Table 1 Details of studies included in meta-analysis (n = 18)

Vincent et al. [2]

Prospective, multiple center, observational study in western Europe

All ICU patients

Not reported

Patients’ admission variables

Corwin et al. [3]

Prospective, multiple center, observational cohort study in the United States

Not reported

Admission to a pediatric, cardiothoracic, cardiac, neurologic, or burn ICU; renal failure on dialysis

Propensity to receive a transfusion

Robinson et al. [32]

Retrospective, observational study

Not reported

Patients with blunt hepatic, splenic, or both injuries

Shock indices and associated injury severity

Croce et al. [31]

Retrospective, observational study

Patients with blunt injury and ISS <25, survival of at least 48 hours, and no blood transfusion within the first 48 hours from admission

Patients who received any transfusion within the first 48 hours from admission, ISS > =25

We use original numbers to analyze RR, because the author reported a distracting result (OR2.46,95%CI, 3.17 to 11.56)

Taylor et al. [19]

Prospective, observational, cohort study

All ICU admissions

Not reported

Unadjusted

Netzer et al. [33]

Prospective, cohort study

Patients with ALI/ARDS

Patients were excluded if they had current or prior congestive heart failure, respiratory disease, or conditions that mimicked ALI/ARDS, including vasculitis with diffuse alveolar hemorrhage; were burned 30% of total body area; or were lung or bone marrow recipients.

Age, gender, APACHE III score, and precipitating event

Ruttinger et al. [34]

Retrospective, observational cohort study

All consecutive cases admitted immediately or delayed after a surgical procedure

Patients who had not undergone surgery during their present hospital stay and who had been admitted only for medical reasons, and patients with a rapidly fatal clinical course or with minimal disease severity

Admission variables, maximum APACHE II score, maximum number of failing organs, duration of invasive ventilation, duration of catecholamine therapy, and duration of renal replacement therapy

Vincent et al. [35]

Prospective, multicenter, observational study

All ICU patients

Not reported

Sex and age, type of admission, main medical history, fluid balance, SAPS II, and severity of organ dysfunction on admission as SOFA score

Bochicchio et al. [36]

Prospective

Trauma patients admitted >48 hours to the ICU

Not reported

Age, sex, race, and ISS

Bursi et al. [37]

Retrospective observational study

Stable patients after elective major vascular surgery

Patients who had hemorrhagic hypovolemic shock requiring emergency RBC transfusion, severely anemic

Baseline characteristics, surgical risk, bleeding, presence of anemia, and propensity to receive transfusion

Engoren et al. [38]

Retrospective study

All ICU patients

Cardiac surgical patients

APACHE II scores and propensity to receive a transfusion

Sakr et al. [21]

Retrospective study

All surgical ICU patients

Not reported

Patients’ propensity to receive a transfusion

Parsons et al. [39]

A secondary analysis

Patients with new-onset ALI, sepsis and shock

Patients with trauma or multiple transfusion

Age, sex, race, randomization arm and APACHE III score

Sheth et al. [40]

Retrospective, observational cohort study

Patients with intracerebral hemorrhage

Patients younger than 18 years of age or with ICH secondary to antecedent head trauma, acute ischemic stroke with hemorrhagic transformation, brain tumor, vascular malformation, venous thrombosis, vasculitis of the central nervous system, hematological malignances, blood dyscrasia, or coagulopathy

Anemia, warfarin use, admission GCS score, hematoma volume, hematoma location, and DNR/CMO status

Park et al. [4]

Prospective, multicenter observational study

Patients with severe sepsis or septic shock

Not reported

Propensity to receive a transfusion

Brophy et al. [41]

A cross-sectional retrospective study

Anemia and renal dysfunction

Patients with anemia of neoplastic diseases or those receiving chemotherapy

Age, race, sex, ICU LOS, ESA use, transfusion status, mechanical ventilation or CPAP status, vasopressor use, severity of, illness, and presence of, following comorbid conditions, GI bleed, sepsis, and neurologic injury.

Silva et al. [42]

Prospective observational cohort study

All ICU admissions

Acute coronary syndrome, ischemic stroke, acute hemorrhage, prior transfusion, pregnant women and Jehovah’s Witnesses

Sex, origin, previous disease, ventilation mode

Sekhon et al. [43]

Retrospective cohort study

Severe TBI patients

Nontraumatic etiology, consciousness, concomitant traumatic quadriparesis

Age, admission GCS score, insertion of EVD, mean 7-day hemoglobin