Wheezing is a relatively high-pitched whistling noise produced by movement of air through narrowed or compressed small airways. It is a symptom as well as a physical finding.
Pathophysiology of Wheezing
Airflow through a narrowed or compressed segment of a small airway becomes turbulent, causing vibration of airway walls; this vibration produces the sound of wheezing.
Wheezing is more common during expiration because increased intrathoracic pressure during this phase narrows the airways and airways narrow as lung volume decreases. Wheezing during expiration alone indicates milder obstruction than wheezing during both inspiration and expiration, which suggests more severe airway narrowing.
By contrast, turbulent flow of air through a narrowed segment of the large, extrathoracic airways produces a whistling inspiratory noise ( stridor Stridor Stridor is a high-pitched, predominantly inspiratory sound. It is most commonly associated with acute disorders, such as foreign body aspiration, but can be due to more chronic disorders, such... read more ).
Etiology of Wheezing
Small airway narrowing may be caused by bronchoconstriction, mucosal edema, or external compression, or partial obstruction by a tumor, foreign body, or thick secretions.
Overall, the most common causes are
COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more (chronic obstructive pulmonary disease)
But wheezing may occur in other disorders affecting the small airways, including heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more (cardiac asthma), allergic reactions, including anaphylaxis Anaphylaxis Anaphylaxis is an acute, potentially life-threatening, IgE-mediated allergic reaction that occurs in previously sensitized people when they are reexposed to the sensitizing antigen. Symptoms... read more , and toxic inhalation Irritant Gas Inhalation Injury Irritant gases are those which, when inhaled, dissolve in the water of the respiratory tract mucosa and cause an inflammatory response, usually due to the release of acidic or alkaline radicals... read more . Sometimes, healthy patients manifest wheezing during a bout of acute bronchitis Acute Bronchitis Acute bronchitis is inflammation of the tracheobronchial tree, commonly following an upper respiratory infection that occurs in patients without chronic lung disorders The cause is almost always... read more . In children, bronchiolitis Bronchiolitis Bronchiolitis is an acute viral infection of the lower respiratory tract affecting infants 24 months and is characterized by respiratory distress, wheezing, and/or crackles. Diagnosis is suspected... read more and foreign body aspiration are also causes (see table Some Causes of Wheezing Some Causes of Wheezing ).
Evaluation of Wheezing
When patients are in significant respiratory distress, evaluation and treatment proceed at the same time.
History of present illness should determine whether the wheezing is new or recurrent. If recurrent, patients are asked the previous diagnosis and whether current symptoms are different in nature or severity. Particularly when the diagnosis is unclear, the acuity of onset (eg, abrupt or gradual), temporal patterns (eg, persistent vs intermittent, seasonal variations), and provoking or exacerbating factors (eg, current upper respiratory infection, allergen exposure, cold air, exercise, feeding in infants) are noted. Important associated symptoms include shortness of breath, fever, cough, and sputum production.
Review of systems should seek symptoms and signs of causative disorders, including fever, sore throat, and rhinorrhea (respiratory infection); orthopnea, paroxysmal nocturnal dyspnea, and peripheral edema ( heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more ); night sweats, weight loss, and fatigue (cancer); nasal congestion, itching eyes, sneezing, and rash (allergic reaction); and vomiting, heartburn, and swallowing difficulties ( gastroesophageal reflux disease Gastroesophageal Reflux Disease (GERD) Incompetence of the lower esophageal sphincter allows reflux of gastric contents into the esophagus, causing burning pain. Prolonged reflux may lead to esophagitis, stricture, and rarely metaplasia... read more with aspiration).
Past medical history should ask about conditions known to cause wheezing, particularly asthma, COPD, and heart failure. Sometimes the patient’s drug list may be the only indication of such diagnoses (eg, inhaled bronchodilators and corticosteroids in COPD; diuretics and angiotensin-converting enzyme inhibitors in heart failure). Patients with known disease should be asked about indicators of disease severity, such as previous hospitalization, intubation, or intensive care unit admission. Also, conditions that predispose to heart failure are identified, including atherosclerotic or congenital heart disease and hypertension. Smoking history and exposure to secondhand smoke should be noted.
Vital signs are reviewed for presence of fever, tachycardia, tachypnea, and low oxygen saturation.
Any signs of respiratory distress (eg, accessory muscle use, intercostal retractions, pursed lip breathing, agitation, cyanosis, decreased level of consciousness) should be immediately noted.
