How do you treat sepsis in the blood?

Antimicrobial tx... By sepsis in the blood, i think you are referring to having bacteria in the blood. If this is suspected, blood cultures are sent to the lab and the patient is treated with antibiotics. Once the blood culture results are known, antibiotic therapy can be adjusted based on the bacteria sensitivities.
Meds & fluids. Often, the patient may require ICU care because the blood pressure is dangerously low or organs are starting to malfunction. Generally, antibiotics/antifungals/antivirals are needed, fluids, vasopressors (if blood pressure is still low despite fluids), and maybe steroids. A med called drotrecogin may be use in serious & specific cases. If kidneys are severely affected, dialysis may be needed.
Source control & Abx. 1. Broad spectrum antibiotics are given after blood and other appropriate cultures are drawn; 2. If the source of the infection is known, then it is either removed or fixed; 3. Supportive management such as intubation, pressors, and fluids help avoid shock and hypoxia, 4. Narrowing focus of you antibiotics once culture sensitives return.