Cardiac Arrest - Ultrasound Detection of Occult Perfusion

This is a multi-center, prospective, observational trial involving sites across the United States and Canada. Patients having suffered an out of hospital cardiac arrest will be enrolled through the emergency department either presenting in cardiac arrest with ongoing CPR or having been resuscitated en-route but re-arresting shortly after arriving in the emergency department. Patients will undergo any echocardiography or vascular ultrasound during the resuscitation at the discretion of the clinical team and based on institutional protocols. The clinical team will be unblinded to any aspect of the resuscitation, including the echo or vascular ultrasound images. Clinical interventions during the pause in CPR will be classified as ACLS interventions for cardiac arrest or non-ACLS interventions for occult perfusion. ACLS interventions include interventions for cardiac arrest such as bolus epinephrin or CPR. Non-ACLS interventions for occult perfusion include interventions for patients with profound hypotension such as continuous adrenergic agents or halting CPR to check a blood pressure. Patients will be determined to have demonstrated occult perfusion based on blinded review of the patient data, ultrasound images, and vascular images. Adjudicated Echo Image Review - Recorded cardiac images blinded to all patient and sonographer information will be reviewed by research staff to identify if a) cardiac activity is present and b) organized cardiac activity is present. Cardiac output will be measured as fractional shortening of the left ventricular chamber. Images will be reviewed separately by expert reviewers blinded to all patient information with adjudication by a third when there is disagreement. Adjudicated Vascular Image Review - Recorded vascular images blinded to all patient and sonographer information will be reviewed by research staff to identify if arterial pulsations are visible. Measurements on the B-mode imaging will include a) artery diameter (superficial to deep) b) artery diameter (side to side) c) depth of artery from skin surface and d) area of the artery cross section at peak systole and peak diastole. The pulsatile index will be calculated as the ratio of the maximal artery diameter during a single pulsation (superficial to deep) to the minimal artery diameter during a single pulsation(superficial to deep). Images will be reviewed separately by expert reviewers blinded to all patient information with adjudication by a third when there is disagreement. Patients will be classified as demonstrating occult perfusion with the following findings: * organized cardiac activity by echo determined to be sufficient to produce an arterial pulse * pulsatile arterial flow visible on vascular ultrasound determined to be significant The study has a number of pre-determined study end points that are observational and associative in nature. They include the following: * Assessment of ECG interpretation accuracy based on comparison of expert review interpretation of ECG and initial clinical interpretation * Exploratory assessment of number of patients treated as cardiac arrest with bolus EPI and CPR that are determined to be occult perfusion better treated with non-ACLS intervention such as stopping CPR and starting continuous adrenergic agents. The methodology for this is not described in full but will involve a modified Delphi of patient data to determine appropriate categorization.