Cough
A sudden explosive expiratory maneuver that tends
to clear material (sputum) from the airways.
Coughing helps protect the lungs against aspiration.
Differences among several sites from which cough stimuli can
originate may result in variations in the sounds and patterns of
coughing. Laryngeal stimulation produces a choking type of cough
without a preceding inspiration. Inadequate mucociliary clearance
mechanisms (as in bronchiectasis or cystic fibrosis) may produce a
pattern of coughing with less violent acceleration of air and a
sequence of interrupted expirations without any intervening
inspiration. Awareness of cough varies considerably. A cough can be
distressing when it appears suddenly, especially if associated with
discomfort due to chest pain, dyspnea, or copious secretions. A
cough that develops over decades (eg, in a smoker with mild chronic
bronchitis) may be hardly noticeable or may be considered normal by
the patient.
Questions should determine how long cough has been
present, whether it began suddenly, if it has changed recently, what
factors influence it (eg, cold air, talking, posture, eating or
drinking, time of day), and whether it is associated with sputum
production, chest or retrosternal or throat pain, dyspnea,
hoarseness, dizziness, or other symptoms. The patient should be
asked what he thinks causes it; he may say "something in my lungs
that needs to be coughed up" or "something tickling the back of my
throat." Patterns of coughing or precipitating factors may be a clue
to its cause; eg, the patient may have noted an association with
work or exercise. A cough induced by postural change may suggest
chronic lung abscess, cavitary TB, bronchiectasis, or a pedunculated
tumor, whereas a cough associated with eating suggests a disturbance
of the swallowing mechanism or possibly a tracheoesophageal fistula.
A cough that appears on exposure to cold air or during exercise may
suggest asthma. A morning cough persisting until sputum is
expectorated typifies chronic bronchitis. A cough that is associated
with rhinitis or wheezing or that is seasonal may be an allergic
response.
During the interview, an alert physician notes
spontaneous coughing, because its sound can yield useful information
(eg, an audible rattle of secretions; the irritable, dry, barking
cough associated with acute tracheitis; or the low-pitched, blowing,
bovine cough without an explosive start heard in a patient with a
paralyzed recurrent laryngeal nerve). A patient who does not cough
spontaneously should be asked to do so after the chest examination.
Waiting until then is advisable because coughing earlier may dispel
secretion sounds or crackles at the bases before they can be
detected. Listening to the patient's lungs over the chest and at his
open mouth both before and after the cough is useful because
movement of secretions may alter physical findings dramatically. On
the other hand, posttussive crackles may appear, particularly over
tuberculous lesions in the upper lobes.
A major function of the cough reflex is to help clear
secretions from the airways, particularly to help expel them through
the larynx. Sputum production should be discussed during the
history; questions about cough and sputum are usually related, but
occasionally someone who denies coughing states that he produces
sputum. Questions can help determine what the sputum looks like and
how easily it is expelled. Changes in character (eg, from clear
white mucus to yellowish, green, or brown purulent material) are
important indicators of infection. Blood streaking and frank
hemoptysis are important and likely to be noted by the patient.
Gritty material in sputum, characteristic of broncholithiasis, may
be less noticeable, and a patient may deny its presence when first
asked but may later notice and report it.
If possible, the patient should expectorate a sputum
specimen during the evaluation. Its gross appearance should be
observed. A microscopic examination of a small drop taken from a
thicker portion of the freshly collected sputum (placed on a glass
slide without staining, compressed with a coverslip, and examined on
low power) can provide useful information. The presence of squamous
cells suggests that the material came from above the larynx; true
sputum expelled from the airways is characterized by the presence of
alveolar macrophages. Wright's stain shows the proportion of
eosinophils; eosinophilia suggests an allergy. Neutrophils
predominate more often in purulent sputum, indicating an
inflammatory, usually infectious process. A Gram stain confirms the
presence of bacteria and is the first step in their
categorization.
Treatment
Treatment of cough mainly consists of treating the
underlying cause. A productive cough should not be suppressed except
in special circumstances (eg, when it exhausts the patient or
prevents rest and sleep) and generally not until the cause has been
identified. Suppressing a productive cough is less advisable because
sputum needs to be cleared. Cough remedies are categorized as
antitussives and expectorants. Mucolytics, proteolytic enzymes,
antihistamines, and bronchodilators are sometimes used.
Antitussives: These drugs may be centrally or peripherally
acting. Centrally acting antitussives inhibit or suppress the cough
reflex by depressing the medullary cough center or associated higher
centers. The most commonly used drugs in this group are
dextromethorphan and codeine.
