In this analysis of a nationwide, population-based OHCA registry, we evaluated the association between prehospital advanced airway methods and clinical outcome of cardiac arrest. The magnitude of the association was different according to the presumed cause of cardiac arrest. There was no statistically significant difference in the effect according to the advanced airway type in total population and arrest with cardiac origin. However endotracheal intubation was associated with better neurologic outcome when the cause of arrest was respiratory. We believe more efficient oxygenation and ventilation through prehospital endotracheal intubation provides a rapid and effective solution to respiratory cause of cardiac arrest, as an antidote for drug intoxication. Although most of cardiac arrest cases receive endotracheal intubation eventually after hospital transport, faster reversal of hypoxia and hypoventilation by prehospital endotracheal intubation in the field might show an effect on minimizing hypoxic brain injury. Based on the results of our study, we suggest that endotracheal intubation should be considered as a first choice of method in OHCA patients whose cause of arrest is suspected to be respiratory, such as respiratory disease, asphyxia and strangulation.
Even after recent prospective clinical trials, defining the optimal choice of prehospital advanced airway methods in OHCA is controversial. Wang et al. compared laryngeal tube and ETI as prehospital airway management methods for OHCA and showed that LT was superior to ETI when measuring 72-hour survival.(13) Benger et al. compared I-gel versus ETI, and there was no difference in survival to discharge or favorable neurologic outcome rate.(22) Jabre et al. compared BVM to ETI and obtained inconclusive results regarding 28-day survival with favorable neurologic outcome. (12) Overall, the results showed no definite benefit of ETI over BVM or SGA. In a nationwide cohort study conducted in Japan, advanced airway management (ETI and SGA) was associated with better survival and more favorable neurologic outcomes compared with no advanced airway management in non-shockable (pulseless electrical activity and asystole) OHCA patients. (23) However, these studies did not consider the etiologies of arrest.
The supraglottic airway can be inserted blindly and therefore has a higher success rate than endotracheal intubation, even for those with low skills, such as EMS providers in Korea. However, compression of important structures such as carotid vessels has been suggested in animal studies in some SGAs due to its morphologic characteristics and mechanism. (24, 25) In severe hypoxia in respiratory arrest, carotid blood flow reduction caused by SGA insertion might be more critical than for other etiologies of cardiac arrest. One case reported ventilation failure of a drowned patient with supraglottic airways due to leakage from high pressure. (26)
Several previous studies have reported negative effects of prehospital advanced airway placement on the outcome of respiratory cardiac arrest.(15, 18) However, these studies included only limited number of patients with medical intrinsic respiratory disease, excluding external causes of arrest, such as asphyxia or hanging. Additionally, the studies only tested the overall effect of prehospital advanced airway rather than the effect of each advanced airway method according to different etiologies, as in our study.
Only witnessed cardiac arrests were enrolled for analysis in our study. We opted not to include patients with arrest not witnessed by initial bystanders. Although our study was a retrospective observational study and there are currently no guidelines for EMS providers to consider cause of arrest when selecting the airway management method, we supposed it might be difficult for EMS providers to estimate the cause of arrest in unwitnessed cases. We believe that, for witnessed cardiac arrest, EMS providers can presume the cause of cardiac arrest based on a history taken from the bystander who witnessed the arrest or could at least determine whether the cause was respiratory or not. Based on the result of our study, we suggest that EMS providers might consider estimated cause when deciding the airway management method in the field.
There are some limitations to our study. First, this was a retrospective observational study; therefore, careful interpretation is needed considering the unique characteristics of our EMS system. Second, we extracted cause of arrest by medical record review. For patients who did not achieve any ROSC and were pronounced dead after initial resuscitation, there might be few clues to estimate the cause of arrest.
Third, the number of patients with favorable neurological outcome in the ETI group with respiratory arrest were very small (9 patients), which leading to wide confidence intervals and making results difficult to interpret. Furthermore, detailed diagnosis of respiratory disease or severity of trauma were not included in our database. Last, there might be unmeasured confounders not included in our registry that could affect both airway management method and outcome.