A water-deficit model

A hypothetical older adult weighs 60 kg and has a sodium concentration of 168 mmol/L. For a classroom estimate, total body water is explicitly assumed to be 50 percent of body weight and the comparison sodium is 140 mmol/L. The supplied deficit formula is total body water multiplied by the ratio of measured sodium to comparison sodium minus one. No instruction is given to administer this entire estimate immediately. The assessment has not yet established hemodynamic stability, duration of hypernatremia, ongoing losses, urine concentration or concurrent disease. The learner must separate a transparent calculation from the monitored clinical decisions that a real person would require.