The lack of subcutaneous partial pressure of oxygen (PO2) rise in response to high fraction of inspired oxygen (FiO2), called the "oxygen challenge test (OCT)", was associated with higher morbidity and mortality in human subjects. Patients had negative O2 challenge test results, indicating that flow-dependent O2 consumption might have been present. Recent reports using the noninvasive transcutaneous PO2 (PtO2) and transcutaneous partial pressure of carbon dioxide probes have observed a relationship between low oxygen challenge test values to mortality and organ failure. The OCT values provides an accessible noninvasive method of detecting early shock.

To date,these studies of OCT in the ICU patients are rarely. No one has quantified OCT to CI, DO2I、ScvO2.

This study explored:

1. relationship between patient factors, hemodynamic variables, PtO2, and OCT to mortality;
2. relationship between PtO2 index, tissue oxygen index, oxygen Challenge index to CI, DO2, ScvO2.

PtO2 index = PtO2/PaO2；tissue oxygen index=PtO2/FiO2；

5min OCT value = challenged 5minPtO2 - PtO2baseline；

10min OCT value= challenged 10minPtO2- PtO2baseline；

oxygen challenge index = （10minPtO2- PtO2baseline）/(10minPaO2-PaO2baseline)

Inclusion Criteria:

• 18 years of age or older
• Requiring a artery catheters, and pulmonary artery catheters or PiCCO-plus or central venous catheters
• FiO2<80% and SpO2>92%
• Consent informed

Exclusion Criteria:

• Not expected to live

The subjects were sequentially admitted to the Department of Critical Care department of Peking Union Medical College Hospital from sept. of 2009 till the end of this study.