A 19-year-old male presents with wheezing and shortness of breath due to an asthma attack. What is a key indicator of possible impending respiratory failure in this situation?

A drop in blood pressure on inspiration, known as pulsus paradoxus, can be a critical sign indicating the potential for impending respiratory failure in a patient experiencing an acute asthma attack. This phenomenon occurs because the increased airway resistance during an asthma exacerbation can lead to compromised cardiac output, especially during inspiration.

In the context of asthma, significant respiratory distress can cause fluctuations in intrathoracic pressure, affecting venous return to the heart and resulting in decreased blood pressure during inspiration. If the drop in blood pressure is notable, it suggests that the patient is struggling to maintain adequate ventilation and perfusion, which can lead to respiratory failure if not addressed promptly.

In contrast, increased oxygen saturation would typically suggest better oxygenation, not the risk of respiratory failure. Normal blood pressure does not indicate an impending crisis, and increased urine output is usually not a relevant parameter in the assessment of acute respiratory distress. Recognizing pulsus paradoxus as a sign of potential respiratory failure is crucial for timely intervention and management in patients with severe asthma exacerbations.