🔍 Question

A 60-year-old woman presents to the emergency department with shortness of breath and a productive cough. She has a 30-pack-year smoking history. Her oxygen saturation is 88% on room air. On examination, she appears distressed, using accessory muscles for breathing, and expiratory wheezes are audible bilaterally. High-flow oxygen supplementation is initiated. Shortly afterward, the patient becomes lethargic and confused.

This clinical deterioration is most likely caused by an increase in which of the following?

A. Pulmonary vascular resistance

B. Reactive oxygen species production

C. Renal bicarbonate reabsorption

D. Respiratory minute ventilation

E. Ventilation-perfusion mismatch

Correct Answer: E. Ventilation-perfusion mismatch

🧠 Key Takeaway

V/Q mismatch worsens CO2 retention in COPD when oxygen disrupts compensation.

⚙️

⚙️ Chronic Smoking

⬇

Airflow Obstruction: Air can’t leave lungs effectively.

⬇

⚖️ V/Q Mismatch:

• Ventilation (V): ⬇

• Perfusion (Q): Maintained or ↑ (due to vasodilation).

⬇

🧠 Chronic Hypoxemia (Low O2):

• Compensation:

• Lungs: ↑ Respiratory Drive to remove CO2.

• Kidneys: ↑ Renal Bicarbonate Reabsorption to buffer acidosis.

Event Trigger: High-Flow Oxygen Therapy

⚙️ Mechanisms of Decline:

• Oxygen floods the system 🪣 → Disrupts compensations.

• ⬇ Hypoxic Pulmonary Vasoconstriction → Perfusion to poorly ventilated areas ↑.

• 🧠 Blunted Respiratory Drive → Lungs stop working as hard.

• ⚖️ Haldane Effect: High O2 displaces CO2 from hemoglobin, leading to CO2 retention.

⬇

Acute Hypercapnia (High CO2)

🧠 Result: Confusion and lethargy.

Imagine oxygen distribution as a water irrigation system 🪣.

• High oxygen: Water flows evenly to all fields, even unproductive ones (poorly ventilated lung areas).

• This wastes resources (oxygen) and causes buildup (CO2 retention).

⚖️ Explanation of Other Differentials

📝 Flashcards

Stay Hungry, Stay Curious!

Your Brother In This Struggle

Dr. Shoaib Ahmad

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