Background: Hypotension is a prevalent complication in patients under general anesthesia since its incidence after general anesthesia induction ranges from 8% to 9%. Due to the circulatory depressive and vasodilatory actions of anesthetic drugs, individuals are especially vulnerable to developing hypotension after induction of general anesthesia. In addition, hypovolemia due to dehydration and inadequate compensatory responses may already exist in certain patients. The patient's intravascular volume status may predict likelihood of hypotension following the onset of general anesthesia. Intraoperative hypotension susceptibility has been demonstrated to be affected by a patient's preoperative volume status, which can vary depending on the patient's physical level, comorbidities, and prior treatments such as bowel preparation and fasting. The purpose of this article is to provide comprehensive information on how to measure the internal vena cava (IVC) diameter and determine the IVC collapsibility index and the IVC distensibility index in patients undergoing mechanical ventilation. For patients undergoing general anesthesia and requiring mechanical ventilation, we felt it was crucial to stress the need for a noninvasive, bedside, objective way of determining volume status. Conclusion: Anesthesiologists routinely use non-invasive ultrasound examination as a helpful tool for assessing patient safety during anesthesia and measuring vital signs such as global left ventricular function, ventricular diameters, pericardial effusion, and inferior vena cava diameter. The greatest diameter of the IVC at the end of expiration during spontaneous respiration (dIVC max) and its collapsibility index (CI) are two ultrasound parameters that are recommended as quick and noninvasive accurate markers for evaluating volume status