This 11-year retrospective observational study identified favourable neurological outcome in 18.9% of paediatric patients 30 days after OHCA. BLS and non-traumatic aetiology for the cardiac arrest were associated with favourable neurological outcome at 30 days, while initial asystole and administration of adrenaline were associated with an unfavourable neurological outcome.

Despite potential advances in managing paediatric OHCA, traditional survival rates remain low. Gelberg et al. [13] observed in paediatric OHCA patients (up to 21 years of age) an increase from 6.2 to 14% in overall 30-day neurological favourable survival from 1990 to 2012. Similarly, Law et al. [14] investigated patients admitted to hospital with out-of-hospital cardiac arrest with only 28.3% bystander CPR and found a survival rate of 20.8%, with only 13.2% having a favourable neurological outcome. In contrast, the survival rate was much higher in our cohort, even though we included patients who were declared dead on-scene. Differences in the approaches of local emergency medical systems might explain this discrepancy.

In our population, two-thirds of the patients were treated with immediate bystander CPR, resulting in 7.1% attaining ROSC before the arrival of the Rega-HEMS team. Additionally, first responder BLS resulted in 4.1% attaining ROSC. All these patients survived with 30-day favourable neurological outcome. The importance of immediate CPR for paediatric OHCA was clearly described earlier [13, 15,16,17,18]. A Japanese OHCA registry analysis from 2005 included 5,170 children under the age of 18 years and found an adjusted odds ratio of 2.59 (95% CI 1.81–3.71) for a favourable neurological outcome with BLS [18]. The fact that the odds ratio in our cohort was four times higher may be a result of improvements in resuscitation in the last 15 years. This includes broad BLS education for laypersons that nowadays also includes teaching CPR to children, [19] the implementation of dispatcher-assisted CPR [20] and the introduction of nationwide first-responder systems [21, 22].

Nonetheless, closing the gap for the one-third of patients not treated with immediate CPR may be challenging, as some patients need to be rescued from remote areas that cannot be directly accessed by foot. A registry analysis underlined that early advanced life support is crucial for favourable neurological survival in adults [23]. These findings may hold true for the paediatric population as well, thus justifying possible interventions by HEMS that provide access to almost all areas.

That said, most resuscitation-awareness campaigns for laypersons focus on adult BLS education [24]. Given the entirely different physiology and aetiology of OHCA in children as compared to adults, of which higher oxygen consumption and hypoxemia is a leading cause, these differences must be considered and incorporated into such campaigns and highlighted in future resuscitation recommendations.

The resuscitation of children, especially after major trauma, represents a substantial challenge for laypersons, as first responders, and for professional medical rescuers, because such cases are rare. Rescuers face significant emotional burdens and the rescue teams are often not as well trained in managing children as victims, as compared to adult patients. The proportion of paediatric emergencies within the total case volume of HEMS is about 8%.25 Traumatic cardiac arrest might be more challenging for dispatchers to identify because it is a rare condition, and the patient’s unresponsiveness might be misinterpreted due to traumatic brain injury. This might lead to less dispatcher-assisted CPR [26]. The invasive measures necessary to correct reversible trauma-related causes (e.g. relief of tension pneumothorax or pericardial effusion) are challenging and rarely performed, even more so in children [25,26,27]. Trauma was the second-most-common cause of out-of-hospital cardiac arrest in children in our study, and boys were more likely to be victims of major trauma (higher risk-taking and older age), which aligns with other reports in the prehospital care of children [4]. The difficulty of access by foot or the need for a helicopter hoist operation often slows down the procedure, resulting in delayed resuscitation efforts [25].

Even in children, unrecognised reversible causes remain a problem in cardiac arrest after major trauma. Ismail et al. demonstrated that 113 (24%) of 472 paediatric trauma patients required chest decompression during treatment, indicating that severe chest trauma is not rare in children [28]. Consistent with this impression, a post-mortem CT study showed that 70 (96%) of 73 children who died had at least one concomitant chest injury, of which the medical team was, in many cases, unaware [29]. Thus, a patient with undiagnosed and untreated severe thoracic injury may not enjoy the benefit of the best resuscitative efforts.

Moreover, in our study, children have a higher survival rate after trauma than adults, but they also usually have worse neurological outcomes than adult trauma patients [30]. In a retrospective study from Japan of 582 children who underwent CPR after trauma, a resuscitation time of more than 15 min was associated with poor neurological outcomes in children [31]. These findings are consistent with our results.

There is an ongoing discussion of the advantages of tracheal intubation in ALS. In our univariable analysis, tracheal intubation was associated with reduced odds for favourable neurological outcome at 30 days, but this no longer held true in the multivariable analysis. This may be explained by the high proportion of patients with favourable neurological survival with ROSC after BLS who were spontaneously breathing without needing airway management in post-resuscitation care. In contrast, a German registry analysis including over 1,700 paediatric OHCA cases found higher odds ratios for ROSC with advanced airway management. Unfortunately, their data lack 30-day survival and neurological outcomes. Compared to our data, the German Registry analyses around 10% of traumatic cardiac arrests and the authors excluded patients declared deceased on arrival, which might explain different findings [6]. A French registry analysis, including over 1,500 paediatric OHCA patients, comparing tracheal intubation with supraglottic airway didn’t find higher odds ratios in their propensity-scored analysis for the outcome ROSC. Furthermore, they found poorer odds ratios for 30-day survival and neurological outcome for patients with tracheal intubation [32].

The multivariable model found an association between adrenaline and reduced odds for 30-day unfavourable neurological outcomes. This association might be explained by resuscitation time bias, which leads to more interventions the longer the duration of CPR is. This hypothesis might be underlined by the finding that a shorter duration of CPR was significantly associated with favourable neurological outcomes in our univariable analysis. Unfortunately, we couldn’t demonstrate this in the multivariable analysis due to too many missing for the duration of CPR.

In our cohort, on-scene time was significantly shorter for patients with favourable 30-day survival. However, this might be explained by the helicopter take-off time-stamp used. In the event of a declaration of death on-scene, legal documents must be filled in by the responsible HEMS physician on-scene, prior to take-off.

Early damage-control surgery may be a crucial factor in survival, especially for patients with traumatic cardiac arrest who are suffering from non-compressible haemorrhage. This might justify the use of scoop-and-run tactics and transport under ongoing CPR, without any delaying interventions being performed on-scene, such as advanced airway management. These interventions could instead be performed in the helicopter on the way to hospital, thus saving precious time.

Due to the retrospective design of our study, one limitation is that missing variables cannot be reproduced, and we did not impute such data. The missions were classified by the treating HEMS physician on-scene according to the NACA score, which included some patients with ROSC upon arrival of the HEMS team. Asystole as the first rhythm and the administration of adrenaline were associated with unfavourable neurological outcome. However, there is a clear association between these factors, as, following the guidelines, all non-shockable (i.e. asystole and PEA) rhythms are treated with adrenaline. We were unable to overcome the potential resuscitation time bias due to missing data. We report a large cohort of traumatic cardiac arrests, which might be caused by selection bias: HEMS can easily reach recreational areas like lakes, rivers, and alpine regions, but landing with a helicopter in cities or crowded areas can be challenging or impossible. Thus, our data might not represent the entire Swiss emergency medical services.