Which symptom is most indicative of a severe asthma exacerbation in a 16-year-old client?

Audible expiratory wheezing is a crucial indicator of severe asthma exacerbation, specifically because it reflects significant airway narrowing and increased resistance within the airways. Wheezing occurs due to turbulent airflow in constricted bronchi, making it an important sign that differentiates mild coughing from a more serious breathing issue. During a severe exacerbation, the wheezing may be loud enough to be audible without a stethoscope, indicating that the airways are critically compromised.

While shortness of breath is common in various stages of asthma and not exclusively tied to severity, substernal retractions also suggest significant respiratory distress but may not be as definitive as audible wheezing. Nasal congestion, though potentially present during an exacerbation, is more related to upper respiratory issues rather than the lower airway pathology characteristic of severe asthma attacks. Thus, the presence of audible expiratory wheezing serves as a strong clinical marker of a severe exacerbation, warranting immediate medical attention.