Have the latest CPR guidelines improved cardiac arrest outcomes?

■ Historically, many recommendations for cardiopulmonary resuscitation (CPR) and emergency cardiac care (ECC) have been made by expert consensus based on animal studies because there were few randomized controlled trials in humans.

■ Now, however, data emerging from large human trials such as the Resuscitation Outcomes Consortium and the Save Hearts in Arizona Registry and Education program have demonstrated that quality chest compressions with less emphasis on ventilation are key to improving survival rates for victims of sudden cardiac arrest.

■ By the time that new CPR/ECC guidelines come out in 2010, a wealth of human resuscitation outcomes data will have been made available to inform the guidelines committee; and recommended changes will likely include continuous chest compression CPR.

■ It is critical for health care providers to remain current regarding standards and guidelines for basic life support and for efforts to develop public CPR training and automated external defibrillator programs to continue.

Since the Standards for Cardiopulmonary Resuscitation and Emergency Cardiac Care were introduced in 1974, several updates to these guidelines have been issued.^1-7 Over this time, the guidelines have come full circle, moving from simple to complicated to simple again. This article compares changes to the guidelines over the years, presenting the evidence and reasoning behind the changes. Current outcomes data are discussed, with emphasis on what is effective in improving survival. The article stresses the importance of high-quality cardiopulmonary resuscitation (CPR), early defibrillation, and the need to train the lay public to recognize cardiac arrest and implement CPR.

A BRIEF HISTORY OF CPR

The currently used closed chest massage for CPR was developed and introduced by William Kouwenhoven in 1958, although some form of the technique had been used by Friedrich Maass and others dating back to the1800s.¹ Artificial respiration has been documented as far back as the 6th century. Modern CPR caught on in the early 1960s because of the fairly simple technique of mouth-to-mouth breathing and closed chest massage.¹ The changes in CPR coincided with developments of new advanced cardiac life support (ACLS) guidelines over the years. Changes in compression and ventilation rates are given in Table 1.

The main changes to the CPR guidelines over the years have consisted of increases in compression rate, decreases in ventilation rate, and, in 2005, a uniform compression-toventilation ratio of 30:2 for all ages older than neonates. The recommended ventilation rate decreased because the earlier rates had been determined to cause hyperventilation, which increases thoracic cavity pressure and cerebral pressure and decreases venous return and coronary perfusion pressures.¹ A ventilation rate of 10 to 12 breaths per minute, or 8 per minute with an advanced airway in place, is currently recommended.¹

In 2000, the pulse check was eliminated for laypersons⁶ because a few small studies had indicated that even medical professionals have difficulty identifying a pulse on an unresponsive victim.8 Experts concluded that it is better to perform CPR on a person who has a pulse than to withhold resuscitation from a victim who is pulseless.⁹ The time spent trying to feel for a pulse in an unresponsive victim significantly delays the start of chest compressions. In other studies, agonal respirations are often misinterpreted by lay persons as “breathing,” which also delays intervention in sudden cardiac arrest. The 2005 American Heart Association (AHA) CPR guidelines therefore began to teach laypersons to begin CPR if a victim is unresponsive and not breathing normally.⁷ The pulse check remains in the protocol for health care providers.⁷

Compression-to-ventilation rates remained at 15:2 from 1974 to 2005, until it became clear that pausing compressions to give ventilations resulted in significant delays in compressions. A porcine research study demonstrated a 30% improvement in cardiac output and cerebral blood flow with a 30:2 compression to ventilation rate.¹⁰ The 30:2 rate was thus recommended by consensus for the 2005 guidelines.^7,10

In 2007, the Resuscitation Outcomes Consortium (ROC) showed preliminary evidence from an observational study that a higher CPR fraction (the length of time that chest compressions are done during a resuscitation episode) has a direct impact on survival to discharge.¹¹ Victims with a 0% to 20% CPR fraction had an 8.6% survival-to-discharge rate, as compared to a 34.2% survival-to-discharge rate for those with a CPR fraction of 81% to 100%.¹¹ A prospective study of 97 in-hospital resuscitations proved that compression rates were less than the recommended amount, even by trained hospital personnel.¹² For 36% of the resuscitation time, compression rates were less than 80 per minute; and for 27% of the time, the rates were less than 70 per minute. Higher compression rates were significantly correlated with initial return of spontaneous circulation.¹²

MINIMALLY INTERRUPTED CARDIAC RESUSCITATION

A prospective study of cardiac arrest victims, conducted in two metropolitan cities in Arizona, looked at minimally interrupted cardiac resuscitation (MICR) compared to standard 2000 AHA emergency medical services (EMS) protocols.¹³ Of 878 cardiac arrests, 218 occurred before introducing the MICR protocol. Four of these 218 (1.8%) survived to hospital discharge. Of 668 cardiac arrests treated with the MICR protocol, 36 survived (5.4%). Patients with witnessed ventricular fibrillation (VF) had a 28.4% survival rate with MICR as compared to 11.9% with standard EMS protocol.¹³ The MICR protocol, developed by the University of Arizona Sarver Heart Center, is highlighted in Table 2.

In 2009, Garza and colleagues described the Kansas City, Missouri, EMS system retrospective cohort study comparing the results of using the 2000 guidelines to the results of using a modified, “minimally interrupted” protocol.¹⁴ The goal was to improve survival to hospital discharge in victims of sudden VF or pulseless ventricular tachycardia (VT) arrest. The protocol was similar to the Arizona protocol detailed in Table 2. The main differences were use of a 100% nonrebreather mask and oral airway for oxygenation with a 50:2 compression-toventilation rate. Ventilations were given by squeezing the reservoir bag on the mask. A 10-second intubation attempt was performed after three complete CPR cycles. EMS personnel used only manual defibrillators because of the delay incurred when an automated external defibrillator (AED) is in analysis mode. With these changes, survival rates improved from 7.5% to 13.9%.¹⁴