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Manual chest compression pause duration for ventilations during prehospital advanced life support – An observational study to explore optimal ventilation pause duration for mechanical chest compression devices

Open AccessPublished:September 06, 2022DOI:https://doi.org/10.1016/j.resuscitation.2022.09.001

      Abstract

      Aim

      Mechanical chest compression devices in the 30:2 mode generally provide a pause of three seconds to give two insufflations without evidence supporting this pause duration. We aimed to explore the optimal pause duration by measuring the time needed for two insufflations, during advanced life support with manual compressions.

      Methods

      Prospectively collected data in the AmsteRdam REsuscitation STudies (ARREST) registry were analysed, including thoracic impedance signal and waveform capnography from manual defibrillators of the Amsterdam ambulance service. Compression pauses were analysed for number of insufflations, time interval from start of the compression pause to the end of the second insufflation, chest compression pause duration and ventilation subintervals.

      Results

      During 132 out-of-hospital cardiac arrests, 1619 manual chest compression pauses to ventilate were identified. In 1364 (84%) pauses, two insufflations were given. In 28% of these pauses, giving two insufflations took more than three seconds. The second insufflation is completed within 3.8 seconds in 90% and within 5 seconds in 97.5% of these pauses. An increasing likelihood of achieving two insufflations is seen with increasing compression pause duration up to five seconds.

      Conclusion

      The optimal chest compression pause duration for mechanical chest compression devices in the 30:2 mode to provide two insufflations, appears to be five seconds, warranting further studies in the context of mechanical chest compression. A 5-second pause will allow providers to give two insufflations with a very high success rate. In addition, a 5-second pause can also be used for other interventions like rhythm checks and endotracheal intubation.

      Keywords

      Abbreviations:

      AED (Automatic External Defibrillator), ALS (Advanced Life Support), BLS (Basic Life Support), BVM (Bag-Valve-Mask), CPR (Cardiopulmonary Resuscitation), EMS (Emergency Medical Services), OHCA (Out-of-Hospital Cardiac Arrest), SAD (Supraglottic Airway Device)

      Introduction

      Chest compressions and ventilations are the cornerstone of cardiopulmonary resuscitation (CPR). Preceding advanced airway management, current guidelines recommend a ratio of 30 chest compressions to 2 ventilations.
      • Olasveengen T.M.
      • Semeraro F.
      • Ristagno G.
      • et al.
      European Resuscitation Council Guidelines 2021: Basic Life Support.
      An insufflation time of one second is recommended. Pauses in chest compressions to give two ventilations should be as short as possible, but should not exceed ten seconds.
      • Olasveengen T.M.
      • Semeraro F.
      • Ristagno G.
      • et al.
      European Resuscitation Council Guidelines 2021: Basic Life Support.
      • Beesems S.G.
      • Wijmans L.
      • Tijssen J.G.
      • Koster R.W.
      Duration of ventilations during cardiopulmonary resuscitation by lay rescuers and first responders: relationship between delivering chest compressions and outcomes.
      When Advanced Life Support (ALS) is provided by Emergency Medical Services (EMS) or resuscitation teams, airway management is provided and insufflations with oxygen are given to improve oxygenation during CPR.
      • van Schuppen H.
      • Boomars R.
      • Kooij F.O.
      • den Tex P.
      • Koster R.W.
      • Hollmann M.W.
      Optimizing airway management and ventilation during prehospital advanced life support in out-of-hospital cardiac arrest: A narrative review.
      Mechanical chest compression devices can be used to provide high quality chest compressions.
      Both the LUCAS® and Autopulse® mechanical chest compression devices in the 30:2 mode provide a fixed 3-second pause after 30 compressions to provide two insufflations. This is based on a theoretical sum of the first insufflation of one second, the first exsufflation for one second, the second insufflation of one second, after which chest compressions are automatically resumed. In clinical practice however, providers may need some more time to provide two insufflations. Recently, technological developments enabled adjustment of this compression pause duration in some of the mechanical chest compression devices. Neither current resuscitation guidelines, nor the manufacturers, provide recommendation on the optimal compression pause duration for mechanical chest compression devices.
      In this study, we aimed to explore the optimal compression pause duration for mechanical chest compression devices, allowing for two adequate insufflations by providers on one hand, and minimally interrupting chest compressions on the other hand. We hypothesized that providers frequently need more time than three seconds to provide two adequate insufflations. To assess the required compression pause duration, we first need to study the time needed to provide two insufflations in 30:2 CPR with manual chest compressions; In the context of manual chest compressions, the compression pauses are not fixed but providers are able to take the necessary time to give two insufflations with an adequate tidal volume and compressions are resumed after two successful insufflations have been provided. With the insight from this study in the setting with manual chest compressions, further studies in the setting of mechanical chest compression can be designed and interpreted, aiming to determine the optimal chest compression pause duration of mechanical chest compression devices for ventilations.

