Swelling at the infusion site may occur with intravenous infusions because the bevel of the needle tip is not completely inside the vessel, thus allowing fluid to seep into the subcutaneous tissue causing swelling. It is possible that the patient is moving around, causing the scalp needle to be touched causing swelling. It is also possible that bleeding back may occur, possibly due to the patient unconsciously raising the arm or lowering the height of the bottle, causing the pressure of the skin strip to be less than the venous pressure, thus causing bleeding back. When the patient coughs hard or laughs, it increases the intra-abdominal pressure or intrathoracic pressure leading to reflux. It may also happen that the fluid does not drip, which may be caused by a folded infusion line, needle blockage during reflux, vascular spasm, or needle outside the vessel. 60% of patients have misconceptions about air bubbles entering the body, and small air bubbles entering the body will carry the air bubbles from the blood circulation to the lungs, where they are absorbed during gas exchange.