We understand the arguments on the quality of CPR and confounders including measuring device and different bed/mattress setting. In our study, we made an effort to achieve adequate quality of chest compressions. Certified BLS healthcare providers participated in the study as compressors and they received a 2-hour training course prior to the trial. The compressor was rotated every 2 minutes to avoid rescuer fatigue. As a result, we achieved a relatively high quality of CPR in terms of maintaining optimal compression depth and chest compression fraction (CCF). A very high CCF above 90% was attained by performing continuous chest compressions after endotracheal intubation. We also achieved optimal compression depth deeper than 50 mm as recommended by the Guidelines (1). Participating hospitals used the bed with a backboard on standard foam mattress. Therefore, use of a compression feedback device (Q-CPR^®, Phillips Healthcare, Seattle, WA, USA) in our study may lead to under compression of the chest due to compression of the mattress as Dr. Oh mentioned (2). However, there is no method to measure actual depth of chest compression during CPR in human to date. A compression feedback device is the only way to measure CPR metrics and analyze the quality of chest compressions. Current guidelines for optimal compression depth are based on the study results used a compression feedback device (345). Actual compression depth to generate adequate hemodynamic efficacy in human remains to be investigated.