A stethoscope is a medical instrument used to listen to the internal sounds of the body, a process known as auscultation. It amplifies faint internal sounds, allowing for clear identification of physiological processes. Accurate placement is important for distinguishing different sounds and gaining meaningful insights into the body’s condition, ensuring clear and unobstructed listening.
Preparing for Listening
Before placing the stethoscope, ensure the instrument is ready and the environment is suitable. A stethoscope typically consists of earpieces, flexible tubing, and a chest piece, which usually has both a diaphragm and a bell. The earpieces should be angled forward, aligning with the natural curve of the ear canals, to create a snug seal and minimize external noise interference. Check that the chest piece is properly rotated to the desired side and that the tubing is free from blockages that could muffle sounds.
A quiet environment is important for effective auscultation, as ambient noise can interfere with subtle body sounds. Patient positioning also plays a role in obtaining clear sounds. For heart and lung auscultation, the patient should ideally be sitting upright in a relaxed position, if possible. This posture helps to optimize the expansion of the chest and the audibility of internal sounds.
Heart Sound Placement
Listening to heart sounds involves placing the stethoscope over specific anatomical landmarks on the chest, where sounds from the heart valves are best heard. These locations are where sounds are best transmitted to the chest wall, not directly over the valves themselves. The diaphragm side of the stethoscope is generally used for heart sounds due to its effectiveness in transmitting higher frequency sounds, such as normal heart sounds (S1 and S2).
To locate these points, a systematic approach is helpful. The right second intercostal space (the space between the second and third ribs) near the sternum is the aortic area, where sounds from the aortic valve are best heard. Moving to the left second intercostal space near the sternum identifies the pulmonic area for hearing the pulmonic valve. Erb’s point, located at the left third intercostal space along the sternal border, is a useful site for hearing both S1 and S2 heart sounds.
Further down on the left side, the tricuspid area is found at the fourth or fifth intercostal space near the lower left sternal border. This location is optimal for sounds from the tricuspid valve. The mitral area, also known as the apex, is located at the fifth intercostal space in the midclavicular line (under the left nipple for many adults). This is where the sounds of the mitral valve are most clearly audible, and it often represents the point of maximal impulse of the heart.
Lung Sound Placement
Auscultating lung sounds requires listening over various regions of the chest, sides, and back to assess all lung lobes. The diaphragm of the stethoscope is typically used for lung sounds, as it is effective for higher-frequency breath sounds. The patient should be sitting upright and instructed to breathe a little deeper than normal through the mouth, which helps to make breath sounds more audible.
On the anterior chest, placement points include above the clavicles to listen to the lung apices, and then systematically moving downwards in a zigzag pattern between the ribs, lateral to the sternum. For example, the second intercostal space can assess upper lobes, while the fourth intercostal space on the right assesses the right middle lobe, and the sixth intercostal space mid-axillary assesses the lower lobes.
For lateral auscultation, the stethoscope is placed in the axillary regions. On the right side, three locations can help assess the upper, middle, and lower lobes, while on the left, two locations cover the upper and lower lobes.
When listening to the posterior chest, avoid placing the stethoscope directly over the scapulae, as this can muffle sounds. The patient can cross their arms to help move the scapulae and expose more lung tissue. Posterior placement begins just above the scapulae to assess the lung apices, then proceeds downwards in a side-to-side, zigzag pattern between the spine and the scapulae. Listening symmetrically at corresponding points on both sides allows for comparison, which is important for identifying any differences in sound.
Other Important Considerations for Accurate Listening
Beyond correct placement, several factors influence the clarity and accuracy of auscultated sounds. Applying appropriate pressure with the chest piece is important. For the diaphragm, a firm but not excessive pressure is needed to flatten the skin and transmit high-pitched sounds effectively. Conversely, when using the bell, designed for low-pitched sounds like certain heart murmurs, only light pressure should be applied, just enough to make a seal without stretching the skin.
Listening directly on the patient’s bare skin is important, as clothing can create rustling noises and dampen internal sounds.
Patient cooperation also contributes to accurate listening, especially for lung sounds. Asking the patient to take deep breaths through their mouth helps to amplify the breath sounds for clearer assessment. Instructing the patient to breathe slowly can prevent hyperventilation or dizziness during prolonged listening.