Medical Emergencies · patient case question
If this patient were to hyperventilate during treatment, a fall in arterial carbon dioxide would produce which physiologic effect?
Patient case: COPD, a Black Tongue, and a Lateral Tongue Mass
Patient: 58-year-old male
Chief Complaint: “My tongue looks black and furry, and there’s a lump on the side of it.”
Background: Chronic obstructive pulmonary disease, GOLD stage III. 40 pack-year smoking history and still smoking one pack daily. Uses a chlorhexidine rinse intermittently. No cardiovascular disease.
Medications: Albuterol inhaler PRN · Tiotropium daily · Inhaled fluticasone
Vital Signs: BP 130/78 mmHg · HR 88 bpm · RR 22 · SpO₂ 92% on room air · T 98.4°F
Findings: Barrel chest, pursed-lip breathing, prolonged expiration. Dorsal tongue with markedly elongated, brown-black filiform papillae. A separate firm, nodular, exophytic mass approximately 15 mm across on the left lateral tongue, present for several months and slowly enlarging. Extensive restorative needs across three quadrants.
Show answer and explanation
Correct answer: A. Decreased respiratory drive with reduced rate and tidal volume
- A. Correct. Arterial carbon dioxide is the primary stimulus to the central chemoreceptors of the medulla. When it falls, that drive is withdrawn and ventilation is suppressed — which is exactly why breathing into a paper bag, allowing carbon dioxide to be rebreathed, relieves the symptoms of acute hyperventilation.
- B. Incorrect. This inverts the physiology. Rising carbon dioxide increases ventilation; falling carbon dioxide decreases it.
- C. Incorrect. Losing carbon dioxide removes acid from the blood, producing respiratory alkalosis. Retaining carbon dioxide would cause acidosis.
- D. Incorrect. Hypocapnia causes cerebral vasoconstriction and reduced cerebral blood flow. That is the mechanism behind the lightheadedness and perioral tingling of a hyperventilating patient.
Note: Correction to source. The original recall recorded “increased tidal volume,” which is physiologically backwards. This same error was identified and corrected in an earlier file in the series. Special caution in COPD: some patients with chronic carbon dioxide retention rely on hypoxic drive, so high-flow oxygen requires care.
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