In our study, the mCRP devices examined all yielded good results with respect to effective chest compression during pre-hospital patient transport. Design-related differences in stability were found, but did not lead to any clinically relevant worsening of chest compression parameters.
Transport situations using mCPR devices that have been investigated to date primarily include ambulance, turntable ladders and helicopter transport [17–20]. In the study by Lyon et al., use of a soft stretcher with AutoPulse achieved good results and was presented as a possibility for improved rescue measures .
Sunde et al. examined compression quality at the site of the incident, when walking on a horizontal plane and on stairs . On the basis of these data and on the study of Gaessler et al., observing lower quality in manual chest compression during ambulance and braking manoeuvres, the use of mCPR devices represents a possibility for effective chest compression with protracted resuscitation .
Over the course of the entire test, only once did two false pressure points occur (corpuls cpr: at beginning of soft stretcher transport). However, since the connection point immediately before the two compressions registered as "incorrect" was checked and found to be correct for the subsequent stages, the most likely reason for an incorrect measurement was that the number of incorrect pressure points of the mCPR devices was low or equal to 0, as in other studies [17, 19, 24].
Nevertheless, displacement of the connection point to the patient was most pronounced with animax mono. Shear and tensile forces on the control lever, which can be turned in all directions, are felt to be the cause, as they promote slippage at the connection point; in contrast to the results of Gaessler et al., in our study this did not lead to an incorrect pressure point [17, 24]. The electrically powered mCPR devices seemed to be less susceptible to external forces by using a LDB (AutoPulse), spineboard (corpuls cpr) or stabilisation belts (LUCAS2).
During the tests, care was always taken to ensure that the mannequin was correctly secured on the gurney, but the manufacturer's precautions (e.g. operate the device only when it is in a secure position) during transport were deliberately disregarded in order not to unnecessarily complicate analysis of the basic data and to reflect realistic use [25, 26]. Despite more or less marked instability, the devices had only a very low risk of slipping in such a way that the correct pressure point would have been lost, from which it can be deduced that regular checks of the compression point are necessary when using mCPR under transport. If this is ensured, as in our experimental design, and any deviations are corrected promptly, then correct cardiac massage should be possible with all devices tested even under transport conditions.
With the manually operated animax mono, the percentage of compressions that were too deep when used in the rescue basket stage (40.1%) was noticeably high. Because there was no high-altitude rescuer available to operate the device, we recorded fewer compressions in absolute terms than in electrically powered mCPR devices, but mechanical resistance in the device should actually prevent compressions that are too deep. One explanation for this observation could be, as with displacements, shear forces at the compression point. In the case of electrically powered mCPR devices, adjustments to the devices via automated calibrations may have played a role with respect to better values during transport: If the compressing agents were paused between stages in order to check the compression point, this could have led to better adaptation to the mannequin. In contrast to the study by Fox et al., the study by Gaessler et al. on ambulance transport with LUCAS2 did not show any compression with a pressure depth that was in line with guidelines [19, 24]. This is an indication that the simulator results for the "proportion of compressions with pressure depth that meets guidelines" must be considered with caution. The mannequin selected by Gaessler et al. [17, 24] could only inadequately represent the dimensions of a human thorax, whereas the mannequin used in our tests seems to be more suitable. According to the manufacturer, corpuls cpr adjusts to the elasticity of the thorax. Use on a mannequin might have led to incorrect pressure depth and thus cannot be transferred to humans. This may also explain the greater scattering in pressure depth observed during basic resuscitation.
Animax mono was subject to fluctuations in frequency and compression-ventilation ratio compared to electrically powered mCPR devices. These were most likely due to the manual operation and related transport influences. More than half of all stages were classified as "Not OK" with respect to the "30:2" compression-ventilation ratio. Measurement of compression frequency revealed that animax mono ranged from 88 to 112 compressions/minute; however, with a median of 100/min (IQR 9), this value was within the recommended range of 100–120/min) . Gaessler et al. made similar observations [17, 24]. However, operation of animax mono requires full attention of the operator, whereas with automated mCPR devices, user interactions such as pauses in ventilation are indicated by an acoustic and/or optical signal. Sunde et al. showed that this makes it easier to maintain the correct compression-ventilation ratio . Consistent frequency of electrically powered mCPR devices has been confirmed in other studies [17, 19, 24].
In all "satisfaction" categories, medians were at least 9.0 for electrically powered devices. Animax mono received significantly lower values ranging from 3.5 ("satisfaction when carrying") to 5.0 ("satisfaction in loading/unloading the ambulance" or "overall satisfaction"). The similarly good performance of all devices for the category "physical burden" was surprising. Obviously, the control lever of animax mono minimized work so much that despite the long muscle-based operation, virtually no increased physical burden was perceived. Overall, participants rated the entire transport on the modified BORG scale as "somewhat/reasonably strenuous". In the study by Fox et al., however, rescuers rated just an eight-minute manual chest compression on the BORG scale (RPE scale; values: 6–20) as "somewhat strenuous" (mean 13.6) ; Animax mono's independence from a battery received not only praise but also disadvantages during transport. An assistant had to operate the device continuously; at the same time, operation of the lever was problematic when using the turntable ladder basket or the cot´s transport frame. During these situations, the lever was elevated to a height that restricted the operator to completely release it to the resting position . AutoPulse was praised for its "flat" design. However, study participants expressed criticism of the large back plate, which led to obstacles when laying the mannequin on the ambulance gurney. The chest compression strap also made it impossible to secure the mannequin correctly on the gurney. For corpuls cpr, participants evaluated the possible combination of a resuscitation arm with a spineboard very differently: immobilization was praised, while the effort required was viewed negatively. LUCAS2 was praised for its simplicity.
A primary limitation of the study is that the mannequin chosen does not allow assessment of blood flow to brain and coronary vessels. Physiological parameters - for ventilation as well - for the assessment of compression quality using mCPR during transport could not be verified. Furthermore, it was shown that resuscitation mannequins could influence the results because their biomechanical properties do not adequately represent the human body and the built-in measuring devices do not have the desired precision, at least for some of the parameters recorded. This study was purely descriptive. However, the small number of cases limits the informative value of the results.