Failure modes: infiltration, phlebitis and the vasovagal faint
Most at-home infusions are uneventful, but three failure modes account for nearly all the problems, and knowing them makes you a safer customer. The first is infiltration: the cannula tip slips out of the vein and fluid runs into the surrounding tissue instead. The signs are a swelling that feels cool and tight around the insertion site and a drip that slows or stalls. It is rarely dangerous with plain saline — the body reabsorbs the fluid — but the infusion must be stopped and resited. This is why the nurse should stay for the entire session and glance at the site regularly, and why any provider whose nurse starts the drip and leaves the room for long stretches is cutting the corner that matters.
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.