The upper border of the liver is percussed in the right midclavicular line, starting in the mid-chest. As the chest is percussed downward, the resonant note of the chest becomes dull as the liver is reached. As percussion continues still further, this dull note becomes tympanic because the percussion is now over the colon. The upper and lower borders of the liver should be no more than 4 inches (10 cm) apart. The technique is illustrated in Figure 17-17.
There are several problems with predicting liver size by percussion. If ascites is present, the examiner can only speculate about the correct size of the liver. A more common cause of
overestimating liver size (false-positive measurement) is some form of chronic obstructive lung disease. This makes percussion of the upper border of the liver difficult. Obesity in a patient can cause problems in both percussion and palpation. Distention of the colon may obscure the lower liver dullness. This may result in underestimating the size of the liver (false-negative measurement).
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