Sickle Cell and Anesthesia

Hemoglobin: Structure and Function Hemoglobin (Hb) is composed of two pairs of sub-units containing protoheme and globin.. The various globin chains differ in the number and sequence of amino acids and are designated by α, β, γ, δ, ε, ζ, and θ. Normal adult RBCs have three types of hemoglobin: HbA (α2,β2) approx. 95%, HbA2 (α2δ2) approx. 2.5 %, and HbF (α2γ2). The spatial relationship of the four subunits determines oxygen affinity as well as physical properties such as Hb solubility and stability. At birth red cells contain 70-90 % HbF until 2-4 months of age. Beta chain production begins shortly before birth and gamma chain production wanes resulting in a normal adult profile by age 4 months. Thus disorders of the beta chain will not manifest themselves in the first few months nor be identified by precipitation screening tests. Hemoglobinopathies can result from either production of an abnormal hemoglobin chain or by under production of a given chain. The most common mechanism of the former type is the result of a single substitution of one amino acid for another on the protein chain, which occurs with sickling disorders. Underproduction of a given chain results in a group of disorders known as thalassemias.