If the arterial line transducer is positioned too low, the measured blood pressure tends to do what?

• A. Under reads
• B. Unchanged
• C. Over reads
• D. Erroneous

Answer: (C)

When the arterial line transducer is positioned lower than the heart, it sits deeper in the fluid column of the body. In a fluid, pressure increases with depth, so the sensor experiences extra hydrostatic pressure from the blood above it. This added pressure makes the reading higher than the true arterial pressure—that's an over-read. The effect is about 0.74 mmHg for each centimeter the transducer is below heart level. If the transducer were higher, you’d see under-reads.