Pulse Oximetry

Advantages of pulse oximetry

  • More sensitive in hypoxemia
  • Readings do not depend on patient’s Hb level
    Unlike SaO2 which is directly measured in blood gas (OxyHb/Total Hb X 100)

Limitations of pulse oximetry

  • Dyshemoglobinemias
    – May underestimate the degree of oxygen saturation in carbon monoxide poisoning
    – In methemoglobinemia, the SpO2 decreases initially but then plateaus off
  • Poor peripheral perfusion
  • Other things
    – Dyes: eg nail polish can interfere with oximetry
    – Exaggerated venous pulsation maybe mistaken for arterial one, leading to spuriously low oxygen saturation techniques.

Reference: Steven McGee. Evidence Based Physical Diagnosis. Pg 203-206



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