Endotracheal tube obstruction by a mucus plug causing a ball-valve effect is a rare but significant complication. The inability to pass a suction catheter through the endotracheal tube with high peak and plateau pressure differences are classical features of an endotracheal tube obstruction. A case is described of endotracheal tube obstruction from a mucus plug that compounded severe respiratory acidosis and hypotension in a patient who simultaneously had abdominal compartment syndrome. The mucus plug was not identified until a bronchoscopic assessment of the airway was performed. Due to the absence of classical signs, the delayed identification of the obstructing mucus plug exacerbated diagnostic confusion. It resulted in various treatments being trialed whilst the patient continued to deteriorate from the evasive offending culprit. We suggest that earlier and more routine use of bronchoscopy should be employed in an intensive care unit, especially as a definitive way to rule out endotracheal obstruction.