Towards a non-invasive cardiac arrest monitor: An in vivo pilot study

Hemodynamic-guided cardiopulmonary resuscitation (HGCPR) achieves better outcomes than standard resuscitation. Currently, HGCPR requires an invasive procedure, infeasible during resuscitation. Non-invasive measures of blood flow could provide useful hemodynamic guidance to rescuers.

We describe initial efforts to develop a device that detects, analyzes, and measures the velocity of carotid artery blood flow (CABF) towards the brain at pre-arrest baseline ('baseline') and during cardiopulmonary resuscitation, here tested in a swine model of cardiac arrest (CA). A key element of that device consists of non-imaging diagnostic ultrasound, due to its simplicity and small form factor, hence potential for deployment during HGCPR in a bandage placed on the neck.

Sixteen mixed-breed domestic swine were sedated, anesthetized and paralyzed, followed by endotracheal intubation and mechanical ventilation. Cardiac arrest was induced with a 3-s 100 mA transthoracic shock or bolus of fentanyl, after which all animals received mechanical CPR. A non-imaging ultrasound probe was manually applied to the neck over the carotid artery to capture CABF during baseline, as verified with diagnostic ultrasound imaging, and during mechanical resuscitation.

We successfully collected CABF measurements at baseline in 14/16 swine and during attempted resuscitation with mechanical chest compression in 5/16 swine. Signal characteristics include peak blood flow both towards (90.4 +/-20.4 cm/s) and away from the brain (-44.2 +/-31.8 cm/s) during resuscitation, each larger than flow towards (41.7+/-14.8 cm/s) and away from brain (-3.0 +/-7.8 cm/s) during baseline.

Measurement of CABF before and during CPR in swine with a non-imaging ultrasound probe is feasible before CA and informative when achieved during CPR. For example, observations of reverse flow within the carotid artery during CPR merits further study for its prevalence and effect on resuscitation outcomes. Also, tissue motion represents a significant obstacle for CABF measurement during CPR. Additional work will determine the feasibility and utility of non-imaging ultrasound measurements of CABF during resuscitation.