Abdominal percussion is a non-invasive physical examination method. By tapping the surface, the technique creates an audible vibration that helps distinguish between air, fluid, and solid organs. This simple procedure allows a clinician to quickly estimate the distribution of gas and the size of underlying organs, forming a foundational part of the physical assessment.
Setting the Stage and Mastering the Basic Strike
Before beginning, the patient should be in a supine position, with the abdomen appropriately exposed from the chest down to the groin. The examiner should be positioned comfortably, typically on the patient’s right side, to ensure optimal reach and technique. Percussion involves the indirect method, which requires the precise use of two fingers.
The middle finger of the non-dominant hand acts as the pleximeter, with only the distal interphalangeal joint making contact. Press down firmly enough to compress the soft tissue without causing discomfort, ensuring any contact from other parts of the hand is avoided to prevent dampening the vibration. The plexor, the middle finger of the dominant hand, is then used to strike the pleximeter finger.
The plexor finger should be held at a 90-degree angle to the surface of the pleximeter, striking near the distal joint, and immediately withdrawn to allow the sound to resonate clearly. Producing a clear, distinct sound requires a light, yet deliberate, tapping force. The sound elicited generally penetrates about five to seven centimeters into the abdomen for diagnostic purposes.
Systematic Mapping of Abdominal Regions
A comprehensive abdominal assessment requires a systematic approach to ensure no area is missed. The most common method involves dividing the abdomen into four quadrants, beginning the percussion process in a consistent location, such as the right lower quadrant. The examiner then proceeds clockwise to the right upper, left upper, and finally the left lower quadrant, percussing multiple points within each area.
Percussing in this methodical pattern helps to establish a baseline of normal sounds across the abdomen. This allows for the identification of the usual distribution of gas-filled bowel loops, which produce a specific sound. The pattern also serves to identify any large, unexpected areas of dullness or tympany that deviate from the expected findings before proceeding to more targeted maneuvers.
Decoding the Sounds: Normal and Abnormal Findings
The sounds produced during percussion are directly related to the density of the underlying tissue. The predominant normal sound heard over the abdomen is Tympany, characterized as a high-pitched, drum-like noise with a long duration. This sound is generated by the vibration of air within hollow structures, such as the intestines and stomach, which are typically gas-filled.
The other expected normal sound is Dullness, which is a flat, short, and quiet thudding sound. Dullness occurs when percussing over dense or solid organs, such as the liver, spleen, or a fluid-filled bladder. The liver reliably produces dullness in the right upper quadrant due to its solid composition, while scattered dullness over the intestines can indicate areas filled with stool or fluid.
Abnormal findings can include Hyperresonance, a sound that is louder and more booming than normal tympany. Hyperresonance suggests the presence of an excessive amount of trapped air. Conversely, a uniformly dull abdomen, where the tympany is absent, may signal a large, underlying mass or a substantial accumulation of fluid. Deviations from the expected pattern, such as dullness over an area that should be tympanic, require further investigation.
Advanced Maneuvers for Organ Borders and Fluid
Beyond the general survey, percussion is used in maneuvers to define organ boundaries or detect abnormal fluid collections. One such application is estimating the Liver Span, the liver’s vertical size. This is achieved by percussing down the right midclavicular line, starting from the lung field (which is resonant), until the sound changes to dullness, marking the upper border, usually around the fifth intercostal space.
The lower border is determined by percussing upward from an area of tympany in the right lower quadrant until dullness is heard, typically at the costal margin. The vertical distance between these two points normally ranges between six and twelve centimeters in the midclavicular line. A second maneuver is testing for Shifting Dullness, which is used to detect the presence of ascites, or free fluid in the abdominal cavity.
When an individual with ascites is supine, the fluid sinks to the flanks, producing dullness, while the air-filled bowel floats to the top, resulting in tympany near the umbilicus. The examiner percusses from the midline toward the flank, noting the point where tympany shifts to dullness. If the patient is rolled onto their side, the previously dull area will become tympanic. This test typically requires at least 1,500 milliliters of fluid to be present.