Discuss with your baby's surgeon and anaesthetist, how long your baby will have to fast before surgery, and how soon afterwards he will be able to resume breastfeeds. Some mothers find they need to express their milk for a few days until their baby is well enough to feed at the breast again. Expressing in this situation relieves the discomfort of overfull breasts and helps to maintain your milk supply. If your baby has a heart condition requiring surgery, you will probably find that after surgery he is much stronger, and more able to stay awake for feeds. Your local Nursing Mothers' Group will have information for you about hiring electric breast pumps .
Many mothers find electric pumps very helpful if they are expressing over a long period of time.
Remember that it is unlikely that all situations here will apply to your baby. Try the suggestions that seem to suit your baby's needs, and use those that help. You will probably find your own ways of overcoming difficulties as you get to know your baby. Also remember that most difficulties will resolve as your baby learns to breastfeed. It is in the early days of establishing breastfeeding that your baby is most likely to need extra help.