Bench Level Oximetry: Pulse Oximetry and CoOximetry

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Bench Level Oximetry Pulse Oximetry and
Co-Oximetry

• Kandi Deshotel
• Sonya Amratlal
• RESC 3621 Physiologic Monitoring
• Tittle M, Flynn M. Correlation of Pulse Oximetry
  and Co-oximetry. Dimensions of Critical Care
  Nursing. 1997 16(2) 88-94.

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Pulse Oximetry

• Today pulse oximetry is currently becoming
  commonplace in critical care environments
• Pulse oximetry is an advancement in noninvasive
  monitoring and assessment of arterial blood
  oxygenation
• The primary purpose is to verify adequate
  arterial oxygenation to help ensure provision of
  sufficient oxygen delivery to metabolize tissues
• WARNING IT SHOULD NOT BE CONSIDERED A
  REPLACEMENT FOR ABG ANALYSIS

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Co-Oximetry

• Ease of Operation
• Intuitive use interface
• Minimal maintenance
• Sampling versatility
• Added Measurement Features
• Fetal Hemoglobin (HbF) correction
• Turbidity correction

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The Study

• The purpose was to assess the correlation of
  arterial oxygen saturation (SaO2) and pulse
  oximetry (SpO2) in 28 ICU patients using the ear
  and finger probes.
• It is important to know whether the correlation
  of pulse oximetry and co-oximetry measurements of
  arterial saturation can be used to make decisions
  related to the oxygen needs of the patient.

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The Findings

• Oxygen Saturation Results

• The SaO2 ranged from 70.7 to 99.5 with a mean
  of 95.3
• The SpO2 by ear probe ranged from 74 to 100
  with a mean of 95.6
• The SpO2 by finger probe ranged from 74 to 100
  with a mean of 96.6

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The Findings

• The correlation between SaO2 and SpO2 measured by
  the finger probe was r 0.92
• The correlation between SaO2 and SpO2 measure by
  ear was r 0.92
• A significant positive correlation of SpO2
  measured by both the ear and finger probe was
  r.79

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Discussions

• Pulse oximetry measured with the finger probe
  appears to correlate better with the SaO2 than
  SpO2 measured with the ear probe
• Question What are some possible reasons that
  caused this to happen in this specific
  population?
• The patients were not significantly hypothermic
  nor hypoperfused
• The probe may have been placed on the ear in an
  area with the most vascularity

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Discussions

• The SaO2 of 90 was based on an interpretation of
  SaO2/SpO2 correlation from baseline ABGs.
• Baseline ABGs varied for each patient however
  was determined at the beginning and based on a
  mean average

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Limitations

• The sample was one of convenience, therefore the
  results cannot be generalized to all patients in
  ICU
• Various ethnic groups were not well represented
• The sample size was too small containing 28 ICU
  patients, however conducted with 60 data points
• Only one pulse oximetry model was evaluated

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Brief on Research 2

• Conducted to determine accuracy and precision of
  the pulse oximetry during exercise.
• Eight white men with COPD were selected for this
  research. Studies were conducted with the
  following methods
• 1) Measurement of SaO2 using a co-oximeter
• from arterial blood at each workload.
• 2) SpO2 and pulse rate were measured using
  
• a Ohmeda 3700 pulse oximeter.
• 3) Heart rate was also monitored using ECG

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The Gold Standard

• In this figure the linear line is our gold
  standard for SaO2 in correlation with SpO2
  configuration.
• The dot furthest left on the top blog the
  patients SaO2 had a reading of 95 and a SpO2
  reading of 85.This allows the room for error to
  be 10 --Thats A LOT!
• The bias of the pulse oximeter measurement
  relative to the SaO2 was 1.7 while the precision
  was 2.9

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SaO2-SpO2 vs. ECG rate- pulse rate

• This graphic allows us to see how the accuracy of
  the SpO2 compared with SaO2 did not improve when
  the pulse and heart rate were equivalent,
  relative to when they were not equivalent. (Note
  this conclusion was held whether the SaO2 was
  uncorrected or corrected for COHb levels)
• This graphic is uncorrected for COHb.
• Note the horizontal line _at_ 0 is considered to be
  the zero balance

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Results

• Oxygen saturation as measures by pulse oximetry
  (SpO2) in patients with COPD undergoing exercise
  testing is not sufficiently accurate to replace
  SaO2 as the golden standard for oxygen
  saturation.
• Accuracy and precision, as determined by bias and
  SD, are not improved when O2 saturation is
  corrected by COHb, nor are they improved when
  pulse and heart rate are equilavent.

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Discussion

• It is critical to understand that the conclusion
  of this study is inaccurate due to the fact of
  the inaccuracy of the Ohmeda 3700, which was
  discovered only after the study had been
  conducted.
• However, graphs conducted through this research
  show great correlation of what is known to be the
  gold standard for oxygen saturation.

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Conclusions

• In the first study of ICU patients the
  correlation on SaO2 and SpO2 showed a positive
  correlation but due to the sample size it was not
  enough to change the Gold Standard.
• In the second study due to the fact that the
  pulse oximeter was inaccurate the study was bias.