a b s t r a c t

Introduction: Space travel is expected to grow in the near future, which could lead to a higher burden of sudden cardiac arrest (SCA) in astronauts. Current methods to perform cardiopulmonary resuscitation in microgravity perform below earth-based standards in terms of depth achieved and the ability to sustain chest compressions (CC). We hypothesised that an automated chest compression device (ACCD) delivers high-quality CC during sim- ulated micro- and hypergravity conditions.

Methods: Data on CC depth, rate, release and position utilising an ACCD were collected continuously during a par- abolic flight with alternating conditions of normogravity (1 G), hypergravity (1.8 G) and microgravity (0 G), per- formed on a training manikin fixed in place. Kruskal-Wallis and Mann-Withney U test were used for comparison purpose.

Results: Mechanical CC was performed continuously during the flight; no missed compressions or pauses were recorded. Mean Depth of CC showed minimal but statistically significant variations in compression depth during the different phases of the parabolic flight (microgravity 49.9 +- 0.7, normogravity 49.9 +- 0.5 and hypergravity

50.1 +- 0.6 mm, p < 0.001).

Conclusion: The use of an ACCD allows continuous delivery of high-quality CC in micro- and hypergravity as ex- perienced in parabolic flight. The decision to bring extra load for a high impact and low likelihood event should be based on specifics of its crew’s mission and health status, and the establishment of standard operating proce- dures.

(C) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Growth in the space tourism sector and a shift toward long-duration interplanetary missions to the Moon and Mars are expected in the near future. These developments come with an increased risk of Medical emergencies to be managed in challenging logistical conditions, as lon- ger missions with older and less healthy individuals may be expected [1,2]. Space travel can affect the cardiovascular system during launch, orbit entry and re-entry extravehicular activity, physical and autonomic stress [1], as well as due to cardiovascular deconditioning in micrograv- ity [3]. Radiation-induced cardiovascular disease can occur during long duration space flight [4]. Although no astronaut has suffered a cardiac arrest requiring cardiopulmonary resuscitation (CPR), there have been

* Corresponding author at: Institute of Mountain Emergency Medicine, Eurac Research, Via Ipazia 2, 39100 Bolzano, Italy.

E-mail address: [email protected] (G. Strapazzon).

several primary minor cardiac events that have self-resolved [5,6] as well as near-drowning events due to technical failure in a spacesuit that could have led to an asphyctic cardiac arrest [1]. Space tourism could even bring people with Cardiovascular risk factors in sub-orbital and spaceflight, and the burden of emergencies (estimated as about 0.06 events per person-year in general population) and sudden cardiac arrest (SCA) could increase [1,7].

Recent guidelines for CPR during spaceflight advise approaching CPR similarly to earth-based ones [8]. There are three main methods to per- form chest compressions (CC) that can be used in microgravity: the Handstand (HS), the Reverse Bear Hug (RBH), and the Evetts- Russomano (ER) [9,10]. Guidelines suggest to start with the ER tech- nique at the site of the emergency (as it allows transportation of the vic- tim) and to shift to HS technique as soon as the victim is restrained and the surface distance allows for its application [8]. However, all tested methods perform below earth-based standards in terms of depth achieved. Even in the most optimal situation where the HS technique is used on a restrained patient, HS technique resulted in suboptimal

https://doi.org/10.1016/j.ajem.2021.12.056

0735-6757/(C) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

compression depth (44.9 +- 3.3 mm), where a compression depth of be- tween 50 and 60 mm is advised in international guidelines [8-10]. Man- ual chest Compression quality deteriorates significantly within minutes even in highly trained and fit rescuers [8,11].

automated chest compression devices (ACCD) can guarantee high- quality and uninterrupted CC. Although survival in a conventional pre- hospital or clinical setting is similar to good quality Manual CPR [12], it seems likely that the performance gain in delivered CC by ACCD in

microgravity could be much higher than the alternative manual tech- niques. The efficacy of using an ACCD in microgravity has never been published, even if an abstract describing potential feasibility has been reported [8]. In this study we investigated under repeatable conditions the quality of mechanical CC (regarding compression depth, rate, pres- sure point, and recoil) during all the phases of a parabolic flight (simu- lating 1 G vs 1.8 G vs 0 G). We hypothesised that an ACCD delivers high- quality CC during all the phases of a parabolic flight.

