Acute episodes of asthma can be mild, moderately severe, or severe, or characterized by imminent respiratory arrest.
During a mild episode, patients may be breathless after physical activity, such as walking; they can talk in sentences and lie down; and they may be agitated. Patients with mild acute asthma are able to lie flat.
In a mild episode, the respiratory rate is increased, and accessory muscles of respiration are not used. The heart rate is < 100 beats/min, and pulsus paradoxus (an exaggerated fall in systolic blood pressure during inspiration) is not present. Auscultation of the chest reveals moderate wheezing, which is often end-expiratory. Rapid forced expiration may elicit wheezing that is otherwise inaudible, and the oxyhemoglobin saturation on room air is > 95%.
In a moderately severe episode, the respiratory rate is also increased. Typically, accessory muscles of respiration are used. In children, also look for supraclavicular and intercostal retractions and nasal flaring, as well as abdominal breathing. The heart rate is 100-120 beats/min. Loud expiratory wheezing can be heard, and pulsus paradoxus may be present (10-20 mm Hg). The oxyhemoglobin saturation on room air is 91%-95%.
Patients experiencing a moderately severe episode are breathless while talking, and infants have feeding difficulties and a softer, shorter cry. In more severe cases, the patient assumes a sitting position.
In a severe episode, patients are breathless during rest, are uninterested in eating, sit upright, talk in words rather than sentences, and are usually agitated. The respiratory rate is often > 30 breaths/min. Accessory muscles of respiration are usually used, and suprasternal retractions are commonly present. The heart rate is > 120 beats/min. Loud biphasic (expiratory and inspiratory) wheezing can be heard, and pulsus paradoxus is often present (20-40 mm Hg). The oxyhemoglobin saturation on room air is < 91%. As the severity increases, the patient increasingly assumes a hunched-over sitting position with the hands supporting the torso, termed the "tripod position."
When children are in imminent respiratory arrest, in addition to manifesting symptoms of a severe asthma episode, they are drowsy and confused; in contrast, adolescents may not appear drowsy or confused until they are in frank respiratory failure. In status asthmaticus with imminent respiratory arrest, paradoxical thoracoabdominal movement occurs. Wheezing may be absent (associated with most severe airway obstruction), and severe hypoxemia may manifest as bradycardia. Pulsus paradoxus noted earlier may be absent; this finding suggests respiratory muscle fatigue.
As the episode becomes more severe, profuse diaphoresis occurs, with the diaphoresis presenting concomitantly with a rise in PCO2 and hypoventilation. In the most severe form of acute asthma, patients may struggle for air; act confused and agitated; and remove their oxygen mask, stating, "I can't breathe." These are signs of life-threatening hypoxia. With advanced hypercapnia, bradypnea, somnolence, and profuse diaphoresis may be present; almost no breath sounds may be heard; and the patient is willing to lie recumbent.
For more on the presentation of asthma, read here.
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Cite this: Zab Mosenifar. Fast Five Quiz: How Much Do You Know About Asthma? - Medscape - Jun 04, 2019.