While attempting to calibrate a polarographic oxygen analyzer, the neonatal/pediatric specialist notices that the analyzer reads 21% when exposed to room air but only reads 64% when exposed to 100% oxygen. The most appropriate action at this time would be to

• A. Reset the zero point
• B. Replace the battery
• C. Replace the fuel cell
• D. Add electrolyte solution

Answer: (B)

Polarographic oxygen sensors depend on a stable power supply to drive the cell and the measurement circuitry. The current produced by the cell increases with oxygen concentration, so a healthy battery must provide enough voltage/current across the full range from room air to 100% O2. If the battery is weak, the electronics can be unable to handle the higher load at 100% O2, causing an abnormally low reading there while room air still shows a plausible value. Replacing the battery restores proper voltage, allowing the sensor to respond accurately to high oxygen levels. If replacing the battery doesn’t fix the issue, then the fuel cell or electrolyte problems would be considered, but the battery is the most likely cause given the pattern of readings.