      Methods

      Setting

      In the Netherlands, dispatchers alert citizen responders, first responders, and two ALS level ambulances in case of (suspected) cardiac arrest.
      • Stieglis R.
      • Zijlstra J.A.
      • Riedijk F.
      • et al.
      Alert system-supported lay defibrillation and basic life-support for cardiac arrest at home.
      ALS level ambulances are staffed with an ambulance nurse and an ambulance driver. Ambulance nurses are trained to perform ALS including advanced airway management, following national ambulance guidelines corresponding with the European Resuscitation Council guidelines. Regional standard operation procedures and specific devices vary.
      The ambulance service of Amsterdam was equipped with a Lifepak® 15 monitor (Stryker Emergency Care, Redmond, WA, USA) and did not use mechanical chest compression devices in the study period. Airway management consisted of bag-valve-mask (BVM) ventilation initially, followed by either the i-gel® supraglottic airway device or endotracheal intubation. Insufflations were provided by a self-inflating bag. Waveform capnography was started at advanced airway management, or earlier at the discretion of the ambulance nurse. After advanced airway management (i-gel® or intubation) was completed, CPR was changed from the 30:2 compression to ventilation ratio to continuous chest compressions with asynchronous ventilations (10 min−1). According to resuscitation guidelines, the ambulance nurse could decide to provide 30:2 CPR after i-gel® placement when there is excessive air leakage.
      • Soar J.
      • Böttiger B.W.
      • Carli P.
      • et al.
      European Resuscitation Council Guidelines 2021: Adult advanced life support.

      Data source

      This study was performed using data from ARREST (AmsteRdam REsuscitation STudies): an ongoing, prospective registry of all-cause out-of-hospital cardiac arrest (OHCA) in the province North-Holland.
      • Blom M.T.
      • Beesems S.G.
      • Homma P.C.
      • et al.
      Improved survival after out-of-hospital cardiac arrest and use of automated external defibrillators.
      Data sources were limited to the ambulance service of Amsterdam, because other EMS services in the ARREST region used mechanical chest compressions devices and were therefore not suitable for analysis. Informed consent was not required by law if the patient was deceased, and in case of survival, deferred informed consent was obtained after hospital discharge. Data sources of ARREST included data from the EMS dispatch center, AED recordings, data from the Lifepak® 15 defibrillator, EMS run report and hospital data. The medical ethics review board of the Academic Medical Center reviewed the study protocol and determined that the Medical Research Involving Human Subjects Act did not apply (number W17_089).

      Sample size calculation

      In order to achieve a 95% confidence interval of 0.25 second under or above the observed mean duration of the time needed to provide two insufflations, a sample size of 385 pauses in compressions was required. With at least three pauses with two insufflations per patient we needed 129 patients to reach the pauses necessary for the analysis.

      Study design and data collection

      All consecutive prehospital resuscitation attempts by EMS for OHCA in adults (≥18 years) between June to December 2017 were screened and included when (A) there was a medical cause of the arrest, (B) manual chest compressions and insufflations were given in the 30:2 ratio, (C) the ambulance run report and Lifepak® 15 data were available, and (D) a minimum of three compression pauses with two insufflations suitable for analysis were available. Patients were excluded when a significant airway or ventilation problem was the cause of the arrest (like anaphylaxis or asthma), based on information from the ambulance run report. All baseline characteristics were routinely collected in the prospective ARREST registry. Data from the Lifepak® 15 defibrillator were transferred to dedicated software (Code-stat® 10, Stryker EMS, Redmond, WA, USA).

