title: Aeromedical evacuation of combat patients by military critical care air transport teams with a lower hemoglobin threshold approach is safe.
abstract: BACKGROUND
  Military critical care air transport teams (CCATT) evacuate critically ill and injured patients out of theater for tertiary treatment. Teams are led by a physician, nurse, and respiratory technician. Current aeromedical guidelines require a hemoglobin (Hgb) of 9 g/dL or greater to evacuate; however, civilians report that an Hgb of 8 g/dL or less is safe in critically ill patients. This study aimed to compare postflight short-term and 30-day patient outcomes for CCATT patients evacuated out of theater with an Hgb of 8 g/dL or less with those with an Hgb of greater than 8 g/dL.
  
  
  METHODS
  We conducted a retrospective record review of all traumatically injured patients evacuated from theater by CCATT between March 2007 and December 2011. We recorded demographics, injury descriptions, vital signs, laboratory values, adverse events, and disposition at 30 days. Patients were separated into those with a preflight Hgb of 8 g/dL or less versus those with greater than 8 g/dL. Continuous data were analyzed using Student's t tests or Wilcoxon tests and reported as mean ± SD. χ or Fisher's exact tests were performed. Stepwise, multifactorial logistic regression models were used. Statistical significance was considered with p < 0.05.
  
  
  RESULTS
  Of 1,252 patients, 1,033 had a preflight Hgb of greater than 8 and 219 had an Hgb of 8 or less. Age, sex proportions, vitals, laboratory values, and Injury Severity Score (ISS; 24±13) were similar. The group with 8 or less had more blast injuries (68% vs. 76%, p = 0.01). No associations were identified between preflight Hgb levels and adverse outcomes. Disposition at 30 days was similar. We also compared preflight Hgb greater than 7 versus 7 or less (n = 1,212 vs. 45). Those with an Hgb greater than 7 had a greater incidence of hospitalization at 30 days (77% vs. 67%, p = 0.04). The group with an Hgb of 7 or less had more subjects discharged home or returning to duty (10% vs. 21%, p = 0.04).
  
  
  CONCLUSIONS
  Evacuating CCATT patients with an Hgb of 8 or less had similar adverse outcomes and mortality at 30 days compared with those with an Hgb greater than 8. Patients with an Hgb of 7 or less had higher rates of hospital discharge and decreased incidence of hospitalization at 30 days.
  
  
  METHODS
  Prognostic/epidemiologic study, level III.
authors.affiliation: From the Air Force En route Care Research Center/59th MDW/ST-United States Army Institute of Surgical Research, (A.G.M., A.T.E., V.J.G., V.S.B.), JBSA Ft. Sam Houston, TX; and Department of Emergency Medicine, San Antonio Military Medical Center, (V.S.B.), JBSA Ft. Sam Houston, TX.
authors.forename: Alejandra G
authors.initials: AG
authors.lastname: Mora
authors.forename: Alicia T
authors.initials: AT
authors.lastname: Ervin
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Ganem
authors.forename: Vikhyat S
authors.initials: VS
authors.lastname: Bebarta