Which of the following is the least appropriate assessment of an infant's oxygenation status?

• A. Arterialized capillary sample
• B. Umbilical arterial line
• C. Pulse oximeter
• D. Transcutaneous electrode

Answer: (A)

When judging an infant’s oxygenation, we rely on measurements that reflect arterial oxygen content and delivery. An umbilical arterial line provides direct arterial blood gas values (PaO2, SaO2) and is highly informative for actual oxygenation status. A pulse oximeter gives noninvasive, continuous SpO2, which tracks oxygen saturation over time. A transcutaneous electrode estimates tissue oxygen tension, offering insight into the oxygen available to tissues. An arterialized capillary sample, while it can approximate arterial values, is not reliable for PaO2 because capillary PO2 varies with peripheral perfusion, temperature, and sampling technique. Because the key indicator of systemic oxygenation is the arterial oxygen content (PaO2/SaO2), the arterialized capillary sample is the least appropriate choice for assessing oxygenation status.