This study was a prospective triple-cross over randomized controlled non-inferiority trial.
Setting and intervention
We described the study-scenario in detail in a previous publication, where we investigated the effect of PPE on the quality of CPR but didn’t evaluate the healthcare workers’ perspective . This part of our trial focusses on the strain on the mental reserves of ambulance crews. We block-randomized emergency medical technicians (EMTs) to teams of two. All teams performed standardized BLS scenarios. This included walking quickly up and down three flights of stairs while carrying standard equipment (backpack and oxygen cylinder). Following this, they performed 12 min of BLS on a manikin (qCPR ResusciAnn, Laerdal®, Norway) in accordance with current ERC guidelines. Every 2 min the team-members swapped between executing chest compressions and performing ventilation. Participants adhered to a rest period of 30 min between each scenario.
For the control scenario, participants wore their standard PPE consisting of EMS uniform, safety boots and examination gloves. For the intervention scenarios, an overall, goggles and either of the following two masks was added: an FFP2 mask with an expiration valve (“Meditrade Respima® EEC” (Meditrade® GmbH, Germany)), or an FFP2 mask without an expiration valve (“Yao Wang Medical Protective Face Mask” (Qingzhou Yaowang Pharmaceuticals Co. Ltd., China)). The Meditrade masks were certified to the N95-standard, whereas the Yao Wang masks were certified to the KN95-standard. These standards a virtually identical for the purpose of this paper in regard to flow rate, maximum inhalation and exhalation resistance. Scenarios were performed in a randomized order.
We tested concentration performance using the d2 test battery including its subsets before and after each scenario .
As a secondary outcome, we investigated dexterity as a measure of psychomotoric strain using the nine-hole peg test (NHPT).
A psychologist experienced in clinical testing (JG) performed both tests.
The primary outcome was the shift in overall concentration performance after each scenario, as measured by the d2 test.
We tabulated all results for each of the three scenarios and calculated absolute differences (with 95% confidence intervals) between the scenarios.
To assess potential carry over, we also analyzed the influence of the sequence in which participants completed the scenarios on the outcome, using regression modelling.
Secondary outcomes included the shift in dexterity, measured by the NHPT, as well as the d2-subscores, i.e., percentage of errors, errors of commission, errors of omission, and processed target objects. Analysis of the secondary outcomes followed the primary outcome. An individual provider served as the unit of analysis.
Sample size considerations were based on the non-inferiority of the primary outcome of shift in overall concentration performance. The reference values for good performance in the d2-test range from 184 to 207 points for 20- to 39-year-old individuals . Based on previous experience, and the known distribution of d2-test results, a clinically relevant non-inferiority limit was defined as 20 points. Considering the reference range, drops or increases of twenty points indicate inferior (below the 25th percentile) or superior (above the 75th percentile) performance, respectively. We needed to include 40 participants to achieve a power of 0.8 at a significance level of 0.05. This was well within the 48 individuals needed to study quality of CPR as outlined in our previous paper .
MS Excel (Microsoft Corporation) and STATA 13SE (Stata Corporation) were used for data management and analysis. We conducted our study following the principles of the Declaration of Helsinki. All participants provided written informed consent before inclusion. The local ethics committee approved the study (#1520/2020).
Patient and public involvement
Although improving the quality of CPR and post-resuscitation care for patients is the ultimate goal of this investigation, caregivers and their neurocognitive performance are the immediate study suspects. Involvement efforts therefore focused on those individuals, and patients or patient representatives were not involved.
We developed the research question and the study protocol together with representatives from the prehospital emergency provider community. EMS recruited the participants. After conclusion of the study, we performed non-structured interviews with all participants to get their feedback on the burden of participation and possible future improvements. Participants were debriefed with their provisional results as feedback.