Transcutaneous Monitoring and Pulse Oximetry

RC 290

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

TCM System

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

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!

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!

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!

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

A negative deflection in relative heating power with a

drop in TCM PO2 usually indicates a perfusion problem

Not a lung problem!

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

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

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

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%

Pulse Oximetry Is Used More for Surveillance than

Diagnosis

Time to relax!