Lucy, 90% of ascites cases are due to cirrhosis. Other possible causes are congestive heart failure, kidney disease, and malignancy.
You asked about IVs in the forearm. If a vein can't be found in the inside of the elbow, they will sometimes use the forearm. In my case, as a former IV drug user, they use some really odd spots. For blood work yesterday, they used a small vein just above my left wrist. That's a spot I point out to them as the best place to try. When I need an IV, there's more of a problem. They cannot find a vein large enough, so someone from interventional radiology or the PIC team has to be called in to locate a vein in my inside upper arm through a portable Doppler (imaging.) And it hurts like hell unless a certain doctor does it. I'll be going through that next week.
Other than that, just keep looking for clues and ask him questions when he's off-guard.
Hugs,
Connie