Sometimes little ones need to undergo general anesthesia for special surgeries or procedures, and often parents are told the baby must fast from midnight on the night before. This is NOT accurate for breastmilk, and we had that discussion at length when one of ours needed a procedure done.
This link provides the pre-operative guidelines from the American Society of Anesthesiologists. While many websites do include the recommendation (babies can have breastmilk until 4 hours pre-surgery) having it printed out and showing it to our care provider in advance of the surgery and then again at our pre-op visit quickly squashed any protests from nurses and staff.
Also remember that you will usually be asked to arrive at the surgery location 2 hours before the scheduled procedure, so you can nurse until 2 hours before you leave home (not 4 hours.) That's 2 extra hours that you can comfort your little one!
While I hope you don't need that, it's important to know if you, clients, or friends or family have a little one needing surgery. It's scary and stressful enough for parents to deal with that situation without having to also withhold nursing from a tired, scared, hungry little one. I hope that will help ease the stress of at least one family!