Transcutaneous paCO2 Monitoring

Transcutaneous CO₂ (TC-CO₂) monitors function by measuring the CO₂ which diffuses out the skin. Modern TC-CO₂ monitors are a highly accurate, non-invasive method for estimating paCO₂.^[1]

Primary Purpose

YKDRH obtained TC-CO₂ monitors for the purpose of monitoring paCO₂ trends in patients receiving high-flow nasal cannula or non-invasive ventilation (i.e. CPAP/BiPAP). This was necessary because end-tidal CO₂ monitoring is not compatible with these interventions.

Important Points

Applicable for all age groups (including extremely premature neonates).
Initial reading requires approximately five minutes to establish.
TC-CO₂ is substantially more accurate than peripheral venous CO₂ for estimating paCO₂.^[1]
Because CO₂ takes several minutes to diffuse out of the skin, the displayed TC-CO₂ reading at any given time reflects the paCO₂ from 2-4 minutes prior.
The tracing is a flat line (rather than the waveform created by exhaled air).
TC-CO₂ is used to follow paCO₂ trends; it DOES NOT measure instantaneous levels. Therefore, TC-CO₂ IS NOT an acceptable substitute for ET-CO₂ in situations such as:
1. Confirmation of ET-tube placement.
2. CPR (neither for CPR adequacy nor ROSC identification).
3. Respiratory monitoring during sedation.
4. Any situation where monitoring for apnea or any rapid changes in paCO₂.
The accuracy of end-tidal CO₂ as an estimate of paCO₂ is largely dependent upon how closely a patient's lung function matches an ideal lung. For patients who are intubated for non-respiratory issues, their lung function should pretty closely approximate an ideal lung, and thus end-tidal CO₂ should estimate paCO₂ with reasonable accuracy. But for patients with lung processes which create V/Q mismatches, end-tidal CO₂ is not a good estimate of paCO₂. In such situations, TC-CO₂ provides a MUCH MORE ACCURATE estimate paCO₂.^[1] Thus, if paCO₂ requires monitoring in patients with ARDS, bronchiolitis, pneumonia, etc., TC-CO₂ should be considered regardless of the type of respiratory support the patient is receiving (i.e. none, high-flow, or intubated). In such a situation, an intubated patient might be monitored with end-tidal CO₂ to watch for apnea and TC-CO₂ to assess adequacy of ventilation over time.