Abstract 64: Concordance between Carotid Pulse Check and Transthoracic Impedance Characteristics in Out-of-Hospital Cardiac Arrest
The emphasis in the new Guidelines for reducing hands-off periods and eliminating pulse checks aims to provide effective standardized cardiopulmonary resuscitation (CPR) for all patients. But eliminating all pulse checks may not be appropriate in all situations. We assessed the hypothesis that certain characteristics of the transthoracic impedance signal can provide a surrogate measure of the presence of a pulse without manual intervention. We sought to determine the relationship between characteristics of the transthoracic impedance signal and the carotid pulse detected by basic life support (BLS) rescuers.
Methods: We selected 42 pre-hospital cardiac arrest victims for whom BLS rescuers using LIFEPAK® 500 AEDs were asked to record the presence of a pulse by manual carotid assessment. Among the 42 patients, 21 had a detectable carotid pulse. Post-event, six blinded reviewers were asked to score 42 short fragments from the continuous impedance signal coupled with ECG signal. The reviewer assessed if the impedance signal was considered compatible with return of spontaneous circulation (ROSC) by looking for organized variations of impedance that were coordinated (synchronous) with ventricular complexes on the ECG. Otherwise flat, non-readable, noisy, or dissociated impedance and ECG variations were rated as non-ROSC. The combined-kappa statistic was used to assess the concordance between reviewers, and the “more-than-two-rating kappa statistic” to assess the concordance between reviewers scoring and clinical pulse assessment by BLS rescuers.
Results: The reviewers detected the pulse on the impedance in 18 of 21 fragments. The reviewers also scored a pulse in 1 patient which the rescuers did not. The concordance between the six reviewers resulted in good strength of agreement (kappa = 0.72, 90% CI: 84 % to 96%). The concordance between reviewers and rescuers achieved a very good strength of agreement (Kappa = 0.81, 91 % CI 79 % to 98 %).
Conclusion: Post-event evaluation of the impedance signal using objective criteria for scoring yields a promising method of ROSC evaluation based on this comparison with rescuer detected carotid pulse. This work confirms that transthoracic impedance can be used as a surrogate measure of ROSC and merits further evaluation.