Transcription
Hello guys, and welcome back. In this video, I'm going to talk about the inferior vena cava. Thank you for watching. Don't forget to like this video and subscribe to my channel. So let's start.
First, let's start with the basics. What is the inferior vena cava? The inferior vena cava, also known as IVC, is a large vein that carries blood from the torso and lower body to the right side of the heart. The IVC gets its name from its structure, as it is the lower or inferior part of the vena cava, which are the two large veins responsible for the blood transport back to the right side of the heart. The inferior vena cava handles blood from the lower body, while the other vein, known as the superior vena cava, carries the blood circulating in the upper half of the body.
Now, what is the inferior vena cava function? The primary function of the IVC is to carry the oxygenated blood that has circulated through the lower half of the body back to the right atrium of the heart. The inferior vena cava is responsible for moving all of the blood below the diaphragm, while the superior vena cava handles the blood above the diaphragm.
Now, from where can we check the inferior vena cava? The inferior vena cava can be imaged during a, from the subcostal transducer position as an echo-free space at the top, ranging from 6 to 15 centimeters from the abdominal wall. The normal inferior vena cava echocardiogram has a pulsation pattern similar to that seen in the jugular venous tracing and exhibits prominent cyclic respiratory changes. Why is this important? Because in right heart failure, the inferior vena cava is usually distended; we diminish respiratory collapse. The diameter of the inferior vena cava is, together with the extent of IVC collapse during inspiration, used for estimation of right atrial pressure. As I said before, the inferior vena cava can be imaged during a cocardiography from the subcostal view. I already have a video on my YouTube channel on how to obtain the subcoastal view, and I will leave the link in the description. However, I will show you briefly how to visualize the inferior vena cava. First, place the transducer in upper mid-epigastric position with the index marker pointing to the left. Then, just tilt the transducer to the right, and you will be able to see the inferior vena cava from the subcostal view. You will be able to see the inferior vena cava, which is that echo-free space under the liver and next to the right atrium.
Now that you've found the inferior vena cava, you can start with the assessment. You mainly need to measure two things in order to assess the inferior vena cava correctly: first is the size of the inferior vena cava, and second is the inspiratory collapse of the inferior vena cava. The normal size of the inferior vena cava is less than 2.1 centimeters, and a normal inferior vena cava will have an inspiratory collapse more than 50% with a sniff, or an inspiratory collapse more than 20% with quiet respiration. It's important to assess the inferior vena cava size and inspiratory collapse in order to assess the right atrial pressure, to define the right ventricular and systolic pressure. An inferior vena cava diameter more than 21 millimeters with decreased inspiratory collapse is considered abnormal. In echocardiography, it is always important to assess the inferior vena cava size and percentage reduction in diameter with sniffing or quiet inspiration. The inferior vena cava diameter is measured perpendicular to the inferior vena cava long axis, approximately one to two centimeters from the right atrial junction at end-expiration. You can measure the inferior vena cava diameter by 2D mode, by M-mode, or you can assess the inferior vena cava size visually. Also, you can visually assess the inferior vena cava inspiratory collapse by 2D mode, or you can measure the inferior vena cava inspiratory collapse by M-mode. Here you can see an inferior vena cava with normal size and normal inspiratory collapse.
Now, how can we estimate the right atrial pressure using the inferior vena cava assessment? If you have an inferior vena cava diameter less than 21 millimeters with an inspiratory collapse more than 50%, this suggests a normal right atrial pressure of less than 5 millimeters of mercury. Now, if you have an inferior vena cava diameter less than 21 millimeters without a good inspiratory collapse, this suggests an intermediate right atrial pressure between 5 and 10 millimeters of mercury. And if the inferior vena cava is dilated with a diameter more than 21 millimeters without a good inspiratory collapse, this suggests a high right atrial pressure more than 15 millimeters of mercury. The IVC diameter and respiratory variation are commonly used echocardiographic indices to estimate right atrial pressure. While dilatation of the inferior vena cava and reduced collapsibility have traditionally been associated with elevated right heart filling pressures, the significance of isolated IVC dilatation in the absence of raised filling pressures remains poorly understood. Some reported cases of inferior vena cava enlargement in the setting of normal right atrial pressure can include highly trained athletes, patients with large body surface area, young adults, those on mechanical ventilation, and those with structural causes such as narrowing of the inferior vena cava, right atrial junction tissue present in the inferior vena cava, or prominent Eustachian valve.
The inferior vena cava can be affected by positional changes; however, the influence of positional change on the inferior vena cava size is not well studied. The American Society of Echocardiography guidelines recommend imaging the inferior vena cava in the left lateral position; however, many labs routinely image the inferior vena cava from the supine position. It's known that the inferior vena cava dimension is larger in the supine position, independent of the cardiac cycle. This may be due to increased intra-abdominal pressure and compression of the IVC by the liver. It's important to know that the inferior vena cava inspiratory collapse will not occur in patients on positive pressure ventilation due to inspiration-induced reductions in venous return. For this reason, it should not be used to monitor right atrial pressure in this setting.
Now let's talk about spontaneous echocardiographic contrast. Spontaneous echocardiographic contrast, or SEC, is a phenomenon of discrete reflections appearing in the blood inside the cardiac chambers, cavities, or vessels without previous injection of contrast or fluids containing micro-bubbles. Spontaneous echocardiographic contrast can be divided into two categories based on its appearance. First, we have the smoke-like spontaneous echocardiographic contrast. It is described as an amorphous swirling light gray haze; its configuration and acoustic density change when observed over several cardiac cycles. Smoke-like spontaneous echocardiographic contrast can be observed in the left and right heart chambers, great vessels, and veins, and is believed to be caused by blood stasis. Smoke-like spontaneous echocardiographic contrast is most commonly observed in patients with dilated left atrium, mitral stenosis, left ventricular dysfunction, and aortic aneurysm or dissection. Smoke-like spontaneous echocardiographic contrast has been associated with stroke and thromboembolic events. The second type is the non-smoke spontaneous echocardiographic contrast. It appears either as a snowstorm or as discrete scatter reflections. In normal physiological conditions, such spontaneous echocardiographic contrast in the left atrium can be enhanced by respiratory maneuvers; its intensity is mild to moderate and is explained by transient stasis, particularly in the pulmonary circulation. Non-smoke spontaneous echocardiographic contrast has been also noticed in the inferior vena cava, although a number of investigators currently state that spontaneous echocardiographic contrast mainly is due to blood stresses associated with thromboembolic events. The etiology of spontaneous echocardiographic contrast and therapeutic approaches are still under investigation.
Thank you very much for watching. Don't forget to like this video and to subscribe to my channel. Bye.