In this prospective randomized controlled trial, investigators aim to study the effects and safety of bicarbonated Ringer's solution in patients with septic shock compared with lactated ringer's solution, and provide evidence for current fluid resuscitation strategies for septic shock.

Although the latest guidelines recommend crystalloids as the first choice for the patients' fluid resuscitation, it still remains controversial that which crystalloid solution is the best choice. It is reported that balanced crystalloid can result in better outcomes than saline for critically ill patients. However, there are few studies conducted between different crystalloid solutions.

Lactated ringer's solution is the longest-used crystalloid solution. Compared with lactated ringer's solution whose anion is lactate, the anion of bicarbonate ringer's solution is bicarbonate. And lactate needs to be metabolized into bicarbonate through the mitochondria of the liver before it can play an alkalization role. Therefore, in theory, bicarbonate ringer's solution does not need to rely on liver metabolism, the onset time to maintain acid-base balance is shorter, and it may be more suitable for patients with severe acidosis. In patients with septic shock, the incidence of moderate to severe metabolic is increased. Bicarbonate ringer's solution can directly supplement the concentration of bicarbonate, while lactated ringer's solution needs to take time and be metabolized in the liver. Thus, we hypothesize that bicarbonate ringer's solution is more effective for patients with shock and metabolic acidosis than lactated ringer's solution.

Inclusion Criteria:

• 1. At the age of 18 to 75;
• 2. Being treated in the ICU;
• 3. Diagnosed as septic shock according tho the definition of Sepsis 3.0 with fluid resuscitation requirement.

Exclusion Criteria:

• 1. Severe hepatic failure;
• 2. Possible brain injury;
• 3. With absolute contraindications for central vena catheterization;
• 4. Ever participated in another clinical trial within 30 days prior enrollment;
• 5. Have corrected metabolic acidosis through alkaline drug application within 24 hours prior to enrollment;
• 6. Hypermagnesemia or hypothyroidism;
• 7. Pregnant of breast-feeding women;
• 8. Considered inevitable death;
• 9. Other situations where investigators think enrollment is not appropriate.