RescueDoppler: Non-invasive Handsfree Carotid Doppler Ultrasound for Continuous Hemodynamic-guided Resuscitation

Introduction: Intermittent carotid pulse palpation (PP) is used to determine the return of spontaneous circulation (ROSC) during cardiopulmonary resuscitation (CPR). PP requires interruption of CPR and has low accuracy. Therefore, we investigated if a novel continuous non-invasive hands-free Doppler ultrasound system (RescueDoppler; RD) could detect the presence of pulse/no pulse and ROSC in an experimental setting with ventricular fibrillation (VF) and severe hypotension. Methods: RD was attached to the neck with a self-adhesive bandage onto twelve pigs (mean weight of 30.4 kg). RD used multirange Doppler, with 32 depth ranges over 8 - 45 mm. The transducer dimension was 30 x 6 mm. The RD probe was placed over the carotid artery, while invasive blood pressure was recorded on the contralateral side. Two profound circulatory disturbances were initiated; 1) severe hypotension by vena cava inferior occlusion (VCO) using a 7 Fr Fogarty catheter with gradual balloon inflation and 2) VF by applying a 7.5 V direct current in the myocardium for 2 seconds using an implantable cardioverter-defibrillator placed in the right ventricle apex. The pigs were defibrillated back to ROSC. Mean velocity over one cardiac cycle (time-averaged velocity; TAV) was compared with mean arterial pressure (MAP). Results: RD detected flow in the carotid artery in all 41 VCO sequences (figure), including the lowest induced systolic blood pressure of 19 mmHg. The intraclass correlation coefficient was 0.76 between TAV and MAP. ROSC was equally identified by RD and invasive blood pressure in all 21 VF sequences where the pigs were defibrillated from VF to sinus rhythm (figure). Conclusion: The RD system was simple and required no ultrasound knowledge. RD detected ROSC and blood flow at extremely low invasive carotid blood pressures during VF and VCO. TAV correlated well with MAP. RD could become an essential non-invasive, hands-free tool for continuous hemodynamic-guided CPR.