Failure modes: infiltration, phlebitis and the vasovagal faint
The second is phlebitis — irritation or inflammation of the vein, showing up as a red, warm, tender streak along the vein's path, sometimes a day later. Certain additives are more irritating than plain fluids, which again rewards slower infusion rates. The third is the vasovagal response: some people faint around needles, full stop. It is a reflex, not a weakness, and the mitigation is simple — you should always be infused lying down or well reclined, never perched on a bar stool. A nurse who checks whether you have fainted before, and positions you accordingly, has done this many times.
Two reassurances backed by physiology: the small air bubbles you may see in the line are not the movie scenario — it takes a large volume of air to cause harm, far beyond what tubing bubbles contain. And infection risk at the insertion site is genuinely low when asepsis is followed: skin cleaned with chlorhexidine or alcohol and allowed to dry, gloves, single-use everything, and a sharps container that the nurse brings and takes away. Watch for that sharps box — its absence is a red flag you can spot from across the room.