Comparison of restrictive and liberal blood transfusion in critically ill adults: a meta-analysis and comprehensive review

Faced with a shortage of blood sources, clinicians have been striving to utilize blood judiciously for critically ill patients. Although some researchers have attempted to explore this issue, there is still no consensus on its applicability in different situations. Therefore, we first conducted a systematic review and meta-analysis by category, providing a more scientific and reasonable basis for clinical treatment decisions. We searched databases up to 11 June 2025, including PubMed, EmBase, Cochrane, and Web of Science. The participants were critically ill adult patients. We collected and grouped different hemoglobin (Hb) thresholds during restricted and liberal blood transfusions. The primary outcomes encompassed mortality rate, length of hospital stay, and adverse reactions. 30,943 critically ill patients were included in 33 studies. Patients with closed head injuries in the restricted group had a higher risk of mortality (RR = 1.78, 95% CI: 1.48–2.15), particularly those with concomitant subarachnoid hemorrhage; Mortality rates were also higher among cardiovascular patients over the age of 60 (RR = 1.54, 95% CI = 1.05–2.24); Tertiary hospitals were found to facilitate patient recovery. Critical patients with closed brain injuries and comorbidities, as well as those over 60 years old with cardiovascular diseases, may benefit from high-threshold liberal strategies. The protocol was registered on PROSPERO with the ID of CRD42024606971.