Hold the Breath for Bystander CPR

TOKYO, March 16 -- Bystander CPR with no mouth-to-mouth ventilation doubled the chance that those in cardiac arrest would have a good neurologic outcome, researchers here reported.

"Cardiac-only resuscitation by bystanders is the preferable approach to resuscitation for adult patients with witnessed out-of-hospital cardiac arrest, especially those with apnea, shockable rhythm, or short periods of untreated arrest," wrote Ken Nagao, M.D., and colleagues, of Surugadai Nihon University Hospital, in the March 17 issue of The Lancet.

They found in a study of more than 4,000 cardiac arrest cases that while any attempt at out-of-hospital resuscitation was better than doing nothing at preserving neurologic function, cardiac-only resuscitation doubled, or nearly doubled, the chance that patients would have a favorable neurologic outcome.

This was especially so when CPR was started within four minutes of cardiac arrest or in those with apnea or a shockable cardiac rhythm.

The findings come as no surprise to Gordon A. Ewy, M.D., of the Sarver Heart Center at the University of Arizona in Tucson.

"We have recommended cardiopulmonary resuscitation by bystander chest-compression-only for out-of-hospital cardiac arrest for years," Dr. Ewy wrote in an accompanying editorial. "This approach has been incorporated into Cardiocerebral Resuscitation, a new approach to resuscitation of victims of cardiac arrest that eliminates early positive-pressure ventilation by emergency personnel, emphasizes continuous chest compressions and improves survival."

In its 2005 clinical guidelines for CPR and emergency cardiovascular care, the American Heart Association recommended that "laypersons should be encouraged to do compression-only CPR if they are unable or unwilling to provide rescue breaths, although the best method of CPR is compressions coordinated with ventilations."

Dr. Nagao and colleagues in the SOS-KANTO study group conducted a prospective, multicenter observational study of patients who had out-of-hospital cardiac arrest.

They enlisted the help of paramedics who, on arrival at the scene of a cardiac arrest, observed and assessed the techniques of bystanders who were performing CPR. The paramedics classified the technique as cardiac-only resuscitation, conventional CPR, pulmonary-only resuscitation, unidentified resuscitation technique (including cases in which there was a change of technique), or chest compression not documented. The paramedics did not assess either the rate or depth of chest compressions.

They also classified the bystanders as a lay person with basic CPR training, a lay person assisted by a dispatcher, a lay person without either training or dispatcher assistance, or an off-duty health worker.

The primary study outcome was a favorable neurologic outcome 30 days after cardiac arrest. They defined a favorable neurologic outcome as a Glasgow-Pittsburgh cerebral-performance category of 1 (good performance) or 2 (moderate disability) on a five-category scale. Categories 3 (severe disability), 4 (vegetative state), and 5 (death) were counted as unfavorable neurological outcomes.

The secondary endpoint was survival 30 days after cardiac arrest, which included all Glasgow-Pittsburgh cerebral-performance categories except 5. Neurological outcomes were assessed by physicians who were blinded to the type of resuscitation.

A total of 4,068 adults had out-of-hospital cardiac arrest witnessed by bystanders. These included 439 patients (11%) who received cardiac-only resuscitation from bystanders, 712 (18%) who had conventional CPR, and 2,917 (72%) who did not receive CPR of any kind from a bystander.

The authors found that "any resuscitation attempt was associated with a higher proportion having favorable neurological outcomes than no resuscitation (5.0% versus 2.2%, P<0.0001)."

Among patients with apnea, 6.2% of those who received cardiac-only resuscitation had favorable neurologic outcomes, compared with 3.1% of those who received standard CPR (P=0.0195).

Among patients who had a shockable heart rhythm 19.4% of those who received compression only had a good neurologic outcome, compared with 11.2% of those who received compressions and breaths (P=0.041).

Resuscitation with chest compressions only, when started within four minutes of cardiac arrest, also doubled the chance of a good outcome, with 10.1% of patients treated this way being in a Glasgow-Pittsburgh category of 1 or 2, compared with 5.1% of patients treated with compressions and breaths (P=0.0221). When resuscitation started four minute or more after arrest, however, only 2% of patients treated with either technique had good neurologic outcomes.

"There was no evidence for any benefit from the addition of mouth-to-mouth ventilation in any subgroup," the investigators wrote.

The authors also performed a logistic regression analysis adjusted for independent predictors of resuscitation, including age, cause of cardiac arrest, technique of bystander resuscitation, resuscitation-related time intervals, and initial recorded cardiac rhythm.

In this analysis, the adjusted odds ratio for a favorable neurological outcome after cardiac-only resuscitation was 2.2 (95% confidence interval, 1.2-4.2) among patients who received any resuscitation from bystanders.

There were no between-group differences in overall survival at 30 days.

The authors suggested several possible explanations for why compression-only CPR is equal to or better than the combined technique.

"If the airway is open, gasping breathing and passive chest recoil provide some air exchange," they wrote. "Measured minute ventilation and arterial oxygenation decrease after four to 10 minutes of resuscitation irrespective of attempts at ventilation. Several studies suggest that ventilation is not essential during the initial 12 minutes of resuscitation with untreated arrest intervals of less than six minutes, and that gasping breathing is associated with a better outcome."

In his editorial, Dr. Ewy counted off eight arguments against the addition of mouth-to-mouth ventilation to chest compressions.

"First, this requirement greatly decreases bystander-initiated resuscitation efforts, an important determinant of survival from out-of-hospital cardiac arrest," he wrote. "Second, studies have long reported that survival is better in individuals with cardiac arrest who receive chest compression only than it is in those in whom no bystander rescue efforts were started until the actual or simulated arrival of emergency personnel. Third, mouth-to mouth ventilations by single bystanders requires inordinately long interruptions of essential chest compressions."

In addition, the use of mouth-to-mouth ventilation during cardiac arrest increases intrathoracic pressures, decreasing venous circulation to the chest, and ventilation may delay compressions in cases where the heart is already full of oxygenated blood, such as arrest induced by ventricular fibrillation.

Dr. Ewy pointed out that "we should continue to follow the newer guidelines of assisted ventilations and chest compressions for respiratory arrest (such as in drowning or drug overdose)." This is because in these conditions "the arterial blood is so severely desaturated that it contributes to hypotension and secondary cardiac arrest."

Dr. Nagao and colleagues noted that their study was limited by the observational rather than randomized design, and by the lack of assessment of the quality of resuscitation performed by bystanders.