Electrolyte Free Water Clearance

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Information about Electrolyte Free Water Clearance
Health & Medicine

Published on July 21, 2009

Author: nephron

Source: slideshare.net

Description

this is an 18 slide subset of the way too long lecture on sodium called Hyponatremia Dreadnaught

True hyponatremia Hyponatremia occurs when water intake exceeds water excretion.

Hyponatremia occurs when water intake exceeds water excretion.

True hyponatremia Hyponatremia does not occur when sodium excretion exceeds sodium intake. Negative salt balance causes hypovolemia

Hyponatremia does not occur when sodium excretion exceeds sodium intake.

If a person drinks more water than the kidney is capable of clearing the excess water will dilute the plasma. Causes of hyponatremia: Increased intake To exceed the maximal renal clearance of water an adult needs to drink about 18 liters a day. clearing

If a person drinks more water than the kidney is capable of clearing the excess water will dilute the plasma.

To exceed the maximal renal clearance of water an adult needs to drink about 18 liters a day.

Water clearance Clearance as a general concept: The clearance of any substance is the volume of blood cleared of that substance in a set unit of time. Water clearance Total water clearance is equal to urine output. Not a useful concept.

Clearance as a general concept:

The clearance of any substance is the volume of blood cleared of that substance in a set unit of time.

Water clearance

Total water clearance is equal to urine output. Not a useful concept.

Free water clearance and soup Imagine urine divided into two components A solute component containing all of the solute at the same osmolality as plasma. Loss of this component does not change plasma osmolality Ladle of soup A free water component providing the balance of the volume. Loss of this solute free water will change serum osmolality. Boiling off water from soup In regards to sodium all that matters is the free water component

Imagine urine divided into two components

A solute component containing all of the solute at the same osmolality as plasma.

Loss of this component does not change plasma osmolality

Ladle of soup

A free water component providing the balance of the volume.

Loss of this solute free water will change serum osmolality.

Boiling off water from soup

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

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

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

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

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

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 +

Free water clearance: The math

Free water clearance: Math Examples

Electrolyte free water clearance Osmolality doesn’t cause problems, rather tonicity causes changes in cell volume which cause clinical syndromes. So free water clearance must be refined to measure clinically significant changes in tonicity.

Osmolality doesn’t cause problems, rather tonicity causes changes in cell volume which cause clinical syndromes.

So free water clearance must be refined to measure clinically significant changes in tonicity.

Electrolyte free water clearance Osmotically active particles (those that contribute to tonicity): Sodium Potassium Albumin, calcium and others Sodium is the dominant osmotically active solute of serum to the point that others can be ignored. Urine has a significant potassium content so in urine sodium and potassium are equal partners in determining urinary tonicity.

Osmotically active particles (those that contribute to tonicity):

Sodium

Potassium

Albumin, calcium and others

Sodium is the dominant osmotically active solute of serum to the point that others can be ignored.

Urine has a significant potassium content so in urine sodium and potassium are equal partners in determining urinary tonicity.

Electrolyte free water clearance Convert the free water clearance calculation to electrolyte free water clearance Substitute urine osmolality with the sum urine Na + K Substitute serum osmolality with serum sodium Free water clearance Electrolyte free water clearance

Convert the free water clearance calculation to electrolyte free water clearance

Substitute urine osmolality with the sum urine Na + K

Substitute serum osmolality with serum sodium

Electrolyte free water clearance: CHF vs. SIADH Heart Failure Urine Osmolality: 800 Serum Osmolality: 270 Urine Volume: 800 Urine Na: 5 Urine K: 40 Serum Na: 125 SIADH Urine Osmolality: 800 Serum Osmolality: 270 Urine Volume: 800 Urine Na: 125 Urine K: 40 Serum Na: 125

Heart Failure

Urine Osmolality: 800

Serum Osmolality: 270

Urine Volume: 800

Urine Na: 5

Urine K: 40

Serum Na: 125

SIADH

Urine Osmolality: 800

Serum Osmolality: 270

Urine Volume: 800

Urine Na: 125

Urine K: 40

Serum Na: 125

Etiology of hyponatremia Hyponatremia occurs when water intake exceeds water excretion. Hyponatremia occurs when water intake exceeds electrolyte free water clearance. Ingestion > EFW clearance

Hyponatremia occurs when water intake exceeds water excretion.

Hyponatremia occurs when water intake exceeds electrolyte free water clearance.

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