      Data analysis

      In Code-stat® 10 software, the thoracic impedance signal, ECG and waveform capnography was visualized (Fig. 1). By using the thoracic impedance signal, all pauses in chest compressions during the resuscitation were identified.
      • Alonso E.
      • Ruiz J.
      • Aramendi E.
      • et al.
      Reliability and accuracy of the thoracic impedance signal for measuring cardiopulmonary resuscitation quality metrics.
      The definition of a pause was the absence of chest compressions for >1.5 seconds, when chest compressions are expected (no spontaneous circulation). If a pause was longer than ten seconds the pause was not included in the analysis. The start and end of a compression pause was annotated and categorized as a pause to give ventilations, to perform interventions (like a rhythm check or endotracheal intubation) or as an unclear pause (unclear impedance signal and/or capnography). All pauses to give two ventilations were eligible for inclusion, regardless of the airway management technique at that moment (BVM or i-gel®). Pauses used for ventilation were categorized by number of insufflations seen during the pause. When available, the waveform capnography signal was used to check and compare the identification of insufflations and ventilation subintervals.
      Figure thumbnail gr1
      Fig. 1Time intervals during a chest compression pause with two ventilations. Green. Thoracic impedance signal. Black. Electrocardiogram. Orange. Waveform capnogram. Intervals. 1. time needed for two insufflations, 2. compression pause duration, 3. delay in starting the first insufflation, 4. first insufflation, 5. first exsufflation, 6. second insufflation, 7. second exsufflation during the delay in resumption of chest compressions, 8. first insufflation in capnography, 9. first exsufflation in capnography, 10. second insufflation in capnography. There is a three second delay in capnography signal due to side-stream measurement of CO2.
      Our primary aim was to determine the time interval from the start of compression pause to the end of the second insufflation (Fig. 1, interval 1). This corresponds with the current pauses on mechanical compression devices are now programmed to accommodate only these actions, leaving out the second exsufflation and possible extra delay in resuming compressions. Secondary aims were to determine the likelihood of achieving two insufflations in relationship with compression pause duration, and in pauses with two ventilations: determining the compression pause duration (Fig. 1, interval 2) and subintervals of in- and exsufflations (Fig. 1, intervals 3–10). These predefined intervals were annotated in Code-stat® in both the impedance signal and capnography waveform.
      The analysis was done individually by HvS and LCD, after which cases were cross-checked by the other author. Any discrepancies were discussed and solved, when needed by a third assessor (RWK).

      Statistical analysis

      Statistical analysis was done in SPSS® (version 28.0, IBM® SPSS®, Chicago, IL). The likelihood of successfully providing two insufflations by a given compression pause duration was calculated on pauses intended for ventilation, leaving unidentified or intervention pauses out of the analysis. To calculate median time needed for two insufflations and compression pause duration, all pauses with two insufflations were used. Median values were reported with interquartile range. Cumulative curves were made, including the 90th percentile. To determine whether few patients with either very short or long pauses did influence the results of the whole group, we performed a sensitivity analysis on just the first three compression pauses with two insufflations per patient. Median duration of the ventilation subintervals were analysed on all pauses with two insufflations. Changes in ventilation- and compression pause duration over the course of the resuscitation were analysed.

      Results

      Within the study period, 756 cases suspected for OHCA were screened for inclusion. CPR was attempted in 362 of these cases. After applying in- and exclusion criteria, 132 cases were suitable for analysis (Fig. 2). Characteristics of included cases are shown in Table 1. Analysis of the 132 cases yielded a total of 2634 pauses. Of these pauses, 1619 were intended for ventilations and in 1364 (84%) two insufflations could be identified (Table 2).
      Figure thumbnail gr2
      Fig. 2Flow diagram of inclusion. CPR. cardiopulmonary resuscitation, EMS. Emergency Medical Services, OHCA. out-of-hospital cardiac arrest, ROSC. return of spontaneous circulation.
      Table 1Characteristics of included cases (n = 132). Values are numbers (percentage).
      Gender

      n (%)
      Male 74 (56%)

      Female 58 (44%)
      Median age in years (range)71 (18–92)
      Airway management technique

      n (%)
      BVM only 20 (15%)

      BVM → SAD 54 (41%)

      BVM → tube 57 (43%)

      BVM → SAD → tube 1 (1%)

      Unknown 0 (0%)
      Moment of start capnography

      n (%)
      During BVM ventilations 39 (30%)

      At start advanced airway management 64 (48%)

      Later during CPR 13 (10%)

      No capnography was used 7 (5%)

      Malfunction 2 (2%)

