The influence of excluding patients with bystander return of spontaneous circulation in the current OHCA database

This population-based observational study was conducted using nationwide OHCA data collected in Japan from 2011 to 2014. The Utstein database was provided by Japan’s Fire and Disaster Management Agency (FDMA). The Institutional Review Board at Kokushikan University approved this study.

Japan encompasses approximately 378,000 km² of land, and populated areas comprise 121,000 km². According to the Statistics Bureau of the Ministry of Internal Affairs and Communications, the population of Japan in 2014 was approximately 127 million.

The primary EMS system in Japan is provided by fire departments (FDs), and there were 752 FDs in 2014. All FDs are overseen by the FDMA. Almost every FD ambulance includes at least one emergency life-saving technician (ELST) who is qualified to provide advanced airway management, endotracheal intubation, intravenous lines, adrenaline administration, and defibrillation with a semi-automated defibrillator. EMS responders follow protocols provided by medical control councils for each region. These protocols are based on guidelines issued by the Japan Resuscitation Council.

We sampled patients with presumed cardiogenic OHCA data registered from 2011 to 2014 according to Utstein-style guidelines in Japan. The exclusion criteria for this study were as follows: unwitnessed by laypeople, witnessed by EMS or fire department personnel, no CPR attempted. (1) Patients who are not ROSC on-scene without performing EMS resuscitation regardless of performing bystander CPR or not in the unknown ECG group. (2) Patients who are ROSC on-scene without received resuscitation attempt by both bystander and EMS in the unknown ECG group. (3) Although cardiac arrest waveform [VF, VT, PEA, asystole] is indicated at EMS arrival, resuscitation attempt is not performed by EMS on-scene, unknown status of bystander CPR or no description of the time of bystander CPR initiation, only rescue breathing CPR, only PAD implementation, response interval negative value, response interval > 23 min (99 percentile) and EMS contact to hospital arrival time > 53 min (99 percentile). A detailed inclusion/exclusion criterion is shown in Fig. 1.

All eligible patients were divided into three groups based on first monitored rhythm. The shockable group included patients with VF or pulseless VT. The non-shockable group included patients with PEA/asystole. Patients that were not applicable for either group were allocated into the unknown group.

In Japan, all OHCA data are prospectively collected by ELSTs or EMS personnel. All records are managed by the FDMA, and the results are published each year. The data are available as a part of the national OHCA registry; however, one must apply to the FDMA in advance to obtain the information. Kokushikan University applied and was granted these data. The records included the following data according to Utstein-style guidelines: prefectures, years, sex, age, bystander-witnessed status, types of bystander(s), bystander CPR, rescue breathing, use of an automated external defibrillator, first monitored rhythm, dispatcher assist, time course of resuscitation (e.g. time of patient collapse, receipt of Japanese emergency call for dispatch a fire engine or an ambulance (call 119), EMS contact with patients, EMS arrival on the scene, and hospital arrival), cause of cardiac arrest, return of spontaneous circulation in the pre-hospital setting, 1-month survival and neurological outcome 1 month after the event. The CPC was diagnosed by physicians. After 1 month, the outcome was followed up and described in all records by EMS personnel.

The act of performing chest compressions with rescue breathing by laypeople was called conventional CPR, and the use of only chest compressions was called chest-compression-only CPR. The response interval was defined as the time from the call to emergency services (119) to patient contact by EMS personnel. When laypeople delivered shocks using AED, the patient and their first recorded rhythms were regarded as the shockable group.

The Glasgow-Pittsburgh CPC scoring was defined as follows: category 1, good cerebral performance; category 2, moderate cerebral disability; category 3, severe cerebral disability; category 4, a coma or vegetative state; and category 5, death. Survival at 1 month post-resuscitation with a favourable neurologic outcome was defined as a CPC score of 1 or 2 [8, 10].

The primary outcome of our study was CPC 1–2 at 1 month post-resuscitation. Field ROSC was considered the secondary outcome of this study.

Figure 1 shows the patient selection process of the study. From 2011 to 2014, we sampled 296,879 patients with presumed cardiogenic OHCA in the database. A total of 91,995 patients were eligible for this study. The patients were divided into three groups based on first monitored rhythm: the shockable group (n = 20,673), the non-shockable group (n = 68,696), and the unknown group (n = 2626).

Table 1 shows the patient characteristics by group, as classified using first monitored rhythm. The median age of study patients was 79 years (IQR, 67–86), and the AED usage rate was 3.5% (3210 patients). Chest-compression-only CPR was the most common bystander intervention. More patients in the unknown group had favourable outcomes (39.2%, 1030 patients) than those in the shockable group (24.2%, 5003) and non-shockable group (1.3%, 899).

Table 2 compares the outcomes of a dataset that included the unknown group with one that excluded this group. The outcomes of patients with non-attempted BCPR are not included in this table. When the unknown group was excluded from the dataset, the proportion of patients with conventional CPR to CPC 1–2 is almost the same (inclusion 16.3%, 1127 patients; exclusion 16.2%, 958 patients). However, exclusion of this group resulted in 2.5% less patients with chest-compression-only CPR (inclusion 54.0%, 3742 patients; exclusion 51.5%, 3038 patients) and 3.2% more patients with PAD to CPC (inclusion 18.6%, 1286 patients; exclusion 21.8%, 1286 patients).

Table 3 shows the presumed effects of bystander interventions on ROSC and CPC 1–2 using multivariable analysis. In the dataset that included the unknown group, the AORs for CPC 1–2 were 1.90 for conventional CPR (95% CI, 1.73–2.08), 2.08 for chest-compression-only CPR (95% CI, 1.95–2.22) and 4.51 for PAD (95% CI, 4.12–4.94). In the dataset that excluded the unknown group, the AORs for CPC 1–2 were 1.58 for conventional CPR (95% CI, 1.43–1.75), 1.69 for chest-compression-only CPR (95% CI, 1.58–1.82) and 6.13 for PAD (95% CI, 5.57–6.74).

In the group that included the unknown group, the AORs for ROSC were 1.49 for conventional CPR (95% CI, 1.40–1.58), 1.42 for chest-compression-only CPR (95% CI, 1.36–1.48) and 4.06 for PAD (95% CI, 3.75–4.39). In the group that excluded the unknown group, the AORs for ROSC were 1.21 for conventional CPR (95% CI, 1.13–1.30), 1.19 for chest-compression-only CPR (95% CI, 1.14–1.25) and 5.24 for PAD (95% CI, 4.83–5.68).

Because of the observational study, unknown bias could have affected its results, such as patient backgrounds and in-hospital care, both of which are not included in the Japanese Utstein database. These factors may have influenced the survival outcomes. Furthermore, we were unable to obtain the actual unknown ECG data, as they were not described in the Japanese Utstein database. Therefore, it requires a further nationwide investigation for acquiring them, and we consider that it will be the next examination of this study. Defibrillation time from collapse was not considered due to the lack of data. In addition, the location of cardiac arrest was available [17‐19], but we could not include the location where PAD was delivered. Moreover, we included the BCPR group, which may have affected outcomes because the quality of CPR was not considered. Assessing the quality of BCPR prior to EMS personnel arrival was not realisable under the present system. Finally, our results cannot be generalised to children nor non-cardiogenic or unwitnessed OHCA patients.