Mount Sinai Expert Guides. Группа авторов
physiology.
Determine global left ventricular (LV) function, systolic function and size:Contractility is best determined using parasternal views.‘Good’ contractility: LV walls almost touch during systole and nearly obliterate ventricular cavity; anterior leaflet of mitral valve moves vigorously in parasternal long axis view.‘Poor’ contractility: minimal wall movement or change in ventricular cavity between systole and diastole.Small ventricular cavity in hypovolemic conditions.
Assess for right ventricular (RV) strain (Figure 4.3):Classic sign of massive pulmonary embolus.RV dilation: RV size exceeds LV size.Paradoxical septal wall motion or ’D’ sign: best seen in parasternal short view; normal LV is circular but increased RV pressure flattens or bows interventricular septum into LV during diastole.McConnell’s sign: RV dysfunction with characteristic sparing of apex; often described as ‘invisible man jumping on trampoline at RV apex’.
BOTTOM LINE/CLINICAL PEARLS
Ribs block US waves and obscure views of heart. Make fine adjustments by rotating and angling cardiac probe so the US beam is parallel to ribs.
Epicardial fat pad may be mistaken for an effusion; it is most prominent anteriorly.
Some views will be difficult to obtain in individual patients. Turning patient into left lateral decubitus position may improve views.
Inferior vena cava (ultrasonography)
Probe selection and orientation
Use phased array ‘cardiac’ probe or curvilinear probe.
Same screen/probe orientation as for subxiphoid view of heart.
Scanning technique
Start with subxiphoid view of heart, then rotate probe 90° so probe indicator points cephalad.
Slide probe slightly right of midline until IVC is visualized in longitudinal plane.
Identify where IVC transitions into right atrium to confirm visualization of IVC versus abdominal aorta (Figure 4.4).
Measure IVC diameter 2 cm caudal to junction of IVC and right atrium.
Use M‐mode on IVC to graphically visualize respiratory variation in IVC caliber.
Clinical application
Estimate intravascular volume and monitor response to fluid challenges by evaluating IVC diameter and collapsibility (Table 4.3).
Correlation between central venous pressure (CVP) and IVC diameter and percentage change with respiratory variation.
If IVC diameter is <1 cm → higher probability of fluid responsiveness.
If IVC diameter is >2.5 cm → lower probability of fluid responsiveness.
IVC diameter between 1 and 2.5 cm → indeterminate probability.
Table 4.3 Intravascular volume estimation.
| Intravascular volume status* | IVC caliber | IVC collapsibility | CVP |
|---|---|---|---|
| Volume depleted | Small (<1 cm) | >50% | <10 cmH2O |
| Volume overloaded | Large (>2.5 cm) | <50% | >10 cmH2O |
* IVC distention with minimal respiratory variation may occur in clinical scenarios other than volume overload (e.g. cardiac tamponade).
BOTTOM LINE/CLINICAL PEARLS
Do not mistake pulsatile abdominal aorta for IVC. If it is the IVC, the vessel can be seen entering the right atrium; also look for hepatic vein entering the IVC.
‘Plump IVC’ does not always indicate volume overload. Assess cardiac function prior to IVC to provide context for IVC findings.
Lung ultrasonography
Probe selection and orientation
Use phased array ‘cardiac’ probe (adequate for majority of lung examinations).
Use linear array ‘vascular’ probe for detailed exam of pleural surface.
Point probe indicator toward patient’s head (general radiology convention).
Scanning technique
Position probe over rib interspace so rib shadows are on each side of US screen.
Identify following normal lung findings (Figure 4.5 and Video 4.1):Pleural line: shimmering echogenic line at top of screen.Lung sliding: periodic movement of pleural line; represents movement of visceral and parietal pleura relative to chest wall.A‐lines: repetitive horizontal artifact resulting from reverberation of US waves between skin and pleural surface; space between A‐lines equal to distance between probe head (on skin surface) and pleural line.Seashore sign: graphical visualization of lung sliding in M‐mode; often described as ‘waves on a sandy beach’ (waves represent motionless chest wall, sandy beach represents air‐filled lung).B‐lines: vertical artifact arising from pleural surface; appears like laser beam that effaces A‐lines and projects to bottom of screen. Usually do not see B‐lines anteriorly; may see a few (1–3) posteriorly in dependent regions in normal scans.
Slide probe vertically down chest wall to examine adjacent interspaces.
Repeat this process in systematic fashion along anterior, lateral, and posterior chest wall.
Clinical application
Assess for pneumothorax:
Absence of lung sliding plus absence of B‐lines (Video 4.2).
Barcode or stratosphere sign: parallel horizontal lines indicating absence of lung sliding in M‐mode (Figure 4.6).
Lung point sign: transition point – between border of pneumothorax and normal pleural interface – where intermittent lung sliding is visualized. It is pathognomonic and helpful in estimating size of pneumothorax.Table 4.4 Features of cardiogenic pulmonary edema and non‐cardiogenic lung injury.Cardiogenic pulmonary edemaNon‐cardiogenic lung injuryHomogenous B‐line distributionSmooth pleural lineAbsence of A‐line patternNon‐homogenous B‐line distributionIrregular pleural surface
Assess for pleural effusion:Effusion appears as anechoic area usually in dependent areas; important to examine posterior chest wall in supine patient.Lung flapping or jellyfish sign: collapsed