Congenital heart disease
Seeking Optimal Relation Between Oxygen Saturation and Hemoglobin Concentration in Adults With Cyanosis from Congenital Heart Disease

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In patients with cyanosis from congenital heart disease, erythropoiesis is governed by many factors that can alter the expected relation between the oxygen saturation (O2sat) and hemoglobin concentration. We sought to define the relation between the O2sat and hemoglobin in such patients and to predict an ideal hemoglobin concentration for a given O2sat. Adults with congenital heart defects and cyanosis were studied prospectively using blood tests and exercise testing. Nonoptimal hemoglobin was defined as any evidence of inadequate erythropoiesis (i.e., iron, folate, or vitamin B12 deficiency, increased erythropoietin, reticulocytosis, or a right-shifted oxygen-hemoglobin curve). For patients without these factors, a linear regression equation of hemoglobin versus O2sat was used to predict the optimal hemoglobin for all patients. Of the 65 patients studied, 21 met all the prestudy criteria for an optimal hemoglobin. For all patients, no correlation was found between O2sat and hemoglobin (r = −0.22). However, a strong linear correlation was found for those meeting the criteria for optimal hemoglobin (r = −0.865, p <0.001). The optimal hemoglobin regression equation was as follows: predicted hemoglobin = 57.5 − (0.444 × O2sat). A negative correlation was found between the hemoglobin difference (predicted minus measured) and exercise duration on cardiopulmonary exercise testing (r = −0.396, p = 0.005) and the 6-minute walk distance (r = −0.468, p <0.001). In conclusion, a strong relation between O2sat and hemoglobin concentration can be shown in stable cyanotic patients and used to predict an optimal hemoglobin. This relation might be useful in defining functional anemia in this group.

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Methods

We prospectively enrolled consecutive adults with congenital heart disease in a descriptive cross-sectional study. Patients gave consent, and institutional ethics review approved the protocol. Patients were included if they had a known congenital defect with a right-to-left shunt. We included patients with a wide range of O2sat, including some patients who had undergone previous repair and had a normal O2sat at the study. All tests were obtained within a 24-hour period. Other data from the

Results

A total of 65 patients were studied (mean age 36 ± 12 years, 67% women). For the whole group, the O2sat at rest was 81 ± 8%, hemoglobin was 19.6 ± 2.9 g/dl, and hematocrit was 60 ± 8%. The anatomic diagnoses are listed in Table 2, as well as their group designation. All but 1 patient had pulmonary vascular disease. Of the 65 patients, 20 had likely been cyanotic at birth, with 45 (largely with simple shunts) having developed right to left shunting over time. No patient was found to have

Discussion

The concept of determining an ideal set point for erythropoiesis in congenital heart disease with cyanosis is not new. An “optimal hematocrit” between oxygen delivery and hyperviscosity was studied decades ago,4 although limited by the use of ex vivo models.5 Few clinical studies have addressed this relation and largely only in children or adolescents.5, 6 A linear relation has been shown, although less steep than ours.5, 7, 8 A right shift of the oxyhemoglobin dissociation curve has been seen

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    Citation Excerpt :

    Although a number of studies in the general population [1,2] and in patients with coronary artery disease [3], heart failure [4,5], pulmonary arterial hypertension [6] and congenital heart disease (CHD) [7,8] have linked high RDW values with a worse prognosis, there are confounding factors, such as renal failure, anaemia and cyanosis, which form part of the causal pathway of anisocytosis that may obscure the real effect of RDW on outcome. In fact, RDW plays an essential role in the differential diagnosis of anaemia [9,10], being an economic tool for detecting low serum apoferritin concentrations in patients with CHD who are cyanotic [11] – a population with a high percentage of anaemia despite optimizing their haemoglobin concentrations [12]. Therefore, RDW may be an epiphenomenon rather than an effective player in the pathogenesis of cardiovascular diseases [13].

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The study was funded by the Clinical Research Committee, Royal Brompton Hospital. Dr. Broberg has received support from the Waring Trust (London, United Kingdom) through the Royal Brompton Hospital and the Tartar Trust (Portland, Oregon) through the Oregon Health and Sciences University. Dr. Gatzoulis and the Royal Brompton Adult Congenital Heart Centre have received support from the British Heart Foundation, London, United Kingdom and unrestricted research funds from Actelion UK (London, United Kingdom).

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