How to use a stethocope correctly

First stethoscope?   Learn how to use it the way it is supposed to.
First stethoscope? Learn how to use it the way it is supposed to.

Do you know how to use your stethoscope correctly? Or do you just enjoy the gurgling noises your stomach makes? If you keep this “tube thingy” around as a toy (and hopefully not to try breaking into safes), there’s not much to add. Just try to store it correctly so it doesn’t lose its shape and clean the earpieces constantly to prevent ear infections. But if you’re a healthcare professional (or in the process of becoming one) you need to get the best out of this diagnostic tool.

How does it work?

The most commonly used stethoscope, and the one  to be described here, it's the acoustic one. Its intended use is to capture vibrations from inside the patient's body and amplify them in the form of sound waves.

When placed on the body, the chest piece, usually composed of a flat bigger side called the diaphragm and a smaller cup-shaped side known as the bell. The diaphragm is mostly composed of plastic. When pressed firmly against the skin, internal vibrations are transmitted through the plastic disk creating acoustic waves that travel through the air filled tubing and into the listener's ears through the earpieces. These captured waves are mostly of higher frequency. With the bell, on the other hand, lower frequency sounds are heard more easily given its hollow nature. However if you put some pressure on the bell it can also capture high frequency sounds.


Ok, so...

You might already know all this. But there are some common mistakes that the stethoscope newbies make. For example, when placing the stethoscope on your ears, make sure that the earpieces fit correctly. Some stethoscope have the ear tubes with the earpieces tilted slightly forward. This is to ensure that the sound follows the natural shape of your ear canal so it can reach your eardrum more readily. Also avoid as possible using your stethoscope over thick clothing or dry hair. They can produce a rustling sound that can be confused with pathologic findings. 

Many stethoscopes, like the Littmann models, have turnable chest pieces so the sound can be directed towards the bell or the diaphragm. After fitting the earpieces into your ears, tap the chest piece lightly to assure that the sound is going to be capture correctly. 

When holding the chest piece, place it between your index and middle finger. This would avoid extraneous sounds.

Listening to the heart

No physical exam can leave this part out. And no, it's not just about placing the chest piece on the, well, chest. Specific sounds regarding the heartbeat can be hear in specific locations in the chest.  This relates to the position of the heart, and its valves, in the chest cavity. Also, some of this sounds differ in pitch, so both the bell and the diaphragm should be used when auscultating the heart.

Place the stethoscope in the right space between the 2nd and 3rd ribs next to the sternum to listen to the flow of blood going through the aortic valve. Move to the left side of the sternum (also to the 2nd interspace) for the pulmonary valve and go down to the lower left sternal area for the tricuspid valve. Don't forget the mitral valve! For this one the location of the apex of the heart should be previously identified, but it is commonly found at the left 5th intercostal space approximately 6cm from the border of the sternum. Some prefer starting the heart auscultation at the apex. All areas were abnormalities are detected should be heard and in the case of irradiation, especially in the case of a murmur, the sound irradiation should also be noted.

The diaphragm of the stethoscope is better for hearing S1and S2. For S3 and S4, sounds with lower pitch, is better to use the bell of the stethoscope. 


Auscultating the lungs

Of course, one of the primary uses of this magnificent tool. The lungs fields can be heard at the front and back of the thorax. Given the high pitch (or frequency) of breath sounds, lungs should be auscultated with the diaphragm of the stethoscope. 

Checking the gut

While listening to the abdomen, signs of obstruction, low mobility or high mobility of the intestines, among other things, can be identified. For auscultation, the abdomen is usually divided into four imaginary quadrants. Start with placing the  diaphragm of the stethoscope lightly on the right lower quadrant of the abdomen and work you way to the others in the clockwise direction, following the path of the large intestine. You should hear gurgling noises occurring at approximately 5-34 per minute (normoactive bowel sounds). 

Make sure to auscultate the abdomen before palpating it or percussing it during physical examination. If the abdomen is palpated or percussed first, the abdominal muscles can tense up and change what is heard during auscultation.  

Other uses during physical examination

For screening blood pressure the traditional way, the bell of the stethoscope is placed lightly under the lower border of the blood pressure cuff (sphygmomanometer). The sound to be heard (Korotkoff) are relatively low in frequency, and thus best heard with the bell of the stethoscope.

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