First, notice that bubbles are stopped by the drip chamber on the IV, or if there's an infusion pump instead of a drip chamber, the pump itself will detect it and stop the flow.
If there is a small bubble or two in the line after the drip chamber or pump, notice that it doesn't go anywhere. It just sits there and doesn't move with the fluid so it never enters your vein.
If the person administering the IV made the serious mistake of not allowing fluid to fill the entire line before attaching it to you, it would still require a very large volume of air to do you any harm, on the order of 100 ml (an entire syringe full of air). This is because bubbles can't travel from the venous circulation to the arterial circulation where they would be dangerous. They will be trapped by the lungs and then slowly reabsorbed. A huge volume of air could cause a "vapor lock" in the right ventricle, which would be dangerous, but small bubbles in an IV are nowhere near enough to do that.
The exception to the above would be in people who have a patent foramen ovale (an opening between the right and left sides of the heart), which could allow air bubbles to pass from right to left. However, a patent foramen ovale is normally covered by a flap of tissue except when you bear down hard. So if you're just laying there in a bed, there is virtually no risk presented to you by air bubbles.
Having a small bubble or two in your venous circulation doesn't make your blood unhealthy or "bad." They're harmless and will be absorbed and disappear within hours.