Oddo M, Levine JM, Kumar M, Iglesias K, Frangos S, Maloney-Wilensky E, Le Roux PD.; Intensive Care Med. 2012 Sep;38(9):1497-504. Epub 2012 May 15.
Purpose: To investigate the relationship between hemoglobin (Hgb) and brain tissue oxygen tension (PbtO2) after severe traumatic brain injury (TBI) and to examine its impact on outcome.
Methods: This was a retrospective analysis of a prospective cohort of severe TBI patients whose PbtO2 was monitored. The relationship between Hgb—categorized into four quartiles (≤9; 9–10; 10.1–11; >11 g/dl)—and PbtO2 was analyzed using mixed-effects models. Anemia with compromised PbtO2 was defined as episodes of Hgb ≤ 9 g/dl with simultaneous PbtO2 < 20 mmHg. Outcome was assessed at 30 days using the Glasgow outcome score (GOS), dichotomized as favorable (GOS 4–5) vs. unfavorable (GOS 1–3).
Results: We analyzed 474 simultaneous Hgb and PbtO2 samples from 80 patients (mean age 44 ± 20 years, median GCS 4 (3–7)). Using Hgb > 11 g/dl as the reference level, and controlling for important physiologic covariates (CPP, PaO2, PaCO2), Hgb ≤ 9 g/dl was the only Hgb level that was associated with lower PbtO2 (coefficient −6.53 (95 % CI −9.13; −3.94), p < 0.001). Anemia with simultaneous PbtO2 < 20 mmHg, but not anemia alone, increased the risk of unfavorable outcome (odds ratio 6.24 (95 % CI 1.61; 24.22), p = 0.008), controlling for age, GCS, Marshall CT grade, and APACHE II score.
Conclusions: In this cohort of severe TBI patients whose PbtO2 was monitored, a Hgb level no greater than 9 g/dl was associated with compromised PbtO2. Anemia with simultaneous compromised PbtO2, but not anemia alone, was a risk factor for unfavorable outcome, irrespective of injury severity.
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