While it is known that suboptimal chest compressions are associated with worse outcomes after cardiac arrest, the optimal combination of chest compression rate (CCR) and chest compression depth (CCD), and whether this should be applied to all patients despite differences in age, sex, and presenting cardiac rhythm is unknown. In this cohort study, 3,643 patients who had an out-of-hospital cardiac arrest and for whom CCR and CCD had been simultaneously recorded during the first 5 minutes of CPR were studied to determine the optimal combination of CCR-CCD associated with functionally favorable survival (defined as modified Rankin scale of 3 or less at the time of hospital discharge). Data was obtained from the National Institutes of Health (NIH) Resuscitation Outcomes Consortium Prehospital Resuscitation Impedance Valve and Early Versus Delayed Analysis (ROC PRIMED) multicenter trial, in which patients were assigned to receive conventional CPR using either an inactive impedance threshold device (ITD) or an active-ITD, with CCR and CCD measurements collected electronically using sensors linked to electrocardiographic monitor defibrillators. At baseline, 64.4% of the 3,643 patients were men, and the mean (SD) age was 67.5 (15.7) years. CPR was performed by bystanders in 41.9% of patients, and 91.1% of patients received at least one prehospital dose of epinephrine. The first cardiac rhythm recorded was asystole in 47.8%, ventricular fibrillation or ventricular tachycardia in 24.5%, and pulseless electrical activity (PEA) in 23.7%. Researchers found that the optimal combination of CCR-CCD associated with the greatest probability of favorable functional outcome was 107 compressions per minute (cpm) and 4.7 cm, with little difference across subgroups (age, sex, or cardiac rhythm). Survival probability was significantly higher with CPR performed within 20% of this combination (86 to 128 cpm, 3.8 to 5.6 cm) than outside of this range (6.0% vs. 4.3%, respectively, OR 1.44, 95% CI 1.07 to 1.94, p=0.02). Finally, survival probability with the identified optimal CCR-CCD was higher with active-ITD use than with sham-ITD use (9.6% vs. 5.3%, respectively, OR 1.90, 95% CI 1.06 to 3.38, p=0.03), and device effectiveness was dependent on being near the optimal CCR-CCD combination. In summary, this study suggests that a chest compression rate of 107 cpm and a depth of 4.7 cm improves outcomes in out-of-hospital cardiac arrests, especially with the use of an ITD, though further investigation and prospective validation is warranted.
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