Correlation between Pulse Pressure Variation (PPV) and Aortic Velocity Time Integral (VTI) variability as measures of fluid responsiveness in patients undergoing major abdominal surgery.

A "major abdominal surgery" is an intraperitoneal procedure that involves either luminal resection or the excision of a solid organ connected to the gastrointestinal tract and does not primarily involve the thorax. Such surgeries may be associated with significant fluid loss as well as significant fluid shifts. These fluid changes may occur preoperatively as well as intraoperatively. Preoperative factors include bowel preparation (elective surgery) and vomiting, gastric decompression and/or drainage, sequestration of fluid, diarrhea, and bleeding (urgent surgery). Intraoperative, factors include insensible losses (traditionally assumed to amount up to 4–8 ml/kg/h for major abdominal surgery), intraoperative bleeding, gastric drainage, and drainage of ascites. These, if not appropriately monitored and treated, may adversely impact surgical outcomes and increase morbidity and mortality. Hemodynamic monitoring in these patients involves the use of various methods to directly measure cardiovascular parameters such as cardiac output, systemic vascular resistance, and central venous pressure. Commonly used techniques include pulmonary artery catheterization, echocardiography, and arterial waveform analysis. Monitoring cardiac output (CO) as an indicator of macrocirculation remains a cornerstone in guiding therapeutic interventions for critically ill patients and during major surgeries. Thermodilution based CO measurement via pulmonary artery catheter (with a swan-Ganz probe) is considered the gold-standard technique, but its invasiveness limits its routine clinical use. Among all the indices of fluid responsiveness, pulse pressure variation (PPV) using arterial cannulation has been one of the most used in clinical practice. PPV reflects the respiratory changes in stroke volume and, thus, should help assess fluid responsiveness. This is assuming that arterial compliance does not change over the respiratory cycle, a hypothesis that has been confirmed experimentally. Today, most hemodynamic monitors allow automatic calculation of PPV with continuous display of its value in real time. Currently, the main focus of research and development is towards less invasive monitors with inherently lower risks of use. Availability of portable ultrasound machines has made noninvasive measurement of hemodynamic parameters, such as aortic blood flow (ABF) or Aortic velocity time integral (VTI), possible. The aortic velocity time integral (VTI) is an echocardiographic tool used to estimate cardiac output (CO) by multiplying it with the aortic valve (AV) area and heart rate (HR). The aortic VTI itself can serve as a left-ventricular (LV) output parameter. n this study we aim to compare PPV with Aortic VTI as measured by Transthoracic Echo in patients coming for major abdominal surgeries.