Sepsis is not a specific disease but abnormal response for infection, leading to organ dysfunction. It is a clinical syndrome consisting of biological, biochemical, and physiological abnormalities which pathophysiology has not yet been fully determined. Sepsis is shaped by pathogenic factors and host factors (eg, gender, race and other genetic determinants, age, comorbidities, environment) and its features evolve over time. What distinguishes sepsis from infection is the presence of abnormal and/or irregular host response and organ dysfunction. It is one of the leading health problems worldwide and one of the leading causes of mortality in hospitalizations. Its estimated that there were 48.9 million cases and 11 million sepsis-related deaths worldwide in 2017, accounting for almost 20% of all global deaths. In an epidemiological study conducted in European intensive care units (ICU), the incidence of sepsis was reported as 38%. Pneumonia, urinary tract, and intra-abdominal infections account for more than 65% of all sepsis cases. According to the Surviving Sepsis Campaign (SSC) data, mortality rates in sepsis are 41% in Europe and 28.3% in the United States (USA). In a multicenter study involving 101,064 critically ill patients in Australia and New Zealand between 2002 and 2012, mortality rates due to sepsis were found to decrease over the years and finally to 18-20%. Recognition of sepsis, which can be very mortal, especially if not recognized fast and treatment not started, requires urgent attention.

Due to the lack of treatment options targeting microcirculatory and mitochondrial dysfunction, treatment has been focused on correcting the macrocirculatory dysfunction in addition to treating the underlying cause during septic shock. In the early phase of septic shock, external losses and hypovolemia are seen because of capillary leakage. Therefore, fluid resuscitation is often recommended to increase cardiac output and improve tissue perfusion. However, large boluses of fluids (\>30 ml/kg) do not reliably increase blood pressure, urine output, and end-organ perfusion, and may lead to iatrogenic damage. Sepsis is characterized by disruptions in tissue perfusion and abnormal peripheral vascular resistance, because of disruptions in microcirculation. therefore, improving vascular function and organ damage is crucial in the management of septic shock. For treatment of hypotension; the need for fluid should be determined and the right amount of fluid resuscitation should be provided to the right patient.

Systemic vascular resistance is a parameter that depends on the afterload of the heart and corresponds to the resistance of the heart while it is working. It is the resistance the heart has to overcome to pump blood to the rest of the body except the lungs. The systemic vascular resistance index (SVRI) is defined as the ratio of mean arterial pressure (MAP) and central venous pressure (CVP) to cardiac index (CI) (SVRI= 80 x (MAP-CVP) / CI). In general, SVRI is proportional to MAP. It decreases due to vasodilation in septic patients. Compared to previous studies, lower SVRI in septic shock was associated with adverse outcomes and increased mortality. Invasive methods such as pulmonary artery catheters or relatively expensive methods such as PICCO are required for SVRI measurement.

Can a more cost-effective and rapid alternative to the systemic vascular resistance index measured by expensive or high-risk methods be found? Ultrasound, as modern stethoscope, is a need especially in every 3 level ICU.

The resistive index (RI) (Pourcelot index) is a noninvasive measurement used to evaluate vessel compliance with Doppler ultrasound. It is determined by a formula calculated between the systolic peak flow rate (PSV) and the end-diastolic flow rate (EDV) ((PSV-EDV)/PSV). Today RI is using for measure to assess tissue perfusion, particularly on the kidney. Renal RI shows changes in renal intravascular volume and hemodynamics. An inverse relationship has been shown between renal RI and MAP in acute kidney injury. Measurement of RI on the peripheral artery correlated with SVRI in a study of patients who had undergone cardiac surgery.

In this study the investigators will compare RI on radial artery in wrist snuffbox (SBRI) with SVRI for primary outcome. Also compare SBRI with MAP, CVP, diastolic shock index, pleth variability index, delta stroke volume index, central venous oxygen saturation (ScvO2) and partial carbon dioxide gap (Pv-aCO2) for secondary outcome.

Each patient will be followed for sepsis and septic shock. In the investigators ICU all sepsis patients has invasive artery canula for real-time monitoring and central venous catheter for blood sampling and need of vasopressor so there won't be any extra risk for this study. If a septic shock patient needs to mechanically ventilated and meets inclusion criteria, the investigators will carry out measurements just after intubation. Or, a mechanical ventilated patient who has developed septic shock; if patient has no spontaneous breathing effort, the investigators will carry out measurements. Also, arterial and central venous blood samples are taken after intubation or septic shock for every 6 hours, daily complete blood count (CBC), C-reactive protein, renal and hepatic blood analysis, and 2 times per week procalcitonin levels as routine at the hospital where the study is taking place in ICU.

Demographic parameters, physical examination notes (capillary refill time, mottling score, urine output, skin turgor), systolic, diastolic and mean arterial pressure, central venous pressure, arterial and central venous blood gas analysis, CBC and biochemistry blood analysis, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, Sequential Organ Failure Assesment (SOFA) score and Nutrition Risk in the Critically Ill (NUTRIC) Score will be noted. For cardiac output monitoring Baxter Starling non-invasive monitor will be used and all hemodynamic parameters will be noted for study during examination.. For measuring SBRI Philips CX50 ultrasound device L12-3 linear probe will be used. Starling monitors 4 electrodes will be placed as specified by the manufacturer. Masimo Rad-87 probe will place hand index or middle finger. SBRI will measure for three times successive with 1.5 centimeters depth and 3 same measurement will be recorded. At the same time baseline evaluation will be started with Starling monitor and all parameters will be noted. After completion of baseline measurement Starling fluid challenge will be initiated as passive leg raising as specified by manufacturer. This procedure takes 3 minutes to calculate and after 2.5 minutes SBRI will be measured again as described above. At the end of fluid challenge all parameters will be noted.