      Unknown 7 (5%)
      BVM: bag-valve-mask, CPR: cardiopulmonary resuscitation, SAD: supraglottic airway device.
      Table 2Characteristics of pauses in included cases. Values are numbers (percentage).
      Total number of pauses2634
      Mean number of pauses per case20.0 (range 4–63)
      Pauses per category
       Ventilation pause1619 (61%)
       Intervention510 (19%)
       Unknown505 (19%)
      Mean number of ventilation pauses per case12.3 (range 3–39)
      Ventilation pauses per category
       No insufflation38 (2%)
       One partial insufflation0 (0%)
       One full insufflation158 (10%)
       One full and one partial insufflation22 (1%)
       Two full insufflations1364 (84%)
       Two full insufflations and one partial insufflation9 (1%)
       Three full insufflations28 (2%)
      Mean number of pauses with two insufflations per case 10.3 (range 3–38).
      The likelihood of successfully providing two insufflations within a compression pause to ventilate increases when a compression pause is longer (Fig. 3). This is observed with compression pause durations up until 5 seconds. Success rate is 97.5% at this length. Further lengthening did not improve the likelihood of providing two insufflations.
      Figure thumbnail gr3
      Fig. 3Likelihood of giving two insufflations versus less than two insufflations in a compression pause intended for ventilation, per compression pause duration. Number of pauses per pause duration is noted on top of bar.
      Further analysis was done on pauses with two ventilations; The cumulative percentage of time needed for two insufflations is shown in Fig. 4A. The median time needed to provide two insufflations was 2.5 (IQR 2.1–3.1) seconds. In 90% of pauses with two ventilations, the second insufflation was given within 3.8 seconds. Median compression pause duration for all pauses with two insufflations was 3.5 (IQR 3.0–4.3) seconds (Fig. 4B). In 90% of pauses with two ventilations, the compression pause duration was within 5.4 seconds.
      Figure thumbnail gr4
      Fig. 4Cumulative percentages of compression pause durations of pauses with two insufflations. (A) Interval 1. Time needed for two insufflations with median (p50), p90 and p100. The percentage at 3 seconds is added because this is the timeframe of most mechanical chest compression devices. (B) Interval 2. Compression pause duration with median (p50), p90 and p100.
      An analysis on the first three compression pauses with two ventilations per case showed a negligible difference with all observed pauses (Supplementary Table 1); The median time needed to provide two insufflations was 2.6 (IQR 2.1–3.3) seconds, with a 90th percentile at 3.8 seconds. Median compression pause duration was 3.6 (IQR 3.0–3.4) seconds.
      In 28% of all pauses with two insufflations, giving two insufflations took longer than 3 seconds (Supplementary Fig. 1). In 98.5% of these pauses, two insufflations are provided within 5 seconds. There is no indication for a change in both the time needed for two insufflations and compression pause duration over the course of the resuscitation (Supplementary Fig. 2).
      Analysis of subinterval medians for pauses with two ventilations showed a delay of 0.2 (IQR 0.1–0.4) seconds in starting the first insufflation after stopping chest compressions. The first and second insufflation took 0.6 (IQR 0.4–0.7) and 0.6 (IQR 0.5–0.8) seconds respectively, the first exsufflation 1.0 (IQR 0.8–1.3) seconds, and the delay until resumption of chest compressions 1.0 (IQR 0.7–1.3) seconds. When comparing intervals noted on the impedance signal with those noted on the capnography signal, insufflation times noted on the capnography signal were slightly longer: 1.0 (IQR 0.8–1.2) second for both the first and the second insufflation (Supplementary Table 2).

