Feedback Devices for Cardiopulmonary Resuscitation: Comparison
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The application of feedback devices for cardiopulmonary resuscitation (CPR) can effectively enhance the quality of life-saving treatment during CPR. 

  • cardiopulmonary resuscitation
  • feedback
  • cardiac arrest
  • basic life support

1. Introduction

Cardiac arrest is a serious threat to human life and health. China is the site of approximately 660,000 cases of out-of-hospital cardiac arrest (OHCA) each year [1]. Even in developed areas such as Shanghai, which boasts a well-equipped medical infrastructure and advanced community healthcare facilities, the average hospital admission survival rate over five years is only 4.14%, and the discharge survival rate is only 1.23% [2]. Cardiopulmonary resuscitation (CPR) is widely believed to be the most effective way to rescue patients suffering from cardiac arrest and restore spontaneous respiration and circulation (known as return of spontaneous circulation, ROSC) [3]. To improve the survival rate of patients, timely and high-quality intervention is essential in every component of the chain of survival. In particular, timely and effective CPR is crucial, with chest compression being a key component [4]. Currently, the primary mode to maintain the quality of CPR is a feedback control system, which provides real-time feedback on the effectiveness of CPR to enhance its quality.

2. Classification of Feedback Devices for Cardiopulmonary Resuscitation

The feedback device for CPR has undergone significant development since its early use as a simple metronome. The metronome provides a fixed beat to assist the rescuer in maintaining a steady compression rate, thereby ensuring the quality of CPR and increasing the likelihood of successful resuscitation [5]. Feedback devices for CPR are generally divided into two categories based on the type of feedback information: auditory–visual feedback devices and physiological information data-monitoring feedback devices. Auditory–visual feedback devices provide a certain beat sound and display compression depth graphically or through color differences and can use sound, graphics, or color to correct the rescuer’s compression rate and depth in real time to ensure the quality of CPR. Physiological information data-monitoring feedback devices can monitor one or more parameters, such as cardiac output (CO), coronary perfusion pressure (CPP), mean arterial relaxation pressure (MARP), ECG amplitude spectrum area (AMSA), ETCO2, pulse oxygen saturation waveform, and regional cerebral oxygen saturation (rScO2), to adjust the compression strategy.

