Tyler Wynn
Breath sounds are the noises produced by the structures of the lungs during breathing. Normal breath sounds are classified as bronchial, vesicular, or bronchovesicular, each with distinct acoustic properties based on the anatomical characteristics of the location being auscultated. Vesicular breath sounds are typically described as soft and low-pitched, with an inspiratory/expiratory ratio (I:E) of about 2:1 and a short expiration without any pause between inspiration and expiration. However, in the context of mechanically ventilated patients, the term vesicular breath sounds may not be accurate. This is because mechanical ventilation involves pushing air directly into the trachea through a narrow tube, generating much higher flow rates than normal quiet breathing, and resulting in different flow patterns that are unlikely to produce the soft and low-pitched sounds characteristic of vesicular breath sounds.
| Characteristics | Values |
|---|---|
| Normal breath sounds | Vesicular, bronchial, or bronchovesicular |
| Vesicular breath sounds | Soft, low-pitched (200 Hz), with an inspiratory/expiratory ratio (I:E) of about 2:1 |
| Bronchial breath sounds | Loud |
| Vesicular breath sounds flow rates | 5-10 L/min at rest, up to 30-40 L/min during exercise |
| Mechanical ventilation flow rates | Up to 240 L/min |
| Mechanical ventilation flow pattern | Descending or square wave ramp, rarely ascending ramp |
| Mechanical ventilation I:E ratio | 1:2 |
| Mechanical ventilation inspiratory pause | Set by default |
| Mechanical ventilation dead space | Additional tubing trapping exhaled CO2 |
| Mechanical ventilation PEEP | Adds back pressure during exhalation to keep lungs open |
| Mechanical ventilation sensitivity | Controls how hard or easy it is for the patient to inhale |
| Mechanical ventilation end-tidal volume | Amount of air lungs return to ventilator during exhalation |
| Mechanical ventilation high-pressure alarm | Sounds when pressure in the circuit increases |
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What You'll Learn
Vesicular breath sounds
The intensity of vesicular breath sounds can be graded on a scale from 0 to 4, with zero being absent and four being louder than normal. The intensity of these sounds can provide clinical insights, as greater intensity can indicate more profound ventilation, while quieter breath sounds may suggest decreased ventilation or the progression of a disease such as asthma.
It is important to note that while vesicular breath sounds are generally considered normal, changes or abnormalities in these sounds can be indicative of a lung condition or an underlying illness. These abnormal breath sounds are referred to as adventitious and may include crackles, wheezes, rhonchi, and other additional noises. Conditions such as asthma, COPD, bronchitis, and chest infections can cause deviations from typical vesicular breath sounds.
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Mechanical breath sounds
The breath sounds produced by mechanical ventilation differ from those of normal respiratory physiology. During natural inhalation, the diaphragm muscle contracts and the chest expands, creating a vacuum that pulls air into the lungs. Conversely, mechanical ventilation works by pushing air into the lungs until a pre-set volume or pressure is reached, after which the air passively leaves the lungs. This difference in airflow patterns results in distinct breath sounds.
In mechanically ventilated patients with normal lungs, the minimal inspiratory flow rate ranges between 45 and 60 L/min. However, in cases with leaks or acute respiratory distress syndromes (ARDS), peak inspiratory flow rates can reach up to 200 L/min. The normal physiological flow pattern is sinusoidal, while the flow patterns in ventilators are typically of a descending or square wave pattern, rarely ascending. This alteration in gas delivery generates turbulent flow, resulting in breath sounds that differ from the soft and low-pitched vesicular breath sounds typically associated with healthy lungs.
The term "vesicular" breath sounds has been contested in the context of mechanical ventilation. It is argued that the breath sounds heard in mechanically ventilated patients should be termed "usual ventilatory breath sounds" or "mechanical breath sounds" to distinguish them from the vesicular breath sounds of normal respiratory physiology. Vesicular breath sounds are characterised as soft, low-pitched (<200 Hz), with an inspiratory/expiratory ratio (I:E) of approximately 2:1, and a short expiration without a pause between inspiration and expiration. The usual flow rates during rest range from 5-10 L/min, while during exercise, they can reach up to 30-40 L/min.
In conclusion, mechanical breath sounds refer to the breath sounds produced by mechanical ventilation, which differ from normal respiratory breath sounds due to variations in airflow patterns and physiological factors. The term "mechanical breath sounds" is preferred over "vesicular" to accurately describe the breath sounds of mechanically ventilated patients.
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Mechanical ventilation vs natural breathing
Mechanical ventilation is a device that breathes for someone who is unable to breathe independently. It is a form of life support that helps patients breathe when they cannot do so on their own. Mechanical ventilation keeps the airways open, delivers oxygen, and removes carbon dioxide. It provides pressure to prevent the alveoli, the small air sacs in the lungs, from collapsing.
During natural inhalation, the diaphragm muscle contracts and the chest expands, creating a vacuum that pulls air into the lungs. Conversely, mechanical ventilation pushes air into the lungs until a pre-set volume or pressure is reached. Once the lungs are full, the ventilator stops pushing air, and the air passively leaves the lungs.