      Discussion

      The main finding of this observational study is that when manual chest compressions are paused to give two ventilations, the second insufflation is completed within 3.8 seconds in 90% of the pauses with two ventilations. In 97.5% of all compression pauses with two ventilations, the second insufflation was given within 5 seconds. In the majority (87%) of chest compression pauses to ventilate, two insufflations were identified. An increasing likelihood of providing two insufflations is seen in pauses up to 5 seconds. Shorter compression pauses (1–3 seconds) more often contain less than two ventilations. Insufflations are given with the recommended duration of one second per insufflation. Pause durations do not change over the course of the resuscitation.
      Mechanical chest compression devices in the 30:2 mode may need to provide a compression pause of more than three seconds to have a high chance (>90%) to actually provide two insufflations. The current 3-second pause of many chest compression devices would be too short to facilitate two full insufflations in 28% of the pauses in our study. This finding in the context of manual chest compressions needs to be confirmed in a future study, in the context of mechanical chest compression. However, a fixed 3-second pause of a mechanical chest compression device could add time-pressure to provide two insufflations, possibly at the expense of an adequate tidal volume. We therefore suggest that the recommended chest compression pause duration to provide two ventilations is five seconds, based on our findings in this study. With a compression pause duration of five seconds, two insufflations can almost always be achieved. Should the two insufflations be provided faster than five seconds, the remaining time allows for the second exsufflation. In this way, high peak intrathoracic pressures are prevented because chest compressions are not started on a fully insufflated chest. A five second pause is well within the recommended maximum pause duration of ten seconds mentioned in current guidelines.
      • Olasveengen T.M.
      • Semeraro F.
      • Ristagno G.
      • et al.
      European Resuscitation Council Guidelines 2021: Basic Life Support.
      Previous studies have provided limited information to guide ideal mechanical chest compression device settings regarding the time to allow for insufflations. In the large RCT’s on mechanical chest compression devices, little data are provided on insufflations.
      • Bernhard M.
      • Hossfeld B.
      • Kumle B.
      • Becker T.K.
      • Bottiger B.
      • Birkholz T.
      Don't forget to ventilate during cardiopulmonary resuscitation with mechanical chest compression devices.
      Previous work by Beesems et al. on manual chest compression pauses, determined a median chest compression pause duration of seven seconds to provide two ventilations in the 30:2 mode in the Basic Life Support (BLS) setting by analysing data from AED’s of trained lay-persons and First Responders.
      • Beesems S.G.
      • Wijmans L.
      • Tijssen J.G.
      • Koster R.W.
      Duration of ventilations during cardiopulmonary resuscitation by lay rescuers and first responders: relationship between delivering chest compressions and outcomes.
      Survival was not decreased with increasing duration of compression pauses, even up to pauses of ten seconds. This finding led to the recommendation in ERC guidelines that rescuers may take up to ten seconds to provide two ventilations.
      • Perkins G.D.
      • Handley A.J.
      • Koster R.W.
      • et al.
      European Resuscitation Council Guidelines for Resuscitation 2015: Section 2. Adult basic life support and automated external defibrillation.
      The findings by Beesems in the BLS setting cannot be applied to the ALS setting; In the ALS setting, one paramedic provides insufflations, while someone else provides chest compressions. This could lead to a shorter compression pause duration when compared to the BLS setting which is based on a single-rescuer giving both chest compressions and ventilations. Furthermore, First Responders use a simple facemask, like the Pocket Mask®, to manage the airway. They might need more time to provide two insufflations when compared to ambulance nurses with more experience and a more advanced airway management technique. In a previous study by Ødegaard et al. in the prehospital ALS context, the median compression pause duration was 5.5 seconds (IQR 4.5–7).
      • Odegaard S.
      • Pillgram M.
      • Berg N.E.
      • Olasveengen T.
      • Kramer-Johansen J.
      Time used for ventilation in two-rescuer CPR with a bag-valve-mask device during out-of-hospital cardiac arrest.
      In all pauses analysed, two insufflations were detected in only 51%. More or less than two ventilations was seen in 29% and in 20% no insufflations were seen. This study, however, does not show the time needed to achieve the second insufflation but only the total chest compression pause duration, so those data are of limited use to support a specific pause duration for mechanical chest compression devices. Our study showed a shorter median compression pause duration (3.5 versus 5.5 seconds).
      Changing the compression pause to five seconds has the potential to improve survival. First of all, optimizing insufflations during mechanical chest compression may improve oxygenation during mechanical CPR. A previous study has shown that a higher arterial partial pressure of oxygen (paO2) is associated with a higher likelihood of return of spontaneous circulation (ROSC) and survival.
      • Spindelboeck W.
      • Schindler O.
      • Moser A.
      • et al.
      Increasing arterial oxygen partial pressure during cardiopulmonary resuscitation is associated with improved rates of hospital admission.
      Furthermore, successfully providing 30:2 CPR has been associated with an improvement in outcome.
      • Chang M.P.
      • Lu Y.
      • Leroux B.
      • et al.
      Association of ventilation with outcomes from out-of-hospital cardiac arrest.
      In addition, heart rhythm checks, which take place every-two minutes during ALS, need to be done within five seconds as well. From a practical point of view, when using mechanical chest compression devices with a pause duration of five seconds, this pause can also be used for the rhythm check. In this way, manually pausing the device for a rhythm check is not necessary. This also accounts for interrupting chest compressions for endotracheal intubation attempts. This can help to prevent undesirable long chest compression interruptions and make things easier in the resuscitation process.
      • Ruiz J.
      • Ayala U.
      • Ruiz de Gauna S.
      • et al.
      Feasibility of automated rhythm assessment in chest compression pauses during cardiopulmonary resuscitation.
      Several limitations in our study should be emphasized. A relatively high percentage of pauses (19%) were unsuitable for analysis because of an unclear thoracic impedance signal. It is conceivable, that these pauses in fact had poor or absent ventilations. Waveform capnography was not always present to double check the thoracic impedance signal clearly identifying ventilations. Furthermore, in our analysis we could not differentiate pauses in which ventilations were given with BVM or a supraglottic airway device. It is possible that this has an influence on pause duration. The Lifepak® 15 can provide a metronome to guide manual chest compressions and ventilations. We did not study the impact of the metronome on pause durations. The metronome may explain why pauses in our study are shorter than those reported by Ødegaard et al., although the impact seems limited in a study by Kern et al.
      • Odegaard S.
      • Pillgram M.
      • Berg N.E.
      • Olasveengen T.
      • Kramer-Johansen J.
      Time used for ventilation in two-rescuer CPR with a bag-valve-mask device during out-of-hospital cardiac arrest.
      • Kern K.B.
      • Stickney R.E.
      • Gallison L.
      • Smith R.E.
      Metronome improves compression and ventilation rates during CPR on a manikin in a randomized trial.
      The thoracic impedance signal is not suitable to determine tidal volumes delivered during ventilations.
      • Losert H.
      • Risdal M.
      • Sterz F.
      • et al.
      Thoracic impedance changes measured via defibrillator pads can monitor ventilation in critically ill patients and during cardiopulmonary resuscitation.
      Therefore, despite complying with the recommended insufflation time of one second, we cannot determine whether or not adequate tidal volumes were given.
      Using the findings of this study as a basis, further research on the quality of ventilations during mechanical chest compression and the effects of a five second pause during mechanical chest compression on CPR quality metrics, ROSC and survival could be performed with a suitable study design. This will provide further insight how to improve ventilation during CPR when using mechanical chest compression devices.

