Which condition makes transcutaneous O2 monitoring unreliable?

• A. Hypoxemia
• B. Normal perfusion
• C. Shock with elevated peripheral resistance
• D. High cardiac output

Answer: (C)

Transcutaneous O2 monitoring depends on adequate skin blood flow to bring arterial oxygen to the sensor; if peripheral perfusion is poor, the sensor cannot accurately reflect true tissue or arterial oxygen levels. In shock with elevated peripheral resistance, blood flow to the skin is markedly reduced, so TcO2 readings become unreliable or unstable because they are driven more by local skin perfusion than by overall oxygenation.

Normal perfusion would produce reliable readings because the skin receives enough blood to equilibrate with arterial oxygen. Hypoxemia lowers arterial oxygen but TcO2 can still track changes if perfusion is intact; high cardiac output tends to improve perfusion, supporting reliable measurements.