The oxygen affinity of sickle hemoglobin

Area of Science:

• Hematology
• Pulmonary Medicine
• Clinical Chemistry

Background:

• The oxyhemoglobin dissociation curve is right-shifted in sickle cell disease (SCD), leading to the assumption of low arterial oxygen saturation (S(o)(2)) even with normal oxygen partial pressure (P(o)(2)).
• Hemoglobin S (HbS) exhibits normal oxygen affinity in the absence of polymer formation, which is minimal under normoxic conditions.

Purpose of the Study:

• To test the hypothesis that in vivo S(o)(2) is normal in SCD patients when P(o)(2) is normal.
• To clarify the relationship between oxygen saturation, oxygen partial pressure, and oxygen affinity in SCD.

Main Methods:

• Retrospective analysis of 50 blood gas and COoximetry samples from SCD patients and matched controls.
• Comparison of SCD data against the Severinghaus curve, stratified by hypoxemia status.

Main Results:

• Non-hypoxemic SCD data and control data closely aligned with the Severinghaus curve.
• Hypoxemic SCD data (S(o)(2) < 92.5%) fell significantly below the standard curve.
• SCD patients exhibit normal oxygen affinity at normal arterial S(o)(2) but reduced affinity under hypoxic conditions.

Conclusions:

• Abnormally low S(o)(2) in SCD patients indicates abnormally low P(o)(2).
• Pulse oximetry accurately reflects S(o)(2) in SCD.
• Low pulse oximeter readings in SCD are reliable indicators of impaired gas exchange.