Backgrounds: Carotid pulses are present in some patients with agonal (abnormal) breathing, who are treated as respiratory arrest. This study aimed to investigate the association of agonal breathing with survival of out-of-hospital cardiac arrest (OHCA) and respiratory arrest (OHRA).
Methods: We categorised 9,374 cases with OHCA and OHRA during the period of 2007–2016 into 5 groups according to respiratory condition and carotid pulse on EMS arrival at patients: no-breathing OHCA (N=8,259), agonal-breathing OHCA (N=260), no-breathing OHRA (N=99), agonal-breathing OHRA (N=204) and no arrest (N=552). According to Utstein classification, the former 2 groups were classified as EMS-unwitnessed OHCA (N=8,519), and the latter 3 groups as EMS-unwitnessed OHRA (N=154), EMS-witnessed OHCA (N=617) or EMS-witnessed OHRA (N=84) depending on subsequent cardiac or respiratory arrest.  
Results: The rate of neurologically favourable 1-Y survival was 1.9%, 26.2%, 15.2%, 14.7% and 14.3%, respectively in no-breathing OHCA, agonal-breathing OHCA, no-breathing OHRA, agonal-breathing OHRA and no arrest on EMS arrival at patients: Cases with agonal-breathing OHCA were more likely to survive than the other groups. When analysed for agonal/no breathing and OHCA/OHRA components after excluding cases with no arrest, OR (95% CI) was 2.13 (1.47–3.09) and 4.23 (2.91–6.13), respectively for OHRA/OHCA and agonal/no breathing components, with a significant interaction (P<0.01). Subgroup analyses for EMS-unwitnessed OHCA revealed that agonal breathing, compared with no breathing, is associated with higher survival rate [26.2% (68/266) vs 1.9% (155/8,259)] and higher proportion of shockable initial rhythm (23.9% [62/260] vs 6.6% [544/8,259]) . Subgroup analyses for EMS-witnessed OHCA and EMS-unwitnessed OHRA disclosed that agonal breathing on EMS arrival is not associated with better outcomes.
Conclusions: Agonal breathing without carotid pulse on EMS arrival is associated with better outcome of EMS-unwitnessed OHCA while agonal breathing with carotid pulse is not associated with outcomes of EMS-witnessed OHCA or EMS-unwitnessed OHRA.

Agonal breathing without carotid pulse on EMS arrival but not agonal breathing with carotid pulse is associated with better outcomes of out-of-hospital respiratory and cardiac arrests