Effects of postural change and mobilization on hemoglobin levels in ICU patients: a prospective intervention study

Abstract Background In the absence of overt bleeding, a gradual decline in hemoglobin (Hb) levels is common following admission of patients to the Intensive Care (ICU). While effects of posture on measured Hb levels have been reported, knowledge about their occurrence and relevance in ICU patients is largely lacking. Such postural Hb changes are generally considered to result from plasma volume shifts. We studied the effects of passive and active postural changes on measured Hb values in hemodynamically stable, non-bleeding ICU patients. Methods In a single-center uncontrolled interventional study in hemodynamically stable adult ICU patients without evidence of bleeding, arterial Hb was measured after ≥ 6 h of supine bedrest, 30 min after a passive change to sitting in bed and subsequently after mobilizing patients to a chair. Baseline values for erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and changes in serum albumin were recorded to explore potential correlations with Hb changes. The data was analyzed using linear mixed modelling. Results Twenty-three patients (median age 72 years, 57% male) were included in the study. The average baseline Hb obtained from the mixed model analysis was 11.1 g/dL (95% confidence interval (CI): 10.0–12.1 g/dL ). A passive change to a sitting position in bed resulted in an increase of 0.4 g/dL (95% CI: 0.2–0.5, p < 0.001), with a further increase of 0.5 g/dL (CI: 0.3–0.6, p < 0.001) after mobilization to a chair. There was a positive correlation between changes in Hb and albumin (supine to sitting in bed: Spearman ρ = 0.76, p < 0.001, supine to mobilized in a chair: Spearman ρ = 0.72, p < 0.001). No significant correlations were observed for Hb changes and ESR, or CRP. Conclusions In ICU patients, modest but significant increases in Hb values were demonstrated following a change from supine to a sitting position, with further increases upon mobilization to a chair. The observed postural Hb changes could affect transfusion decisions for Hb values near generally accepted transfusion thresholds.