Can decreased cardiac output cause somebody delirium?

Yes: If by delirium you mean changes in your state of consciousness then yes. Decreased cardiac output means that your heart is not pumping the needed amount of blood per minute to maintain normal body functions including that of your brain. Delirium can have many other causes that are probably more common than low cardiac output so check with your doctor.

Yes, if pronounced: Significantly decreased cardiac output leading to a markedly low blood pressure may lead to delirium or lethargy.

Low cardiac output: leads to low blood pressure and less oxygen and glucose for your brain. This is a well known cause of delirium and encephalopathy. Low cardiac output can be caused by cardiomyopathy, heart failure or severe systemic illness such as sepsis. It is a very serious condition.