Which factor is NOT associated with an increased risk of sickling in patients with sickle-cell disease?

Which factor is NOT associated with an increased risk of sickling in patients with sickle-cell disease?

• A. Inhaled nitric oxide
• B. Dehydration
• C. Metabolic acidosis
• D. Hypoxemia

Answer: (A)

Sickling occurs when hemoglobin S polymerizes as red cells become deoxygenated. Factors that raise the amount of deoxygenated HbS or concentrate HbS inside the cell promote this polymerization. Dehydration concentrates hemoglobin within red cells, increasing HbS polymer formation. Metabolic acidosis lowers pH, which enhances deoxygenation and thus polymerization. Hypoxemia lowers the available oxygen, raising the fraction of deoxy-HbS and promoting sickling. Inhaled nitric oxide does not act as a trigger for HbS polymerization. It helps by dilating vessels and can improve microvascular blood flow and reduce some endothelial activation, potentially reducing vaso-occlusion rather than increasing sickling risk. Therefore inhaled nitric oxide is not associated with an increased risk of sickling, making it the correct choice.

Sickling occurs when hemoglobin S polymerizes as red cells become deoxygenated. Factors that raise the amount of deoxygenated HbS or concentrate HbS inside the cell promote this polymerization. Dehydration concentrates hemoglobin within red cells, increasing HbS polymer formation. Metabolic acidosis lowers pH, which enhances deoxygenation and thus polymerization. Hypoxemia lowers the available oxygen, raising the fraction of deoxy-HbS and promoting sickling.

Inhaled nitric oxide does not act as a trigger for HbS polymerization. It helps by dilating vessels and can improve microvascular blood flow and reduce some endothelial activation, potentially reducing vaso-occlusion rather than increasing sickling risk. Therefore inhaled nitric oxide is not associated with an increased risk of sickling, making it the correct choice.