Examination focuses on the lungs, particularly adequacy of air entry and exit, symmetry of breath sounds, and localization of wheezing (diffuse vs localized; inspiratory, expiratory, or both). Any signs of consolidation (eg, egophony, dullness to percussion) or crackles should be noted.
The cardiac examination should focus on findings that might indicate heart failure, such as murmurs, a 3rd heart sound (S3 gallop), and jugular venous distention.
The nose and throat examination should note appearance of the nasal mucosa (eg, color, congestion), swelling of the face or tongue, and signs of rhinitis, sinusitis, or nasal polyps.
The extremities are examined for clubbing and edema, and the skin is examined for signs of allergic reactions (eg, urticaria, rash) or atopy (eg, eczema). The patient’s general appearance is noted for constitutional signs, such as the cachexia and barrel chest of severe COPD.
The following findings are of particular concern:
Accessory muscle use, clinical signs of tiring, or decreased level of consciousness
Fixed inspiratory and expiratory wheezing
Swelling of the face and tongue (angioedema)
Interpretation of findings
Recurrent wheezing in a patient with a known history of disorders such as asthma, COPD, or heart failure is usually presumed to represent an exacerbation. In patients who have both lung and heart disease, manifestations may be similar (eg, neck vein distention and peripheral edema in cor pulmonale due to COPD and in heart failure), and the exact etiology is often hard to determine. When the cause is known asthma or COPD, a history of cough, postnasal drip, or exposure to allergens or to toxic or irritant gases (eg, cold air, dust, tobacco smoke, perfumes) may suggest a trigger.
Acute (sudden-onset) wheezing in the absence of symptoms of an upper respiratory infection (URI) suggests an allergic reaction or impending anaphylaxis, especially if urticaria or angioedema is present. Fever and URI symptoms suggest infection, acute bronchitis in older children and adults, and bronchiolitis in children < 2 years. Crackles, distended neck veins, and peripheral edema suggest heart failure. Association of wheezing with feeding or vomiting in infants can be a result of gastroesophageal reflux.
Patients with asthma usually have paroxysmal or intermittent bouts of acute wheezing.
Persistent, localized wheezing suggests focal bronchial obstruction by a tumor or foreign body. Persistent wheezing manifesting very early in life suggests a congenital or structural abnormality. Persistent wheezing with sudden onset is consistent with foreign body aspiration, whereas the slowly progressive onset of wheezing may be a sign of extraluminal bronchial compression by a growing tumor or lymph node.
Testing seeks to assess severity, determine diagnosis, and identify complications.
Chest x-ray (if diagnosis unclear)
Sometimes arterial blood gas (ABG) measurement
Sometimes pulmonary function testing
Severity is assessed by pulse oximetry and, in patients with respiratory distress or clinical signs of tiring, ABG testing. Patients known to have asthma usually have bedside peak flow measurements (or, when available, forced expiratory volume in 1 second [FEV1]).
Patients with new-onset or undiagnosed persistent wheezing should have a chest x-ray. X-ray can be deferred in patients with asthma who are having a typical exacerbation and in patients having an obvious allergic reaction. Cardiomegaly, pleural effusion, and fluid in the major fissure suggest heart failure. Hyperinflation and hyperlucency suggest COPD. Segmental or subsegmental atelectasis or infiltrate suggests an obstructing endobronchial lesion. Radiopacity in the airways or focal areas of hyperinflation suggest a foreign body.
If the diagnosis is unclear in patients with recurrent wheezing, pulmonary function testing can confirm airflow limitation and quantify its reversibility and severity. Methacholine challenge testing and exercise testing can confirm airway hyperreactivity in patients for whom the diagnosis of asthma is in question.
Treatment of Wheezing
Definitive treatment of wheezing is treatment of underlying disorders.
Wheezing itself can be relieved with inhaled bronchodilators (eg, albuterol 2.5 mg nebulized solution or 108 mcg metered dose inhalation). Long-term control of persistent asthmatic wheezing may require inhaled corticosteroids, long-acting beta agonists, leukotriene inhibitors, or other therapies.
Intravenous H2 blockers (diphenhydramine), corticosteroids (methylprednisolone), and subcutaneous and inhaled racemic epinephrine are indicated in cases of anaphylaxis.
Asthma is the most common cause, but not all wheezing is asthma.
Acute onset of wheezing in a patient without a lung disorder may be due to aspiration, allergic reaction, or heart failure.
Reactive airway disease can be confirmed via spirometry.
Inhaled bronchodilators are the mainstay of acute treatment.
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