In 2008, the American Heart Association (AHA) announced its support for "hands-only," or compression-only, CPR for lay bystander use in witnessed, out-of-hospital cardiac arrest in adults.(1) What is compression-only CPR, and what happens if we don’t immediately ventilate adult victims of sudden cardiac arrest. Finally, what does this mean for EMS?
For lay rescuers, compression-only CPR is composed of three important steps: 1) recognizing the need for CPR, 2) alerting EMS by calling 9-1-1 and 3) performing uninterrupted, forceful compressions in the middle of the victim’s chest until professional assistance arrives.
This alternative BLS method was developed after several important discoveries during the past decade. First, the incidence of bystander BLS assistance during cardiac arrest has been declining. In the 1980s, 40–60% of out-of-hospital cardiac arrest victims received some bystander CPR, but this rate has fallen to 10–20% since 2000. Several reports suggest most people are reluctant to attempt mouth-to-mouth breathing on a collapsed stranger.(2-4) Suggested reasons for the decline include lack of training, the complexity of the task and fear. Hence, the change in the AHA guidelines for lay rescuers.
But EMS still follows the 2005 AHA/International Liaison Committee on Resuscitation guidelines, which recommend attempting two rescue mouth-to-mouth breaths after every 30 compressions. So, how does this guideline affect our survival rates?
One study showed that the average time needed to perform the two breaths with standard CPR was not the recommended four seconds but 16 seconds for lay rescuers; first-year medical students took an average of 14 seconds, and firefighter/paramedics took 10 seconds.(5-7)
These interruptions of chest compressions have profound effects on the circulatory support provided during resuscitation. In single-rescuer performance of BLS, this results in 16 seconds of no chest compressions after every cycle of either 15 or 30 compressions. If 15 compressions are performed at the recommended rate of 100 per minute, this provides nine seconds of circulation followed by 16 seconds of no circulation, repeated each cycle. During the first minute of full BLS, even an ideally performed effort results in only 30 chest compressions delivered.
If the recommended 30:2 ratio is followed, a maximum of 47 compressions can be delivered in the first minute. Even this higher number of chest compressions delivered in the first minute falls well below what has been shown in animal models and human clinical experience as necessary for optimal resuscitation success and long-term survival.(8,9) Fewer than 50 compressions delivered per minute is simply suboptimal.
The Intended Effects of CPR
Interruption of chest compressions for any reason, including attempts at mouth-to-mouth breathing, has an adverse effect on resuscitation hemodynamics. Coronary perfusion pressure generated by cyclic chest-compression relaxation takes time to build up and falls off dramatically with any interruption. The pressure gradient responsible for myocardial perfusion during CPR must be regenerated after each and every interruption of compressions. With interruption to attempt rescue breathing, the hemodynamic support provided during CPR is typically optimal for only about one-third of the time compressions are performed. It’s nil when compressions aren’t performed.(10)
What really matters in the first few minutes of resuscitation effort for ventricular fibrillation (V-fib) is circulation, not ventilation. Sudden collapse in an adult with V-fib is generally accompanied by a lung and arterial circulation full of oxygen. The crucial task is circulating those oxygen molecules to the tissues of the central nervous system and myocardium. Attempts to ventilate in the first few minutes of resuscitation effort are misplaced and unnecessary.
One study reports the de-saturation curve during V-fib cardiac arrest treated with chest compression-only BLS CPR.(11) Due to the limited blood flow generated even with excellent chest compressions, the rate of oxygen extraction and desaturation is markedly slowed compared to normal physiological conditions. The arterial saturation was still 70% even after 10 minutes of V-fib treated exclusively with chest compressions only. Although this isn’t a normal saturation level, it is enough to sustain the heart and brain temporarily.
Can Compression-Only CPR Improve Outcome?
In our experimental cardiac arrest model, it does. Our group at the University of Arizona began to study the effect on survival and neurological outcome of omitting this mouth-to-mouth breathing. Initial studies in our large animal experimental laboratory showed that survival after 15 minutes of V-fib cardiac arrest were similar with or without mouth-to-mouth breathing (see Table 1).(12-16)
Using a more realistic pause to attempt the two rescue breaths, we found in a simulated single-rescuer scenario that chest compression-only CPR was superior to chest compressions and mouth-to-mouth breaths (15:2 ratio). Neurologically normal 24-hour survival was seen in 12 of 15 animals receiving compression-only CPR compared with only two of 15 in those receiving chest compressions and ventilation when 16 seconds were used to deliver the two breaths.(17)
Several studies have observed similar outcomes for out-of-hospital cardiac arrest in those treated with compression-only CPR versus those treated with chest compressions and ventilation, while documenting both were superior to no bystander CPR.(18-20) Another study demonstrated similar survival in out-of-hospital cardiac arrest victims randomized to receive either dispatch-assisted bystander CPR instruction for chest compressions with ventilations or compression-only CPR.(21) Another study found that delivering compressions only was easier to perform.(5)
Three landmark clinical observational studies published in 2007 showed equivalent or slightly better survival rates with compression-only BLS compared with attempts by bystanders at both compressions and assisted ventilations.(22-24) In the first of these three reports, the SOS-KANTO Group from Tokyo reported on nearly 10,000 cardiac arrests in 58 communities. Their primary endpoint of 30-day survival with favorable neurologic outcome was significantly better with compression-only BLS for those with witnessed cardiac arrest and a shockable rhythm (19% versus 11%).(22)
A summary of the seven clinical trials to date is shown in Table 2. No negative effect of eliminating rescue breathing was seen with the use of compression-only CPR; it was equivalent to chest compressions plus attempted ventilation CPR, and both were substantially better than no bystander CPR attempt at all.
However, some believe the 2005 recommendation of a 30:2 ratio will be as good as or better than compression-only CPR. Although no clinical study has yet compared compression-only BLS with the 30:2 ratio, such a comparison has been done in a cardiac arrest experimental model.25 Using a clinically realistic scenario, 64 swine were studied with a variety of untreated V-fib periods varying from three to six minutes, then randomized to either continuous chest compressions or 30:2 compressions to ventilations. Compression-only CPR produced significantly greater 24-hour neurologically normal survival than did 30:2 CPR when 16 seconds were used to deliver the two breaths (23/33 versus 13/31).
Experimental laboratory data and clinical observational studies support bystander compression-only CPR with no attempt at assisted or rescue breaths as the optimal early treatment for witnessed adult cardiac arrest. The advantages are fewer interruptions in compression-provided circulation and better delivery of the oxygen already present in the lungs and arterial circulation. Such an approach has been used in Tucson since late 2003 and within the state of Arizona since 2005, resulting in tripled overall survival in Arizona for out-of-hospital cardiac arrest.(26) The role of ventilation by EMS during cardiac arrest is less certain, but it will most likely be de-emphasized in the future.
Disclosure: Dr. Kern has reported serving on the advisory board of and as a consultant for Physio-Control, Inc.