air in the syringe giving fragmin

i would like to know please what is the correct way to administer fragmin and whether the air is left inside the syringe when administering or if the air should be removed.

 I was always taught that air should be left inside the syringe to reduce bruising...please can you tell me if this is correct?

 If there is any literature that can back up the answer to the question...i would grateful if you could email this to me or tell me where i can find it

 much appreciated

Student nurse Pip