title: Accurate feedback of chest compression depth on a manikin on a soft surface with correction for total body displacement.
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 50mm. Compression depth measurements by the devices and the manikin were compared.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Academic Medical Center, Department of Cardiology, Amsterdam, The Netherlands. Electronic address: s.g.beesems@amc.nl.
authors.forename: Stefanie G
authors.initials: SG
authors.lastname: Beesems
authors.affiliation: Academic Medical Center, Department of Cardiology, Amsterdam, The Netherlands.
authors.forename: Rudolph W
authors.initials: RW
authors.lastname: Koster
mesh_terms: D061725:Accelerometry / Q000295:instrumentation*; D016887:Cardiopulmonary Resuscitation / Q000193:education* / Q000379:methods; D019245:Compressive Strength; D004867:Equipment Design; D004869:Equipment Safety; D005246:Feedback; D006336:Heart Massage / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008348:Manikins; D011312:Pressure; D012680:Sensitivity and Specificity; D016683:Supine Position
keywords: Accelerometer; Basic life support; Cardiopulmonary resuscitation; Chest compression; Feedback; Feedback devices