How to elicit Shifting dullness?

This method may also be called as shifting tympanicity

• Patient lies supine with thighs flexed.
• Patient is asked to evacuate his/her bladder (full bladder will unnecessarily hamper the midline percussion).
• Now palpate the abdomen (by dipping method) for any visceromegaly (liver, spleen, kidney lump, if any organ is enlarged, avoid percussion over them.
• Starting from the eigastrium percuss in the midline from above downwards. percuss the midline to verify resonance. Note the maximum point of tvmpanicity. Usually it is somewhere around the umbilicus.
• Now percuss laterally to one side (suppose, the right side) from the maximum point of tym-panicity noted in the midline, keeping the pleximeter finger parallel to long axis of abdomen or arbitrary border of the fluid level. 
• When you get a dull note, mark it with a skin pencil but keep on percussing towards the flanks (to diagnose that the dullness is continuous and not a localised one due to colonic growth, faecolith etc.) and again return to the first noted point of dullness.
• Now turn the patient to left lateral position, keeping the fingers in the point of dullness noted in the right flank. Turning is done in such a way that your fingers in the right flank become the highest point of the patient’s body. Now wait for few seconds (usually 1/2 to 1 minute) for the intestine to float up.
• Percuss the dull point noted in the right flank and it will be tympanitic now. Go on percussing upto the end point of the right flank which now shows tympanitic resonance.
• Next go upto the midline and now the midline which was tympanitic initially will be dull on percussion. So the dullness in the right flank changes to tympanitic note and the midline becomes dull from the original tympanicity. This is shifting dullness.
• The same procedure is repeated in the left flank starting from the midline.

Minimal fluid required for demonstration of shifting dullness :
It is said that at least 1 /2 to 1 litre of fluid is required to demonstrate shifting dullness.
Absent shifting dullness in the presence of fluid in the abdomen :
The possibilities are :

• Fluid is encysted i.e. ovarian cyst.
• Small collection of free fluid.
• Loculated ascites in tuberculous peritonitis.

Shifting dullness in the absence of fluid in the abdomen
False positively in paralytic ileus (rare).
What is meant by free fluid in ascites ?
The fluid shifts or changes its position with the intestinal air with change of posture which never
occurs in encysted fluid and thus, shifting dullness is never found in encysted fluid in the abdomen.
Why do we percuss the midline first. in performing shifting dullness ?
While the patient lies supine, the intestine will float in the midline (in health as well as in a patient
of ascites) and will give tympanitic note on percussion. To follow’ the cardinal rules of percussion, we percuss the midline first (tympanitic) and then the flanks (dull) so. we percuss from more resonant to less resonant  area.
Masssive hepatosplenomegaly with ascites : how to elicit shifting dullness ?

• First percuss the midlinc and there will be presence of tympanitic note on percussion. 
• Now ask the patient to sit and again percuss the midline form above downwards.
• In the presence of free fluid in the abdomen, the lower part of midlinc will be dull in sitting position (bladder must be evacuated)
• Actually, in the presence of gross visceromegaly, clinical detection of ascites is very difficult.

Unilateral shifting dullness :

• It is found in splenic rupture and is known as Ballance's sign. 
• The blood present in the left flank becomes clotted (near the spleen) and wont not shift to right side in right lateral position but the blood present in the right side (haemoperitoneum) is shifted to the left side.