Inflammation physiopathology
Physiopathology
The main asthma mechanism is caused by the reduction of the caliber of the airway. Factors that may contribute to this are enlargement of the bronchial wall caused by edema and cellular infiltration. Every time a major inflammation trigger appears (as it happens when there is a viral infection), the reduction of the bronchial caliber will increase the resistance of the airway, with a reduction in the expiration flow and air entrapment with pulmonary hyperinflation. These changes are related to the increase of respiratory work, altering the ventilation/perfusion ratio, and according to the severity, hypoxemia in the beginning. Only if the obstructive phenomenon progresses until it surpasses the capacity of the respiratory muscles does it cause fatigue and alveolar hypoventilation with global respiratory failure.
The degree of BHR is related to the degree of present inflammation and the enlargement of the bronchial wall. Respiratory infections are the most frequent trigger of asthma crisis for all ages, especially in children that present with episodic disease. In infants and preschoolers, respiratory syncytial virus, rhinovirus, and parainfluenza virus are the most common triggers.
Clinical Aspects
Asthma is a chronic disease with one of the highest prevalence rates in childhood, and it is the most important cause of school absenteeism and frequent hospitalizations, with a corresponding high cost for health systems.
Because of the edema, bronchospasm, and increase of bronchial secretions, the most common symptoms of asthma appear: cough, chest whistle and rhonchus, chest oppression, and various degrees of respiratory failure. If symptoms progress, the patient will present an acute asthma crisis that will be proportional to the degree of airway obstruction. To measure the intensity of the compromise of the airway, clinical scores have been designed, plus pulse oximetry.
A complete clinical evaluation is always important, with a detailed anamnesis and a good physical examination. Laboratory tests can be useful because they help determine the severity of the obstruction. In the periods between episodes, the patient may present no symptoms or signs.
There is no unique phenotype for asthma in children, and therefore the initial symptoms may be unspecific. During the first years, asthma can be presented as a crisis of cough and wheezing that are indistinguishable from infant transient or early wheezing. Nevertheless, the diagnosis of asthma can be suspected if there is also a persistent rhinitis, an atopic dermatitis, asthma family history, and a good clinical response to inhaled salbutamol. A predictor index (API+) can certify an atopic asthma, although this is not as useful for non-atopic asthmatics.
Children may only present with persistent cough, which may be dry or productive, and in the lung examination a prolonged exhalation along with rhonchus, without wheezing. Sometimes it is recommended to manually compress the chest during exhalation to evidence the presence of wheezing that is not perceptible during auscultation. In children who are under 3 months old, a small airway obstruction may produce crackles instead of the expected wheezing, which can still be treated with inhaled salbutamol.
If the child has no symptoms, the appearance of cough and/or wheezing during playtime, laughing, crying, cold, smoke exposure, and excitement is a strong indicator of a diagnosis based on bronchial hyperreactivity, and it constitutes a good parameter for treatment efficacy. It is convenient to ask if there is a seasonal prevalence, specially during spring, which would indicate pollen allergy.
Allergic rhinitis signs tend to coexist and are usually underrated, but they will increase their intensity as the child grows. Allergic conjunctivitis may also be present.
During an asthma crisis the child is usually agitated, has difficulty speaking and feeding, with orthopnea, anguish, chest oppression, feeling of lack of air or suffocation, tachypnea, intense chest retraction, hyperresonant chest, easily heard wheezing, sometimes crackling from small airway obstruction, and reduction of pulmonary murmur in the most severe cases, along with cyanosis and alteration in consciousness.
Asthma Clinical Spectrum
Recurrent wheezing syndrome in infants or preschoolers, or atopic or non-atopic persistent wheezing, which can be reversed with the use of inhaled beta-agonist.
Recurrent obstructive acute laryngitis in infants and preschoolers, alternating with episodes of recurrent wheezing.
Classic asthma, with its cough and chest wheezing exacerbations. Respiratory distress may be absent or present.
Exercise-induced asthma in teenagers as the only symptom, as the consequence of BHR (characteristic feature of more severe asthma), and night asthma caused by greater fluctuations of the peak expiratory flow (PEF), along reduction of pulmonary function during early morning.
Chronic cough, recurrent tracheitis that is alarming to the family. Methacholine test may be positive, which helps confirm the diagnosis.
Allergic chronic rhinitis, chronic rhinosinusitis, recurrent hoarseness from posterior discharge, which in a child may cause oral breathing. Snoring may also be present.
Recurrent pneumonia (pneumonia or pseudo-pneumonia, atelectasis).
A 4-year follow-up in newborns showed that among children who did not present with wheezing only 11% was complicated with pneumonia; in contrast, 78% of the children who had persistent wheezing presented with pneumonia.
Differential Diagnosis
If the patient’s asthma does not respond to treatment, among other matters it is convenient to confirm the diagnosis and rule out other causes that may secondarily cause an obstructive bronchial syndrome, such as cystic fibrosis, foreign body aspiration, heart disease, bronchopulmonary dysplasia, ciliary dyskinesia, voice cord malfunction, or malformations of the airway that may go unnoticed if there is no clinical suspicion.
Diagnosis
In children, asthma diagnosis is mainly clinical, especially if the child is under 5 years old, although it can be suspected in an infant. Diagnosis is based on the presence of at least three episodes with a suggestive clinical condition: cough crisis, wheezing, and chest rhonchus with spontaneous improvement, or if a good response to inhaled salbutamol is confirmed. In the older child, paleness, allergic shiners, presence of the Morgagni fold, rough skin, and hyperkeratosis in the extension surface of limbs, with allergic rhinitis, are seen. The functional diagnosis can benefit from laboratory tests that may confirm the clinical suspicion, such as spirometry and flow measurement, which show the reduction of the exhalation flow rates, especially for FEV1, Tiffeneau (FEV1/FVC) under 70%, and a significant response to salbutamol. Bronchial challenge tests, such as the exercise test, must also be considered if they show drops more than 15% in the PEF and more than 10% for the VEF1. Chest X-rays may also be useful, as they can rule out complications and support the differential diagnosis.
Clinical score in infants and preschoolers
Score | Respiratory frequency | Wheezing | Cyanosis | Use of accessory muscles | |
|---|---|---|---|---|---|
<6 m | >6 m | ||||
0 | <40 | <30 | No | No | No |
1 | 41–55 | 31–45 | Expiration only | Perioral with crying | + |
2 | 56–70 | 46–60 | Inspiration and expiration | Perioral at rest | ++ |
3 | 70 | >60 | Inspiration and expiration at distance | Generalized at rest | +++ |
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