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.

This single-center, prospective observational study is designed to evaluate the clinical utility of intra-osseous (IO) infusion incritically hematology patients ，including:① Highly suspected or diagnosed patients with rapidly progressing highly lethal hematological diseases;② Patients with hematological disorders complicated by severe complications, including granulocyte deficiency, thrombocytopenia, severe anemia, advanced tumors, septic shock, sepsis, etc DIC、 Severe gastrointestinal bleeding, involvement of the central nervous system or intracranial hemorrhage, etc;③ Patients with hematological diseases combined with important organ dysfunction, including respiratory failure, heart failure, renal failure, liver failure, etc;④ Patients undergoing hematopoietic stem cell transplantation or those experiencing serious complications in new immunotherapy, such as hyperacute graft-versus-host disease (GVHD), grade 3-4 cytokine release syndrome (CRS) or immune effector cell associated neurotoxicity syndrome (ICANS), grade 3-4 immune checkpoint inhibitor associated interstitial lung disease, etc;⑤ Other critically patients who require life support and 24-hour monitoring.

An IO cannula will be inserted into the proximal tibia, and the following parameters will be prospectively recorded: time to vascular access, first-pass success rate, infusion flow during dwell, hemodynamic recovery, efficiency of volume resuscitation, stability of vaso-active drug delivery, and the incidence of procedure-related adverse events (local infection, fat embolism, osteomyelitis, bleeding, nerve injury). The study will explore whether IO access can serve as a reliable, rapidly established "non-collapsible" vascular route.The catheter will be removed within 24 h (maximum 96 h in exceptional cases); lidocaine step-wise analgesia will be administered according to consensus recommendations. Follow-up data will be captured in real time through an electronic case-report form (eCRF); inflammatory markers, coagulation profile, and organ-function indices will be measured by the central laboratory, while imaging specialists will assist in complication screening. The trial is intended to generate the first evidence base for IO infusion in Chinese hematology critical care and to provide feasibility and effect-size data for subsequent multicentre randomized controlled trials.

Inclusion Criteria:

• 1. Age: 18 to 65 years old. 2. Critically patients with hematologic diseases, including:① Highly suspected or diagnosed patients with rapidly progressing highly lethal hematological diseases;② Patients with hematological disorders complicated by severe complications, including agranulocytosis, thrombocytopenia, severe anemia, advanced tumors,septic shock, sepsis, DIC、 severe gastrointestinal bleeding, involvement of the central nervous system or intracranial hemorrhage, etc;③ Patients with hematological diseases combined with important organ dysfunction, including respiratory failure, heart failure, renal failure, liver failure, etc;④ Patients undergoing hematopoietic stem cell transplantation or those experiencing serious complications in new immunotherapy, such as hyperacute graft-versus-host disease (GVHD), grade 3-4 cytokine release syndrome (CRS) or immune effector cell associated neurotoxicity syndrome (ICANS), grade 3-4 immune checkpoint inhibitor associated interstitial lung disease, etc;⑤ Other critically patients who require life support and 24-hour monitoring.

Exclusion Criteria:

• 1. Fracture at the intended puncture site (due to the risk of fluid extravasation into subcutaneous tissues).

  2. Extensive soft tissue injury at the intended puncture site, resulting in insufficient anatomical landmarks for safe puncture.

  3. Local infection in the intended puncture area. 4. History of major orthopedic surgery in the intended puncture region. 5. Presence of a local prosthetic implant. 6. A site previously used for intraosseous (IO) access within the last 24 hours (to avoid re-puncture).

Study Population: Fifty-two adult patients (18-65 years) with critical hematologic disorders and poor vascular access will be enrolled. All are at imminent risk of death and include: ① rapidly progressive, highly lethal hematologic malignancies; ② severe complications such as agranulocytosis, major bleeding, DIC, CNS involvement, or sepsis; ③ concomitant respiratory, cardiac, renal, or hepatic failure; ④ life-threatening toxicities from HSCT or novel immunotherapies (hyperacute GVHD, grade 3-4 CRS/ICANS, grade 3-4 ICI-related pneumonitis); ⑤ any other critically ill patient requiring 24-h organ-supportive care.