Pulse Oximetry - Indication - Limitations

Limitations

Pulse oximetry measures solely oxygenation, not ventilation and is not a complete measure of respiratory sufficiency. It is not a substitute for blood gases checked in a laboratory, because it gives no indication of base deficit, carbon dioxide levels, blood pH, or bicarbonate (]) concentration. The metabolism of oxygen can be readily measured by monitoring expired CO2, but saturation figures give no information about blood oxygen content. Most of the oxygen in the blood is carried by hemoglobin; in severe anemia, the blood will carry less total oxygen, despite the hemoglobin being 100% saturated.

Erroneously low readings may be caused by hypoperfusion of the extremity being used for monitoring (often due to a limb being cold, or from vasoconstriction secondary to the use of vasopressor agents); incorrect sensor application; highly calloused skin; or movement (such as shivering), especially during hypoperfusion. To ensure accuracy, the sensor should return a steady pulse and/or pulse waveform. Pulse oximetry technologies differ in their abilities to provide accurate data during conditions of motion and low perfusion.

Pulse oximetry also is not a complete measure of circulatory sufficiency. If there is insufficient bloodflow or insufficient hemoglobin in the blood (anemia), tissues can suffer hypoxia despite high oxygen saturation in the blood that does arrive. In 2008, a pulse oximeter that can also measure hemoglobin levels in addition to oxygen saturation was introduced by Masimo. In addition to the standard two wavelengths of light, the devices use multiple additional wavelengths of light to quantify hemoglobin.

Since pulse oximetry only measures the percentage of bound hemoglobin, a falsely high or falsely low reading will occur when hemoglobin binds to something other than oxygen:

  • Hemoglobin has a higher affinity to carbon monoxide than oxygen, and a high reading may occur despite the patient actually being hypoxemic. In cases of carbon monoxide poisoning, this inaccuracy may delay the recognition of hypoxia (low blood oxygen level).
  • Cyanide poisoning gives a high reading, because it reduces oxygen extraction from arterial blood. In this case, the reading is not false, as arterial blood oxygen is indeed high in early cyanide poisoning.
  • Methemoglobinemia characteristically causes pulse oximetry readings in the mid-80s.

The only noninvasive method allowing continuous measurement of the dyshemoglobins is a pulse CO-oximeter, invented in 2005 by Masimo. It provides clinicians a way to measure the dyshemoglobins carboxyhemoglobin and methemoglobin along with total hemoglobin.

Read more about this topic:  Pulse Oximetry, Indication

Other articles related to "limitations":

Section 91(27) Of The Constitution Act, 1867 - Scope of The Federal Power - Limitations
... asserted that limitations on rights must be motivated by an objective of sufficient importance ...
Preferential Bidding System - Constraints
... CBA) - ALPA, AFA, IBT Airline Policies - FRMP, Fairness These include Flight Time Limitations (FTL) - Daily, Weekly, Monthly, Quarterly and Yearly Flight Duty Period Limitations (FDP ... Separation of assignments, base allocation of crew members, Reserve limitations, Crew Training Requirements ...
Metal Gear Solid 4: Guns Of The Patriots/Archive 1 - Reception - Konami Review Limitations
... Several publications have commented on limitations given to pre-release reviewers by Konami, including discussion on the length of cutscenes and size of the ... These limitations resulted in Electronic Gaming Monthly delaying its review ... the game either, claiming Konami have withheld review code because of non-compliance with the limitations ...
Super Mario's Wacky Worlds - Overview - Limitations
... Due to the limitations of the CD-i, several features could not be included in the game, such as large numbers of sprites on the screen, Mode 7 and many visual effects ...

Famous quotes containing the word limitations:

    Much of what contrives to create critical moments in parenting stems from a fundamental misunderstanding as to what the child is capable of at any given age. If a parent misjudges a child’s limitations as well as his own abilities, the potential exists for unreasonable expectations, frustration, disappointment and an unrealistic belief that what the child really needs is to be punished.
    Lawrence Balter (20th century)

    No man could bring himself to reveal his true character, and, above all, his true limitations as a citizen and a Christian, his true meannesses, his true imbecilities, to his friends, or even to his wife. Honest autobiography is therefore a contradiction in terms: the moment a man considers himself, even in petto, he tries to gild and fresco himself.
    —H.L. (Henry Lewis)

    Growing up means letting go of the dearest megalomaniacal dreams of our childhood. Growing up means knowing they can’t be fulfilled. Growing up means gaining the wisdom and skills to get what we want within the limitations imposed by reality—a reality which consists of diminished powers, restricted freedoms and, with the people we love, imperfect connections.
    Judith Viorst (20th century)