由于任何这些代替物都不会在体内存在很长时间，他们对那些需要长期输血的病人用处不大。

And since none of the <em>substitute</em>s lasts long in the body, they would not help patients who need chronic transfusions.

我们打算把它当作是临时的代替物.

It was intended as a stopgap.