Transcutaneous Monitoring and Pulse Oximetry

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Transcutaneous Monitoring and Pulse Oximetry

• RC 290

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TCM PO2 and PCO2 via Skin Electrodes

• Continuous and non-invasive
• Digital readout plus hard copy
• TCM values show values of O2 and CO2 at tissue
  level
• These values are a affected both by lung function
  and perfusion
• TCM used more in infants than adults because
  infants have thinner skin and less sub-Q fat

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TCM System
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TCM Electrodes

• PO2 is a Clark electrode
• PCO2 is a Severinghaus electrode
• Electrodes should not be placed over bone
• Electrodes may be heated to arterialize the
  site
• Heated electrodes need to be moved every 4-8
  hours

• Water or a sealant solution should be placed on
  the skin to prevent an air bubble from forming
  between the skin and electrode
• Electrodes usually sloped, ie 2 point
  calibration

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TCM Monitor Unit

• Controls for electrode temperature and high and
  low limits for alarms
• Digital display of TCM values
• Power or energy indicator (shows how much is
  being used to heat electrode
• This is the perfusion monitor!

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Power/Energy Level Changes

• After the unit is started and stabilizes, the
  relative heating power indicator is zeroed
• If it starts to have a positive deflection, this
  means it is taking more power to keep the
  electrode heated to the set temperature
• This means perfusion has increased!

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Power/Energy Level Changes (cont.)

• If relative power starts to have a negative
  deflection, this means it is taking less energy
  to keep the electrode at the set temperature
• This indicates decreased perfusion!
• TCM values and arterial values have poor
  correlation with decreased perfusion!

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If relative heat energy does not have a negative
deflection, correlation between TCM and arterial
values is good

• Decreased TCM PO2 without negative deflection of
  relative heat energy usually indicates a
  pulmonary problem

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A negative deflection in relative heating power
with a drop in TCM PO2 usually indicates a
perfusion problem

• Not a lung problem!

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TCM Uses

• Making ventilator changes
• Effects of activities on infant
• Feeding, handling, etc
• Effects of respiratory therapies
• O2 changes, PD P, suctioning , etc
• Identifying the direction of shunt in PDA

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Shunt Direction in PDA Using TCM

• Two TCM PO2 electrodes
• One is placed pre-ductal and the other is
  post-ductal
• If difference is greater than 15 mmhg, PDA is R-L

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TCM Does Not Replace ABGs

• It does cut down on the number of ABGs and is a
  good indicator of when they need to be done

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Pulse Oximetry in Neonates

• Advantages
• Less costly than TCM
• Less maintenance than TCM

• Disadvantages
• Does not give a direct indication of perfusion
• Can not assess ventilation/PCO2
• Does not give good indication of hyperoxia
• Alarms should be set between 92 and 95

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Pulse Oximetry Is Used More for Surveillance
than Diagnosis
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Time to relax!