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Inferior Vena Cava Supporting Literature:
Emergent Question (s): What is the fluid status of my patient? What is the inferior vena cava diameter? Is the inferior vena cava collapsible?
Probe Type: Cardiac (phased array) or Abdominal (curvilinear) probe; 2-5 MhZ
Clinical Scenario: Patients who are hypotensive and volume status determination to be made to see if volume responsive would benefit from this examination.
Scanning Technique:The probe marker should be facing towards the patient’s right side. The patient is usually in the supine position. Patients who have intra-abdominal surgery repair, other surgical wounds, or obese may be difficult to examine. Two methods are usually employed in finding the right views to visualize the inferior vena cava as it enters the right atrium. The first method is to use the subcostal view (described in this chapter), and placing the right atrium in the center of the ultrasound image. After the right atrium is well positioned in the center, the IVC is followed out of the atrium and the probe is turned counterclockwise so that the probe marker is going towards the patient’s head [Figure 1]. Another method is to place the probe in the subcostal location right below the xiphoid process with the probe marking facing towards the patient’s head and then fanning slightly towards the right of the patient [Figure 2]. The IVC size is usually measured 1-2 cm distal to the hepatic vein takeoff (if visualized), and collapsibility is visually measured (greater than or less than 50%) or actually measured by using the M-Mode during inspiration [Figure 1b]. If there are abdominal wounds or surgical sites, the clinician can move the probe towards the liver and angle towards the heart to obtain a view of the IVC.
Supporting Literature:Risk of organ failure and mortality is influenced by systemic perfusion [1, 2]. Evaluation of the inferior vena cava size and collapsibility is a potential method of non- invasive adjunct to estimate central venous pressure, especially since the accuracy of physical examination for this purpose has been questioned [3, 4]. Bedside ultrasound evaluation of the inferior vena cava can estimate central venous pressure with acceptable predictive value and reliability between operators [5, 6]. The size and collapsibility of the inferior vena cava has been used in the non acute settings for estimation of right atrial pressures. IVC diameter less than 2 cm in many studies have been shown as a great predictor of low CVP. IVC diameters greater than 2 cm are less predictive, and in some studies have found that 25% of patients with IVC diameters greater than 2 cm have correlations with central venous pressure less than 10 mm HG [7-9]. IVC collapsibility greater than 50% has been shown to be less reliable than absolute size, but still can be used in spontaneously breathing patients to assist in volume status assessment. The sniff maneuver produces more negative intrathoracic pressure and may lead to a greater collapse of IVC. Also IVC collapsibility is affected by positive pressure ventilation mode and whether the patient has spontaneous breaths (negative intrathoracic pressure) or mechanically ventilated breaths (positive intrathoracic pressure). Last movement of the IVC relative to the ultrasound beam during inspiration can cause translational artifact and can influence the calculation of collapse [10].