      Conclusions

      When manual chest compressions are paused to give two ventilations, frequently (28%) more than the current 3-second timeframe of mechanical chest compression devices is needed to provide two insufflations. The optimal chest compression pause duration for mechanical chest compression devices appears to be five seconds, which warrants further studies in the context of mechanical chest compression. A 5-second pause will allow providers almost always (97.5%) to be able to provide two insufflations, while still staying within the recommended maximum timeframe of ten seconds. Additionally, a 5-second pause can also be used to perform a rhythm check during Advanced Life Support, which could reduce unnecessary long chest compressions interruptions. Further research is needed to study ventilation during mechanical chest compression and the impact of this strategy on CPR metrics and outcome.

      Conflicts of Interest

      HvS reports grants to his institution from Stryker Emergency Care, the Zoll Foundation and the AMC Foundation. LD reports no conflict of interest. MWH reports grants to his institution from ZonMW, EACTA and ESA and consulting fees paid to his institution from CSL Behring, IDD Pharma and MSD, all outside the scope of this study. RK reports grants, non-financial support and personal fees from Stryker Emergency Care, and personal fees from HeartSine.

      Sources of funding

      The ARREST registry is maintained by an unconditional grant of Stryker Emergency Care, Redmond, WA. This study has not received specific funding.

      CRediT authorship contribution statement

      Hans van Schuppen: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization. Lotte C. Doeleman: Software, Validation, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization. Markus W. Hollmann: Validation, Writing – review & editing, Supervision, Project administration. Rudolph W. Koster: Conceptualization, Methodology, Validation, Writing – original draft, Writing – review & editing, Supervision, Project administration.

      Acknowledgments

      We would like to thank Mette Ekkel, Vera van Eeden, Emma Linssen and Remy Stieglis for data management, Steffie Beesems for helping in the design of this study, and the ambulance nurses and EMS Medical Directors for collaborating with ARREST.

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