Finally got a clear image of his right hand at 33:39, a view from the back, and 38:07 lifting his hand for a fist bump (CSPAN recording). No IV port. So unless you are suggesting that medical folks arrived and inserted it right after he talked before the fireworks, it is just a reflection of light off his hand.
This micro-investigation of shadows and reflections in public images really isn't helpful (shadows imagined to wetting his pants; coat tails imagined to a towel and now light reflections on his hand. Does anyone seriously think that Trump would allow himself to be photographed in public in urine soaked clothing, sitting on a towel to protect a couch, or with an IV port in his hand?
Suggesting that he would give a major speech with an IV port in his hand is beyond reality, and suggesting that it was inserted between his speech and the fireworks is not far behind.
I did, however, discover something interesting while trying to verify that he didn't have anything in his hand during the speech. I expected to have lots of opportunities of accordion hands to examine the back of his hands. I fast forwarded through his speech (no sound, of course) and until the last 5 minutes of his 38+ minute speech, his right hand never let go of its death grip on the podium - and if his left hand did it was only very briefly - although he repositioned the left a few times. All of the gestures were brief and much more subdued than usual. Since he usually talks with his hands, that was curious - perhaps he got tired of everyone mimicking his accordion hands.