Introduction. Life-threatening complications of allogeneic hematopoietic stem cell transplantation (allo-HSCT) can have a significant influence on the short-term and long-term prognosis in recipients of hematopoietic stem cells (allo-HSCs).Aim — to determine the life-threatening complications and the risk factors of their occurrence and to evaluate the short-term and long-term prognosis in critically ill allo-HSCs recipients.Materials and methods. All patients over the age of 18 who underwent allo-HSCT from 01.01.2012 to 01.01.2022 were included in the retrospective study. Patients were divided into two groups: those who required intensive care unit (ICU) admission and those who did not require ICU admission. In the group of ICU admitted allo-HSCs recipients the reasons of ICU admission, timing of their occurrence and the results of life support were recorded. The risk factors of life-threatening complications occurrence and prognostic factors were analyzed.Results. In total, 174 (26.7 %) of 652 allo-HSCs recipients required ICU admission. The risk factors of life-threatening complications were: allo-HSCT in patients with acute leukemia who did not achieve complete remission (hazard ratio (HR) = 2.10; 95 % confidence interval (95% CI): 1.28–3.44; p = 0.003), allo-HSCT without conditioning in patients with hematopoietic aplasia after chemotherapy (HR = 30.63; 95% CI: 8.787–107.04; p < 0.001), graft failure (HR = 2.51; 95% CI: 1.58–3.97; p < 0.001) and poor graft function (HR = 2.85; 95% CI: 1.6–5.05; p < 0.001), acute graft versus host disease (GVHD) (HR = 2.04; 95% CI: 1.459–2.85; p < 0.001). The main reasons of ICU admission were sepsis and/or septic shock (SS) (27.9 %), acute respiratory failure (23.9 %), neurological disorders (17.7 %). The type and periods of allo-HSCT influenced the timing and structure of critical illnesses. The ICU mortality rate after all ICU admissions and readmissions was 59.8 % with a maximum follow-up of 9 years. The risk factors of ICU mortality were the occurrence of critical conditions after +30 days of allo-HSCT, the need for mechanical ventilation and vasopressors. The overall survival (OS) rate of ICU admitted allo-HSCs recipients was 13.8 %. Sepsis and/or SS that occurred in the early phase after allo-HSCT were characterized by the most favorable long-term outcome (OS — 43.8 %) among all complications of the peritransplantation period. The OS of patients discharged from the ICU was worse than OS of patients who did not require ICU admission (34.6 % vs. 58.3 %; p = 0.0013). Conclusion. Transplant centers should have a specialized ICU because more than a quarter of allo-HSCT recipients experience life-threatening complications at different allo-HSCT periods. Sepsis and SS occurring in the early pre-engraftment phase had a more favorable prognosis than other life-threatening complications. The long-term outcomes in allo-HSCs recipients who survived critical illness are worse than in recipients who did not require ICU admission.
