Emergency Medical Service (EMS) system in Japan
In 2019, there were 726 fire stations with dispatch centers in Japan. The Fire and Disaster Management Agency of Japan supervise the EMS system. In Japan, the emergency team is usually not permitted to terminate the resuscitation of patients with OHCA in a prehospital setting. All patients with OHCA are transported to hospital except in cases of decapitation, incineration, decomposition, and rigor mortis. Therefore, the Japanese EMS system is ideal for investigating the association between physician involvement during pediatric OHCA and patient outcomes. In a prehospital setting, the EMS team, comprising three people, can perform the following procedures for patients with OHCA: (i) obtain and assess an initial electrocardiogram (ECG), (ii) use an automated external defibrillator; place a peripheral intravenous line, administer Ringer’s lactate solution, and administer adrenaline (epinephrine) intravenously; and ventilate using a bag valve mask; and (iii) establish an advanced airway using an endotracheal tube, a laryngeal mask airway, a Combi-tube, and an esophageal gastric tube airway. Some procedures require instructions from a physician remotely. Patients with OHCA are treated according to Japanese cardiopulmonary resuscitation (CPR) guidelines, which are based on guidelines issued by the American Heart Association, the European Resuscitation Council, and the International Liaison Committee on Resuscitation. If an EMS team determines that it would be preferable to have a physician at the scene, the team picks up a hospital physician while enroute to the scene or calls a physician to attend the scene. However, there are no strict criteria for requesting physicians to attend a scene, with many complex factors such as the severity of the patient's illness, geographical conditions, and local medical resources influencing this decision.
We collected patient data from an ongoing prospective Japanese nationwide prehospital database, namely, the All-Japan Utstein Registry of the Fire and Disaster Management Agency. The database has been described in detail elsewhere.3,4,9 Briefly, this population-based registry covers approximately 127 million residents in Japan. All patients with OHCA have been registered. Data have been collected since January 2005 and continue to be accumulated. The registry is based on the International Utstein style.10 The database contains patients’ age (years), sex, date of the OHCA, call time to the EMS, suspected etiology of cardiac arrest, type of witness, interventions by bystanders (chest compression, rescue breathing, and defibrillation), provision of dispatcher CPR instructions, initial ECG rhythm at the time of EMS contact, interventions by healthcare providers (defibrillation, advanced airway device use, intravenous fluids, and adrenaline use), EMS arrival time at the scene, and outcomes (ROSC, 1-month survival, and 1-month cerebral performance categories [CPCs]).
We collected data concerning pediatric patients with OHCA (age range, 0–18 years) from January 1, 2005 to September 9, 2017. We excluded patients with unrealistic time records, unknown outcome status, and patients who did not receive any resuscitation by bystanders or healthcare providers.
We divided the patients into two groups: 1) patients who received physician involvement on site during OHCA (physician-present group), and 2) patients who did not (physician-absent group). Physician involvement was defined in the database as any physician present, regardless of whether or not a procedure was performed.
Variables and outcomes
We considered the following variables: age, sex, year of the OHCA, season, call time to EMS, suspected etiology of cardiac arrest, type of witness, interventions by bystanders (chest compression, rescue breathing, and defibrillation), the provision of dispatcher CPR instructions, initial ECG rhythm at the time of EMS contact, and time from emergency call to EMS arrival at the scene, to perform adjustments required for these patients.
We subdivided the patients into the following age categories: new-borns and infants (0 years), toddlers to younger grade-schoolers (1–7 years), children (8–12 years), and adolescents (13–18 years).11–13 The year of the OHCA was categorized as follows: 2005–2009, 2010–2013, and 2014–2017. We also categorized the seasons as follows: January–March, April–June, July–September, and October–December. We divided the time of cardiac arrest into morning (0600 h to 0900 h), daytime (0900 h to 1700 h), evening (1700 h to 2200 h), and night-time (2200 h to 0600 h) based on previous studies and patterns of medical staffing.11,14,15 The etiology of cardiac arrest was grouped into cardiac causes, other medical causes (respiratory disease, cerebrovascular disease, malignant tumor, hypothermia, anaphylaxis, and any medical disease), and external causes (traffic accident, suffocation, drowning, and trauma). The time from the emergency call to the EMS arrival at the scene was divided equally into four categories: <6 min, 6–7 min, 8–9 min, and > 9 min.
The primary outcome was 1-month neurologically favourable survival using Glasgow-Pittsburgh CPCs as measures of neurological outcomes.10 CPCs are defined as follows: CPC1, good cerebral performance; CPC2, moderate cerebral disability; CPC3, severe cerebral disability; CPC4, coma and vegetable state; and CPC5, brain death. We defined CPC1 and CPC2 as ‘neurologically favourable survival.’16 The secondary outcomes were ROSC and 1-month survival rates.
Continuous variables are expressed as mean and standard deviation, and categorical variables are expressed as frequencies and percentages.
We used absolute standardized differences to assess differences in the variables between the groups. We regarded an absolute standardized difference of < 10% as well balanced.17,18
Unadjusted outcomes were compared using chi-square tests. In adjusted analyses, we used a generalized linear model to compare the outcomes between the groups with and without physician involvement during pediatric OHCA. We used the following independent variables: physician involvement, age, sex, year of the OHCA, season, time of arrest, suspected etiology of cardiac arrest, witness status, interventions by a bystander, provision of dispatcher CPR instructions, initial ECG rhythm at the time of EMS contact, and time from emergency call to EMS arrival at the scene. Subgroup analyses were performed for each variable to investigate its association with 1-month neurologically favourable survival. To confirm the robustness of our results, we performed a sensitivity analysis using overlap weights to balance the patients’ backgrounds between the groups.19–21 Overlap weights are a propensity score weighting method to adjust for potential confounders.22 The weights are defined as a value of 1 – the propensity score for treated patients and the propensity score itself for untreated patients. In this study, we calculated the propensity score for receiving physician care using a multivariable logistic regression model including the following variables: age, sex, year of the OHCA, season, time of arrest, suspected etiology of cardiac arrest, witness status, interventions by a bystander, provision of dispatcher CPR instructions, initial ECG rhythm at the time of EMS contact, and time from emergency call to EMS arrival at the scene. We then constructed an overlap-weighted generalized linear model to compare primary outcomes.
We reported the results as risk differences, 95% confidence intervals (CIs), and two-sided P-values. We considered a two-sided P-value of < 0.05 as statistically significant. Statistical analyses were performed using STATA (version 16.0; StataCorp, College Station, TX, USA) software.
This study was approved by the Institutional Review Board of the International University of Health and Welfare, Narita Hospital, Japan (approval number: 21-Im-043, September 28, 2021). The requirement for informed consent was waived due to the use of anonymized data.