Final answer:
Prior to a blood transfusion, a nurse must ensure the patient's blood type is checked for compatibility and obtain informed consent. In emergency situations where there's no time for typing, type O blood may be used.
Step-by-step explanation:
An essential nursing action prior to starting a blood transfusion is checking the patient's blood type. This is a critical step because the patient must receive blood that matches their own ABO and Rh blood types to avoid a potentially lethal hemolytic transfusion reaction (HTR). However, in situations where a patient is experiencing a life-threatening hemorrhage and there's no time for blood typing, type O blood, also known as the universal donor, may be transfused because it is most likely to be compatible with all recipients.
Informed consent is also essential, as it ensures that the patient is aware of and agrees to the procedure. While administering pre-transfusion medication may sometimes be necessary depending on the patient's condition, it is not a universal step like blood typing and informed consent. Lastly, ensuring the availability of a blood transfusion set is an important practical step to have everything ready for the transfusion.