Falsely low pulse oximetry

Q: All of the following may falsely give a low reading of pulse-oximetry EXCEPT? - Select one

A) Methemoglobinemia

B) Sickle cell disease

C) Severe anemia 

D) Arterial pulsation  

E) Nail polish

Answer: D

Although pulse-Ox can be generally trusted in patient monitoring, clinicians need to be aware that there are many conditions where the monitor may display falsely low readings. In an Inpatient setting, one of the frequently ignored situations is in patients with venous congestion (instead of arterial congestion/pulsation - choice D) due to tricuspid valve insufficiency or severe cardiomyopathy. Any hemodynamic condition that leads to venous congestion may generate falsely low SaO2 readings. To make things more complicated, even arterial blood gas may not be completely reliable due to 'backing up' of pulsatile venous blood as part of the arterial sample.

Venous pulsations may also occur when an adhesive around the probe is too tight on the finger, the probe is in a dependent position (e.g., a forehead probe in a patient in the Trendelenburg position), and in cases of arteriovenous shunting. In such situations, loosening or repositioning the probe may resolve the issue.

#hemodynamic

#oxygenation

References:

1. Secker C, Spiers P. Accuracy of pulse oximetry in patients with low systemic vascular resistance. Anaesthesia 1997; 52:127.

2. Stewart KG, Rowbottom SJ. Inaccuracy of pulse oximetry in patients with severe tricuspid regurgitation. Anaesthesia 1991; 46:668.

3. Torp KD, Modi P, Pollard EJ, et al. Pulse Oximetry. [Updated 2023 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470348/