Monitoring oxygenation

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Monitoring oxygenation

• Alexander C. White MD
• New England Sinai Hospital

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Outline

• Why 21
• Essential physiology
• SpO2
• Useful formulas

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21

• oxygen in the atmosphere
• Age of adulthood
• Legal age for alcohol consumption
• Card game
• Movie MIT
• 21st century

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Composition ofdry atmosphere, by volume5
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Minor components of air not listed above
includecitation needed
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(No Transcript)
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Oxygen transport

• Dissolved oxygen
• PaO2
• Bound oxygen
• SpO2

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Dissolved oxygen

• Henrys Law
• Dissolved O2 proportional to PaO2
• 0.003 ml O2 per 100 ml blood
• PaO2 100 mm Hg 0.3 ml O2 per 100 ml
• If CO 30 L/min 90 ml per min
• Butcan need 3000 ml O2 per minute

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Oxygen content of blood

• CaO2 (1.34 x Hb x SaO2) 0.003 x PaO2

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The power of hemoglobin
Marino ICU Book
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O2 Concentration in whole blood
Marino ICU Book
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The importance of hemoglobin

• 98-99 of Oxygen in the blood is carried on
  Hemoglobin

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Hemoglobin molecule
Heme
Globin
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Hemoglobin

• Structure
• Iron porphyrin compound
• 4 globin chains
• Hemoglobin A, F and S
• Cooperative binding- the more globin binds O2 the
  more it wants to bind O2

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• Those who get what they want
• Those who want what they get
• Hb wants all the oxygen it can get ( Wall Street)

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Oxygen dissociation curve
Google images 2008
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ODC

• PaO2 40 ..SpO2 75
• PaO2 100SpO2 97
• Curve is shifted to right temp, Pco2, H, 2,3
  DPG
• Left shift with CO

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Oxygen delivery and uptake

• Do2 Q x (1.34 x Hb x SaO2) X 10
• Vo2 Q x 13.4 x Hb x (SaO2 SvO2)

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Septic shock

• Goalsto optimize organ function by optimizing
  oxygen delivery

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Figure of Sickle cell
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Monitoring during mechanical ventilation

• Ventilator function
• Lung mechanics
• Sedation
• Hemodynamics
• Tissue oxygenation
• Gas exchange

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Ventilator function
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Lung mechanics during mechanical ventilation
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Sedation

• Monitoring
• Sedation and weaning from mechanical ventilation

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Hemodynamics

• Software to track changes
• Trend watch
• Networking
• Multiple ventilators
• rapid response team

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Pulse oximetry

• Concentration of a substance can be determined by
  its ability to transmit light
• Beer Lambert Law

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Pulse oximetry
HbO2
X 100
HbO2 HbR COHb MetHb
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Continuous pulse oximetry

• Two wavelengths of light
• 660 940 nm
• Pulsating vascular bed

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Accuracy and response time

• SaO2 gt 70 2
• SaO2 50-70 3
• Delayed response time
• Finger
• Vasoconstriction
• Bradycardia

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Sources of error

• Dyshemoglobinemia and vascular dyes
• Motion artefact and low perfusion
• Venous congestion, AV fistulas
• False low SaO2
• Dark nail polish
• False low
• Pigmented skin
• Need SaO2 of 95 in AA, 92 in W

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Sources of error

• Increase in bias and reduced precision
• Hb lt 8
• SaO2 lt 54
• False elevation in SpO2 with hyperbilirubinemia
• Technology getting better all the time

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Methemoglobinemia

• Fe2 to Fe3
• Causes
• Cytochrome b5 reductase deficiency
• Dapsone
• Chloroquine
• Sulfonamides
• Benzocaine, Lidocaine

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Methemoglobinemia

• PaO2 normal
• Saturation gap (Low SpO2, ABG sat is higher)
• Chocolate colored blood
• Treatment
• Stop offending agent
• Methylene Blue
• Ascorbic acid (G6PD defic)
• Hyperbaric oxygen and exchange transfusion

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Carbon monoxide poisoning

• Exposure to CO ( fire)
• Tissue ischemia
• Brain, heart, elevated lactate
• SpO2 in normal range, normal PaO2
• Elevated carboxyhemoglobin on ABG ( co-oximetry)

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Carbon monoxide poisoning

• Treatment
• Oxygen ( reduces half life of carboxyhemoglobin
  to lt 100 min)
• Hyperbaric oxygen
• (COHb gt 25)
• Tissue ischemia
• Pregnancy (COHb gt 20)

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Failure of oximetry in COHb
Up to date 2009
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Interpreting the data
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Bibliography

• Monitoring during mechanical ventilation
• Hess DR.
• Physiology The Essentials West