I. Preparation & General Principles

1. Patient Position: Ensure the patient remains comfortably supine, with knees slightly flexed to relax the abdominal muscles.

2. Examiner Position: Stand on the patient's right side.

3. Technique: Use the middle finger of your non-dominant hand (the pleximeter finger) pressed firmly against the abdominal wall. Strike this finger sharply with the tip of the middle finger of your dominant hand (the plexor finger), using a quick, sharp wrist action. Listen carefully to the sound produced.

4. Expected Sounds:

   • Tympanic (Drum-like): A hollow, resonant sound, typically heard over gas-filled structures like the intestines. This is the predominant sound over most of the abdomen.

   • Dull: A flat, thudding sound, heard over solid organs (like the liver or spleen), fluid (like a distended bladder or ascites), or solid masses.

   • Stony Dull: A very flat, intense dullness, suggestive of a large amount of fluid (e.g., significant ascites).

II. Systematic Percussion of All Quadrants

• Gently percuss all nine regions of the abdomen. Note the predominant sound (usually tympanic) and identify any areas of dullness. This helps to detect distension (generalized tympany), organomegaly, or large masses.

III. Specific Organ Percussion

1. Liver:

   • Upper Border (Liver Dullness): Percuss downwards in the right mid-clavicular line starting from the chest (usually around the 2nd or 3rd intercostal space), moving towards the abdomen. Note where the resonant lung sound changes to a dull liver sound (normally around the 5th intercostal space). This marks the upper border of the liver.

   • Lower Border: If the liver is enlarged and its edge is not palpable below the costal margin, you can try to percuss its lower border. Start from a tympanic area in the right iliac fossa and percuss upwards towards the right costal margin until you detect dullness. This is less reliable than palpation for the lower border.

   • Liver Span: Measure the vertical distance between the percussed upper and palpated (or percussed) lower borders in the mid-clavicular line (normal: 10-12 cm in males, 9-11 cm in females).

2. Spleen:

   • Traube's Space: This is a semi-lunar area in the left lower chest, bounded superiorly by the 6th rib, laterally by the mid-axillary line, and inferiorly by the left costal margin. It's normally tympanic due to the stomach and colon.

     • Procedure: Percuss this space.

     • Observation: Dullness in Traube's space suggests splenomegaly, but can also be caused by left pleural effusion, gastric mass, or a full stomach.

   • Castell's Sign:

     • Procedure: Percuss the lowest intercostal space in the left anterior axillary line (usually the 8th or 9th).

     • Observation: If it's resonant on full expiration but becomes dull on full inspiration, this suggests mild splenomegaly (a positive Castell's sign). This is considered a sensitive sign for subtle splenic enlargement.

3. Urinary Bladder:

   • Procedure: Percuss the suprapubic area (hypogastrium).

   • Observation: A distended bladder will present as a dull area above the pubic symphysis.

4. Percussion of Masses:

   • If you detected a mass on palpation, percuss its borders to confirm its size and extent, noting whether it's dull (solid/fluid-filled) or tympanic (gas-filled).

IV. Percussion for Ascites (Fluid in Peritoneal Cavity)

1. Shifting Dullness (Most Important):

   • Procedure:

     • With the patient supine, percuss from the center of the abdomen (tympany) outwards towards the flanks. Note where the percussion sound changes from tympanic to dull (this marks the fluid level).

     • Keep your pleximeter finger on the dull area in the flank.

     • Now, ask the patient to turn onto their side, away from your percussing hand. Wait 20-30 seconds for the fluid to shift.

     • Percuss the same spot again.

     • Observation: If the dullness has now become tympanic, and if you then percuss downwards on the new dependent side and find dullness again, it confirms shifting dullness, indicating the presence of at least 1-1.5 liters of fluid.

2. Puddle Sign (For Minimal Ascites):

   • Procedure: The patient lies prone for 5 minutes, then gets onto hands and knees (knee-elbow position) so the abdomen is dependent. Place a stethoscope over the most dependent part of the abdomen. Gently flick one flank repeatedly with your fingers while listening through the stethoscope. Slowly move the stethoscope towards the opposite flank.

   • Observation: A change in the intensity and character of the percussion note (becoming louder or clearer) as the stethoscope moves towards the opposite flank suggests minimal fluid (as little as 120 mL). This is a more subtle sign.

V. Other Relevant Percussion Areas

• Renal Angle: Percuss the renal angle (the area formed by the 12th rib and the erector spinae muscles in the back). It's normally resonant due to the colon. Dullness here might suggest kidney enlargement or a retroperitoneal mass.