2.1. Audio-Visual Feedback Devices

In 2015, the American Heart Association endorsed the use of feedback devices during CPR to enhance resuscitation quality [4]. Even for medical professionals, accurately assessing the depth and frequency of CPR may be challenging [9,10][6][7], and the quality of resuscitation may decline due to fatigue. Additionally, perceived compression depth and rate may differ from actual ones [11][8], which underscores the need for audio-visual feedback devices to improve CPR quality and enhance resuscitation quality. Currently, the development of audio-visual feedback devices for CPR has reached a relatively mature stage. These devices are predominantly based on two main components: pressure sensors and accelerometers. Pressure sensors measure the force applied to the patient’s chest, which is set based on the patient’s weight and the desired depth of compression. However, since it cannot detect individual compression, a pressure sensor-based feedback device can only provide feedback on compression depth and not on compression rate. On the other hand, accelerometers measure the acceleration of the patient’s chest and use these data to calculate the distance moved during compression. The latest CPR feedback devices on the market are predominantly based on accelerometers, with some models also integrating pressure sensors. While an accelerometer-based feedback device is equipped with an electronic processor capable of calculating the compression rate, it is not well-suited for monitoring the quality of ventilation [12][9]. As the earliest device with cardiopulmonary resuscitation feedback function, CPR-plus boasts several advantages, including non-invasiveness, portability, and easy use. The CPR-plus is shown in Figure 1a. It achieves compression depth measurement via a pressure-sensitive compression plate and features a metronome for prompt pacing.
Applsci 13 10222 g001
Figure 1.
(
a
) CPR-plus, (
b
) CPREzy™ device, (
c
) CPRmeter™, (
d
) CPRmeter™ function.
CPREzy™ is a portable device specifically designed to enhance manual chest compression during cardiopulmonary resuscitation. By utilizing a row of glowing LED lights, it provides a readable and user-friendly display of the current compression force to make it easier for rescuers to observe. The appearance of the CPREzy™ device is shown in Figure 1b, with the compression pad located in the lower half of the device (A) and a smaller upper half (B) consisting of a light indicator. It is imperative for rescuers to verify that none of the green LEDs are activated during the upstroke phase of compression, which signifies the successful release of pressure between consecutive compression cycles.  The Laerdal CPRmeter™, developed by the Norwegian company Laerdal, is based on an accelerometer design. To enhance measurement accuracy, a pressure sensor was incorporated [16][10]. The appearance of the CPRmeter™ device is shown in Figure 1c. The top surface of the CPRmeter™ features a gray, hard rubber cap that serves as the contact surface for the rescuer’s hand. Feedback is provided through a 26 × 26 mm color display. Compression depth is represented by a white bar that moves up and down between two green fields, with the two fields turning gray when the compression depth is too deep or too shallow, as seen in Figure 1d. Compression rate is displayed on a speedometer-like display, with the pointer located in the green range and lit up when the rate is appropriate [17][11]. The CPRmeter™ can be connected to the HeartStart MRx defibrillator (Philips Medical System), allowing for the integration of defibrillation and CPR feedback devices [12,23][9][12]. The second-generation CPRmeter™ 2 can be combined with the CPRmeter™ app to promote quality improvement initiatives by sharing details of the CPR, such as compression depth, compression frequency, time duration, and chest compression scores. After the resuscitation is completed, the CPRmeter™ application can report, share, and export statistical data to enable a more detailed analysis of the resuscitation details. The Zoll PocketCPR™ is a small, battery-powered device used for CPR made in the United States. Its appearance is depicted in Figure 2a. It utilizes an accelerometer to measure the frequency and depth of compression and can be placed on the victim’s chest to provide audio prompts to guide the rescuer in performing CPR, if desired. The feedback on compression depth is provided through the flashing of LED lights, with the metronome increasing the LED flashing rate to reflect the correct compression depth and rate according to the CPR guidelines [12][9].
Applsci 13 10222 g002
Figure 2.
(
a
) Zoll Pocket CPR, (
b
) Cardio First Angel™, (
c
) True-CPR, (
d
) Palm CPR feedback device.
Cardio First Angel™ (CFA), on the other hand, shown in Figure 2b, is an entirely mechanical feedback device designed to assist with cardiopulmonary resuscitation (CPR) by providing audio feedback on chest compression. Intriguingly, this device does not require any power source. It relies on a specially designed spring system that emits a sound upon achieving the correct compression depth from 50–60 mm. 
The True-CPR developed by Physio-Control is a smart compression feedback device from the United States that can provide real-time CPR feedback, displaying compression depth and rate on a highly visible dial. The external appearance of the True-CPR device is depicted in Figure 2c.
Corscience’s Feedback Sensor Push (COR.CPR-RRB) is a sophisticated device for monitoring chest compression. It delivers precise measurements of compression depth and frequency, thereby enabling comprehensive data collection, analysis, and transfer. Notably, the device can be integrated with a host system, such as a defibrillator or monitor, further enhancing its utility [25][13].
Beaty, a device developed by Medical Feedback Technologies, offers real-time audio feedback regarding the efficacy of chest compression during the process of cardiopulmonary resuscitation (CPR) through the utilization of pressure sensors. This device serves as a guiding mechanism for medical professionals to precisely calibrate the depth of chest compression. Moreover, an audible alert is activated upon the achievement of a compression depth of 5 cm [26][14].
CPR-1100 CPR Assist, developed by Nihon Kohden, presents chest compression depth and frequency information. This device employs orange lights to indicate the recommended compression frequency and blue lights to signify the desired compression depth.
The Sunlife Palm CPR chest compression feedback meter, developed by China Suzhou Shangling Research, provides indicator lights on the top to give feedback on compression depth by quantity and color and feedback on compression rate by R light color. The Palm CPR is shown in Figure 2d. 

