In a patient with respiratory distress, capnographic shark-fin waveforms are observed. What is the most likely finding?

• A. Bronchospasm
• B. Pulmonary edema
• C. Pneumothorax
• D. Acute Respiratory Distress Syndrome

Answer: (A)

Shark-fin capnographic waveforms reflect expiratory flow limitation from airway constriction. When the airways narrow, especially in severe bronchospasm, expiration becomes slow and uneven. CO2-rich air takes longer to be expelled, so the expiratory limb of the waveform loses its sharp, flat plateau and instead climbs in a slanted, rounded “shark-fin” shape. This pattern is a hallmark of obstructive airway disease like asthma or a bronchospasm during distress, making bronchospasm the most likely finding.

Other conditions can alter the capnogram, but not with this distinctive obstructive expiratory pattern. For example, issues like fluid in the lungs or edema, collapse or puncture of a lung, or widespread inflammatory injury each produce different waveform changes tied to their effects on ventilation and perfusion rather than the pronounced, slow expiratory rise seen with bronchospasm.