Take utmost care in hygiene and sanitation of dogs surroundings during heat period. Organisms such as Escherichia coli, Staphylococcus, Streptococcus, Klebsiella, Pasteurella, Pseudomonas and Proteus species can ascend through vagina into uterus (cervix is open during heat period). And after closing of cervix this infectious agents starts multiplying and can lead to Pyometra.
For IV injection, always use single new needle for each case. Never forcefully prick on the vein. Just gently slide it in to the vein. Always have the cut edge of the needle facing away from animal.