Pulse oximetry measures oxygen saturation in the blood by detecting light absorption of oxygenated and deoxygenated hemoglobin. It was originally developed in the 1930s-1940s and further advanced in the 1970s. Pulse oximetry is now considered the fifth vital sign. It provides a noninvasive method to monitor oxygen saturation, with readings of 92% or above having high sensitivity and specificity for excluding hypoxemia. However, pulse oximetry has some limitations, including reduced accuracy at very low saturations, and inability to detect carboxyhemoglobin or methemoglobin. It also provides no information on pH, PCO2, or hemoglobin levels.

1. PULSE OXYMETRY
DrTanveerKamal Fahim
Resident – Pulmonology , Phase B
,NIDCH

3. • In 1935, Karl Matthes (German physician 1905–1962)
developed the first 2-wavelength ear O2 saturation meter red
and green filters
• The original oxymeter was made by Glenn Allan Millikan in the
1940s
• Further developed in 1972, by Takuo Aoyagi and Michio
Kishib, bioengineers, at Nihon Kohden using the ratio of red to
infrared light absorption of pulsating components at the
measuring site
• By 1987, the standard of care for the administration of a
general anesthetic in the U.S. included pulse oximetry infrared

4. PULSE OXYMETRY
Pulse oxymetry measures Hb oxygen saturation (How
much of the Hb in the blood is carrying the Oxygen) by
detecting the absorption of light at two specific
wavelengths that correspond to the absorption peaks of
oxygenated and deoxygenated haemoglobin
Also measures pulse rate per minute

5. •An oxygen saturation of 92% or above measured by
pulse oximetry has a sensitivity of 100% and
specificity of 86% for excluding hypoxaemia
•Pulse Oxymetry is also regarded as “The Fifth Vital
Sign” now

6. ACHIEVING DESIRABLE OXYGEN
SATURATION RANGES IN ACUTE ILLNESS
• Recommended target saturation range foracutely ill patients
not at riskof hypercapnic respiratory failure is 94–98%
• Formost patients with known COPDorotherknown risk
factors forhypercapnic respiratory failure (morbid obesity,
cystic fibrosis , chest wall deformities orneuromuscular
disorders orfixed airflow obstruction associated with
bronchiectasis) a target saturation range is 88–92%

14. • Finger and earlobe measurements are more accurate than
measurements from a probe applied to the toe
• Finger probes may be more accurate than ear

17. Oximetry gives a normal reading in most patients with
anaemia because the oxygen saturation of the available
haemoglobin is normal
Although the total amount of haemoglobin available for
oxygen
transport is reduced
These patients have normal oxygen saturation
levels despite having ‘anaemic hypoxia’ which may cause
considerable reduction in the total oxygen content of the blood
PULSE OXIMETRY IN ANAEMIA

18. LIMITATIONS OF PULSE OXYMETRY
• Accurate within 1–2% of directly measured SaO2 in most patients
but the erroris greateris in patients with very low saturation (below
80–85%)
• The accuracy of oximeters in shock, sepsis and hypotension is
largely unknown
• It is important to ensure that the oximeterhas a good signal and to
avoid artefact due to motion, nail varnish orotherpotential sources
of error

19. • The accuracy of oximetry is unreliable in the presence of
carbon monoxide ormethaemoglobin
• Both of these substances have similar light absorption
characteristics to oxyhaemoglobin so an apparently normal
SpO2 in a patient with carbon monoxide poisoning or
methaemoglobinaemia may be falsely reassuring

20. • Oxymetry can be misleadingly normal in smokers because
of raised carboxyhaemoglobin levels which will cause a
reduced blood oxygen content despite an apparently normal
oxygen saturation and a normal PO2
• Patients who have smoked cigarettes in the previous 10
hours may therefore be at increased risk from hypoxaemia

21. • Measurements on sleeping patients should be recorded over
several minutes to avoid the possibility of a normal transient
nocturnal dip in oxygen saturation
• If desaturation is noted during sleep look for evidence of snoring or
sleep apnoea

22. Accuracy is diminished in patients with poor peripheral perfusion
which may occur chronically in conditions such as systemic
sclerosis or acutely in patients with hypotension or
hypovolaemia
Pulse oximetry gives no information concerning pH, PCO2 and
Hb level
Probe may need to be tried on different fingers or toes or on the
earlobe to obtain the best available signal

23. Oxymetry may be less accurate in acutely ill patients on
ICUs
In the case of sickle cell crisis, pulse oximetry may
underestimate the level of oxygenation
There are some patients with poor perfusion for whom pulse
oximetry measurements cannot be made-cold peripheries
(eg, Raynaud’s phenomenon) severe hypotension and
peripheral ‘shut down’

24. • The presence of a normal SpO2 does not exclude the need for
blood gas measurements specially if the patient is on
supplemental oxygen therapy
• Pulse oximetry will be normal in a patient with a normal oxygen
tension (PO2) but abnormal carbon dioxide tension (PCO2) or
with a low blood oxygen content due to anaemia

25. • Pulse oximetry gives no information concerning pH, PCO2
or haemoglobin level
• So blood gases and full blood count tests are required as
early as possible in all situations where it is important

26. THANK YOU ALL