A saline flush is the method of clearing out feeding tubes and intravenous lines (IVs) of any food, medicine, or other perishable liquids so that they can keep the area of entering clean and sterile. Typically in flushing a intravenous cannula, a 5ml syringe of saline is emptied into the medication port of a the cannula's connecting hub after insertion.[1] Blood left in the cannula or hub can lead to clots forming and blocking the cannula. Flushing is required before drip is connected to ensure that the IV is still patent.
Flushing is also used after medications are delivered by the medication port to ensure all the drug is delivered fully. If multiple medications are given through the same line flushing can be used in between drugs to ensure that the medicines won't react. This is especially important if complex regimes of intravenous medication is used such as in chemotherapy.
Flushing with saline should be painless if the cannula is in its proper place, although if the saline is not warmed there may be a cold sensation running up the vein. A painful flush may indicate tissuing or phlebitis and is an indication that the cannula should be relocated.[1]
Solutions other than plain saline may be used. Heparinised saline may be used in flushing arterial lines, to prevent clotting and blockage of the line.