Abstract Body: BACKGROUND
Guidelines for resuscitation of OHCA recommend that advanced airway management be performed without interrupting chest compressions. However, the extent and impact of interrupting ventilation during OHCA resuscitation is unknown. We described the apnea interval that occurs during endotracheal intubation (ETI) and its associated clinical outcomes.

METHODS
We conducted a cohort investigation of adult ventricular fibrillation (VF)-OHCA patients who underwent attempted paramedic ETI during resuscitation in a metropolitan EMS system from 2017–19. We defined apnea interval as the elapsed time from the last breath delivered before an ETI attempt to the first breath delivered after the attempt. We collected patient, care, apnea interval and outcome data from review of OHCA and airway registries linked to digital defibrillator recordings. The defibrillator recording included an audio channel, ECG, transthoracic impedance, and end-tidal carbon dioxide biosignals. Using multivariable logistic regression, we determined the relationship between apnea interval (longest quartile [>120s] vs the shorter 3 quartiles [<120s]) and two outcomes: return of spontaneous circulation (ROSC) and survival to hospital discharge.

RESULTS
Among 185 eligible patients, median age was 63 [54–74] years, 32 (17%) were female, 181 (98%) had successful prehospital ETI, 106 (57%) achieved ROSC, and 53 (29%) survived to hospital discharge. The median apnea interval during attempted ETI was 89s [65–115s]: 16s pre-laryngoscopic, 53s laryngoscopic, and 7s post-laryngoscopic. Median chest compression fraction was 85% [79–89%] overall and 90% [76–97%] during the apnea interval. Non-airway care during the apnea interval occurred in more than half (94, 51%) of cases, most commonly as medication administration (68, 37%), defibrillation (36, 19%), and multiple laryngoscopic attempts (13, 7%). Apnea interval >120s compared to <120s was associated with a lower likelihood of ROSC (AOR=0.41 [0.20–0.83]) but not hospital discharge (AOR=0.84 [0.38–1.88]).

CONCLUSIONS
In this cohort of VF-OHCA patients, the median apnea interval during attempted ETI was 89s, with an interquartile range of 50s. Apnea interval >120s was associated with lower likelihood of ROSC but not hospital discharge. Given its variability and relationship to near-term resuscitation outcomes, the apnea interval may be a modifiable intervention that can affect OHCA survival, supporting the need for further investigation.