Great, the next child needs 10 mg which is what you have left in your 100 mg ampoule of pethidine.
The operation has ended but the child refuses to start breathing - Not so great!
Unbeknownst to you, the manufacturer has very thoughtfully given a bonus of 0.15 ml, or the equivalent of 7.5 mg, of pethidine in the ampoule to compensate for the dead space found in most syringes. This means that the child received 10 + 7.5 mg or 17.5 mg instead of 10 mg, almost double the intended the dose.
Don't believe me? Next time you ask for pethidine, look carefully at the
labelling and you'll find I'm telling you the truth. This is also found in the
50 mg ampoule of pethidine and many other drugs as well.
Furthermore, if you are drawing up only small volumes, pay attention to the
volume of drug in the dead space of the syringe as this amounts to about 0.1 ml
which may or may not be significant.