Final answer:
In an emergency situation, you can give a patient type O blood until cross-matched blood is available. Type O blood is considered the universal donor because it can be transfused to patients of any blood type without provoking a major immune response.
Step-by-step explanation:
In an emergency situation when you have no time to wait for cross-matched blood, you could give a patient type O blood until the cross-match is available. Type O blood is considered the universal donor because it does not display A or B antigens on the red blood cells, so it can be transfused to patients of any blood type without provoking a major immune response. However, it is important to note that introducing type O blood into an individual with type A, B, or AB blood may introduce antibodies against A and B antigens present in the type O plasma.