Fig. 1. Panel A. Upper vision of LUCAS 3’s floor attachment system: a) aircraft belts for LUCAS 3; b) aircraft belts for manikin; c) aeronautical belts for the head of the manikin; d) wired Laerdal SimPad PLUS; e) LUCAS 3; f) GoPro Hero5 Session camera; g) manikin; h) carabiners and connection to the aircraft rails. Panel B. Front vision of LUCAS 3: a) aircraft belts for LUCAS 3; b) aircraft belts for manikin; c) LUCAS 3 piston; d) wired Laerdal SimPad PLUS; e) watch for time-in-flight record; f) aircraft rails; g) carabiner and connection with the pencil; h) data sheet for in flight recording. Panel C. Test session during microgravity conditions.

1. Methods

The study was performed during the 4th Swiss Parabolic Flight Cam- paign in Dubendorf, Zurich (Switzerland) organized by the Swiss SkyLab Foundation on June 11, 2020. The review board of the flight cam- paign approved the study protocol (protocol number VP-152).

• 1. Study setting

We employed the LUCAS 3 (Stryker, MI) ACCD and a training mani- kin fitted with a standard compression spring (Laerdal Resusci Anne QCPR, Stavanger, Norway) with the capability to record the characteris- tics of CC via a connected tablet (Laerdal SimPad PLUS, Stavanger, Norway). The manikin was placed on the aircraft’s floor and fixed with certified aeronautical belts (Fig. 1). We positioned the ACCD on the manikin, and after testing during the flight at 1 G, data were col- lected during the parabolic flight.

• 1. Parabolic flight

The parabolic flight was carried out using a modified, two-engine Airbus A310 type 304 “ZERO-G” aircraft specifically predisposed for parabolic flights with a central experimental area where micro- and hypergravity were experienced. During the steady flight, gravity expe- rienced was 1 G (i.e. normogravity). During flight at 7,000 m, parab- olas were initiated by gradual increase of the attitude to around 50? from a steady horizontal flight. During this phase of approximately 20 s, the aircraft and crew experienced an acceleration of 1.8 G. The aircraft then followed a free-fall trajectory forming a parabola lasting approximately 20 s, during which there was a microgravity (0 G) pe- riod. An exit phase at 1.8 G, symmetrical with the entry phase, was performed on the descending part of the parabola to return the air- craft to stabilised altitude level within about 20 s. Data were collected during 16 hypergravity, 9 normogravity and 8 microgravity periods (each of ~20 s).

• 1. Data collection

We collected data on quality of mechanical CC in term of compres- sion rate, depth, release and position. Data were collected during the chest compression with three different methods: a) the wired Laerdal SimPad PLUS (Stavanger, Norway); b) the LUCAS 3 log files (Stryker, MI); and c) the video recorded during all phases of the experiment by GoPro Hero5 Session camera (Woodman Labs, Inc., CA) fixed as a single-body with the ACDD-manikin system (Fig. 1). Specifically, video data was analysed with custom software written in Phyton based on the OpenCV 3.0 library. A region of interest channel and spatial reliabil- ity tracker to track with high accuracy the movement of the LUCAS 3 piston was implemented to calculate compression rate and estimate depth and release.

• 1. Statistical analysis

Kruskal-Wallis test was used to compare compression depth, re- lease and rate during 0 G, 1 G and 1.8 G and Mann-Whitney U test was used for pairwise comparisons. The percentage of effective chest compressions was analysed by means of Pearson’s chi-squared test; an effective chest compression was defined as a compression with a depth of >=50 mm at the correct position (mid-chest). P-values of pairwise comparisons were adjusted by means of Holm-Bonferroni correction. SPSS version 26 statistical software (IBM Corp., Armonk, NY) was used. Tests were two-sided and p < 0.05 was considered statistically significant. Values are reported as mean +- standard deviation.

