Advanced Cardiac Life Support (ACLS) and Therapeutic Hypothermia

Chapter 49


Advanced Cardiac Life Support (ACLS) and Therapeutic Hypothermia



Sudden cardiac arrest (SCA) is defined as the immediate cessation of mechanical cardiac function and the concomitant global loss of blood flow. SCA is a leading cause of death in the United States with approximately 300,000 Americans succumbing to SCA each year. Advanced Cardiac Life Support (ACLS) represents a set of highly time-sensitive therapeutic maneuvers used to support and ultimately restore circulation (see Figure 49.1 for overview of the SCA survival time line). ACLS includes cardiopulmonary resuscitation (CPR), endotracheal intubation, electrical defibrillation for appropriate cardiac rhythms, and the use of specific pharmacologic interventions. ACLS algorithms (see Appendix D for ACLS algorithms) are widely used during both in-hospital SCA (by trained nurses and physicians) and out-of-hospital SCA (by ambulance personnel). ACLS certification is required for a large number of health care providers.



A multisite study from 2008 evaluating cardiac arrest survival outcomes revealed a wide range of survival to hospital discharge rates in the United States, from 3% to 16% with an overall 8% survival for out-of-hospital cardiac arrest. Survival from in-hospital cardiac arrest is somewhat higher, with a large registry study documenting 18% survival to hospital discharge. Since the development and implementation of rapid response teams (RRTs; also known as medical emergency teams or METs [see Chapter 110]) to respond to impending arrest events in the hospital, the demographics of in-hospital cardiac arrest has shifted, with fewer SCA events on the general wards and more events taking place in intensive care units (ICUs). The overall impact of RRTs on SCA survival, however, remains controversial and a topic of ongoing investigation.


Although the sequence of actions required in ACLS had been generally considered complete once a patient had regained a pulse, the introduction of a powerful post-resuscitation treatment option, therapeutic hypothermia (TH), has broadened the scope of resuscitation care. TH, the intentional lowering of core body temperature after initial resuscitation, has been shown to improve both survival and neurologic outcomes following SCA. This chapter provides an overview of cardiac arrest resuscitation care as well as important aspects of post-resuscitation care including TH. Although reference will be made to the ACLS protocols and guidelines established by the American Heart Association (AHA), they will not be restated here. Clinicians should consult ACLS manuals and AHA reference materials for specific protocol information (see Appendix D for 2010 ACLS algorithms).



Cardiopulmonary Resuscitation


A crucial first step to restoring circulation is the immediate performance of cardiopulmonary resuscitation (CPR), a technique that took its modern form in the 1960s. Promptly delivered CPR, performed correctly and effectively, can increase the chances of survival two- to threefold. Consensus resuscitation guidelines promulgated by the AHA recommend chest compressions at a rate of 100 per minute and ventilations, using mouth-to-mouth or bag-valve-mask technique, with approximately 8 to 10 breaths per minute. The AHA recommends “pushing hard and fast,” with compression depth of 1.5 to 2 inches of chest deflection in adults, ensuring full chest recoil and minimizing interruptions in chest compressions (see Table 49.1 for key aspects of correct CPR performance). Recommendations for basic life support (BLS) care changed in 2005, from compression-to-ventilation cycles of 15:2 to the currently recommended 30:2 for adult patients, in order to circulate as much oxygenated blood to vital organs as possible. It is estimated that CPR only generates 20% to 30% of normal cardiac output, and blood flow depends greatly on the quality of this intervention. For every minute CPR is not performed after the heart has stopped, the chances of survival decrease approximately 10% to 15%.




Monitoring the Quality of CPR


Although CPR seems simple to perform, both in-hospital and out-of-hospital investigations have shown that incorrectly or suboptimally performed CPR is common in actual practice and can compromise patient survival. One study found that rescuers’ chest compression rates were less than 90 per minute 28% of the time, compression depth was too shallow in 61% of compressions, and ventilation rates were often too high. A number of studies have shown that defibrillation efficacy and successful restoration of a pulse are sensitive to compression rate and depth. Additionally, an out-of-hospital investigation showed that hyperventilation during CPR may significantly decrease survival. To address these major discrepancies in cardiac arrest care, a variety of devices have been developed with a goal of improving CPR quality by providing rescuers with immediate audio or visual feedback on CPR performance. These devices are either freestanding or incorporated into standard defibrillators; they have a “pad” or “puck,” which is outfitted with an accelerometer and force detector. The rescuers perform CPR through these sensing pads, placed on the chest of the patient in the same place rescuers normally put their hands for CPR. Another modality used to improve CPR quality has been simple metronome devices—for example, a ventilatory-assist device currently in use flashes an indicator light at a rate of 10 per minute, prompting appropriate ventilation rates by rescuers.


A more dramatic approach to improving CPR quality has been to automate the process via devices that provide battery or compressed air–powered chest compressions by either a circumferential belt around the victim’s chest or a piston device positioned over the sternum, respectively. Initial studies suggest that human CPR with feedback devices and mechanical CPR devices may improve performance and possibly survival from cardiac arrest, although further confirmation is required. An additional advantage of the CPR feedback approach is the ability to record CPR performance for later quality assurance processes and educational purposes. Debriefing has been shown to improve both CPR quality and initial resuscitation success.




