The acute phase of brainstem hemorrhage generally lasts about two to three weeks, or 14 to 21 days, but it also needs to be specifically assessed based on the different conditions of the patient.

If the hemorrhage in the brainstem is relatively severe and located in an important functional area, then the critical period may be appropriately extended. For example, if the hemorrhage is in the medulla oblongata and has already caused respiratory and circulatory failure, as well as unstable vital signs and a comatose state, then the critical period could even reach about one to two months, because it is often necessary to use a ventilator to assist breathing, and the patient's comatose state does not allow for full consciousness.

However, for some brainstem hemorrhages, such as a small hemorrhage in the pons that only causes the clinical symptom of headache in the patient, the critical period is generally no more than two weeks. Thus, each patient's condition is different.