The purpose of this study is to analyze the relationship of the area under the curve (AUC) and/or the amplitude (Amp) of pulse oximetry plethysmographic waveform (POP) with partial pressure of end-tidal carbon dioxide (PETCO2) which could be used to reflect its quality in cardiopulmonary resuscitation (CPR), and then to determine the critical threshold of POP parameters in high quality CPR.

Inclusion Criteria:

• Cardiac arrested
• The time from cardiac arrest to receiving basic life support is less than 10 minutes
• Get advanced life support (endotracheal intubation and PETCO2 monitoring)

Exclusion Criteria:

• Defuse CPR
• chronic obstructive pulmonary disease (COPD) with type II respiratory failure
• Terminal malignant tumors or terminal stage of other diseases
• Rib fracture
• Cardiac arrest caused by hemorrhagic shock pulmonary embolism and cardiac tamponade
• Sever anemia(HGB<7g/dl)
• Untreated tension pneumothorax
• Tinea unguium, dyeing Fingernails and other factors affect the monitor of Pulse Oximetry Plethysmographic Waveform such vasculitis and Raynaud's phenomenon

Patients who were admitted to the participant hospitals and met the inclusion criteria were included in the study.