Dextromethorphan, a congener of the
narcotic analgesic levorphanol, has no significant analgesic or
sedative properties, does not depress respiration in usual doses,
and is nonaddictive. No evidence of tolerance has been found during
long-term use. The average dosage for adults is 15 to 30 mg 1 to 4
times/day, given as a tablet or syrup; for children, 1 mg/kg/day is
given in divided doses. Extremely high doses may depress
respiration.
Codeine, which has antitussive,
analgesic, and slight sedative effects, is especially useful in
relieving painful cough. It also exerts a drying action on the
respiratory mucosa that may be useful (eg, in bronchorrhea) or
deleterious (eg, when bronchial secretions are already viscous). The
average adult dosage is 10 to 20 mg po q 4 to 6 h as required, but
doses as high as 60 mg may be necessary. The usual oral dosage for
children is 1 to 1.5 mg/kg/day in divided doses q 4 to 6 h. Codeine
in these amounts has minimal respiratory depressant effects. Nausea,
vomiting, constipation, tolerance to antitussive as well as
analgesic effects, and physical dependence can occur, but potential
for abuse is low.
Other centrally acting antitussives include
chlophedianol, levopropoxyphene, and noscapine in the nonnarcotic
group and hydrocodone, hydromorphone, methadone, and morphine in the
narcotic group.
Peripherally acting antitussives may act on either the
afferent or the efferent side of the cough reflex. On the afferent
side, an antitussive may reduce the input of stimuli by acting as a
mild analgesic or anesthetic on the respiratory mucosa, by modifying
the output and viscosity of the respiratory tract fluid, or by
relaxing the smooth muscle of the bronchi in the presence of
bronchospasm. On the efferent side, an antitussive may make
secretions easier to cough up by increasing the efficiency of the
cough mechanism. Peripherally acting agents are grouped as
demulcents, local anesthetics, and humidifying aerosols and steam
inhalations.
Demulcents are useful for coughs
originating above the larynx. They form a protective coating over
the irritated pharyngeal mucosa. They are usually given as syrups or
lozenges and include acacia, licorice, glycerin, honey, and wild
cherry syrups.
Local anesthetics (eg, lidocaine,
benzocaine, hexylcaine hydrochloride, and tetracaine) are used to
inhibit the cough reflex under special circumstances (eg, before
bronchoscopy or bronchography). Benzonatate (100 mg po tid), a
congener of tetracaine, is a local anesthetic; its antitussive
effect may be due to a combination of local anesthesia, depression
of pulmonary stretch receptors, and nonspecific central
depression.
Humidifying aerosols and steam
inhalations exert an antitussive effect by acting as a
demulcent and by decreasing the viscosity of bronchial secretions.
Inhaling water as an aerosol or as steam, with or without
medicaments (sodium chloride, compound benzoin tincture,
eucalyptol), is the most common method of humidification. The
efficacy of added medicaments has not been clearly proved.
Expectorants: These drugs are intended to help expel
bronchial secretions from the respiratory tract by decreasing their
viscosity, thus facilitating removal, and by increasing the amount
of respiratory tract fluid, thus exerting a demulcent action on the
mucosal lining. Most expectorants increase secretions through reflex
irritation of the bronchial mucosa. Some, like the iodides, also act
directly on the bronchial secretory cells and are excreted into the
respiratory tract.
The use of expectorants is highly controversial. No
objective experimental data show that any of the available
expectorants decreases sputum viscosity or eases expectoration. Data
may be lacking partly because of inadequate technology for obtaining
such evidence. Thus, the use and choice of expectorants are often
based on tradition and the widespread clinical impression that they
are effective in some circumstances.
Adequate hydration is the single most important
measure that can be taken to encourage expectoration. If it is
unsuccessful, using an expectorant in addition may produce the
desired result.
Iodides are used to liquefy tenacious bronchial
secretions (eg, in late stages of bronchitis, bronchiectasis, and
asthma). A saturated solution of potassium iodide is the least
expensive, most commonly used preparation. The initial dose is 0.5
mL po qid, in a glass of water, juice, or milk after meals and at
bedtime, which is increased gradually to 1 to 4 mL qid. To be
effective, iodides must be taken in doses approaching intolerance.