1. Results

Eight consecutive parabolas were done during a 26-min flight (see video in the Supplementary Video 1). Each of the eight microgravity phases of each parabola lasted from 22 to 26 s. Data from eight parab- olas were analysed by LUCAS 3 log files and the video recorded; data from the last four parabolas were analysed from the Laerdal SimPad PLUS.

Mechanical chest compression was performed continuously during the flight; the LUCAS 3 log file did not record any missed compression or pause. No displacement or other technical problem of the device were reported. Depth, release and rate during the last four parabolic flights are shown in Fig. 2. There was a minimal but statistically signifi- cant variation in compression depth during the different phases of the parabolic flight (Table 1). Depth of CC in hypergravity conditions was higher than in microgravity (50.1 +- 0.6 vs 49.9 +- 0.7, p = 0.047) and

normogravity conditions (50.1 +- 0.6 vs 49.9 +- 0.5, p < 0.001). CC re- lease was lower in hypergravity than in normogravity (0.7 +- 0.6 vs 0.0 +- 0.1, p < 0.001) and microgravity conditions (0.7 +- 0.6 vs 0.2 +- 0.4, p < 0.001) (Table 1). The rate of CC recorded via the manikin during the different phases of the flight remained stable (p = 0.939), similarly to data from the LUCAS 3 log file. Effective CC differed during micrograv- ity compared to hypergravity (73% vs 87%, p < 0.001) but not compared to normogravity conditions (73% vs 79%, p = 0.098).

Qualitative analysis of video recording data of the entire flight con- firmed the absence of clinically relevant variations in the quality of CC including all the eight parabolas (data not shown).

1. Discussion

This is the first study that report the feasibility and effectiveness in terms of Quality of chest compressions delivered with an ACDD during microgravity and hypergravity conditions. Mechanical CC were per- formed continuously during the entire flight without any missed CC, pause or displacement of the ACDD from the manikin. Different phases of the flight caused expected changes in the quality of mechanical CC (regarding depth and release) that were not clinically relevant during microgravity and hypergravity conditions compared to normogravity.

The mean range of depth, rate and recoil of CC recorded during all phases of the parabolic flight can be considered within the one advised by international guidelines [13], as the change in depth was in the range of decimals of mm. We consider the minor deviation in mean depth of CC below the threshold of 50 mm of no clinical significance. Our results were better than the values obtained with the three main methods to perform manual CC in microgravity, that all performed below guidelines set standards in terms of CC depth achieved and the ability to sustain compressions [13]. The HS method resulted in a mean CC depth of

47.3 +- 1.2 mm, the RBH of 41.7 +- 6.2 mm [9] and the ER showed incon- sistent results ranging from 27.1 +- 7.9 mm to 42.3 +- 5.6 mm [14,15]. The use of an ACCD allowed to continuously deliver high-quality CC. The monitoring system did not show any missed compression, pause, displacement or other technical problem even in a complex scenario of rapid changes of gravity. This is in line with the experiences of pre- hospital Emergency medical service providers, where ACCD are em- ployed especially when the access to the patient is limited, or transfers have to be made while guaranteeing correct continuous CC, with the ability to maintain CC for longer periods, such as in the helicopter emer- gency medical services [16].

The treatment of cardiac arrest consists of early, good quality CC and defibrillation. Defibrillation in microgravity has been tested successfully [17], and a defibrillator is available in the International Space Station [18]. With the addition of an ACCD astronauts could have the chance to provide high quality CC also for prolonged time, potentially improv- ing outcome in case of a SCA in a situation with limited resources and spaces as well as with challenging conditions (i.e., microgravity). The re- cent guidelines for CPR during spaceflight heve already suggested the

Fig. 2. Compression depth, release and rate during the last four parabolas. Each parabola is depicted with grey and pink colours. Grey colour represents the hypergravity phases (1.8 G) and pink the microgravity phase (0 G). White background represents the steady flight (normogravity, 0 G).

use of an ACCD as an option t[8]. However, time to first CC and defibril- lation may be prolonged by the use of ACCD in space as it was shown in helicopters [16]. One of the most challenging points would be to

develop a specific standard operating procedure (SOP) to allow not only a rapid application of a defibrillator but also a swift and effective deployment of the ACCD to minimise compromised perfusion time.

