A stethoscope is a medical instrument used for auscultation. This tool allows practitioners to amplify and isolate acoustic signals generated by the heart, lungs, and other organs. Accurate information about a patient’s health often depends on the precise placement of the stethoscope’s chest piece on the body.
Preparing for Auscultation
Before placing the chest piece, ensure the earpieces are correctly oriented. The metal eartubes are angled to align with the natural slope of the ear canal. Insert the tips pointing forward, toward the listener’s nose, to create an acoustic seal and direct sound effectively. This snug fit also blocks out distracting ambient noise.
The chest piece typically has two sides, a diaphragm and a bell, designed to capture different sound frequencies. The diaphragm is the larger, flat side used for high-frequency sounds, such as normal heartbeats and most lung sounds. Firm pressure is applied to the skin, which stretches the membrane to better transmit these higher-pitched vibrations.
The bell is the smaller, cup-shaped side designed to detect low-frequency sounds, including certain heart murmurs and extra heart sounds (S3 and S4). Use the bell by placing it very lightly on the skin, forming a seal without significant pressure. Applying too much pressure stretches the skin, effectively turning the bell into a diaphragm and filtering out the low-frequency sounds.
Locating Heart Sounds
Heart auscultation involves listening over the four primary valve areas, which are points on the chest where valve sounds are best transmitted. These areas do not correspond exactly to the anatomical location of the valves but rather to where the sounds are projected most clearly through the chest wall.
Aortic and Pulmonic Areas
The Aortic area is located at the second intercostal space just to the right of the sternum. Moving directly across the sternum to the second intercostal space on the left side brings the listener to the Pulmonic area. Both of these areas allow for clear listening of the semilunar valves, which are responsible for the second heart sound, often described as the “dub” sound.
Tricuspid and Mitral Areas
The Tricuspid area is found at the lower left sternal border, usually around the fourth intercostal space. This position is best for hearing the closure of the tricuspid valve, which contributes to the first heart sound, or the “lub” sound. The Mitral area, also known as the cardiac apex, is located at the fifth intercostal space on the left side, along the midclavicular line. This spot is closest to the heart’s strongest point of pulsation and is where the mitral valve sounds are most distinct.
Listening to Lung Fields
A thorough lung assessment requires placing the stethoscope over the anterior, posterior, and lateral chest walls. Systematic placement ensures all lung lobes are evaluated, as sounds vary across regions. The diaphragm is generally used for this assessment, as lung sounds are high-frequency.
On the patient’s back, place the stethoscope in a ladder pattern, moving from the top of the lungs down to the base. Compare symmetrical points on the left and right sides of the chest to identify differences in airflow. Avoid placing the chest piece directly over the scapulae or the spinal column, as bone obstructs sound transmission.
Anteriorly, placement starts above the clavicles to listen to the apex and continues downward through the intercostal spaces. In female patients, gently displace breast tissue to ensure the stethoscope is placed directly on the chest wall. To evaluate the lateral lung fields, place the stethoscope along the sides of the chest near the midaxillary line, with the patient’s arm raised. Instruct the patient to breathe deeply through an open mouth, which maximizes the audibility of breath sounds.
Non-Cardiopulmonary Uses
Beyond the heart and lungs, the stethoscope evaluates blood flow and digestive function. A common application is measuring blood pressure, which involves placing the chest piece over the brachial artery. This artery is located in the antecubital fossa, the triangular area on the anterior side of the elbow.
Place the stethoscope directly over the artery, just below the blood pressure cuff. Light pressure, typically using the bell, detects the low-pitched Korotkoff sounds that signal systolic and diastolic pressures. Avoid pressing too firmly, which distorts the sounds, or placing the chest piece underneath the cuff, which leads to inaccurate measurements.
Auscultation of the abdomen is another frequent use for listening to bowel sounds. The abdomen is divided into four quadrants, and the stethoscope is systematically placed in each one. The diaphragm is generally used to detect the high-frequency gurgling and clicking sounds produced by peristalsis. Listening begins to the right of the umbilicus, over the small bowel, before proceeding to the other quadrants.