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Plasma Exchange Equation:
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The Plasma Exchange equation estimates the remaining concentration of a substance after performing therapeutic plasma exchanges, accounting for hematocrit and number of exchanges performed.
The calculator uses the Plasma Exchange equation:
Where:
Explanation: The equation models the exponential decline in substance concentration with each plasma exchange, adjusted for the patient's hematocrit which determines the plasma fraction removed.
Details: Accurate calculation of remaining concentration is crucial for therapeutic drug monitoring, antibody removal estimation, and determining when target levels have been achieved.
Tips: Enter initial concentration in appropriate units, number of exchanges performed (can be fractional), and patient's hematocrit as a fraction (e.g., 0.45 for 45%).
Q1: Why is hematocrit important in this calculation?
A: Hematocrit determines the plasma fraction removed with each exchange. Lower hematocrit means more plasma (and substance) is removed per exchange.
Q2: Can this be used for any substance removed by plasma exchange?
A: Yes, for substances that are primarily confined to the plasma compartment and not significantly redistributed during the exchange process.
Q3: How accurate is this calculation in clinical practice?
A: It provides a good estimate but actual results may vary due to factors like substance redistribution, ongoing production, or extravascular stores.
Q4: What's the typical range for hematocrit values?
A: Normal hematocrit ranges are approximately 0.40-0.54 for males and 0.36-0.48 for females.
Q5: Can I use this for calculating exchange requirements?
A: Yes, you can work backwards to estimate how many exchanges are needed to reach a target concentration.