Acute kidney injury(AKI) is one of the most common complications that occur up to 35% of critically ill patients. Septic AKI accounts for one third of them. Patients with septic AKI are widely treated with Continuous renal replacement therapy (CRRT). However, previous studies have hardly documented improvement of mortality in septic AKI patients. Otherwise, Fluid overload in septic shock patients who are undergoing CRRT is proven to be a significant predictor for mortality. Recent studies showed efficacy of bioelectrical impedance analysis and lung ultrasound in assessing fluid status of the patients. Thus, hypothesis of the study is that fluid assessment and control of fluid status using BIA and Lung Ultrasound could be related to the outcome of septic AKI patients who undergo CRRT. In this study, the investigators measure the fluid status of the patients by bioelectrical impedance analysis and lung ultrasound for experimental group, while for control group, fluid status would be determined clinically by the physician. Ultrafiltration rate of experimental group is adjusted to be equal to the value of overhydration measured by BIA.

Inclusion Criteria:

1. body temperature < 36 °C or > 38 °C
2. heart rate > 90 BPM
3. respiratory rate > 20 or aPaCO2 < 32 mmHg on ABG
4. White blood cell count < 4,000 cells/mm3 or > 12,000 cells/mm3 or band forms (immature white blood cells) ≥10%
5. Evidence of infection
6. WBCs in normally sterile fluid
7. Perforated viscus
8. radiologically proven infection
9. more than Injury stage in AKI according to RIFLE criteria
10. septic AKI which is not explained by other cause
11. patients signed a written informed consent.

Exclusion Criteria:

1. Younger than 19 years old, older than 80 years old
2. Previously undergoing dialysis treatment due to ESRD
3. Underlying malignancy, Life expectancy shorter than 3 month
4. AKI due to other than sepsis
5. patients with intracardiac device such as Pacemaker, CRT, ICD