SM 214 Hypernatremia Flashcards
How do changes in tonicity make people feel sick?
Changes in tonicity cause changes in cell shape, which lead to sickness
What is the surrogate marker of tonicity?
Serum Sodium = Effective mOsm/Total Body Water
What determines transmembrane water flow?
Effective osmols on either side of a membrane
What is it hard to measure tonicity?
Ineffective mOsms
What is hypernatremia often called?
Dehydration
Can you be dehydrated and volume deplete?
Yes
Where are the baroreceptors?
Carotid Bodies and the Aortic Arch
What are the portions of urine volume?
Isotonic with plasma and electrolyte free portions
What does the electrolyte free water clearance tell us?
How much water is lost through the kidneys (or isn’t lost)
What determines how much salt is reclaimed from the urine?
Signaling on the levels of salt in the bloodstream determine how much water to keep via the release of ADH (or, alternatively, not releasing ADH)
What makes up the medullary gradient?
Na, Cl, and Urea up to 1200 mOsm’s
How does urine osmolarity relate to urine volume?
Low urine volume suggests high urine osmolarity and vice versa
What triggers thirst?
A rise is plasma osmolarity detected by osmoreceptors in osmoreceptors
What do osmoreceptors detect to release ADH?
Plasma tonicity is detected by osmoreceptors, not osmolarity
What signals other than tonicity can cause ADH release?
Severe volume loss, pain, nausea
Which signal is ADH release more sensitive to, changes in tonicity or changes in volume?
ADH release is more sensitive to changes in tonicity early, but at severe volume depletion, ADH release is controlled by the volume depletion and continues to be released even if tonicity is normalized
What are the symptoms of hypertonic hypernatremia?
Seizures, Coma, Thirstiness
What determines the severity of symptoms with hypertonic hypernatremia?
The rate of change in increase in serum sodium osmolarity
How does hypertonicity effect the brain?
Immediately, water flows out of neurons and into the hypertonic ECF
It quickly begins accumulating electrolytes in neurons to restore volume
It slowly accumulates organic molecules, to raise tonicity and restore volume
What happens if too much water is added too quickly to a hypernatremic patient?
Cerebral edema
Which produces cellular dehydration, volume depletion or hypertonicity?
Hypertonicity
What is lost in volume depletion?
Water and NaCl
Does dehydration tend to produce volume depletion?
Typically, no, because a lot of water would need to be lost to cause hypertonicity and the resulting volume depletion is incompatible with life
How does volume depletion effect diuresis?
Volume depletion = lower GFR = less diuresis
What are the two ways to develop hypertonic hypernatremia?
You receive hypertonic salt or you suffer persistent water losses that are not replaced by intake
What causes persistent hypertonic hypernatremia?
Absent thirst or access to water
What populations tend to have hypertonic hypernatremia?
People in nursing homes with low access to water
What are the 3 types of hypertonic hyprnatremia?
Hypertonic Na gain, polyuric or non-polyuric
What are examples of hypertonic Na gain?
Drinking sea water
Hypertonic feeding - TPN
Primary aldosteronism
What is the effect of acute hypertonic Na gain?
Water is drawn from the ICF to the ECF, causing brain shrinkage and elevation of EABV
What causes non-polyuric hypertonic hypernatremia?
Volume deplete patinets in:
Hypodipsia
Fever, sweating
Vomiting
Diarrhea
What is primary hypodypsia?
People who genetically don’t want water
Do fever and sweating produce hypertonic or hypotonic cells?
Fever and sweating produces hypotonic losses and causes a hypertonic state in the body
What type of GI losses cause hypernatremia?
Vomiting or osmotic diarrhea, but not secretory diarrhe abecause it is isotonic
How does failure to replace water drive up hypenatremia?
Volume is lost without volume replacement
How are polyuric hyponatremia’s divided?
Polyuric hyponatremia is broadly classified as solute diuresis and pure water diuresis
Does hyperkalemia cause diabets insipdus?
