on ways to improve circulation and simplify the delivery of compressions and ventilations.
Immediate Resuscitation:
The earlier the intervention from the cardiac collapse, the higher chances are for survival. Based on the idea that most of the victims of cardiac arrest are initially approached by laypersons, a specific emphasis has been placed to increase the rate of bystander CPR. Specifically, when there is unwillingness to provide rescue breathing, radio dispatchers should encourage chest compression-only CPR to facilitate rapid initiation of chest compression.
The AHA has recently made a recommendation that promotes compression only CPR for bystanders, because a large body of evidence suggests that for the initial treatment of cardiac arrest, there is no significant down side to bypass ventilations. Fear of disease transmission from mouth-to-mouth ventilation and the challenges of trying to teach mouth-to-mouth ventilation have shifted the emphasis of pre-EMS arrival telephone instructions to focus rescuers on chest
compressions only.
Based on a solid body of evidence, early defibrillation in a witnessed arrest is currently a Class I recommendation. The defibrillation I waveform type recommended has been the biphasic electrical counter-shock since it has been shown to decrease defibrillation thresholds when compared to monophasic shock[2].
Nearly all new external defibrillators are currently manufac-tured to deliver biphasic shocks. AEDs manufactured prior to 2005 need to be reprogrammed to deliver single shocks. AEDs manufactured after 2005 typically have this new programming.
Improving Circulation:
Most pre-hospital cardiac arrests cannot be treated within the 4 Minutes of the electrical phase. During the circulatory phase (4-10 minutes of cardiac arrest), there is a need for immediate compressions to generate blood flow and partially replete the cells’ energy required for generation of an organized rhythm. It has been recently shown that when the time between the telephone call and paramedic arrival is longer than 4-5 minutes, CPR first before shock improves survival rates[3].
The focus of modern CPR is more compressions and fewer ventilations. They call for
immediate chest compressions, and once an advanced airway has been established, continuous chest compressions without interruption for ventilations.
For Basic Life Support (BLS), the compression-to-ventilation ratio is currently set at 30:2 to provide fewer interruptions of ‘compressions for ventilation.
During CPR, even in the best of circumstances, the generated cardiac output is During Advanced Life Support (ALS), uninterrupted compressions with a rate of 100 per minute are recommended. The rescuers who are responsible for the ventilation should deliver 8-10 breaths per minute with special care not to hyperventilate. Rescuers should rotate frequently (every 1-2 minutes) to avoid excessive fatigue, which is known to diminish the quality of CPR.
Ventilations:
Periodic ventilation during CPR is important to provide oxygen to the blood and tissues. However, a fundamental shift in the 2005 AHA/ECC guidelines is to prevent excessive ventilation rates, which have been shown to be life-threatening, if not deadly[4].
Each time intrathoracic pressure is increased with a positive pressure ventilation,
venous return to the heart is inhibited and intracranial pressure is increased. As such, the benefits of positive pressure ventilation must be weighed against the harm associated with too much ventilation. In addition, the unwillingness of the layperson to provide CPR due to the fear of communicating diseases and the inherent aversion to mouth-to-mouth ventilation should be taken under consideration.
Based in part on this rediscovered physiology, the new guide-lines recommend a reduced ventilation rate during BLS of two breaths after 30 continuous compressions and of only 8-10 breaths/minute for ALS. Moreover, each BLS and ALS breath should
be delivered with a tidal volume of only -500 cc and over a period of only 1 second. These subtle but fundamental changes in ventilation technique assure optimal circulation during conventional manual closed-chest CPR.
Compressions:
Chest compressions or “external cardiac massage” was first introduced into the modern medical literature by Jude, Kouwenhoven, and Knickerbocker in 1960[5].
Generation of blood flow during compressions results from an increase in intrathoracic pressure (Thoracic Pump Theory), the mechanical effect of compressing the heart between the sternum and spine (Cardiac Pump Theory), and the cardiac valvular system, that allows mainly unidirectional flow. In the guidelines, the importance of compressions during CPR is recognized and, therefore, pushing “hard and fast” is recommended. A depth of 1.5-2 inches (5 cm) is considered adequate compression depth [6].
The rate should be 100 compressions per minute since lower rates decrease forward blood flow[7]. Interruptions should be minimized, since every time compressions are stopped, it takes a significant amount of time to re-establish adequate aortic pressure and coronary perfusion pressure[8]. Pulse checks should not last more than 10 seconds.
An important point in the guidelines is that uninterrupted chest compressions should be delivered both before and immediately after the delivery of a shock. Chest compressions for 90 seconds to 3 minutes before defibrillation help to prime the pump, making successful return
of spontaneous circulation most likely after defibrillation. Chest compressions for 60 seconds to 2 minutes immediately after defibrillation are thought to help prevent the hypotension and asystole that is often observed when a defibrillation shock is delivered.
As a result, rather than check for a pulse after a defibrillation shock in a patient who has been in VF for >4 minutes, the rescuers should immediately resume CPR to maintain circulation, even if the heart is spontaneously beating.
Compression-Only (Hands-Only) CPR:
Significant animal investigations have shown that for the usual times of witnessed cardiac arrest, compression-only CPR provided comparable to standard CPR hemodynamics and survival outcomes[9]. A recent study showed that minimally interrupted cardiac resuscitation (MICR) improves survival in out-of-hospital cardiac arrest[10].
Decompressions:
With each chest wall decompression, the negative intrathoracic pressure naturally generated by the elastic recoil properties of the chest wall acts to promote venous return to the heart, thereby increasing preload for the next compression cycle. Incomplete decompression, like hyperventilation, is a common mistake that also decreases blood flow to the heart and brain during CPR.
A recent randomized trial showed that many rescuers fail to decompress completely.
This results in a sustained end-diastolic increase of intracranial pressure. This phenomenon, when examined in a porcine model of cardiac arrest, revealed two fundamental effects. First, incomplete chest wall recoil caused a significant decrease of mean arterial pressure, an increase in RA pressure, and thus decreased coronary perfusion pressures.
Second, incomplete chest wall recoil caused an increase of intracranial pressure, leading to a significant decrease in cerebral and systemic perfusion pressures [11].
Recommendations:
In the event that an adult suddenly collapses, trained or untrained bystanders should-at a minimum-activate their community emergency medical response system (telephone) and provide
high-quality chest compressions by pushing hard and fast in the center of the chest, minimizing interruptions according to the published guidelines (Class 1).
2- If a bystander has not received training in CPR, then hands-only CPR is strongly encouraged (Class IIa). The rescuer should continue hands-only CPR until an Automatic External Defibrillator (AED) arrives and is ready for use, or Emergency Medical Service (EMS) providers take over care of the victim.
3- When the bystander has received training in CPR, he or she could provide either conventional CI’R using a 30:2 compression-to-ventilation ratio (Gass IIa) or hands-only CPR (Class Ila). CPR with either of the two techniques should be continued until defibrillation is possible or EMS providers take over.