PULSE OXIMETRY

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PULSE OXIMETRY

• CASE
  STUDIES

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CASE 1 Methemoglobinemia and its
Effects on Pulse Oximetry

• Cited from Critical Care Medicine Journal
• July 1991

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Patient History

• 61 y/o white male
• History of diabetes mellitis, coronary heart
  disease, peripheral vascular disease, COPD,
  colonic polyps, and dermititis herpetifromis
• Scheduled to undergo DISTAL FEMORAL ARTERY BYPASS
  SURGERY

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Examination Findings

• Pulmonary Function mild obstructive ventilatory
  insufficiency
• ABG pH 7.40
• PaO2 74mmHg
• PaCO2 37mmHg
• SaO2 78
• CarboxyHb 1.9
• MetHb 10.0

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• After the patient is intubated and 100
  Oxygen is delivered, the pulse oximeter is
  displaying a percentage saturation of only 85.
• QUESTION 1
• What action should be taken?

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Answer 1 An ABG should be taken

• The new readings indicate a SaO2 of 99 with
  metHb level of 13.3
• The patient appeared dusky and the sample taken
  was dark in color
• Question 2
• What are the normal values for MetHb?
• What about CarboxyHb?

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Answer 2 Normal ranges for all types of Hb

• Met Hb 3
• CarboxyHb 3(but can be as high as 15 in
  smokers)
• Question 3
• Why does this error occur when excess MetHb is
  present?

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Graph 1

• MetHb absorbs strongly at 660 and 940nm

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MEDICATIONS THAT CAUSE METHEMOGLOBINEMIA

• Nitrates
• Sodium Nitroprusside
• Phenacetin
• Sulfates
• Lidocaine
• Cetacaine

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CONCLUSION

• It is important as practitioners that we
  understand the limitations of the devices we
  choose in order to avoid inappropriate therapy,
  as well as our alternative approaches in the
  incident that these limitations occur.

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CASE STUDY 2 Use of Pulse-ox in New
SaO2-oriented technique for Bronchopulmonary
Lavage

• Cited in Chest Journal, November 1991
• The term Bronchopulmonary Lavage
• The washing out, or cleansing of the air
  passages (bronchi) as well as the lungs

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Patient Presentation

• 52 y/o female weighing 53kg
• Suffers from alveolar proteinosis
• Has previously undergone bronchopulmonary lavage
  18 times in the past 6 years
• She is seeking the new SaO2-oriented technique
  versus previous conventional method

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OR monitors include

• Pulse oximeter
• Precordial/Esophageal stethoscope
• Blood Pressure cuff
• EKG
• Capnometer
• Radial catheter for ABG

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RESULTS
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CONCLUSION

• Bronchopulmonary Lavage with use of pulse
  oximeter allowed for a better determination of
  how much fluid should be drained
• Duration was shorter
• Overall a safer procedure and efficient outcomes

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Questions

• 1.) What are some indications that would suggest
  a bronchopulmonary lavage be performed?

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Case Study 3 Transesophageal versus
Surface Pulse Oximetry in Intensive Care Unit
Patients

• Cited in Critical Care Medicine Journal
• July, 2000

This study is based on 40 patients rather than
just one All patients had severe trauma or
disease and required controlled
ventilation and heavy sedation
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PURPOSE

• To compare oximetry readings of transesophageal
  oximetry and surface pulse oximetry with those
  values obtained from an arterial blood gas
• Compare which variables may or may not effect
  both types of oximetry readings

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METHOD

• For transesophageal oximetry, a probe with a
  sensor (based on reflectance spectroscopy) is
  placed deep into the esophagus
• After 10 minutes of equilibrating the ABG,
  surface pulse oximeter, and the transesophageal
  oximeter, the results are compared

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RESULTS

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CONCLUSION

• Transesophageal oximetry has excellent proximetry
  in comparison with the readings from an arterial
  blood gas
• The transesophageal oximeter is less likely to be
  effected by variables such as core temperature
  and blood pressure

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QUESTIONS??

• 1.) If my body temperature increased, how would
  my saturation from the pulse oximeter compare to
  that of the ABG?
• And if the temperature decreased?
• 2.) Can you think of any limitations to using
  the transesophageal oximetry method?

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