Getting air out of a cartridge
Small bubbles clinging to the glass are harmless and normal. A large pocket at the top is worth clearing, because it takes up volume the pen expects to be liquid. Stand the cartridge upright, tap the side, let the air rise, then prime two clicks.
How worried should you actually be
For subcutaneous injection with a tiny pen needle, the horror stories about air in the bloodstream do not apply. This is not an intravenous line. The real problem with air is duller: it occupies space, so a cartridge with a big bubble delivers slightly less liquid than the dial promises.
That is a dosing accuracy issue, not a safety one, and it is easily solved.
Where the air comes from
- Filling at an angle, so liquid drops through air instead of running down the wall
- Pushing the syringe fast, which whips bubbles into the liquid
- Filling in two passes, letting air in between them
- Shaking or inverting the cartridge after filling
Getting it out
Stand it upright, stopper down
Air rises. Give it thirty seconds and most of it collects at the top on its own.
Tap the glass firmly
Fingernail against the side, at the height of the bubbles. This dislodges the ones stuck to the wall so they can rise.
Load and prime pointing up
With the pen vertical and the needle at the top, dial two clicks and press. Any air at the top goes out ahead of the liquid.
Prime again if nothing appeared
No bead at the tip means air is still coming through. Repeat until you see liquid.
Prime every time you fit a new needle, bubbles or not. The needle itself holds a small amount of air, and two clicks clears it. Skip it and your first dose is short.
Questions
- Is a small air bubble dangerous?
- For a subcutaneous injection with a pen needle, no. The practical concern is accuracy rather than safety, because the air takes up space the dial counted as liquid.
- Why do bubbles keep appearing overnight?
- Dissolved gas coming out of solution as the liquid warms, which is normal. Standing the cartridge upright and priming before use handles it.