Diagnose It Answer — April 19, 2026

17-year-old female brought in by her mother with shortness of breath and chest tightness that started suddenly at a friend's house. She is unable to complete sentences, speaking only in 1–2 word bursts. She is hunched forward on the stretcher with visible accessory muscle use and audible wheezing. Her mother reports she used her rescue inhaler four times in the past hour without improvement.

Moderate persistent asthma diagnosed at age 7. Prescribed fluticasone inhaler daily (admits she has not been using it for the past month) and albuterol MDI PRN. Prior hospitalizations for asthma: one ICU admission at age 14. Allergy history: cats, dust mites, tree pollen. No current oral steroids. Mother reports her peak flow meter readings this week have been 'lower than usual.'

BP 128/82 mmHg, HR 128 bpm, RR 34 breaths/min, Temp 37.1°C, SpO2 89% on room air — improved to 94% on 6L face mask. Patient is diaphoretic, agitated, and sitting upright. Pulsus paradoxus measured at 18 mmHg (normal <10 mmHg), indicating significant air trapping and intrathoracic pressure variation.

Diffuse bilateral expiratory and inspiratory wheezing — 'tight' high-pitched wheeze throughout all lung fields. Prolonged expiratory phase. Accessory muscle use prominent. No crackles, no fever. Peak expiratory flow rate (PEFR): 28% of predicted — severe obstruction. Continuous albuterol nebulization initiated. IV magnesium sulfate 2g over 20 minutes ordered. IV methylprednisolone 125mg given. Heliox considered. Anesthesia at bedside given severity.

ABG on 6L face mask: pH 7.37, PaCO2 42 mmHg, PaO2 68 mmHg — a 'normal' PaCO2 in a severely tachypneic asthmatic is a critical warning sign of impending respiratory failure (patient should be blowing off CO2 and have a low PaCO2; normalization indicates fatigue). Potassium 3.2 mEq/L (beta-agonist effect). WBC 11,200/µL. Chest X-ray: hyperinflation, no pneumothorax, no consolidation, no mucous plugging visible. IgE elevated at 420 IU/mL.