Yes
How does nephrogenic diabetes insipidus indirectly cause hypercalcemia?
Damage to the kidneys prevents filtation of calcium
What genetic mutations predispose nephrogenic diabets insipidus?
V2R (X-linked) and AQPD2
How should Na intoxication with neurologic symptoms be treated?
Administer D5W, but don’t let serum Na fall too fast
How is sodium serum corrected for a high serum glucose?
Serum Na + (Glucose - 100)/100*2; need to correct because hyperglycemia draws water into ECF and lowers Serum Na
How should hypernatremia due to sweating or GI losses be treated?
Treat with 0.9% saline + potassium to replace the salt and potassium losses
How should central Diabetes Insipidus be treated?
2mg Desmopressin every 12 hours until the polyuria resolves, then switch to intranasal desmopressin
How is nephrogenic DI treated?
Combination of low Na/protein diet, thiazide diuretics, and NSAIDS
How do you calculate the osmolarity of a solute?
Concentration of a solute * number of ions per solute
What is a normal urine output?
There isn’t one; it’s just the amount needed to get rid of the solute generated by diet and metabolism
What is the formula for urine volume?
Urine Volume = Solute Intake Conc / Average Urine Conc
What is solute diuresis?
A diuresis that aims to excrete large amounts of solute, which drag some water along with it, to produce urine of high osmolarity
What is water diuresis?
A diuresis that aims to excrete large amounts of water, with some solute in it that was not removed, to produce urine of low osmolarity
How do solute diuresis compare to water diuresis?
Salt diuresis = get rid of solute but due to high flow rate, less time to remove water, so Uosm > Posm
How do water diuresis compare to solute diuresis?
Water diuresis = get rid of excess water, but due to high flow rate, not enough time to remove all solute, but Uosm < Posm
How does diabetes insipidus cause glycosuria and polyuria?
Glucose filtration exceeds PCT reabsorptive capacity
Glucose conc rises in the tubule, drawing water
Increased water decreases sodium conc in tubule
Less sodium is able to be taken up the NKKC in TALH
Interstial gradient is lost and dilute Glucose containing urine is produced
Why is polyuria caused by diabetes insipidus?
Excess glucose in the urine draws out water causing more frequent urination
How does diabetes insipidus disrupt the interstial medullary gradient?
More water in the urine to quench glucose lowers the effective sodium concentration, preventing the NKKC from reabsorbing sodium and setting up the corticomedullary gradient
How does the loss of ADH in diabetes insipidus effect urine osmolarity?
Urine osmolarity decreases in a dose response to the withdrawal of ADH
What organ secretes ADH?
The Posterior Pituitary
How does Central Diabetes Insipidus respond to Desmopressin?
Uosm rises by more than 100%
How does Nephrogenic Diabetes Insipidus respond to Desmopressin?
No increase in Uosm
What can cause combined loss of water and solute that leads to hypernatremia?
Extra-renal conditions: gastroentiritis, vomiting, sweating
What can cause renal loss of water that leads to hypernatremia?
Renal loss leading to hypernatremia includes: CKD, DM, and diuretics
What can cause free water loss that leads to hypernatremia?
Central Diabetes Insipidus and increased Insensible Losses
What causes Central Diabetes Insipidus?
Inadequate production of ADH
Is Central Diabetes Insipidus acquired or genetic?
Both
What causes Nephrogenic Diabetes Insipidus?
Tubular unresponsiveness to ADH
Is Nephrogenic Diabetes Insipidus acquired or genetic?
Both
What is a potential iatrogenic cause of Hypernatremia?
Hospitalization with hypertonic fluid infusions
What responses does hypernatremia trigger?
Increased Sodium concentration raises plasma osmolality, triggering an increase in thirst and ADH release
Describe the urine in Diabetes Insipidus?
Urine is dilute: Uosm < Posm
Normal urine volume
How long should it take to correct hypernatremia?
48 hours to avoid cerebral edema and seizures
