MCQ 4:

Decrease in spO2 is seen in all except:

a – Meth-hemoglobinemia

b- Carboxy-hemoglobinemia

c – Sulfhemoglobinemia

d – Fetal hemoglobin

 

Ans: Carboxy-hemoglobinemia

 

The effect of HbCO may be discerned by examining its absorption spectrum. At 920 nm, HbCO has an extremely low absorbance and therefore does not contribute to total absorbance. At 660 nm,
however, HbCO has an absorbance very similar to that of HbO2 , and SpO2 will therefore be falsely high. (ref: Miller)

COHb is typically read by a two-diode oximeter as 90% oxyhemoglobin and 10% reduced hemoglobin, resulting in false elevations of SpO₂. In the emergency department setting or shortly after ICU admission, a gap between pulse oximetry and Po₂ or cooximetrically measured oxygen saturation may suggest elevated COHb levels, particularly in patients with smoke inhalation or potential carbon monoxide poisoning. (Ref: Irwin and Rippe)