The correct answer is:

The only relative contraindication for an arterial puncture is a coagulation defect. 

• Make sure that you absolutely need this information before considering an arterial puncture in a patient with a coagulation defect. 
• Consider a finger or an ear oximeter.
• Be sure to keep the puncture site compressed for at least five minutes and follow though to make sure that there is no bleeding
• Only attempt to puncture superficial arterial sites. Never go for the femoral or other deeper vessels where compression is difficult. Occult bleeding can occur into deeper tissues and may be overlooked until it is too late.