How do you auscultate well?
Short answerGood auscultation is a comparison. You listen at the same points, in the same position and with a similar breath. At each level you compare the right side with the left.
What should you prepare before you start listening?
The quality of auscultation is often decided before the stethoscope touches the chest. So spend the minute before the examination on five preparations.
- Room. Close the door and stop the television and any conversation. Background noise easily masks short, faint crackles.
- Contact. Place the chest piece directly on the skin. If it slides over clothing, a cable or chest hair, it makes crackling noises (Pitfalls and artefacts). A cold chest piece makes the muscles tense, so warm it in your hand first.
- Position. If possible, sit the patient up and ask them to fold their arms in front. This moves the scapulae outwards, so you can listen over a larger area of lung. If the patient cannot sit, turn them onto their side to listen to the back. Record the position in your note.
- Breathing. Tell the patient: "Open your mouth slightly and breathe in and out a little more deeply and slowly than usual." Breathing through the mouth reduces sounds from the nose. As airflow rises, the breath sound becomes louder. This follows from the first rule: no flow, no sound.
- Patient comfort. Fast, deep breathing for a long time can make the patient dizzy. So allow a few normal breaths in between.
Diaphragm or bell?
The two sides of the stethoscope filter sound differently. If you press the diaphragm firmly on the skin, low-pitched sounds become weaker and high-pitched sounds stand out. This is the right choice for most lung sounds, such as crackles, wheezes and bronchial breathing.
The bell passes low-pitched sounds better when it rests lightly on the skin. But if you press the bell hard, the skin beneath it is stretched and works as a diaphragm. The bell then loses this advantage.
On the chest, the bell is most useful where the diaphragm cannot sit flat. These places are the deep intercostal spaces of a cachectic patient, the chest of a small child and the supraclavicular fossa.
In what order should you listen?
Start on the back of the chest. Work down from the top (apex) to the base. At each level, listen to one side and then straight away to the same point on the other side. When you hear two sounds one after the other, you pick up small differences more easily.
Then move to the side of the chest. The right middle lobe and the lingula are easily missed when you listen only from behind. The best window for these lobes is the axilla, together with the front of the chest.
Listen to the front last. Start above the clavicle and work downwards. Do not listen over breast tissue. Ask the patient to lift the breast gently.
How long should you listen at each point?
At each point, listen to at least one full respiratory cycle, that is, one inspiration and one expiration. Crackles last only milliseconds and may not be equally clear on every breath. So wait for two or three more breaths at any point you are unsure about.
When you hear a finding, stop and describe it with the four questions: When? What does it sound like? Where? What changes it? First note where the sound falls in the respiratory phase. Then listen to the neighbouring points and to the other side. Work around the sound until you find its border.
A finding with a mapped border tells far more than a note saying "crackles on the right". You answer the last question, what changes the sound, with the manoeuvres below.
Do not move the chest piece in the middle of a respiratory phase. A sliding chest piece interrupts the sound and also adds a friction artefact.
How do you find out what changes the sound?
Hearing a sound is only half the job. What changes the sound shows where it comes from. Five manoeuvres tell you this.
- Cough. Ask the patient to cough hard a few times, then listen to the same point again. Coarse crackles and rhonchi that change or disappear with coughing suggest mobile secretions. Late inspiratory fine crackles and a pleural friction rub do not change, and secretions do not explain them.
- A few deep breaths. Ask for several deep breaths in a row, then listen again. Soft crackles heard at the bases after shallow breathing may disappear. Crackles that persist are significant. If "diminished breath sounds" improve with deep breathing, airflow was low.
- Change of position. Turn the patient onto their side, sit them up or ask them to lean forward. This changes crackles in the dependent (lowermost) regions and changes regional ventilation. The border of a free effusion may also move with the fluid.
- Breath-holding. Ask the patient to hold their breath for a few seconds. If the sound stops, its source is breathing. If a rub continues, it may be pericardial. Other sounds that continue come from the heart, from muscle or from the room.
- Bronchodilator. After the inhaler, listen to the same points with a similar depth of breathing. If the wheeze becomes shorter and less widespread, this is consistent with a response to treatment. But if the breath sounds have also become quieter, consider that airflow may have fallen.
These two examples recreate the same point before and after coughing. Coughing clears some of the sounds caused by secretions.
What are the most common mistakes?
These mistakes are common:
- Listening through clothing or sliding the chest piece over the skin.
- Writing "breath sounds diminished" while the patient is breathing shallowly.
- Listening to only one side or only to the back.
- Listening while the patient is talking or swallowing.
- Writing a disease name instead of describing the sound, for example "pneumonic crackles".
In a quick examination, it is enough to place the stethoscope over clothing.
Clothing weakens the sound and adds friction noise. Even in a short examination, listen on bare skin.
The right and left sides are normally identical.
In a healthy person the two sides are roughly symmetrical, but they are not mirror images. Small differences are normal. Differences that are large, new or present on every breath matter (The limits of normal).
This lesson continues with Voice transmission tests and percussion, Pitfalls and artefacts and A good examination note.
- Before you listen, quieten the room, place the chest piece on bare skin, sit the patient up and ask for slightly deeper breaths through an open mouth.
- Listen to most lung sounds with the diaphragm pressed firmly. Use the bell, placed lightly, where the diaphragm cannot sit flat.
- Listen to the back first, then the sides and the front last. At each level, compare the two sides one after the other.
- Listen to at least one full respiratory cycle at each point. When you hear a finding, stop, find its border and describe it with the four questions.
- Coughing, deep breaths, a change of position, breath-holding and a bronchodilator show what changes the sound and where it comes from.
Going deeperresidents · specialists · numbers and sources
Why do you listen by comparison?
When airflow is held equal, the amplitude of the inspiratory sound at the chest wall is about 1.99–2.43 times that of the expiratory sound. This phase difference is not marked in the tracheal sound. Even with matched airflow, the left posterior base has been measured as about 32% louder than the same point on the right.
One study examined seven pairs of symmetrical points in 42 healthy adults aged 18–22 years. Some spectral measures showed significant right–left asymmetry. The direction and size of the difference varied with the point and, for some measures, with sex. So the right standard is not mirror symmetry. It is the variability expected at matched points.
Position, volume and flow
In six healthy young men with equal airflow, sound intensity was higher over the dependent (lower) lung when they lay on their side (lateral decubitus). The differences between the sitting, supine and prone positions were less consistent.
Lung volume also changes the sound. Over the lower lobes and in the 150–300 Hz band, the amplitude difference between neighbouring points can vary with volume by up to about 11 dB.
In multichannel measurements, total sound energy changes rapidly with airflow. The normalised regional distribution of sound is relatively stable when inspiratory flow is above about 1 L/s. Maps obtained at very low flow are less comparable. The details are in the lesson The limits of normal.
The stethoscope itself
The acoustic stethoscope is a good listening tool, but it is not a calibrated measuring system. The frequency response that reaches the ear depends on the chest piece, the diaphragm or bell, the enclosed air volume, the tubing and the earpieces together. With digital stethoscopes, even different units of the same model can respond measurably differently. So for serial monitoring, use the same device, the same points and the same position.
See the reference list for sources.
Check yourself
3 short questions. The explanation opens when you choose an answer.