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It is probably extravasation - oozing of a little blood outside the vein. It gets organised and will be absorbed over time.
There is also possibility of thrombophlebitis
- inflammation of the vein - from the cannula
, medicine and so on. It also generally clears, when the cannula is removed. Rarely the thrombosis
may become worse - see you doctor, if there is any change or worsening.
Wishing speedy recovery