Define the effect of epidural block on HPV by EIT.

Epidural block may affect the physiological mechanism of hypoxic pulmonary vasoconstriction, which is still poorly understood. Electrical impedance tomography might be helpful in establishing the hypoxemia etiology at bedside via combining regional ventilation and perfusion information.

Inclusion Criteria:

• Age 18 - 80 years Existing central venous and arterial access Chest circumference 70 - 150 cm

Exclusion Criteria:

• Contraindication to central venous injection of 5 % sodium chloride (NaCl)

Contraindications of PulmoVista 500:

Patients with pacemakers, defibrillators or other electrically active implants Patients with damaged skin or impaired skin contact of the electrodes due to wound dressings Patients where the attachment of the patient belt could pose a risk to the patient, e.g. patients with spinal lesions or fractures Patients with uncontrolled body movements Extremely obese patients (BMI>50) Patients during pregnancy Patients with massive lung edema Use during electricity-based therapies, such as electrosurgery or electrocautery Use in the presence of strong magnetic fields Use in conjunction with other bioimpedance measurement devices

Patients requiring thoracic surgery are given combined epidural anesthesia.