Updated guidelines on cardiopulmonary resuscitation. A report from SHM 2006.

Forget everything you know about cardiopulmonary resuscitation, because most of it is outdated or just plain wrong. For too long, the advanced cardiac life support guidelines (ACLS) have been based on expert consensus rather than on empiric data, and this has led to the development of increasingly complicated algorithms, which may paradoxically hinder simple effective interventions. Now that more studies have been done, including critical appraisals of actual resuscitations, the American Heart Association, in conjunction with the International Liaison Committee on Resuscitation, has issued new guidelines that were published in a supplement to the December 13, 2005 issue of the journal Circulation.[1] The new guidelines were the subject of the presentation, "Evidence-Based Resuscitation," given by Jason Persoff, MD, of the Mayo Clinic, Jacksonville, Florida, at the 2006 Society of Hospital Medicine meeting in Washington, DC.
Through a series of engaging and interactive clinical vignettes, Dr. Persoff explained how many of our core assumptions about cardiac resuscitations are not supported by empirical data. For example, most clinicians in the session were quite surprised to learn that age is not an independent predictor of a poor outcome after a cardiac arrest. Such an assumption leads many healthcare professionals to counsel patients and families that resuscitations are rarely successful and that few survivors will ever return to premorbid function. In fact, on average, 15% of in-hospital resuscitations are successful, and this number rises to ~25% when the initial rhythm is ventricular tachycardia (VT) or ventricular fibrillation (VF). Even more encouraging is the observation that less than 25% of these survivors will suffer moderate or severe cognitive deficits, and that up to 60% will be able to return to independent living.[1] This information should enable healthcare professionals to provide more accurate and useful information to their elderly patients when discussing advanced directives.
The new guidelines are based on several observations:

Performing Chest Compression

Dr. Persoff went on to explain that despite repeated training, chest compressions are generally not performed correctly -- a shortcoming that leads to higher mortality. When performed perfectly, CPR can restore one third of the normal cardiac output, 10%-15% of the normal cerebral blood flow, and 1%-5% of the normal cardiac blood flow. However, perfect CPR requires 100 compressions per minute of adequate depth to compress the thorax. This turns out to be a very challenging proposition even for the most physically fit. The individual running the code should begin with the assumption that the person performing chest compressions will need to be rotated every 30 seconds.

Overestimating Ventilation

The next common misconception about cardiac resuscitation is an overestimate of the utility of ventilation. Dr. Persoff made the following observations: First, oxygenation cannot occur in the absence of circulation; second, during resuscitations, ventilation is almost always performed incorrectly; third, despite the assumption that one can effectively reverse metabolic acidosis by hyperventilating a patient, the maximum change in PCO2 that can be achieved with ventilation is ~25 mm hg. This change in PCO2 would yield a maximal pH change of ~0.2 -- a difference of questionable clinical importance in the face of severe lactic acidosis.
An excessive focus on ventilation may have a number of unintended consequences. First, it may lead to less effective chest compression due to interruptions from bagging and intubation. Second, there is a tendency for rescuers to overventilate patients, which may result in breath stacking or auto positive end expiratory pressure (auto-PEEP). Paradoxically, this can lead to worse oxygenation, as increased intrathoracic pressure will decrease cardiac output and may precipitate iatrogenic hypotension. Rescue breathing should be administered at a ratio of 2 breaths per 30 chest compressions, but CPR should never be stopped, and patients should never be overventilated.

Focus on Defibrillation

The third and most important change in the new guidelines is a primary focus on defibrillation. The majority of survivable cardiac arrests are due to either VT or VF, and for every 1-minute delay in defibrillation there is an absolute decrease in survival of 7%. Therefore, defibrillation of VT or VF remains the primary goal of all resuscitations. There are several important additional points. First, the previous ACLS guidelines recommended the use of stacked shocks without intervening chest compressions because monophasic defibrillators have a low success rate with an initial shock, and often require repeated shocks to decrease the chest wall impedance. With the increased use of biphasic defibrillators, VT and VF are terminated in ~90% of patients with a single shock, and the data suggest that patients who do not convert are more likely to benefit from the rapid resumption of CPR rather than further attempts at defibrillation. Finally, after patients are successfully defibrillated, the majority will continue to have a nonperfusing rhythm for several minutes (pulseless electrical activity or asystole), and CPR should be continued for 5 cycles (30 compressions and 2 breaths) before the rhythm and pulse are reassessed.

Sidebar: Changes in the 2005 Guidelines

Major changes in the 2005 advanced cardiac life support guidelines include:

Increased emphasis on the importance of chest compressions: rescuers will be taught to "push hard, push fast" (at a rate of 100 compressions per minute), allow complete chest recoil, and minimize interruptions in chest compressions.
Recommendation of a single (universal) compression-to-ventilation ratio of 30:2 for single rescuers of victims of all ages (except newborn infants), and that each rescue breath be given over 1 second and produce visible chest rise.
A new recommendation that single shocks, followed by immediate CPR, be used to attempt defibrillation for VF cardiac arrest. Rescuers should not check the rhythm or a pulse immediately after shock delivery -- they should immediately resume CPR, beginning with chest compressions, and should check the rhythm after 5 cycles (or about 2 minutes) of CPR.

Pulseless Electrical Activity

Dr. Persoff concluded his talk with a discussion of pulseless electrical activity (PEA), which he indicated remains the final common pathway of all unsuccessful resuscitations. Of interest, Dr. Persoff stated that PEA is the only ACLS algorithm where the rhythm is actually "normal." Studies done with the use of transthoracic echocardiograms show that, in most cases of PEA, the heart is beating, but it is doing so ineffectively due to impaired contractility, diminished preload, or external compression (eg, tamponade or tension pneumothorax). When dealing with PEA, it is still critical to look for reversible causes -- the 5 Hs (hypovolemia, hypoxia, hydrogen ion [acidosis], hyper/hypokalemia, and hypothermia) and 5 Ts (tablets [drug overdose, accidents], tamponade [cardiac], tension pneumothorax, thrombosis [coronary], and thrombosis [pulmonary embolism]). Dr. Persoff warned, however, not to forget "iatrogenic hyperventilation." For all PEA arrests, it is essential to correct hypotension, hypovolemia, and hypoxia with epinephrine, IV fluids wide open, and oxygen. Dr. Persoff urged clinicians to reacquaint themselves with transcutaneous pacing (TCP) for bradycardia, as it is the best and safest -- but least understood -- intervention for bradycardia. In the new ACLS guidelines, TCP remains a class I recommendation for symptomatic bradycardia secondary to type II second-degree block or third-degree AV block, and is the appropriate bridge to transvenous pacemaker placement.