Bronchodilators 29-Nov-2017
Adrenoceptor agonists (sympathomimetics)
Selective beta 2 agonists produce bronchodilation. A short-
acting beta 2 agonist (such as salbutamol p. 156 and
terbutaline sulfate p. 158 ) is used for immediate relief of
asthma symptoms while a long-acting beta 2 agonist is used
in addition to an inhaled corticosteroid in children requiring
prophylactic treatment.
Adrenaline/epinephrine p. 136 (which has both alpha-and
beta-adrenoceptor agonist properties) is used in the
emergency management of acute allergic and anaphylactic
reactions, in angioedema, and in cardiopulmonary
resuscitation; it is also used as a nebuliser solution to treat
severe croup.
Long-acting beta 2 agonists
Formoterol fumarate p. 154 and salmeterol p. 155 are longer-
acting beta 2 agonists which are administered by inhalation.
They should be used for asthma only in children who
regularly use an inhaled corticosteroid.
Vilanterol is a long-acting beta 2 agonist available in a
combination inhaler withfluticasone furoate.
Combination inhalers that contain a long-acting beta 2
agonist and a corticosteroid ensure that long-acting beta 2
agonists are not used without concomitant corticosteroids.
Oral
Oral preparations of beta 2 agonists may be used for children
if an inhaler device cannot be used but inhaled beta 2 agonists
are more effective and have fewer side-effects.
Parenteral
Beta 2 agonists can be given intravenously in children with
severe or life-threatening acute asthma.
Antimuscarinic bronchodilators
Ipratropium bromide p. 153 by nebulisation can be added to
other standard treatment in life-threatening acute asthma or
if acute asthma fails to improve with standard therapy.
Ipratropium bromide can be used to provide short-term
relief in chronic asthma, but short-acting beta 2 agonists act
more quickly and are preferred.
The aerosol inhalation of ipratropium bromide has a
maximum effect 30 – 60 minutes after use; its duration of
action is 3 to 6 hours.
Theophylline
Theophylline p. 169 is a xanthine used as a bronchodilator in
asthma. It may have an additive effect when used in
conjunction with small doses of beta 2 agonists; the
combination may increase the risk of side-effects, including
hypokalaemia.
Theophylline is given by injection as aminophylline p. 167 ,
a mixture of theophylline with ethylenediamine, which is
20 times more soluble than theophylline alone.
Aminophylline injection is needed rarely for severe acute
asthma.
Compound bronchodilator preparations
In general, children are best treated with single-ingredient
preparations, such as a selective beta 2 agonist or ipratropium
bromide, so that the dose of each drug can be adjusted.
Oxygen
Overview
Oxygen should be regarded as a drug. It is prescribed for
hypoxaemic patients to increase alveolar oxygen tension and
decrease the work of breathing. The concentration of oxygen
required depends on the condition being treated;
administration of an inappropriate concentration of oxygen
may have serious or even fatal consequences. High
concentrations of oxygen can cause pulmonary epithelial
damage (bronchopulmonary dysplasia), convulsions, and
retinal damage, especially in preterm neonates.
Oxygen is probably the most common drug used in
medical emergencies. It should be prescribed initially to
achieve a normal or near-normal oxygen saturation. In most
acutely ill children with an expected or known normal or low
arterial carbon dioxide (PaCO 2 ), oxygen saturation should be
maintained above 92 %; some clinicians may aim for a target
of 94 – 98 %. In some clinical situations, such as carbon
monoxide poisoning, it is more appropriate to aim for the
highest possible oxygen saturation until the child is stable.
Hypercapnic respiratory failure is rare in children; in those
children at risk, a lower oxygen saturation target of 88 – 92 %
is indicated.
High concentration oxygen therapyis safe in uncomplicated
cases of conditions such as pneumonia, pulmonary
thromboembolism, pulmonaryfibrosis, shock, severe
trauma, sepsis, or anaphylaxis. In such conditions low
arterial oxygen (PaO 2 ) is usually associated with low or
normal arterial carbon dioxide (PaCO 2 ), and therefore there
is little risk of hypoventilation and carbon dioxide retention.
In severe acute asthma, the arterial carbon dioxide (Pa
CO 2 ) is usually subnormal but as asthma deteriorates it may
rise steeply (particularly in children). These patients usually
require high concentrations of oxygen and if the arterial
carbon dioxide (PaCO 2 ) remains high despite other
treatment, intermittent positive-pressure ventilation needs
to be considered urgently.
Oxygen should not be given to neonates except under
expert supervision. Particular care is required in preterm
neonates because of the risk of hyperoxia.
Low concentration oxygen therapy(controlled oxygen
therapy) is reserved for children at risk of hypercapnic
respiratory failure, which is more likely in children with:
.advanced cysticfibrosis
.advanced non-cysticfibrosis bronchiectasis
.severe kyphoscoliosis or severe ankylosing spondylitis
.severe lung scarring caused by tuberculosis
.musculoskeletal disorders with respiratory weakness,
especially if on home ventilation
.an overdose of opioids, benzodiazepines, or other drugs
causing respiratory depression.
Until blood gases can be measured, initial oxygen should be
given using a controlled concentration of 28 % or less,
titrated towards a target concentration of 88 – 92 %. The aim
is to provide the child with enough oxygen to achieve an
acceptable arterial oxygen tension without worsening carbon
dioxide retention and respiratory acidosis.Domiciliary oxygen
Oxygen should only be prescribed for use in the home after
careful evaluation in hospital by a respiratory care specialist.
Carers and children who smoke should be advised of the risks
of smoking when receiving oxygen, including the risk offire.
Smoking cessation therapy should be recommended before
home oxygen prescription.Long-term oxygen therapy
The aim of long-term oxygen therapy is to maintain oxygen
saturation of at least 92 %. Children (especially those with
chronic neonatal lung disease) often require supplemental
oxygen, either for 24 -hours a day or during periods of sleep;
many children are eventually weaned off long-term oxygen
therapy as their condition improves.
Long-term oxygen therapy should be considered for
children with conditions such as:
.bronchopulmonary dysplasia (chronic neonatal lung
disease);
.congenital heart disease with pulmonary hypertension;
.pulmonary hypertension secondary to pulmonary disease;BNFC 2018 – 2019 Airways disease, obstructive 151
Respiratory system3