Some level of blood loss is to be expected during major surgery. There is no way to avoid it. The surgical team will then plan ahead to prevent blood loss and set up blood transfusions when necessary.
That said, excessive blood loss is very dangerous and often fatal, and it should be avoided at all costs. As noted by leading medical experts, “higher operative blood loss and transfusion requirements have been associated with…complications and mortality.” They do note that the long-term survival rate of a patient who has excessive blood loss does not seem to be impacted, but the short-term survival rate is the concern. In other words, if the person lives through the procedure, they can typically recover, but the threat is that patients may not live through the surgery at all.
Your surgical team has an obligation to work as hard as they can to keep you safe from harm. That does not mean that every surgery will be a success or that patients will never pass away. However, it means they have to give you the type of care that you should reasonably expect, they have to take expected steps to rectify a problem and they need to avoid serious errors and mistakes during the procedure. When surgeons do not give you this type of care, it could be an example of extreme negligence and unprofessional behavior.
If you suffer serious health complications as a result, you may have a right to compensation. The same is true if you lose a loved one to excessive blood loss or other such issues during surgery.