How do you assess for shifting dullness in a patient?

How to Assess for Shifting Dullness

To assess for shifting dullness, percuss the patient's flanks while they are supine, mark the dullness-tympany interface, then have the patient roll to the opposite side and observe if the dullness shifts to the dependent side. 1

Technique for Assessing Shifting Dullness

Initial Assessment

• Begin by having the patient lie in a supine position 1
• Inspect the abdomen for fullness or bulging, which may suggest the presence of ascites 1
• Approximately 1,500 mL of fluid must be present before flank dullness is detectable 1

Percussion Technique

1. First percussion (patient supine):

   • Percuss from the midline of the abdomen toward the flank 1
   • Note where the sound changes from tympany (resonant sound over gas-filled bowel) to dullness (over fluid) 1
   • Mark this tympany-dullness interface on the patient's skin 1

2. Position change:

   • Ask the patient to roll onto their side (toward the opposite side of the initial percussion) 1
   • Wait 1-2 minutes to allow fluid to redistribute 1

3. Second percussion (patient on side):

   • Percuss the same area again 1
   • If ascites is present, the area of dullness will have shifted (moved) to the dependent side 1
   • The previously dull area may now be tympanic 1

Interpretation

• Positive shifting dullness: The boundary between tympany and dullness moves when the patient changes position 1
• Negative shifting dullness: No change in the percussion note with position change 1

Diagnostic Value

• Shifting dullness has 83% sensitivity and 56% specificity in detecting ascites 1
• If no flank dullness is present in the supine position, the patient has less than a 10% chance of having ascites 1
• The fluid wave test is an alternative method but is more cumbersome and less reliable than shifting dullness 1

Clinical Pearls

• In obese patients, physical examination for ascites is challenging, and abdominal ultrasound may be required to confirm the presence of fluid 1
• Approximately 75-85% of patients with ascites have cirrhosis as the underlying cause 1
• Jugular venous distension should be assessed, as its presence suggests cardiac rather than hepatic causes of ascites 1
• Brain natriuretic peptide (BNP) levels can help distinguish between cardiac ascites (median pro-BNP: 6100 pg/mL) and cirrhotic ascites (median pro-BNP: 166 pg/mL) 1

Common Pitfalls

• Failure to allow sufficient time (1-2 minutes) after position change for fluid to redistribute 1
• Not percussing systematically from tympany toward dullness 1
• Relying on the fluid wave test, which is less sensitive than shifting dullness 1
• Misinterpreting obesity as ascites; a slowly enlarging abdomen over months to years is more likely due to obesity than ascites 1