258 diagnostic ultrasound ultrasound in shock figure

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258 Diagnostic ultrasound Ultrasound in shock
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Figure 14.4 Inferior vena cava (IVC) draining into the right atrium (RA). The hepatic vein (*) drains through the liver (L) into the IVC. (A) (B) Figure 14.5 ( A ) Small-diameter IVC (arrows) behind liver (L) draining into right atrium (RA). ( B ) Variation in diameter during respiration measured using M-mode. This patient should be fluid-responsive. Diagnostic ultrasound 259 Ultrasound in shock
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Table 14.1 Inferior vena cava diameter, respiratory variation, and right atrial (RA) pressure IVC (cm) Respiratory change RA pressure (cm H 2 O) < 1.5 Total collapse 0–5 1.5–2.5 > 50% collapse 5–10 1.5–2.5 < 50% collapse 11–15 > 2.5 < 50% collapse 16–20 > 2.5 No change > 20 Reproduced with permission from Wong & Otto 2000 [ 1 ]. (A) (B) Figure 14.6 ( A ) Large-diameter IVC in a patient with fluid overload. A pericardial effusion (arrow) is also visible. In real time a lack of variation in IVC diameter would be noted by M-mode, as noted by the arrows in ( B ) another patient. 260 Diagnostic ultrasound Ultrasound in shock
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It may be more helpful to think of the extremes of IVC appearance on ultrasound and how that predicts fluid responsiveness in the hypotensive patient. Table 14.1 describes the range of IVC diameters and respiratory variation, and the expected correlation to CVP (right atrial pressure). In spontaneously breathing patients, an IVC diameter of < 1.5 cm with complete inspiratory collapse is associated with a low CVP and fluid respon- siveness [ 2 4 ]. Variation in IVC diameter with respiration is lower in patients with CHF than without CHF ( 5 ). In contrast, patients with an IVC diameter of > 2.5 cm with no respiratory change are unlikely to respond to a fluid load and are likely to have a high CVP ( > 20 cm H 2 O) [ 2 , 4 , 6 ]. These patients may benefit more from inotropy or afterload reduction. Figure 14.6 demonstrates increased IVC diameter in a patient with fluid overload. In mechanically ventilated patients, this phenomenon is reversed because inspiration now results in positive thoracic pressure. Therefore, IVC distensi- bility has been studied as a predictor of fluid responsiveness. Respiratory variation in IVC diameter of 13–18% was predictive of fluid responsiveness in two studies [ 7 , 8 ]. The FAST exam Although the FAST exam was discussed in Chapter 2 as it relates to a trauma assessment, there are other disease states which can cause bleeding into the peritoneum or thoracic cavity. Ruptured ectopic pregnancy, bleed- ing from malignancies, postoperative complications, and other etiologies can cause hypotension from bleeding. In these settings the sonographic evaluation will be similar to the one performed as part of a trauma evaluation. Note that the FAST exam is most sensitive for fluid when the patient is in the Trendelenberg position. Be cautious when performing and interpreting the examination when the patient is not in this position. For example, patients in an optimal position for mechanical ventilation (head of bed elevated 30 degrees) will not demonstrate fluid in Morison’s pouch or the left upper quadrant until a significant amount of fluid is present. In those patients, the
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