Table 1

Compression depth, release and rate and percentage of effective chest compressions during microgravity, normogravity and hypergravity.

	Microgravity (0 G)	Normogravity (1 G)	Hypergravity (1.8 G)	p-value
Compression depth (mm), mean +- SD	49.9 +- 0.7	49.9 +- 0.5	50.1 +- 0.6	<0.001
Compression release (mm), mean +- SD	0.2 +- 0.4	0.0 +- 0.1	0.7 +- 0.6	<0.001
Compression rate per minute, mean +- SD	101.4 +- 0.5	101.3 +- 0.5	101.3 +- 0.5	0.939
Effective chest compressions?, %	73%	79%	87%	<0.001

* Chest compression with depth >= 50 mm on a mid-chest level.

Optimal cardiac arrest response manoeuvres in microgravity already differ on the phase of the CPR [8] and the integration of the use of an ACCD could substitute one of the different manual techniques based on the usAge SItuation. Optimal transfer, as well as restraining methods and fitting devices should be determined through practising complete cardiac arrest response scenarios in a follow up study and in a scenario that allows the simulation of longer microgravity periods.

Cons of an ACCD in spaceflights are the added weight (approxi- mately 8 kg for the current device but down to 3.5 kg for others, that could better justify the estimated cost of 20,000 $/kg to put in orbit extra load [1]), despite that an ACCD could remain in service for several years and has to be transported only once in its lifecycle (e.g. to the In- ternational Space Station). Other disadvantages could be the potential adverse effects on structural integrity of the spacecraft caused by ACCD vibrations and the additional training required to restrain effecively the ACCD and the victim in microgravity [7].

• 1. Limitations

Parabolic flights mimic microgravity during spaceflight but are lim- ited in time, and therefore it was not possible to record longer sessions of chest compressions. Our study did not include the process of deliver- ing next to the victim, restraining and fitting an ACCD because the alter- nating gravity phases experienced during a parabolic flight do not make that feasible (every phase of each parabola last from 20 to 26 s) and safety regulation does not allow for it.

1. Conclusions

The use of an ACCD allows to continuously deliver high-quality CC and, even in a complex scenario of rapid changes of gravity, the moni- toring system did not show any missed compression, pause, displace- ment or other technical problem. Specific SOP and training should be developed for the practical application of ACCD in case of SCA during spaceflight. Its deployment should not delay the delivery of manual CC, and the decision to bring one-time extra load for a high impact and low likelihood event (i.e. SCA) should be based on the specifics of the mission and health status of its crew.

Authors’ contributions

AF and GS contributed to conceptualisation and development of the study design. AF, MvV, TS, TDC, MP and GS participated in data collec- tion and analysis. TDC performed the statistical analysis. AF, MvV, TDC and GS oversaw the interpretation of results. AF, MvV, TS, TDC and GS did the literature review and wrote the manuscript. All authors critically reviewed the final draft of the manuscript and have given approval for the version submitted.

Funding

This study was supported by internal funding only.

Availability of data and materials

The datasets during and/or analysed during the current study avail- able from the corresponding author on reasonable request.

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Declaration of Competing Interest

The authors declare that they have no competing interests.

Acknowledgements

We thank Laerdal Italia Srl (Bologna, Italy) and Croce Bianca (Bol- zano, Italy) for lending the equipment for the study. The authors thank the Department of Innovation, Research, University and Museums of the Autonomous Province of Bozen/Bolzano, Italy for covering the Open Ac- cess publication costs.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi. org/10.1016/j.ajem.2021.12.056.

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