This is a prospective, observational, cohort study which will be conducted in the critical care department at holy family hospital, New Delhi. Patient who are above the age of 18 years old, in shock, which is defined as: or mean arterial pressure <65 mmHg, decreased urine output (< 0.5ml/kg/hour), or serum lactic acid >2 mEq/L after fulfilling the eligibility criteria and the written consent process will be enrolled in the study. Baseline vital variables heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse pressure will be noted by the invasive arterial waveform trace on the MX430 Philips Intellivue patient monitor by one observer.

A second observer will do a carotid ultrasound using the linear array transducer with a frequency of 13–6 MHz of the Philips CX50 echocardiography machine.Corrected carotid artery flow time is measured.

A third observer trained in critical care ultrasound will measure Left ventricular outflow tract velocity time integral (LVOT VTI) in an apical 5 chambers cavity window with a low frequency phased array probe(1-5MHz).

Three observers will be blinded to each other’s findings to decrease the bias.

A Fluid challenge of 4ml/kg will be infused over five minutes.

Post fluid challenge all hemodynamic parameters (HR, SBP, DBP, MAP, PP) will be noted immediately after bolus immediately and two minutes post fluid challenge.

Corrected carotid flow time will be measured within 2 minutes of fluid challenge by the same observer and with the same methodology.

LVOT VTI will be measured at the previously marked sight by the same observer and previously mentioned methodology within 2 minutes of fluid challenge. Average of the three readings will be calculated.

Through the course of study, the three observers will be blinded to each other findings. To reduce inter observer variability same observer will do the repeat ultrasounds also. The maintenance fluid and further treatment will be decided as per the discretion of the treating physician.

This study aims to analyze and compare the changes in corrected carotid flow time, pulse pressure, and mean arterial pressure in response to fluid challenge in patients experiencing undifferentiated shock. By examining these hemo dynamic parameters, we hope to enhance our understanding of fluid resuscitation’s effectiveness in this critical patient population.