Pulse Ox and diabetes

 Q:  Pulse-oximetry reading in a poorly controlled diabetic patient would be falsely? (select one)

A) high

B) low

Answer: A 

Diabetic patients with glycohemoglobin A1c (HbA1C) higher than 7 may falsely read pulse ox's arterial oxygen saturation (SaO2) high. This is due to high hemoglobin oxygen affinity. 

The pulse ox's modus operandi is based on Beer-Lambert law. According to this law: "absorption of light of a given wavelength passing through a non-absorbing solvent, which contains an absorbing solute, is proportional to the product of the solute concentration, the light path length, and an extinction coefficient." 

The higher the HbA1C, the higher is the reading of the solute concentration.

#hematology

References:

1. Pu LJ, Shen Y, Lu L, et al. Increased blood glycohemoglobin A1c levels lead to overestimation of arterial oxygen saturation by pulse oximetry in patients with type 2 diabetes. Cardiovasc Diabetol 2012; 11:110.

2. Jubran A. Pulse oximetry. Intensive Care Med 2004; 30:2017.

3. Bongard F, Sue D. Pulse oximetry and capnography in intensive and transitional care units. West J Med 1992; 156:57.