Hyponatremia Infusion Plots - Edelman in Pictures
When prescribing fluids to a patient with hyponatremia, it is common practice to estimate their expected impact on the plasma sodium concentration (PNa). This is easily done with the Edelman equation using one of the multiple calculators available, but it adds an extra work step.
Contour Plots
For any specific fluid volume, the expected change in PNa depends only on the baseline PNa and the total body water water. Their relationship can thus be demonstrated graphically with contour plots (see map insert).
Here I show plots for some fluid regimens commonly used in patients with hyponatremia. They show the expected change in PNa, as a function of baseline PNa (x-axis) and the total body water (y-axis).
Contour plots are a way to show a three-dimensional surface on a two-dimensional plane. They graph two predictor variables on the x- and y-axis and a response variable as contours of certain values.
They are widely used in cartography, where contour lines on a topological map indicate elevations that are the same. (See here)
These plots give a snapshot of the expected changes in PNa and should help in developing a “feeling“ for the direct effects of common hypertonic, hypotonic and isotonic fluid regimens. For clinical practice, a rough estimate of the expected change in PNa will usually suffice, so the hassle of exact calculation might be safely omitted.
Hypertonic solutions:
Expected change in plasma sodium concentration (in mmol/l) solely due to 150cc of Hypertonic Saline (3%).
Expected change in plasma sodium concentration (in mmol/l) solely due to 500cc of Hypertonic Saline (3%).
Hypotononic solutions:
Expected change in plasma sodium concentration (in mmol/l) solely due to 500cc of Water or Glucose solution.
Expected change in plasma sodium concentration (in mmol/l) solely due to 500cc of Water or Glucose solution.
Isotonic solutions
Expected change in plasma sodium concentration (in mmol/l) solely due to 1000cc of Normal Saline.
Expected change in plasma sodium concentration (in mmol/l) solely due to 1000cc of Lactated Ringer’s.
Expected change in plasma sodium concentration (in mmol/l) solely due to 1000cc of 1.4% Sodium Bicarbonate.
The calculations are based on this formula:
This work is not to be considered medical advice. Under no circumstances shall the creator be responsible for any damages arising from the use of this work.