Hi Sandra,
I am not sure there is a short term medication for anxiety. If I understand correctly, your man is going to have Transurethral Needle Ablation. Transurethral needle ablation (TUNA) is a simple, safe, and relatively inexpensive procedure using needles to deliver high-frequency radio waves that heat and destroy prostate tissue. You can read more about the procedure here, and basically it is considered to be one of the less invasive and more simple treatments for Benign Prostatic Hyperplasia.
The best thing to do is speak to the doctor and let the doctor know that the anticipation of this surgical procedure is affecting your 85 year old adversly. If there is something that can be prescribed short term, the doctor will be able to work that out for you.
If you would like information about the TUNA procedure, you can visit this page at HealthCentral's sister site, www.prostatecommons.com.
Good luck and stay in touch. Let us know how the surgery goes!Vicki M