A 45-year-old with known asthma arrives in the ED with wheezing after albuterol at home, speaks in short phrases, has accessory muscle use, SpO2 93% on room air, and no recent peak flow, arterial blood gas, or sputum assessment documented. Which additional assessment best completes information gathering for clinical judgment?

The correct assessment completes guideline-based severity staging for moderate exacerbation after failed home albuterol, where short phrases, accessory use and SpO2 93% show increased work and hypoxemia without failure, so peak expiratory flow quantifies airflow limitation while pulse oximetry trends track oxygenation response and focused auscultation assesses air movement and symmetry to guide bronchodilators, steroids, oxygen and disposition. Peak flow with arterial blood gas and auscultation fails by acuity matching because gas analysis is reserved for severe deterioration, silent chest, inability to speak, depressed mentation or suspected hypercapnia rather than a conversant patient with moderate hypoxemia, and it omits required oximetry trending. Peak flow with sputum eosinophil testing and auscultation fails by timeliness because eosinophils inform chronic phenotype and future biologics but do not stage acute obstruction or detect desaturation, again omitting oximetry trends. Oximetry with auscultation and vital sign review fails by objectivity because without peak flow there is no quantified comparison to personal best or predicted, which the stem flags as missing and which best tracks treatment response since wheeze intensity correlates poorly. Exam caveat is that diminishing wheeze with poor movement can mean worsening obstruction, and practical check is to document pre- and post-treatment peak flow percent with SpO2 trend, sentence ability, accessory use and lung findings to decide discharge, observation or admission.