TUCSON—The effectiveness of cardiopulmonary resuscitation (CPR) may actually suffer when a single rescuer interrupts chest compressions to provide rescue breathing. A new study provides at least part of the reason why: Such interruption decreases coronary perfusion pressure (CPP) and left ventricular (LV) blood flow.[1]

Both clinical research and animal studies have shown that bystander CPR using chest compressions alone is as effective as a technique combining compressions with rescue breathing. To investigate why this may be so, Robert A. Berg, MD, and coworkers from the University of Arizona College of Medicine in Tucson compared the efficacy of the two techniques in a group of 14 pigs. At baseline, all animals were similar in terms of weight, hemoglobin concentration, blood pressure, heart rate, and central venous pressure.

Ventricular fibrillation (VF) was induced in the animals for three minutes to simulate untreated cardiac arrest. Next, the animals were randomly assigned to receive 12 minutes of either chest compressions alone or compressions plus rescue breathing. To simulate the action of paramedics, animals were resuscitated in accordance with American Heart Association algorithms for VF. They were then placed in a simulated intensive care setting for one hour.

Once resuscitated, the animals were placed in one of five categories according to their neurological outcome. Those in category 1 showed no sign of neurological deficit, while those in category 5 were unresponsive to their environments. The researchers found that although all of the animals survived to 24 hours after resuscitation, two of those in the chest compressions plus rescue breathing group had neurological outcomes that ranked them in categories 2 (mildly abnormal, lethargic) or 3 (severely disabled, unable to walk). Of those in the compressions-only group, only one pig was placed in category 2. The rest showed no sign of neurological deficit.

LV blood flow was higher in the pigs given chest compressions than in those receiving compressions plus rescue breathing. In the early stages of CPR, mean LV blood flow was 96 versus 60 mL/100 g/min, respectively; after more prolonged CPR, it was 79 versus 52 mL/100 g/min.

There were differences in CPP between the two groups as well. During early CPR, mean CPP was 29 mm Hg in the pigs given compressions only versus 26 mm Hg in those given compressions plus rescue breathing. The corresponding figures for late CPR were 18 and 21 mm Hg, respectively.

The pigs given compressions plus rescue breathing also experienced a decrease in diastolic pressures during the rescue breaths. The researchers attribute this to the pause required after each 15 compressions, which lowered CPP. Mean CPP was 14 mm Hg during the first two compressions following rescue breaths, compared with 21 mm Hg during the final two compressions in each cycle.

In an interview with PULMONARY REVIEWS, Dr. Berg, chief of the Pediatric Critical Care Section at the University of Arizona, said that there was no evidence that the decreases in myocardial perfusion resulted in myocardial injury, but that these findings should “change our attitudes towards interruptions in compressions. During CPR, continuous, uninterrupted compressions are important. The obvious implication is that interruptions for movement of the patient, endotracheal intubation, ECG recognition, placement of a defibrillator, etc, are harmful. Moreover, longer interruptions in chest compressions are more harmful.” He denied that rescue breathing should be eliminated from single-rescuer CPR scenarios to simplify CPR training, as this “could be a great disservice for victims of asphyxial arrests—eg, submersion events.” He added, “Although there is increasing evidence in animals and humans that chest compressions alone may be as good or better than chest compressions plus rescue breathing in the setting of short periods of CPR for VF, I think we must know more before we recommend changes in single-rescuer protocols.” Dr. Berg concluded by saying that “this is a fertile area for research and development in our clinical care.”

—Owen McCarthy

Reference
1. Berg R, Sanders A, Kern K, et al. Adverse hemodynamic effects of interrupting chest compressions for rescue breathing during cardiopulmonary resuscitation for ventricular fibrillation cardiac arrest. Circulation. 2001;104:2465-2470.

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