Mechanical ventilation differs from natural breathing in the way air reaches the trachea. During natural breathing, air passes through various humidification systems, such as the nose and sinuses, before reaching the trachea. In contrast, mechanical ventilation pushes air/oxygen directly through a narrow tube to the trachea, generating flows of up to 240 L/min.
The breath sounds produced by mechanical ventilation are also distinct from those of natural breathing. Vesicular breath sounds, typically described as soft and low-pitched, are challenging to detect in mechanically ventilated patients due to differences in flow patterns. Instead, breath sounds associated with mechanical ventilation are often termed "usual ventilator breath sounds" or "mechanical breath sounds," characterized by turbulent flow and an altered gas delivery mechanism.
Mechanical ventilation is typically a temporary measure, used during surgery, in intensive care settings, or when an individual is very ill, to stabilize the patient while other treatments are administered. The duration of mechanical ventilation can vary from hours to months, depending on the patient's condition and progress.
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High-pressure alarms
Mechanical ventilators are equipped with several alarms, including high-pressure alarms, which are the most common type. High-pressure alarms are triggered when the pressure in the circuit exceeds a preset limit during the inspiratory phase of breathing. Typically, this limit is set approximately 10 cmH2O above the peak inspiratory pressure (PIP).
Other causes of high-pressure alarms include pulmonary conditions such as pulmonary edema, pneumothorax, and bronchospasm, which can increase airway resistance or decrease lung compliance. In such cases, it is important to consult a physician or skilled clinician. Additionally, factors such as coughing, gagging, or excess secretions can trigger the alarm, requiring suctioning of the patient.
To troubleshoot a high-pressure alarm, it is recommended to perform endotracheal suctioning if necessary and to insert a bite block or pharyngeal airway to prevent the patient from biting the tube. Any kinks in the circuit should be rectified, and the endotracheal tube should be repositioned if it is not correctly placed. Water in the circuit should be removed, and patient-ventilator asynchrony should be evaluated and addressed. Inspecting for a malfunction of the inspiratory or expiratory valves is also crucial.
It is important to address high-pressure alarms promptly to ensure patient safety and maintain effective ventilatory support.
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Abnormal breath sounds
Breath sounds are the noises produced by the structures of the lungs during breathing. When lungs are functioning normally, they create a smooth, soft sound when breathing in and out. These are also called vesicular lung sounds. Vesicular lung sounds usually mean that there is nothing blocking the airways, and they are fully open (not narrowed or swollen).
However, there are instances when abnormal breath sounds can be heard. These abnormal breath sounds are also called adventitious sounds. They can be described as crackling, rattling, clicking, whistling, gurgling, or other noises. The most common abnormal lung sounds include rhonchi, crackles (rales), and pleural rub. Rhonchi are continuous, low-pitched sounds that are best heard when breathing out. The sound might move around to different parts of the chest when the patient coughs, moving mucus around. It is sometimes described as snoring or gurgling. A wheeze, on the other hand, is a continuous, high-pitched hissing sound. It is more commonly heard when breathing out but can sometimes be heard when breathing in, especially in patients with asthma. A pleural rub is a rough, grating sound caused by the lining of the lungs (pleurae) rubbing against each other. It is usually louder than other lung sounds due to its generation closer to the chest wall.
The presence of abnormal breath sounds can indicate underlying conditions or pathology. For example, the presence of bronchial breath sounds outside their normal geographic territory on the chest can indicate pulmonary consolidation or collapse. The ease of transmission of certain frequency sounds can also change with pathology. In patients with lobar pneumonia, the normally air-filled lung instead contains fluid, which transmits sounds better than air, resulting in increased vocal resonance. Other conditions that can cause abnormal lung sounds include respiratory infections such as bronchitis or croup, chronic obstructive pulmonary disease (COPD), cystic fibrosis, anaphylaxis, foreign objects, pulmonary edema, and interstitial lung disease.
It is important to note that a provider cannot diagnose a patient based solely on lung sounds. They will consider other factors such as symptoms, health history, and additional tests to understand the underlying cause of the abnormal breath sounds.
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Frequently asked questions
Breath sounds are the noises produced by the structures of the lungs during breathing. They are best heard with a stethoscope, a process called auscultation. Normal breath sounds occur in all parts of the chest area, including above the collarbones and at the bottom of the rib cage.
Normal breath sounds are classified as bronchial, vesicular, or bronchovesicular, each with different acoustic properties based on the anatomical characteristics of the location being auscultated. Vesicular sounds are usually soft and low-pitched, with an inspiratory/expiratory ratio (I:E) of about 2:1. Vesicular sounds indicate that there is nothing blocking the airways, and they are fully open (not narrowed or swollen).
Mechanical ventilation is different from natural breathing. During natural inhalation, the diaphragm muscle contracts and the chest expands, creating a vacuum that pulls air into the lungs. A ventilator, on the other hand, works by pushing air into the lungs until it reaches a pre-set volume or pressure. Due to these differences, the breath sounds produced by a mechanically ventilated patient are not considered "normal" or "vesicular". Instead, they are referred to as "usual ventilator breath sounds" or "mechanical breath sounds".
