This study is an observational study. Investigate the relationship of oxgenation and lung regional ventilation and perfusion assessed by the indicator based-EIT method in the critically ill patients in ICU

1. Written informed consent was obtained from all patients or next of kin before data were included in the study.
2. When the research team was available, adult patients within 1w, who were sequentially admitted to the Department of Critical Care Medicine and required central venous catheters for resuscitation were eligible for the study.
3. Information collected at enrollment included demographic characteristics such as age, sex, Acute Physiology and Chronic Health Evaluation II score (APCHEII); . The global hemodynamic, respiration condition and PaO2 were measured. At the same time, the lung regional ventilation and perfusion assessed by the indicator based-EIT method(injection 10%NaCL).
4. The 10%NaCL was injected by the central venous catheter.

Inclusion Criteria:

• Time of admission ICU < 7days
• Age (> 18 years old)
• Have been placed central venous catheter based on clinical requirement

Exclusion Criteria:

.Chest skin injured and cannot be monitored by EIT.

• Severe Hypernatremia
• Pregnancy

adult patients within 7days, who were sequentially admitted to the Department of Critical Care Medicine and required central venous catheters for clinical requirment were eligible for the study.