Final answer:
The patient's symptoms suggest infiltration as the likely complication from IV therapy, which is characterized by swelling and pain at the catheter site due to IV fluid or medication leaking into the surrounding tissue.
Step-by-step explanation:
The patient's symptoms of pain at the site, swelling, and warmth around the catheter suggest the complication of infiltration. Infiltration occurs when the IV fluid or medication leaks out of the vein and into the surrounding tissue. This can often result in swelling and discomfort at the site of the catheter. Phlebitis, which is inflammation of the vein, and thrombophlebitis, which includes both inflammation and a blood clot in the vein, typically come with signs of redness and pain along the path of the vein rather than swelling from fluid leakage, while a hematoma involves a localized collection of blood outside the blood vessels. Considering the symptoms provided, infiltration is the most likely complication the patient is experiencing.