To date, the optimal packing strategy for emergency kits has not been established. While some literature exists on improved packing of in-hospital emergency kits [7, 16], the urban prehospital setting has not yet been investigated. The present study investigated 80 simulated experiments, each with four tasks and four emergency kits. For our primary endpoint in comparing a novel TPO kit and novel non-TPO kit we did not observe a difference in total equipment retrieval time between these kits.

The participants in our study were predominantly young males who regularly worked with emergency kits. This setting is vastly different to previous studies conducted in clinical settings in which most participants were female and with low exposure to emergency kits [7]. Sex differences in handling of emergency equipment have not been investigated to date.

Optimal packing strategies for emergency kits have yet to be established and are likely to depend on several factors. Firstly, some emergency kits may serve a very specific purpose and can therefore be designed under more restrictive assumptions. Schyma et al. optimized an airway bag for in-hospital remote site resuscitation, achieving a 29% decrease in preparation time and a 87.5% reduction in errors; 68.3% of the study participants also perceived the task as being less difficult [16]. In the prehospital emergency setting, however, a single kit needs to serve a wide variety of purposes, ranging from basic diagnostics to potentially highly invasive procedures.

Secondly, the intended use setting plays an important role. Most existing research focuses on the design of in-hospital crash carts [8, 12, 17]. Villamaria et al. have measured the times taken by teams in responding to cardiac arrests, and found that crash carts arrive a median 68 s after the cardiac arrest team has been activated [17]. Crash carts were less readily available in non-patient areas, and it took longer for the crash cart to arrive at the scene of the cardiac arrest. Consequently, even in-hospital teams frequently use smaller, more portable emergency kits (e.g., backpack) for remote emergency response and during patient transport [7, 11]. While some research into the content and organization structure of in-hospital emergency kits has been published [8, 12, 18], prehospital and clinical settings differ significantly. Prehospital emergency services usually work in smaller teams and tighter spaces, and handle a more diverse set of emergencies. The present study was conducted in an urban prehospital EMS setting with a highly modular structure and a variety of units providing different expertise and equipment. Most studies investigating the contents and—in part—packing strategies for emergency kits operated in different settings, such as mountain rescue [2], in-flight emergencies [3], and austere environments [2]. These settings constrain the design of emergency kits so that the results of these studies are of limited value for other settings.

Thirdly, familiarization with the emergency kits is likely to affect performance. Uniquely, TPO has been proposed to offer a benefit for emergency kits which are used only on rare occasions [7] In our data, however, equipment retrieval times did not vary significantly between the two unfamiliar emergency kits (novel TPO versus novel non-TPO), regardless of their organization. Our experiments thus contradict existing literature on TPO. Data on the performance of TPO versus non-TPO emergency kits after adequate equipment familiarization is lacking.

When preparing equipment for a procedure, forgetting items is a common problem and is comprehensively documented in the literature [7, 16]. Cognitive aids have therefore been recommended for complex procedures with significant risk [19, 20]. In recent years, mnemonics, checklists [21], prepacked kits [16], and dedicated staging area backgrounds (kit dump sheets) [21] have been described. Sommer et al. [7] have described TPO as a novel cognitive aid strategy for use in unexpected emergency settings in which crash carts are infeasible and where other cognitive aids might not be readily available. They were able to not only demonstrate a significant reduction in missing items across all tasks (neonatal endotracheal intubation, neonatal intravenous access, neonatal intraosseous access), but also a significant reduction in retrieval times. Despite these promising results, our experiments did not reproduce these results: using TPO kits did not result in more complete retrieval compared to traditional kits, and retrieval time was comparable across all emergency kits. Exploratory analysis did, however, reveal quicker retrieval times when using the novel TPO system compared to the novel non-TPO system to prepare for a forearm splint. Assuming that in real-life settings different tasks are assigned different priorities (based on urgency and expected task frequency), some backpack designs may perform differently than in our simulated setting which prioritized each task equally. These priorities should be considered when designing an emergency kit because it may be feasible to optimize kits under these constraints and a TPO strategy could prove beneficial.

Despite the precise task assignments, surplus items were retrieved for every task. The most common surplus items were a lubricant gel for endotracheal intubation and an alcoholic swab for intraosseous access. Both of these items were removed from initial versions of the checklists after being frequently missed in the piloting phase. Only very few participants misunderstood the initial assignment and retrieved items for similar but different tasks (e.g., retrieval of an intraosseous drill while preparing for intravenous access). The wide range of the surplus items suggests a high inter-provider-variability in clinical practice from experienced healthcare providers.

Successfully employing TPO will always require that equipment required for multiple tasks is stored in multiple locations, as can be seen from the packaging table provided by Sommer et al. [7]. This redundancy is likely to lead to increased weight of emergency kits, representing an added physical burden for already strained emergency medical services workers [22]. Moreover, some of the assumptions and perhaps even personal experiences of the kit designers themselves are manifested in the organization of the TPO modules: as demonstrated by commonly omitted and surplus items, providers may have different definitions of the equipment a task entails. We hypothesize that highly standardized procedure definitions and processes could circumvent this complication, as is the case for airway management in many emergency medical services, especially those with a high rate of invasive procedures [23, 24].

Our study has several strengths. Highly standardized conditions allowed the different emergency kits to be objectively assessed. Careful randomization and blind analysis reduced relevant biases. A large sample size supports the outcome of statistical tests.

Despite these strengths, relevant study limitations need to be acknowledged. Firstly, while simulations are an important tool for safely evaluating new equipment or procedures, they cannot completely mirror their real-life use. However, this study design was selected to maximize consistency between experiments. Secondly, participants had not previously worked with the emergency kits provided, and the participants were not examined after the initial learning phase with the respective kits. This limits generalizeability of our results to every-day use of TPO but adds important data to the previously established hypotheses that TPO might benefit users with limited exposure to these emergency kits. Finally, task-oriented package organization is not strictly defined, and TPO may be variously interpreted by the different organizations and providers.