This document discusses sodium regulation and hyponatremia. It explains that sodium levels indicate osmolality rather than having direct effects. Changes in sodium cause cell volume changes through osmosis. Hyponatremia occurs when water intake exceeds electrolyte free water clearance by the kidneys. Symptomatic hyponatremia is treated aggressively while asymptomatic cases are managed conservatively to avoid complications like central pontine myelinolysis from overcorrection.

1. is Hard Joel M. Topf, MD Nephrology Sodium

3. Osmosis: the thought experiment

15. Hillier Study on Pseudohyponatremia Na = 140 - 0.016 Glucose Na = 140 - 0.024 Glucose Na = 141 - 0.016 Glucose Na = 151 - 0.04 Glucose

23. Free water clearance 0.5 liter free water Solute component (plasma osmolality 284 mOsm/kg) Use clearance to calculate the osmolar clearance 1 liter 142 mOsm/Kg 0.5 liter 284 mOsm/Kg

24. Free water clearance Solute component (Solute Clearance) ? 0.5 liter Zero mOsm/Kg Free water component (Free water Clearance) The free water component equals urine volume minus the solute component 1 liter 142 mOsm/Kg 0.5 liter 284 mOsm/Kg

25. Free water clearance 0.5 liter 568 mOsm/Kg 1 liter 284 mOsm/Kg -0.5 liter 568 mOsm/Kg

26. Free water clearance Solute component (plasma osmolality 284 mOsm/kg) Use clearance to calculate the osmolar clearance 1 liter 284 mOsm/Kg 0.5 liter 568 mOsm/Kg

27. Free water clearance Solute component (Solute Clearance) ? Free water component (Free water Clearance) 0.5 liter 568 mOsm/Kg – 0.5 liter Zero mOsm/Kg 1 liter 284 mOsm/Kg

28. Free water clearance: Implications Dilute urine increases serum osmolality Concentrated urine de-creases serum osmolality Dilute urine Solute free water Concentrated urine Negative free water Na + Na +

29. Free water clearance: The math

30. Free water clearance: Math Examples

42. ADH is normally used to regulate osmolality We start with an increase in the plasma osmolality This is detected by the brain The brain releases ADH ADH acts on the kidney The kidney reacts by retaining water and producing a small amount of concentrated urine. The retained water goes here not here

47. The response to hyponatremia Low sodium concentration causes water to move into the cells. In the brain this causes an increase in ICP. Compensated chronic hyponatremia is essentially asymptomatic.

48. The problem with compensation The starting point is after compensation has reduced the amount of intracellular solute and the ICP Now, an over-eager intern sees the low sodium and starts an infusion of 3% NaCl to raise the sodium to normal. Sodium 108 The sodium draws water from the inside of the cells causing the brain to shrivel. The problem with interns Sodium 134

55. Chronic or acute hyponatremia

59. Water restriction is ineffective

72. Inability to drink

75. Consequences and compensation