This single-center, prospective observational study will enroll 52 critically hematology patients aged 18-65 years including agranulocytosis, thrombocytopenia, severe anemia, advanced tumors, septic shock, sepsis DIC、 severe gastrointestinal bleeding, involvement of the central nervous system or intracranial hemorrhage, patients undergoing hematopoietic stem cell transplantation，etc. Vascular access will be established via intraosseous (IO) needle placement, primarily to evaluate first-attempt puncture success rate, therapeutic efficacy, and overall survival rate. Secondary endpoints include infusion speed, hemodynamic improvement, and procedural complications such as local infection and fat embolism. The study aims to definitively assess the efficacy and safety of IO infusion as a rapidly established, "non-collapsible" alternative vascular access route in the hematologic intensive care setting.