Sonographic Cardiac Activity Correlates with End-Tidal Carbon Dioxide and Cardiac Rhythm in Out-of-Hospital Cardiac Arrest

The majority of cardiac arrests that occur in the United States are treated by EMS, which has stimulated interest in the use of prehospital ultrasound as a prognostic tool. Though end-tidal carbon dioxide (EtCO2) and cardiac rhythm have demonstrated prognostic value in out-of-hospital cardiac arrest (OHCA), few studies of ultrasound in the prehospital setting have attempted to address the same question. This retrospective study assesses the association between sonographic cardiac activity and contemporaneous measurements of EtCO2 and cardiac rhythm. Sixty-six cases of paramedic-performed cardiac sonography for OHCA were reviewed and clinical data for each case was abstracted directly from the monitor/defibrillator record. The mean timing of the initial ultrasound was 21 minutes (95% CI [18.7,23.3]) into the resuscitation. Organized cardiac activity was associated with higher mean EtCO2 than absence of organized activity (49.7mmHg (95% CI [44.4,55.0]) versus 28.3mmHg (95% CI [24.3,32.3]), p<0.001). Organized sonographic activity was also associated with contemporaneous cardiac rhythm (p=0.018) and was most frequently observed in PEA with a sinus rhythm. Paramedics interpreted intra-arrest cardiac ultrasound with 95.7% agreement with physicians (κ = 0.940). Mean pause in compressions to acquire ultrasound was 14.9 seconds (95% CI [13.3,16.6]).