Ultrasound of the IJ in Dyspnea
Study with patient at 45°
Find the meniscal level at end expiration
Measure height from sternal notch and add 5cm for pressure in cmH20
American Journal of Emergency Medicine 2000;18(4):432)
ULTRASOUND OF NECK VEINS WITH NORMAL CVP As the patient with a normal CVP (0 to 10 cm of H2O) assumes a semiupright position, the pressure in the jugular vein falls. At some point in the neck, the extravascular tissue pressure is greater than the local venous pressure and the vessel collapses. In the longitudinal plane, the shape of the IJV in this transitional zone resembles a wine bottle with a wide inferior base tapering to a narrow superior neck (Figure 3). It is in this tapering portion of the IJV that the vein walls will appear to flutter in real-time. This is the site of the jugular venous pulse. The most superior point of this tapering portion is the location of vein collapse and is the sonographic equivalent of the top of the column of blood in the jugular vein. Occasionally, this point has been referred to as a meniscus.2 It is an inaccurate analogy, because a true meniscus does not exhibit this tapering shape. In the sitting position, the patient with a normal CVP will have an IJV that is almost completely collapsed. In the transverse plane it will either be nonvisualized or appear as a small crescent or slit (Figure 4). The IJV will transiently distend with forced expiration or Valsalva but will promptly collapse with normal respiration. In the semiupright position with a normal CVP, the top of the column of blood will be inferior to the clavicles and the IJV will be collapsed in the middle of the neck. The reclining angle must be lowered until the IJV becomes distended. The vein should be visualized by scanning the neck in the transverse plane. The probe is then moved in a superior direction on the neck to locate the point
of vein collapse. The point under the transducer on the neck is marked. The vertical distance in cm between this point and the angle of Louis is measured; 5 cm is added to obtain the estimated CVP. ULTRASOUND OF NECK VEINS WITH ELEVATED CVP If the CVP is elevated above 10 cm of H2O, the IJV becomes distended, even in the semiupright position. Scanning the midneck in the transverse plane, the IJV will assume an oval or round appearance. With the patient in a semiupright position it will appear as large or larger than the adjacent CCA (Figure 1). Occasionally, a patient with an extremely elevated CVP (above 20 cm of H2O) must be scanned in the standing position to locate the point of vein collapse between the clavicle and the angle of the mandible. Again, the vertical distance between the point of collapse and the angle of Louis is measured; 5 cm is added to obtain the estimated CVP.
ULTRASOUND OF NECK VEINS WITH LOW CVP If the CVP is very low (less than 0 cm of H2O) the vein will appear almost collapsed, even in the supine position. The sonographic appearance will be similar to the patient with a normal CVP in the upright position (Figure 4). TECHNICAL POINTS Several caveats are important when scanning the IJV. Veins are low-pressure vessels and when located superfi- cially are easily compressed. Gentle pressure with the transducer is all that is necessary; too much pressure will collapse the vein and mislead the clinician. Because the examination is performed in real-time, any operator-induced collapse should be obvious. If a high frequency transducer is not available, a lower frequency probe (5 MHz) may be substituted, but image resolution will be poorer. Image depth must be decreased manually to optimally visualize superfi- cial structures. The vessels should be scanned with the head in a neutral position, as the IJV tends to collapse with extension of the neck.12 The point of collapse may fluctuate up and down slightly with normal respiration, as pressure in the central veins is affected by intrathoracic pressure. There is usually a fall of the point of collapse of several cm on normal inspiration.7,13 Mark the point in the neck at endexpiration; this is the same phase of respiration that the CVP is measured with a central catheter and pressure transducer.14 Position the patient so the point of vein collapse is located in the middle third of the neck. The IJV, even with a normal CVP, may be distended at the base of the neck. This is because the vessel is splinted open by the negative intrathoracic pressure as it enters the chest cavity. This is also where thin, mobile valves in the IJV are often located.
e thyroid gland is located medial to the vessels low in the neck. Cysts and nodules are common and are usually clinically insignificant. Always start by scanning the right IJV but confirm findings by examining the contralateral vein. If the patient has had previous neck surgery, IJV cannulation, or irradiation, the vein may not distend normally with elevated pressure. ROLE OF JUGULAR VENOUS ULTRASOUND Ultrasound of the internal jugular vein is probably the easiest examination for the novice sonographer to master. However, not every patient needs an ultrasound examination of his or her jugular vein. As clinicians, it is important to perform an adequate visual inspection of the jugular pulse.15 Nonetheless, there are situations with some patients where the physical examination does not furnish the information needed. Bedside sonography performed by emergency physicians provides immediate, important information that would otherwise require the use of invasive catheters.
| | |Back to top