2.2. Research on Feedback Devices Based on Physiological Information Data Monitoring in China and Abroad

Simple feedback systems have been shown to improve the effectiveness of chest compression during CPR. However, a limitation of such systems is the lack of personalization for individual patients and a standardized execution. To address this issue, feedback devices utilizing physiological data monitoring are needed. Due to the limitations of the prehospital environment, invasive detection is often difficult. A study by Lampe et al. at Northwell Health established a time-dependent function correlating carotid blood flow during cardiac arrest resuscitation and response to varying chest compression. By predicting the carotid blood flow generated by subsequent chest compression, the study aimed to optimize CPR parameters in real time, maximizing carotid blood flow [29][15]. Sebastian et al. evaluated the feasibility of using a machine-controlled closed-loop CPR (MC-CPR) system to optimize coronary perfusion pressure (CPP) during CPR. Their real-time hemodynamic simulations demonstrated that MC-CPR, controlled by a closed-loop machine, significantly outperformed the AHA CPR guidelines in improving coronary perfusion pressure [30][16]. 

2.3. Application Status and Effects of Cardiopulmonary Resuscitation Feedback Devices

CPR feedback devices are widely utilized in CPR training. In studies investigating CPR training, it has been observed that training with a feedback device enhances CPR competency and overall quality more significantly than traditional CPR training methods [35][17]. Furthermore, the utilization of feedback devices can augment skill acquisition and overall performance in cardiopulmonary resuscitation [36][18]. From a practical standpoint, the combination of current CPR audio-visual feedback devices and smartphones offers a more accessible feedback tool for emergency situations. By utilizing the data collected through a smartphone’s built-in accelerometer, real-time assessment of compression depth and frequency can be achieved, aligning closely with the actual values. This enables accurate real-time feedback on CPR quality through a dedicated CPR mobile application [38][19].

2.4. Integration of Feedback Devices with Defibrillator and Related Equipment

Real CPR Help™ is an enhanced functionality integrated into Zoll’s AED Plus, utilizing accelerometer technology within the ZOLL defibrillator electrodes, furnishing real-time feedback concerning the accuracy of CPR compression in terms of depth and frequency. Audio and visual prompts guide the operator through the CPR process.

3. Current Limitations of Cardiopulmonary Resuscitation Closed-Loop Feedback Devices

To improve the quality and success rate of CPR and provide effective guidance for rescuers, as well as personalize chest compression for cardiac arrest patients, feedback devices for CPR are continuously being developed. These feedback devices have achieved significant results in terms of improving the quality of CPR and increasing the survival rate of cardiac arrest patients. However, some limitations and problems still remain.
  • Limited Application Scenario
The application scenario for these devices is limited, and their reliability is questionable in special environments such as earthquakes, fires, explosions, mine collapses, traffic accidents, uneven support surfaces, soft compressible situations, and patient transport. The measurement results during artificial CPR may not be accurate when using a manual chest compression auditory feedback device, and the reliability of the device is questioned.
  • A Non-Intuitive Feedback Mode
The closed-loop feedback mode used in these devices is not intuitive, and its practicality is moderate. The moving parts of the pressure sensor may cause harm to the rescuers, and additional force may be required to perform chest compression due to the obstruction of the device. This increases the fatigue of the rescuers, making it harder for them to provide effective CPR. Due to the feedback device generally providing indications of compression through indicator lights, it takes time for unfamiliar users to learn and understand, which may delay the time of on-site rescue.
  • Limitations of Feedback Parameters
Artificial chest compression audio-visual feedback devices primarily provide feedback on the quality of CPR, such as compression rate and depth. However, they do not assess the patient’s physiological response to CPR, presenting a limitation in the scope of their feedback.
  • Limited Contribution to Improving Chest Compression Quality
The current audio-visual feedback devices on the market are only able to provide feedback on the depth and frequency of the compression, and some products can only provide feedback on the depth. During chest compression, body posture, hand placement, and compression position significantly influence the quality of cardiopulmonary resuscitation (CPR). However, the current audio-visual feedback devices lack the ability to comprehensively assess and provide guidance on these critical aspects. As a result, the effective utilization of such devices requires individuals who have undergone relevant training. Furthermore, these current audio-visual feedback devices are unable to provide personalized guidance based on the unique differences of individual patients. Simple feedback systems for artificial chest compression can enhance compression effectiveness, ensure AHA cardiopulmonary resuscitation guideline adherence, reduce the risk of chest compression, and achieve the recommended compression depth and frequency. However, these systems have a limitation in adjusting compression parameters according to the patient’s physiological state. The closed-loop feedback in automatic chest compressors offers a viable solution to this issue. These compressors incorporate a real-time monitoring and closed-loop feedback module for physiological parameters, utilizing the feedback from physiological parameters of cardiac arrest cases to assess the effectiveness of chest compression and achieve individualized closed-loop control of automatic chest compression.

