A shark-fin capnograph most likely indicates which problem?

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Capnography shows how air exits the lungs during exhalation, so the shape of the expiratory portion of the waveform tells you about airway flow. A shark-fin pattern means the expiratory flow is hindered, causing a slow, uneven rise in CO2 and a curved, slanted plateau. This reflects expiratory obstruction—airways are narrowed or obstructed during exhalation, as seen with bronchospasm or other forms of airway resistance. By contrast, cardiac arrest would reduce or abolish the CO2 signal, hyperventilation would produce a rapid, shallow exhalation with a diminished or altered waveform, and normal exhalation has a quick rise to a smooth, flat plateau. So the shark-fin capnograph most likely indicates expiratory obstruction.