In relation to this, O2 is transported dissolved in solution in <2% and combined with Hb in >98%, so in the anesthetic–surgical patient or those with critical illnesses, the evaluation and determination of blood Hb is very important to prevent or control states of anemia and hypoxia, especially in those individuals where the risk of hemorrhage may be high [7]. This evidence concerns the gene GSTM1 and anemia (phenotype).