You are treating a 9-year-old male who is short of breath and has a history of asthma. At the scene, he presents in severe respiratory distress, with intercostal retractions, lethargy, and expiratory wheezing. His pulse is 136 beats/min, respirations are 32 breaths/min, and SpO2 is 95%. You have assisted the patient with his albuterol MDI and are transporting him emergently to the hospital. As you reassess the patient, which finding is most concerning?

A) SpO2 of 94%
B) Increased wheezing heard bilaterally
C) Heart rate of 68 beats/min
D) Blood pressure of 100/64 mmHg

C) Heart rate of 68 beats/min