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obstructive pulmonary disease, and other chronic conditions. However, in the acutely decompensating patient the diagnosis of pulmonary embol- ism must be suspected. In this setting, an evaluation for DVT (described (A) (B) Figure 14.2 Dilatation of the right ventricle (RV) compared to the left ventricle (LV) in apical 4 chamber view (panel A) and subxiphoid view (panel B). Figure 14.3 High right heart pressures flatten the interventricular septum (*) between the dilated right ventricle (RV) and left ventricle (LV). Diagnostic ultrasound 257 Ultrasound in shock
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in Chapter 8 ) can provide additional information and help inform the diagnosis. Hyperdynamic left ventricle Increased contractility of the left ventricle, or near-complete obliteration of the LV cavity in systole, may be seen in a variety of conditions including hypertrophic cardiomyopathies, anemia, thyrotoxicosis, sepsis, and hypo- volemia. In the acutely decompensating patient the latter two diagnoses are most likely, and distributive shock from blood loss, sepsis, or other acute cause must be considered. Hypodynamic left ventricle In contrast, global loss of contractility in the left ventricle can suggest a primary cardiac cause for the hypotension, as occurs with myocardial infarc- tion or myocarditis but can also be seen with toxins, sepsis, or cardiac “stunning.” It can also be found in congestive heart failure (CHF) and other chronic conditions. In either case, a diffusely hypokinetic left ventricle sug- gests that the patient will not respond well to fluid bolus, and inotropes or pressors may be of benefit. Assessments of cardiac contractility are most useful when combined with an estimation of IVC size and respiratory variation. This helps rapidly inform the decision to use fluids or inotropes/pressors as the next management step in shock. Inferior vena cava Many authors have attempted to demonstrate a correlation between IVC appearance and central venous pressure (CVP), with varied success. Although measurement of the IVC diameter has been described from a transverse and longitudinal approach, many have described the longitudinal approach as more optimal in the adult patient, and the transverse approach more optimal in the pediatric patient. This view allows visualization of the IVC along with hepatic vein confluence and the IVC entry into the right atrium ( Figure 14.4 ). Measurement of the IVC diameter is recommended at a point approximately 2 cm distal to the diaphragm. During inspiration, negative intrapleural pressure causes negative intra- luminal pressure and increases venous return to the heart, speeding blood through the extrathoracic IVC. Given that the extrathoracic IVC is such a compliant vessel, this causes the IVC diameter to decrease with normal inspiration ( Figure 14.5 ). Therefore, in patients with low intravascular volume, the inspiration to expiration diameter ratios change much more than in patients with normal or increased intravascular volume. M-mode can be used to quantify the ratio of maximum and minimum diameters of the IVC during respiration.
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