Septic shock is defined as a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality. Clinically, septic shock is identified by the need for vasopressor therapy to maintain a mean arterial pressure (MAP) of more than or equal to 65 mm Hg, along with a serum lactate level more than 2 mmol per L, despite adequate fluid resuscitation. Septic shock is a distributive shock which results from vasodilation and later damage to the microvascular endothelium resulting in capillary leakage and edema. So, exact titration of fluid becomes very important to maintain organ perfusion and to prevent the development of multi organ dysfunction syndrome (MODS). Organ systems affected in MODS include lungs resulting in acute respiratory distress syndrome (ARDS), kidney resulting in acute kidney injury (AKI), heart resulting in septic cardiomyopathy, brain resulting in septic encephalopathy and so on. Among these complications, AKI is one of the most common, affecting nearly 50 percent of patients in intensive care units. According to the KDIGO (Kidney Disease: Improving Global Outcomes) 2012 Clinical Practice Guidelines, acute kidney injury (AKI) is defined as any of the following: An increase in serum creatinine by more than or equal to 0.3 mg per dL within 48 hours, or an increase in serum creatinine to more than or equal to 1.5 times baseline, known or presumed to have occurred within the prior 7 days, or a urine output less than 0.5 mL per kg per h for 6 hours. 

Septic shock patients have developed AKI even with proper monitoring of parameters such as mean arterial pressure, central venous pressure, and lactate. The pathophysiology of AKI is due to variation in perfusion due to hemodynamic instability, excessive venous congestion, inflammation, and cytokine induced circulatory damage. These commonly used methods of monitoring fluid responsiveness have less sensitivity in predicting MODS, as none of these can quantify perfusion at organ level, further necessitating the need for newer indices. Hence the new techniques such as renal doppler have been evaluated to predict the risk of AKI in patients with sepsis.