Elsevier

Resuscitation

Volume 85, Issue 11, November 2014, Pages 1439-1443
Resuscitation

Accurate feedback of chest compression depth on a manikin on a soft surface with correction for total body displacement

https://doi.org/10.1016/j.resuscitation.2014.08.005Get rights and content

Abstract

Objective

TrueCPR is a new real-time compression depth feedback device that measures changes in magnetic field strength between a back pad and a chest pad. We determined its accuracy with a manikin on a test bench and on various surfaces.

Methods

First, calibration and accuracy of the manikin and TrueCPR was verified on a drill press. Then, manual chest compressions were given, on a firm surface and on a foam or air mattress, with feedback of the TrueCPR or Q-CPR accelerometer, to achieve a depth of 50 mm. Compression depth measurements by the devices and the manikin were compared.

Results

On a hard surface TrueCPR showed a systematic underestimation of 2–3 mm in the drill press. Manual tests on a hard surface showed a slightly larger underestimation of 4.5 mm. When guided by TrueCPR on a foam or air mattress, the TrueCPR measured a mean(±SD) chest compression depth of 52.0(±1.9) mm and 49.4(±2.6) mm respectively, while the manikin measured 54.4(±1.8) mm and 52.1(±1.4) mm, respectively (p < 0.001). When guided by the Q-CPR accelerometer on a foam or air mattress, the accelerometer measured depth of 54.3(±3.6) mm and 56.0(±3.8) mm respectively, compared to the manikin 42.4(±2.3) mm and 34.9(±3.6) mm, respectively (p < 0.001).

Conclusion

TrueCPR measures depth precisely, independent of the stiffness of the surface upon which the CPR is being performed with a constant inaccuracy of <4.5 mm. A sternum-only accelerometer substantially overestimates depth when performing CPR on a soft surface. Correction for body displacement on a soft surface is essential for accurate delivery of chest compressions within the recommended depth range.

Introduction

According to the Guidelines 2010 for cardiopulmonary resuscitation (CPR) chest compression is given in periods of 2 min, interrupted briefly (5 s) for ventilation. The optimal chest compression depth according to the ERC Guidelines 2010 includes: compressing the chest to a depth of at least 5 cm (for an adult), but not exceeding 6 cm and allowing the chest to relax completely after each compression.1

Chest compression depth is linearly related to cardiac output, which is also linked to the likelihood of achieving a return of spontaneous circulation after defibrillation.2, 3 Fatigue, limited muscle strength and fear of doing harm frequently result in delivery of chest compressions less deep than recommended.

Rescuers can be assisted to achieve the recommended compression rate and depth by prompt/feedback devices that measure the displacement of the sternum during compressions. These devices may be built into an automated external defibrillator (AED) or manual defibrillator, or are stand-alone devices. The use of such prompt/feedback devices to improve the quality of CPR have shown to be beneficial with less deviation from recommended rate and depth.4, 5, 6 When chest compressions are performed on a victim lying on a soft surface such as a mattress, the chest is displaced downwards as well as being compressed. Because accelerometer based devices measure the motion of the surface of the chest, they are unable to distinguish between chest displacement and chest compression and, consequently, may overestimate compression depth.7

The TrueCPR (Physio-Control Inc, Redmond, WA, USA) is a new, commercially available device that claims to measure true chest compression depth and consists of a chest pad which is placed on the sternum and a back pad, which is placed beneath the patient. The device measures distance by sending and receiving electromagnetic signals between the chest pad and the back pad. The compression depth, chest recoil and compression rate are displayed on the device for visual corrective feedback, as well as a metronome for auditive rate support.

The objective of the study is to investigate if the TrueCPR is accurate by measuring compression depth on a manikin, independent from the stiffness properties of the surface. We compared the TrueCPR with a pressure-accelerometer based device, the Q-CPR (Laerdal Medical, Stavanger, Norway) that measures sternal displacement and the pressure given by the rescuers hand, and tested both devices on a manikin on a hard surface and various types of softer surfaces.

Section snippets

Study design

The Laerdal manikin model Resusci Anne SkillReporter (Laerdal Medical, Stavanger, Norway) is a common manikin used for teaching CPR performance. The manikin weighs 9.5 kg and allows the recording of depth parameters during CPR using the Laerdal PC SkillReporting System. The Resusci Anne SkillReporter was used during all evaluations. Data measuring chest compression (sternal–spinal displacement) were recorded directly to a laptop with dedicated software (Laerdal PC SkillReporting system). Because

Accuracy of the TrueCPR device in the drill press

The TrueCPR showed a systematic underestimation of 2–3 mm in the drill press on a hard surface compared to the depth as measured by the manikin (p < 0.05), over the whole range (30–55 mm) of compression depth (Fig. 3).

Manual manikin chest compressions

When CPR was guided by feedback from the TrueCPR on the manikin on the floor, the TrueCPR measured a mean(±SD) chest compression depth of 50.4(±1.6) mm, while the simultaneous measurement of the manikin was significantly higher with mean(±SD) chest compression depth 54.9(±1.8) mm (p < 

Discussion

This is the first study of the TrueCPR device, a novel device that is commercially available for training and clinical use. The main finding of this study is that the TrueCPR measures depth on a manikin with a systematic underestimation of 3–4.5 mm independent of the stiffness of the surface upon which CPR is being performed. The TrueCPR therefore is an instrument with a known but constant small inaccuracy. In contrast, the accelerometer, while slightly more accurate on a hard surface, has a

Limitations

Quality of CPR involves more than chest compression depth, but also includes full relaxation and compression rate. In this study we focused only on compression depth, as this is influenced by the surface on which CPR is performed.

There are several factors that limit the applicability of findings from manikin studies to device use in humans. The chest compression feedback devices we tested use force information in addition to displacement information. Although standard manikins have a linear

Conclusion

The TrueCPR measures depth precisely, independent of the stiffness of the surface upon which CPR is being performed but with a constant inaccuracy of 3–4.5 mm. It eliminates the inaccuracy and overestimation of the true compression depth caused by a soft surface. Correction for body displacement on a soft surface is essential for accurate delivery of chest compressions within the recommended depth range under all clinical circumstances. Data from outcome of cardiac arrests that are calculated

Conflict of interest statement

RWK receives support for the ARREST study with an unconditional grant of Physio-Control Inc, Redmond, WA, USA, which had no control over data analysis or the writing process of the paper. The TrueCPR device used for this study was made available by Physio-Control.

Acknowledgment

We thank Cees Kes from the mechanical department of the Academic Medical Center for manufacturing the manikin support and dedicated drill head.

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A Spanish translated version of the summary of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2014.08.005.

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