打击乐

Percussion is a commonly used clinical skill that is most useful in the examinations of the chest and abdomen. Simply stated, percussion refers to the striking of one object against another to produce sound.

The discovery of percussion’s usefulness in medicine dates back to the 1700s. In former years of this century, an Austrian innkeeper’s son, named Leopold Auenbrugger, discovered that he could take inventory by tapping his father’s beer barrels with his fingers. Then, in 1761, while practicing medicine, he applied this technique on his patients and published the first description of the diagnostic utility of percussion. However, his findings faded into obscurity until the French physician, Jean-Nicolas Corvisart, in 1808, rediscovered Auenbrugger’s writings and used them to teach percussion to his medical students. Since then this technique has become an integral part of day-to-day clinical practice.

This video will first illustrate the types of percussion and the commonly heard percussion notes. Then, we’ll go over the procedure and considerations for performing this technique during a physical examination.

There are several types of medical percussion techniques. The historic type is ‘direct percussion’ in which the plexor-that is the tapping finger-strikes directly against the patient’s body, but this method is obsolete and is no longer employed in clinical practice. It has been supplanted by ‘indirect percussion’ in which the plexor finger strikes a pleximeter, which is typically the middle finger of the non-dominant hand placed against the patient’s body.

The third type is the ‘auscultatory percussion’, which relies on using a stethoscope to discern differences in sounds created by the plexor finger. Auscultatory percussion is a commonly used alternative method to assess liver size using the ‘liver scratch test’. With the stethoscope held over the patient’s liver, the examiner gently scratches the patient’s skin while listening for changes in sound quality as the plexor finger makes its way over the liver edge.

Another percussion technique is called the ‘fist percussion’, which is performed using the ulnar aspect of the plexor fist. Again, this can be performed either directly against the patient’s body, or by using an indirect method in which the examiner’s non-plexor hand is placed palm down on the patient’s body wall and the plexor fist strikes the dorsum of the hand to attenuate the force of the blow. Here, the examiner’s motion should be brisk with movement originating at the elbow, and it is critical to deliver the right amount of force-enough to uncover tenderness in a patient with pathology, but not so much to cause undue discomfort or pain in a patient without any disease.

Now, let’s talk about the notes normally heard while performing indirect percussion. The percussion notes differ in relative intensity, pitch, and duration depending on the density of the underlying structure.

A tympanitic sound is loud, high-pitched, and longer in duration than other sounds. It is normally heard over parts of the gastrointestinal tract that contain air, such as the stomach. A resonant note is also loud, but low-pitched, and long in duration. It is normally heard over the lung tissue. A dull note is medium in intensity, pitch and duration, and it appears over solid organs like the liver. A flat percussion note is soft, high-pitched, short and therefore hard to listen to. This note can be appreciated by percussing over the extremely dense quadriceps muscles, but percussing in this location holds no clinical utility. However, if a flat note is heard over the lungs, it may indicate pleural effusion, and if heard over a protruded abdomen it may indicate ascites. Another pathological percussion sound is hyperresonance, which, as compared to the resonant sound, is louder in intensity, lower in pitch and longer in duration. Hyperresonant sounds on lung percussion may indicate pneumothorax or chronic obstructive pulmonary disorder.

Now that you know about the types of notes heard during indirect percussion, let’s briefly review the general steps for performing this technique. Before starting with the exam, make sure that your fingernails are clean, groomed, and trimmed. Wash your hands with soap and water, or apply topical disinfectant solution. Warm your hands with warm water or by rubbing them together before patient contact.

To percuss, place the pleximeter finger firmly against the body surface being examined. Make sure the entire distal phalanx is in contact with the patient, but the rest of the fingers should be splayed out to avoid making contact, as this could dampen the sound. With the tip of the plexor, strike the distal interphalangeal joint of the pleximeter using a quick, relaxed, snapping motion from the wrist. After the strike, lift plexor finger rapidly to avoid sound dampening.

In addition to the sounds, note the amount of vibration in the pleximeter. The differences in vibration are subtle and require keen attention and practice to appreciate. The gas-filled structures might lead to more movement of the pleximeter finger, whereas the solid or liquid-filled regions may cause decreased vibration. During any physical exam, percuss at each point a few times in rapid succession to ensure consistency of notes before moving to the next spot.

In addition to performing percussion accurately, one must also pay attention to a few other factors that might affect the percussion notes.

Make sure percussion is done directly on the patient’s skin. Performing percussion on the patient with clothing on is impermissible. While the use of gloves might be necessary for infection control purposes, in cases where gloves are necessary, the clinician must account for the difference in the way the percussion note will “feel” on the pleximeter finger, because the vibrations will feel different.

Note that the pressure applied with the pleximeter finger affects the percussion note. Inadequate pressure can cause artificial dullness, and more pressure can augment the sound. Also, the force with which the plexor strikes may affect the interpretation of one’s findings. Striking more forcefully with the plexor finger is rarely helpful, though striking too lightly can also lead to artificial dullness. Remember that the percussion notes and vibrations are also impacted by the subcutaneous fat, which, if excess, may dampen the movement of the pleximeter. Finally, when examining a particular area of the body, maintain a consistency in the technique. To optimally compare sounds from one region to another, keep the amount of pressure with the pleximeter finger, the force with the plexor, the strike spot, and the part of the plexor finger used, all the same throughout the exam.

You’ve just watched JoVE’s video on percussion performed during a physical examination. This presentation covered the types of percussion procedures, the commonly witnessed percussion notes, the technique and factors that may affect the findings of this procedure. Percussion revolutionized bedside diagnostics in the eighteenth and nineteenth centuries and it still remains an important method that enables clinicians to evaluate deep anatomic structures that cannot be visually inspected. As always, thanks for watching!