Effect of iron deficiency on tissue oxygen delivery in cyanotic congenital heart disease

Abstract

To test the hypothesis that tissue oxygen delivery would be affected by diminished oxygen stores in cyanotic congenital heart disease, serum ferritin, transferrin saturation, hemoglobin, red cell mean corpuscular volume (MCV), red cell 2,3-diphosphoglycerate (DPG), P50, blood gases, oxygen saturations and systemic oxygen transport were measured in 29 hypoxemic infants and children. For the group, aortic saturation was 81 ± 9%, PaO 2 was 50 ± 12 mm Hg, hemoglobin 16.2 ± 2.1 gm/dl and systemic oxygen transport 620 ± 145 ml/min/ m 2. P50 was increased above normal values (28.8 ± 2.3 vs 26.6 ± 1.1 mm Hg, p < 0.01), and DPG was 2.35 ± 0.54 μmol/ml, at the upper limits of normal for this assay. Iron deficiency was present in 8. When patients with P50 ≥30 mm Hg and P50 < 30 mm Hg were compared, iron stores were diminished in the high P50 group: [serum ferritin (19 ± 8 vs 53 ± 48 ng/ml, p = 0.0006), transferrin saturation (11 ± 6 vs 23 ± 11%, p = 0.003) and MCV (79 ± 8 vs 86 ± 4 fl, p = 0.05)]. Hemoglobin, aortic oxygen saturation, PaO 2 and systemic oxygen transport were similar in both groups. In children with iron sufficiency, 15 of 21 had MCV >90th percentile for age and sex (p < 0.001 versus expected distribution). Also, MCV > 90th percentile for age and sex had a positive predictive value of 0.88 for iron sufficiency. This study demonstrates that diminished iron stores in cyanotic congenital heart disease are associated with a more right-shifted oxyhemoglobin dissociation curve (increased P50). In addition, MCV was larger than in normal patients and, if > 90th percentile for age and sex, suggested iron sufficiency.