# Percussion

Percussion

Percussion helps to distinguish distension due to bowel gas from solid masses and free fluid in the abdomen. Percussion is most sensitive when the examiner moves from resonant parts of  the abdomen to dull areas. In patients with free fluid in the peritoneal cavity , percussion from the centre to the periphery reveals dullness of  flanks. Shifting dullness is elicited if  the patient is re-examined lying on his or her side. The margin of  dullness is then found to shift when the patient has moved. Free fluid can also give rise to ‘fluid thrill’; this is feeling the vibrations from a tap in one flank on the other flank while pressure is kept on the midline to prevent vibrations through the abdominal wall. Percussion is also a very sensitive and refined method of - testing for rebound tenderness. If  the patient winces with pain on abdominal percussion it denotes underlying peritonitis.