The electrical impedance tomography (EIT) is a bedside, non-invasive, non-radiation imaging tool for lung mornitoring. Currently, the EIT saline-contrast method for lung perfusion evaluation has been widely used in clinical. However, this technique requires the patient to hold breath for 8-30s to avoid the respiratory interference. Hence, it is not suitable for patients that can not tolerate breath hold or unable to maintain a steady apnoea. This study aims to develop an algorithm system based on low frequency band pass filter for EIT saline-contrast lung perfusion estimation without ventilation interruption, and investigate the correlation and agreement of EIT results between the novel method and the conventional breath-hold method.

Inclusion Criteria:

• In need of lung perfusion assessment due to clinical condition
• With central venous catheter

Exclusion Criteria:

• Pregnant or breastfeeding females
• contraindications to the use of EIT (automatic implantable cardioverter defibrillator, chest wounds limiting electrode belt placement, implantable pumps, etc.)
• severe hyperchloremia (>155 mmol/L)
• unable to tolerate breath-hold maneuver
• edema disease (nephrotic syndrome, cirrhotic ascites, congestive heart failure, etc.)
• Patients with severe hypernatraemia or hyperchloremia and severe hypertonicity
• Hypertension (>160/100 mmHg), hypokalaemia (> 3.5 mmol/L)
• Acute renal failure in oliguric stage, chronic renal failure with reduced urine output and poor response to diuretics