Epidemiology of out-of-hospital cardiac arrests that occur secondary to chemical asphyxiants: A retrospective series.

AIM: To determine the epidemiological characteristics, temporal trends and survival outcomes of OHCAs precipitated by chemical asphyxiation.

METHODS

We conducted a retrospective cohort analysis of OHCAs attended by paramedics in Queensland, Australia between 2011 and 2020. Patients were classified into two groups depending on the asphyxiating agent involved; simple (argon, carbon dioxide, helium, liquified petroleum gas, nitrogen) and systemic (carbon monoxide, cyanides, hydrogen sulfide, methemoglobin-inducing substances, smoke inhalation). Incidence rates, characteristics and outcomes were described for the entire cohort and independently for each group, with the groups then compared. Temporal trends of asphyxiant utilisation were also described.

RESULTS

During the study period, 50,669 OHCAs were attended, with 551 (1.1%) attributable to chemical asphyxiation. The incidence rate was 1.1 per 100,000 population with no significant temporal changes. Suspected suicide was the primary cause of exposure (-95.8%), with systemic asphyixants the dominant agent reported in comparison to simple agents (66.4% vs 33.6%). Over the 10-year period, events precipitated by carbon monoxide decreased by 26.2% (p for trend < 0.001), helium remained unchanged (p for trend = 0.302) and incidents involving nitrogen increased by 28.7% (p for trend < 0.001). Overall, 14.2% (78/551) of the study cohort received a resuscitation attempt by paramedics with 6.4% of these incidents witnessed and 2.6% involving patients presenting in a shockable rhythm. Survival rates were low, with 6.4% surviving the index event, and 1.3% surviving to hospital discharge with a normal neurocognitive function.

CONCLUSION

OHCA precipitated by chemical asphyxiation is relatively infrequent and associated with poor survival outcomes.