In older animals, chest radiographs
and electrocardiogram (ECG) are often recommended to ensure there is no
pre-existing pathology in the
heart or
lungs that might increase the risk of an adverse reaction.
Respiratory or cardiac arrest can be caused by a variety of factors including
pre-existing disease of the thorax, (including the
heart or
lungs), other systemic disease (particularly involving the liver
and / or kidneys where anesthetics must be cleared from the body), blockage of the air passageway (blocked ET tube, regurgitation of material from stomach, blood)
and overdose of the anesthetic agent (s).