4. Equipment Support of CPR Feedback Physiological Parameter Monitoring

4.1. End-Tidal Carbon Dioxide Monitoring Equipment

The infrared method is routinely utilized in clinical settings, primarily due to its main absorption wavelength for CO2 at 4260 nm. Based on this property, CO2 concentration can be deduced from its absorption rate. Two modes of application are prevalent for the infrared method: bypass flow and mainstream flow [45][20]. In mainstream flow mode, the sensor is directly connected to the patient’s tracheal tube connector, becoming an integral part of the artificial airway. The airflow actively traverses the sensor. The key advantages of the mainstream infrared method lie in its swift medical diagnostic response due to the sensor’s direct contact with the airflow. Infinium Medical has developed the Cleo EtCO2 Monitor with Vitals, an intuitive device for non-invasively measuring patients’ vital signs, including blood pressure, SpO2, rapid temperature, and exhaled carbon dioxide. The device supports continuous monitoring over extended periods and is applicable in a variety of settings. Its uses encompass both intubated and non-intubated applications, on-site inspections, bedside monitoring, and more [46][21]. Masimo’s Emma Capnograph, a portable real-time carbon dioxide analyzer, provides continuous and clear visualizations of carbon dioxide measurements. The device can display EtCO2 and respiratory rate measurements, along with real-time ETCO2 waveforms within a timeframe of 15 s [47][22].

4.2. The Application of End-Tidal Carbon Dioxide in Cardiopulmonary Resuscitation Feedback

End-tidal carbon dioxide (ETCO2), serving as an indirect measure of blood flow during cardiopulmonary resuscitation (CPR), is widely employed as a guiding tool in the CPR process [48][23]. Throughout the course of CPR, ETCO2 maintains a direct correlation with cardiac output, thus making it a common metric for gauging output during CPR [49][24]. Existing research suggests a linear relationship between the depth of chest compression and end-expiratory carbon dioxide values. An analysis utilizing mixed-effects models on a sample of 230 subjects revealed a 4.0% increase in ETCO2 (p < 0.0001) for each 10 mm augmentation in chest compression depth and a 1.7% increase (p = 0.02) in ETCO2 with every 10-compression/min increase in chest compression frequency [50][25].

5. Conclusions

Modern CPR is a crucial step in basic life support, and to improve the quality of CPR and minimize the risk of injury, real-time and effective CPR feedback is vital. CPR feedback devices can truly improve CPR quality in training and real life. In complex out-of-hospital settings such as accidents, they can also provide effective assistance and improve the efficiency of treating cardiac arrest patients, thus exhibiting a broad scope of applicability. Over time, CPR feedback devices have evolved from simple visual and auditory feedback based on manual compression to personalized feedback from automated CPR machines using real-time physiological monitoring. The latest CPR devices leverage technological advancements to provide increasingly intelligent feedback, incorporating a diverse range of monitoring data with deep learning algorithms to predict blood flow perfusion and support accurate compression.

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