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

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. 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 50mm. Compression depth measurements by the devices and the manikin were compared. On a hard surface TrueCPR showed a systematic underestimation of 2-3mm in the drill press. Manual tests on a hard surface showed a slightly larger underestimation of 4.5mm. 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). TrueCPR measures depth precisely, independent of the stiffness of the surface upon which the CPR is being performed with a constant inaccuracy of <4.5mm. 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