Transcutaneous and End-Tidal CO₂ Measurements in Hypoxia and Hyperoxia

Area of Science:

• Physiological monitoring
• Aerospace medicine
• Respiratory gas analysis

Background:

• Transcutaneous measurement of carbon dioxide (CO₂) is explored for monitoring tactical jet aircrew.
• Clinical settings suggest transcutaneous CO₂ (tcPco₂) can mirror arterial CO₂ (PaCO₂).
• End-tidal monitoring (PETco₂) provides high-fidelity estimates of PaCO₂ in laboratory settings.

Purpose of the Study:

• To examine the correspondence between end-tidal (PETco₂) and transcutaneous PCO₂ (tcPco₂).
• To assess the utility of these measures under simulated tactical jet aircrew conditions.

Main Methods:

• Healthy volunteers were studied under laboratory conditions.
• Varied conditions included hyperoxia, hypoxia, rest, exercise, skin temperature changes, hyperventilation, and CO₂ retention.
• Bland-Altman and regression analyses were used.

Main Results:

• Neither PETco₂ nor tcPco₂ consistently followed arterial CO₂ (PaCO₂) changes.
• tcPco₂ varied with local skin temperature.
• Transcutaneous oxygen partial pressure (tcPo₂) and skin temperature significantly influenced tcPco₂.
• Absorption atelectasis from 100% O₂ breathing caused PETco₂ to deviate from PaCO₂.

Conclusions:

• tcPco₂ is not a useful trend indicator for PaCO₂ in dynamic environments like tactical jet aircraft.
• PETco₂ is also unreliable for monitoring CO₂ status in pilots breathing near 100% oxygen.