Their usefulness is limited by low patient acceptance because they
have an unpleasant taste and because side effects (eg, acneiform
skin eruptions, coryza, erythema of face and chest, painful swelling
of the salivary glands) are common. The side effects are reversible
and subside when the drug is stopped. Iodinated glycerol is better
tolerated than potassium iodide solution but is probably less
effective. The usual oral dosage is 60 mg as tablets or elixir qid;
it should be avoided in patients sensitive to iodide.
Prolonged use of iodides or iodinated glycerol can lead to
hypothyroidism.
Syrup of ipecac 0.5 mL po qid (Note:
This is much less than the emetic dose) can be used as an
expectorant in patients sensitive to iodides. It is useful for
relieving laryngeal spasm in children with croup and often clears
thick, tenacious mucus from the bronchi.
Guaifenesin (100 to 200 mg po q 2 to 4 h) is the most
commonly used expectorant in OTC cough remedies. It has no serious
adverse effects, but there is no clear evidence of its
efficacy.
Many other traditional expectorants (eg, ammonium
chloride, terpin hydrate, creosote, squill) are found in numerous
OTC cough remedies. Their efficacy is doubtful, particularly in the
dosages of most preparations.
Less commonly used drugs: Mucolytics (eg,
acetylcysteine) have free sulfhydryl groups that open mucoprotein
disulfide bonds, reducing the viscosity of mucus. As a rule, their
usefulness is restricted to a few special instances such as
liquefying thick, tenacious, mucopurulent secretions (eg, in chronic
bronchitis and cystic fibrosis). Acetylcysteine is given as a 10 to
20% solution by nebulization or instillation. In some patients,
mucolytics may aggravate airway obstruction by causing bronchospasm.
If this occurs, these patients may inhale a nebulized
sympathomimetic bronchodilator or take a formulation containing
acetylcysteine (10%) and isoproterenol (0.05%) before taking the
mucolytic.
Proteolytic enzymes (eg, pancreatic
dornase) are useful only when grossly purulent sputum is a major
problem. They seem to offer no advantage over mucolytics. Local
irritation of the buccal and pharyngeal mucosa and allergic
reactions commonly follow repeated doses. Dornase alfa, the new
highly purified recombinant human deoxyribonuclease I (rhDNase),
seems likely to become important in the treatment of cystic
fibrosis, although its place has not been defined.
Antihistamines have little or no use
in treating cough. Their drying action on the respiratory mucosa may
be helpful in the early congestive phase of acute coryza but may be
deleterious, especially to patients with a nonproductive cough
resulting from retained viscous airway secretions. They may also be
beneficial in chronic cough due to postnasal drip associated with
allergic sinusitis.
Bronchodilators (eg, ephedrine and
theophylline) may be useful if cough is complicated by bronchospasm.
Atropine is undesirable because it thickens bronchial
secretions. The anticholinergic drug ipratropium bromide can often
ameliorate an irritating type of cough and does not adversely affect
mucus secretions. Inhaled corticosteroids have become a mainstay in
the treatment of cough in asthma.
Drug combinations: Many prescription and OTC cough remedies
contain two or more drugs, usually in a syrup. They may include a
centrally acting antitussive, an antihistamine, an expectorant, and
a decongestant. Bronchodilators and antipyretics are also often
present. These combinations are aimed at treating the many symptoms
of an acute URI and should not be used to manage cough alone. Some
antitussive combinations are appropriate for cough (eg, a centrally
acting antitussive, such as dextromethorphan, and a peripherally
acting demulcent syrup for cough originating above the larynx).
However, the components of some combinations (eg, expectorants and
antihistamines) have opposing effects on respiratory tract
secretions, and many combinations contain suboptimal or ineffective
concentrations of potentially useful ingredients.
Choice of drug therapy: As a rule, when cough alone is a major
problem, using a full dose of a single drug aimed at a specific
component of the cough reflex is preferred. For simple suppression
of a nonproductive cough, dextromethorphan is preferred, but codeine
is also useful. The more potent narcotic antitussives should be
reserved for cases in which analgesic and sedative effects are
required and the cause is likely to be temporary. To increase
bronchial secretion and liquefy viscous bronchial fluid, adequate
hydration (by drinking water or inhaling steam) is used; a saturated
solution of potassium iodide or syrup of ipecac given orally may be
tried if hydration alone is unsuccessful. To relieve cough
originating in the pharyngeal region, demulcent syrups or lozenges,
combined if necessary with dextromethorphan, are used. For
bronchoconstriction associated with cough, bronchodilators, possibly
combined with expectorants, are advised; inhaled corticosteroids may
be effective in some cases.
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