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Transcutaneous CO2 monitoring

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Using transcutaneous measurements has the potential to reduce the number of blood gases needed to manage ventilation, result in more stable oxygen and carbon dioxide status and alert medical and nursing staff to a change in condition of the baby, although evidence to support this is currently not available (Bruschettini). The transcutaneous sensor heats the skin underneath the sensor improving local perfusion which enables monitoring of transcutaneous CO2 (tcPCO2) and O2 (tcPO2).

Relative heating power (RHP) relates to the power required to maintain the sensor at the set temperature. A well perfused baby requires a higher RHP than a poorly perfused baby to keep the sensor temperature stable and leads to a more accurate estimate of arterial PCO2. The RHP trendline, therefore, reflects local skin perfusion.

Transcutaneous 1

Eligible patients

Babies with significant respiratory illness (i.e. FiO2 > 60%, PCO2 > 8 kPa (arterial or capillary), change to HFOV, underlying pathology of PPHN, MAS, CDH) or babies needing a reduction in number of blood samples can be started on transcutaneous monitoring after discussion with SMO.

Relative contraindications

  • Fragile skin (such as EB)
  • Arterial line in place
  • Body cooling, poor perfusion (due to sepsis or cardiac condition), or inotropic support as these may lead to falsely high tcPCO2 and falsely low tcPO2


  • SenTec should never be switched off and needs to display "ready for use"
  • Take sensor out of docking station
  • Check integrity of sensor membrane before use
  • Select NICU mode and check alarm limits
  • Alarm limits
    • Temperature set at 41 °C
    • Site time set at 2 hours
    • tcPCO2 accepted between 4-8 kPa and tcPO2 accepted between 4-10 kPa
    • Alarm limits may be changed after discussion with SMO in selected babies. This needs to be documented in medical and nursing notes.
  • Have attachment rings (MAR or SF-MAR) and contact fluid ready

Patient preparation

  • Choose relevant attachment ring
    • MAR: standard ring, which will "stick" better
    • SF-MAR: individually packaged for more sensitive or fragile skin
  • Choose 2 (or 3) sites to place attachment ring on (see below diagram)
  • Clean the skin with saline and allow to dry well prior to placing attachment ring.

Sensor application

Transcutaneous 2

Please note: The forehead is not used as sensor application site in our NICU due to the risk of scarring from a burn

  1. Transcutaneous 3Apply ONE drop of contact gel to the skin in the centre of the ring.
  2. Hold sensor by cable. Insert nose of sensor at an angle (as shown) then apply light downward pressure with forefinger to snap it into place. (Think of 'landing' it like an airplane)
  3. Twist the sensor in the ring (full 360° if possible) to spread contact gel evenly.
  4. After sensor application, tcPCO2 readings typically stabilize within 2 to 10 minutes. After stabilisation, the displayed value turns from grey to green.

Changing Sensor site / Reset site timer

Sensor timer has been set to alarm after 2 hours. When sensor requires changing, a low priority alarm sounds, the message 'Site Time Elapsed' is displayed in the Status Bar and the 'Remaining Monitoring Time' icon turns red.

  1. Ensure a second attachment ring is already applied to the patient and add a drop of contact fluid to the new site attachment ring.
  2. Take the sensor off the current site and wipe clean gently (tissue first then alcohol swab).
  3. To RESET the site-timer: press ENTER while the sensor is still OFF the patient.
  4. Inserting the Sensor back into the Docking Station (after cleaning with tissue and alcohol swab) will also reset the "Site time".

Sensor calibration and storage

Transcutaneous 4The sensor is both calibrated and stored (between patients) in the docking station. Calibration is required after 12 hours of use, when the sensor is properly disconnected for more than 30 min or when the sensor has been dislodged for more than 5 min. The message "calibrate sensor" will appear in the status bar.

  • Clean sensor with tissue and alcohol swab
  • Open the Docking Station door and insert sensor into docking station door (red light will be visible)
  • Close docking station door. Monitor will automatically start calibration if necessary and display "calibration in progress". This should take 2-5 min.

Membrane changes

Membrane changes are necessary when the membrane is damaged or missing, or when an air bubble is present underneath the membrane. Furthermore, the membrane needs changing every 42 days. This membrane change is done by the CCN or shift coordinator. Please see for a membrane change tutorial and for a tutorial on replacement of the insert into the membrane changer.

Trouble shooting

The site timer doesn't revert to a full 2 hour period:

  • This generally occurs when a calibration is required within the next 2 hours. You can:
    • Calibrate the sensor now (see above for process)
    • Leave sensor on and calibrate when calibration is due. Sensor can be replaced in same attachment ring but make sure the sensor doesn't stay in this attachment ring for longer than allocated site time (mostly 2 hours).

The tcpCO2 and /or tcpO2 reading don't stabilise within 10 min:

  • Check if attachment ring is attached properly
  • Check if contact gel was used
  • Check local or general perfusion of patient

Both transcutaneous measurements and RHP have changed significantly in a short period of time; this may reflect a change in local skin perfusion.

Transcutaneous measurements have changed significantly but RHP is stable; this likely reflects a true change in arterial blood gases.


Bruschettini M, Romantsik O, Zappettini S, Ramenghi LA, Calevo MG. Transcutaneous carbon dioxide monitoring for the prevention of neonatal morbidity and mortality. Cochrane Database of Systematic Reviews 2016, Issue 2. Art. No.: CD011494. DOI:

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Document Control

  • Date last published: 01 April 2019
  • Document type: Clinical Guideline
  • Services responsible: Neonatology
  • Owner: Newborn Services Clinical Practice Committee
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years