30:2 versus 15:2 versus Hands-Only CPR


The 2005 AHA guidelines implemented an important change in the compression-to-ventilation ratio for basic life support CPR, from 15:2 to 30:2. This change acknowledged the then newly recognized significance of decreasing the “no flow time,” or the time the rescuer is not compressing on the chest despite a continued pulseless state. Frequent pauses during CPR decrease the likelihood that a defibrillatory shock will be successful and have also been shown in animal studies to decrease the probability of pulse restoration. For intubated patients (and therefore CPR performed by trained hospital personnel), the AHA recommendation is to perform compressions at 100 per minute while simultaneously ventilating at a rate of 8 to 10 per minute. For CPR performed by the lay public, based on data from a number of out-of-hospital SCA cohort studies, the AHA has endorsed the use of a BLS variant without ventilations, known as “hands-only CPR,” with the notion being that mouth-to-mouth ventilation is both difficult to perform and an important deterrent to performing CPR at all. Although this notion of omitting ventilations certainly does not apply to the in-hospital SCA patient population, there is growing evidence that compressing the chest efficiently and effectively should be prioritized over ventilations at least initially during resuscitation efforts, and therefore the quality of compressions should be emphasized.



Defibrillation


Defibrillation, the delivery of a therapeutic electrical shock to the myocardium, is the primary therapy available to treat ventricular fibrillation and pulseless ventricular tachycardia (VF/VT), the two most common arrhythmias associated with out-of-hospital cardiac arrest. Successful defibrillation depolarizes most of the functioning myocardium, momentarily inducing a pause in myocardial conduction and in principle allowing the sinoatrial node to regain control and initiate a normal perfusing rhythm. As a practical matter, defibrillation is performed either directly via electrode paddles or pads applied to exposed myocardium (internal paddles) or indirectly via the patient’s chest (external pads or paddles). Defibrillation can be performed via a manual defibrillator, in which a rescuer identifies a rhythm and determines whether a shock is indicated, or an automatic defibrillator, which electronically determines the cardiac rhythm and performs the shock without rescuer input.


Automatic external defibrillators (AEDs) are commonly found installed in airports or other public settings and have been shown to dramatically improve survival from out-of-hospital cardiac arrest. Although often successful when administered promptly and correctly, defibrillation success diminishes quickly when the shock is delayed. This results because shockable rhythms tend to decay within several minutes toward a less shockable form of ventricular fibrillation or asystole. Delayed defibrillation occurs during both out-of-hospital and in-hospital cardiac arrest resuscitation and is associated with poor outcomes from SCA.



Biphasic versus Monophasic Defibrillation


Until the early 2000s, most defibrillators used a monophasic waveform with current flowing in one direction between electrodes. Newer research supports the use of a biphasic waveform, where current polarity reverses from one electrode to the other during the shock. Biphasic defibrillation has a higher first shock success rate than monophasic defibrillation for cessation of VF/VT. Successful biphasic defibrillation requires less energy than monophasic shocks, with a maximum recommended charge of 200 joules (J) for biphasic versus 360 J for monophasic defibrillation. Additionally, biphasic defibrillation may result in less shock-induced myocardial dysfunction, which could be partly responsible for subsequent restoration of cardiac output.


Current ACLS guidelines state that health care providers should use a biphasic defibrillator if available and select the energy setting recommended by the manufacturer (generally either 150 or 200 J). If the specific device parameters are unknown, providers should use 200 J for the first shock and an equal energy “dose” for subsequent shocks. For monophasic defibrillators, 360 J is the generally accepted highest charge level. The most effective energy level is not currently known, nor is it known whether a fixed or escalating energy level is best when multiple shocks are required.



CPR Interactions with Defibrillation


Unless immediate defibrillation is available within 4 to 5 minutes of VF/VT onset, studies have suggested that a patient’s chance of survival increases when CPR is performed before attempting defibrillation. In addition, the quality of the delivered CPR affects defibrillation success. Specifically, pauses in CPR and chest compressions with inadequate depth decrease the probability of successful defibrillation (Figure 49.2). This indicates that the longer myocardial tissue remains without blood flow, the less likely a defibrillatory shock will succeed in restoring a normal sinus rhythm. CPR may therefore act as a primer by restoring some circulation to the heart before defibrillation. The 2005 AHA consensus guidelines for CPR recommend that high-quality compressions continue while the defibrillator is being prepared and charged. This is a safe, proven method to reduce preshock pauses.



Ever since the introduction of defibrillation, common sense has dictated that physical contact with the patient should be avoided during a shock in order to prevent stray electrical current from injuring the rescuer. Although the risk of inadvertent shock to a rescuer exists if a rescuer is still in contact with the patient during defibrillation, the chance of this occurring is very small and new evidence suggests that the risk may be negligible. Some experts suggest that defibrillation could be performed, in theory, by a gloved rescuer without stopping CPR and therefore maximizing the chance for successful shock. Current guidelines still recommend that all rescuers cease contact with the patient before defibrillation, as further research is needed to examine the safety of hands-on defibrillation.

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Jul 7, 2016 | Posted by in CRITICAL CARE | Comments Off on Advanced Cardiac Life Support (ACLS) and Therapeutic Hypothermia

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