Chest compression are the core of resuscitation efforts in any patient with confirmed or suspected cardiac arrest. Good CPR should not be thought as heart-only process, but a combination of heart and brain.
Standard cardiopulmonary resuscitation consists of manual chest compressions to maintain blood flow and positive-pressure breathing to maintain oxygenation until spontaneous circulation is restored. Chest compressions are interrupted frequently by ventilations given as rescue breathing during the treatment of out-of-hospital cardiac arrest. These interruptions reduce blood flow and potentially reduce the effectiveness of CPR. Observational studies involving humans with out-of-hospital cardiac arrest of presumed cardiac cause have suggested that continuous compressions are associated with better survival than interrupted compressions. Nichol et al. conducted a randomized trial to test whether continuous chest compressions, as compared with chest compressions interrupted for ventilation, during CPR performed by emergency medical service (EMS) providers affected the rate of survival, neurologic function, or the rate of adverse events.
In the large randomized trial conducted by Nichol et al. involving adults with out-of-hospital cardiac arrest, a strategy of continuous manual chest compressions with positive-pressure ventilation was not associated with a significantly higher rate of survival to discharge. During the active-enrollment phase, 1129 of 12,613 patients (9.0%) in the intervention group (which received continuous chest compression) and 1072 of 11,035 (9.7%) in the control group (which received interrupted chest compressions) survived to hospital discharge (difference with adjustment for cluster and sequential monitoring, −0.7 percentage points; 95% confidence interval [CI], −1.5 to 0.1; P=0.07).
In the study by Nichol et al., secondary outcomes included neurologic function at discharge, which was measured with the use of the modified Rankin scale (scores range from 0, indicating no symptoms, to 6, indicating death, with a score of ≤3 indicating favorable neurologic function) on the basis of review of the clinical record, and adverse events. Among patients with available data on neurologic status, 883 of 12,560 patients (7.0%) in the intervention group and 844 of 10,995 (7.7%) in the control group survived with a modified Rankin scale score of 3 or less (difference with adjustment for cluster, −0.6 percentage points; 95% CI, −1.4 to 0.1; P=0.09).
Hospital-free survival in the Nichol trial was defined as the number of days alive and permanently out of the hospital during the first 30 days after the cardiac arrest. Hospital-free survival was significantly shorter in the intervention group than in the control group (mean difference, −0.2 days; 95% CI, −0.3 to −0.1; P=0.004).
Previous observational studies have shown large increases in survival rates among patients with a shockable rhythm with the implementation of continuous compressions by EMS providers versus compressions interrupted for ventilations. Among patients with a noncardiac cause of cardiac arrest who were treated by laypersons or those with a nonshockable rhythm who were treated by EMS providers, continuous compressions were not associated with a significant improvement in outcome. In these previous studies, participating EMS agencies did not measure CPR process when implementing continuous compressions, and implementation occurred simultaneously with other changes, including directions to give intravenous epinephrine early, to use a nonrebreather mask with passive ventilation, to defer airway insertion, and to reduce the number of defibrillations given with each rhythm analysis. In the initial reports of implementation of continuous compressions, most patients received rescue breathing by means of positive-pressure ventilation with a bag-valve mask. Other interventions that each patient received were not reported. It seems plausible that some of the observed improvement in these previous studies was due to improved CPR process (e.g., compression rate and depth), concurrent improvements in the system of care, or Hawthorne effects (changes in behavior resulting from awareness of being observed) rather than to the implementation of continuous compressions alone.
- Rapid initiation of chest compression increases survival with better neurological outcome.
- Avoiding interruptions during chest compression is key for brain perfusion.
- Defibrillate for shockable rhythms.
- Teaching the general public on how to do high quality chest compressions can make a real difference.