cardiorespiratory arrest

My father(age 69) was diagnosed with lung cancer.He did not smoke or drink alcohol-Broncho-alveoli cancer.It had also spread to lymph nodes.He was given tablets.He took a couple of them.The third day his blood pressure fell down.He was administered with medicines to improve blood presure.But the following dy he passed away.Doctors gave reason for death as "cardiorespiratory arrest".Wanted to find out what was the atcula reason formy dad's death.Was it bcoz of medicines or any thing else?