In patients with refractory VF/VT, the presence of gasping during resuscitation was an independent prognostic factor for better neurological outcomes at 6 months after onset. Patients who gasped both times during EMS activity and on hospital arrival, indicating continuous presentation of gasping, had a better neurological outcome than those with only one or the other.

In studies comparing ECPR and conventional CPR in patients with an initial VF/pVT rhythm, the outcomes of the ECPR group were generally favorable [8, 10, 19]. However, it is inconclusive whether ECPR should be performed in all refractory cardiac arrests with VF/pVT and if ROSC cannot be achieved before hospital arrival. The ARREST trial demonstrated the usefulness of ECPR in patients who could not obtain ROSC even after three defibrillation shocks, whose body morphology could accommodate ECMO, and whose estimated time to the emergency department was shorter than 30 min [10]. Although the neurological outcome at 6 months was promising (40%), the trial only included patients who required at least three defibrillation shocks and did not show the usefulness of ECPR on patients with refractory VF/pVT who did not obtain ROSC after 1–2 defibrillation shocks and were converted cardiac rhythm to PEA/asystole. The INCEPTION trial investigated whether ECPR could be compared with conventional CPR in patients with refractory VF/pVT who had witnessed and failed to obtain ROSC at 15 min ACLS [8]. As the neurological outcome for patients undergoing ECPR for the initial cardiac rhythm of VF/pVT and with witnessed onset was 20% (including approximately 26% of patients who did not receive ECPR), this could be lower in patients with early waveform VF/pVT without witnessed onset, even if ECPR is performed. The SAVE-J study targeted the initial cardiac rhythm of VF/pVT, cardiac arrest on arrival at the hospital, and no ROSC even after 15 min of ACLS after arrival [19]. Although the rate of obtaining a favorable neurological outcome for ECPR was 12.3% in the SAVE-J study, our results suggest a 23% chance of a favorable neurological outcome when gasping is observed during resuscitation, which may be a realistic strategy, including the implementation of ECPR. The initial cardiac rhythm of VF/pVT is considered an adequate adaptable indicator of ECPR, and we provide the additional finding that gasping during resuscitation increases the probability of acquiring favorable neurological outcomes.

To date, studies on the signs of life have focused on their presence or absence [11,12,13,14, 17]. However, in reality, these studies regarded cases with signs of life observed during ambulance transport as the same phenomenon, whether the sign of life was observed at the beginning and disappeared shortly during transport or it was observed continuously during transport. In the present study, gasping data were available during EMS transport and on arrival at the hospital. The OR for favorable neurological outcomes was 27.44 higher in patients with gasping at both times. Gasping at two different times may potentially suggest that gasping continuously exists during resuscitation. Continuous gasping expression suggests that CPR was consistently effective during resuscitation and generated sufficient cerebral blood flow to produce respiration. Thus, the present study demonstrates that continuous gasping expression is more relevant to favorable outcomes than gasping expression at a certain point. In addition, the relationship between the timing of emerging signs of life and outcomes should be examined in the future.

The SAVE-J study also provided data on cases, where ECPR was not performed for refractory VF/pVT [19]. Analysis of the usefulness of gasping during resuscitation in all refractory VF/pVT cases, including patients who did not undergo ECPR, showed that gasping during resuscitation was significantly associated with a favorable neurological outcome. Thus, gasping during resuscitation is a favorable factor in refractory VF/pVT, with or without ECPR. When ECPR was not introduced in patients with refractory VF/pVT with gasping, the acquisition rate of favorable neurological outcomes was 5.6%, compared with 23.4% in the ECPR implementation group (Additional file 9). Although ECPR appears to improve outcomes, more cases need to be included. In the future, the accumulation of outcomes in patients with refractory VF/pVT and gasping during resuscitation, with and without ECPR, will clarify whether gasping should be included in the criteria for ECPR implementation.

The present study had several limitations. First, the cases analyzed in the present study were from 2008 to 2011, making them somewhat older. Second, the number of patients with favorable neurological outcomes was relatively low at 18 (8.5%). This may have caused bias in the present analysis. Third, although a potential prognostic factor for OHCA is prehospital airway management [21], the information was not collected in the SAVE-J study [19] and, therefore, could not be included in the analysis. Fourth, in the multivariate analysis of neurologic outcomes (Table 2), "Therapeutic temperature management," which was not significantly different in the univariate analysis, was selected by the stepwise forward variable selection method. This was presumably included in the stepwise variable selection method because of its increased predictive (discriminative) power when combined with other variables. All patients in the favorable neurological outcome group received "Therapeutic temperature management," and those who did not receive "Therapeutic temperature management" were included only in the unfavorable neurological outcome group (Additional file 1). Thus, while it remains a presumption, the inclusion of "Therapeutic temperature management" as a variable in the multivariate logistic regression analysis may have been valuable in enhancing the predictive power and, consequently, selected for its contribution to the discrimination of outcomes. The forced entry of a variable (bystander CPR attempt), which was significantly different in the univariate analysis, instead of "Therapeutic temperature management," did not change the prognostic advantage of gasping (Additional file 10).