Aclient with a tentative diagnosis of lung cancer is scheduled for a mediastinoscopy with biopsy. which is a priority nursing action

The nurse should "advise the client to avoid eating or drinking anything for several hours before the test".

Clients are required to eat nothing by mouth before the test so that no aspiration happens during the procedure.
A mediastinoscopy with biopsy refers to a minor surgical method that accumulates tests of lymph nodes (which are groups of cells that assume a key part in fighting off infections, viruses and microorganisms in your body). A specialist takes the tissue test from your chest. 

The answer is observations and interpreting.