Hypernatremia & Hyponatremia Flashcards
Normal serum sodium is between _ and _
Normal serum sodium is between 135-145 mEq/L
We care about the serum sodium levels because sodium is a major determinant of _
We care about the serum sodium levels because sodium is a major determinant of volume status and serum osmolality
* Normal 285 mOsm/kg
Serum osmolality equation
Serum osmolality equation = (2Na) + (Glucose/18) + (BUN/2.8)
Hypernatremia presents with symptoms such as _
Hypernatremia presents with symptoms such as dehydration, polyuria, polydipsia, seizures/coma
Hypernatremia is caused by either a _ in Na+ or a _ in H2O
Hypernatremia is caused by either an increase in Na+ or a decrease in H2O
Primary causes of hypernatremia include:
Primary causes of hypernatremia include:
1. Diabetes insipidus
2. Hyperaldosteronism
3. Decreased H2O intake
4. Increased H2O loss
Central diabetes insipidus is caused by _
Central diabetes insipidus is caused by lack of ADH
Nephrogenic diabetes insipidus is caused by _
Nephrogenic diabetes insipidus is caused by resistance to ADH
* Receptors are not responding
A patient has hypernatremia, excessive thirst and heavy urination; the first step in diagnosis is _
A patient has hypernatremia, excessive thirst and heavy urination; the first step in diagnosis is water deprivation
* If urine is still dilute: diabetes insipidus
* If urine is concentrated: psychogenic polydipsia
A patient has hypernatremia, excessive thirst and heavy urination; if the water deprivation reveals concentrated urine then it suggests _
A patient has hypernatremia, excessive thirst and heavy urination; if the water deprivation reveals concentrated urine then it suggests psychogenic polydipsia
* This is often seen in psychiatric patients
A patient has hypernatremia, excessive thirst and heavy urination; if the water deprivation reveals dilute urine then it suggests _
A patient has hypernatremia, excessive thirst and heavy urination; if the water deprivation reveals dilute urine then it suggests diabetes insipidus
* Next we administer ADH (desmopressin)
How can we differentiate between nephrogenic and central DI?
We differentiate between nephrogenic and central DI via ADH administration
If ADH is administered, we expect the urine to be (dilute/concentrated) in nephrogenic DI
If ADH is administered, we expect the urine to be dilute in nephrogenic DI
* Because we are still not responding to ADH
If ADH is administered, we expect the urine to be (dilute/concentrated) in central DI
If ADH is administered, we expect the urine to be concentrated in central DI
* The problem with central DI was that we were unable to make ADH to bring back free water and concentrate the urine
* Now, with the administration of ADH the urine is finally concentrated
How do we manage hypernatremia?
Hypernatremia is managed with:
* Fluid replacement
* Thiazide diuretics
* NSAIDs (nephrogenic DI)
* Desmopressin (central DI)
Thiazide diuretics work via _ to treat nephrogenic DI (in combination with NSAIDs)
Thiazide diuretics work via blocking the Na/Cl cotransporter to treat nephrogenic DI (in combination with NSAIDs)
* This blocks Na+ reabsorption in the DCT but also causes the sympathetic nervous system to increase reabsorption in the PCT
NSAIDs are used to treat nephrogenic DI via _ (in combination with thiazide diuretics)
NSAIDs are used to treat nephrogenic DI via blocking prostaglandin production (in combination with thiazide diuretics)
* Prostaglandins are ADH antagonists
Water balance in the body is maintained by:
Water balance in the body is maintained by:
1. The osmotic release or inhibition of release of ADH
2. The response of the kidney to ADH
3. Stimulation of thirst
We have an osmostat in the _ region of the brain that stimulates thirst
We have an osmostat in the hypothalamus that stimulates thirst
Explain the pituitary-renal feedback system that maintains the amount of water in the body
Loss of water –>
Rise in serum tonicity –>
ADH is released & Thirst initiated –>
ADH stimulates increased tubular reabsorption of water,
Thirst increases water intake –>
Both act to dilute the body fluid –>
Inhibition of ADH & inhibition of thirst –>
Loss excess water
What does it mean when the urine is maximally concentrated?
Maximally concentrated urine (1200):
* The goal is to excrete solute in as small amount of urine as possible
* Low water intake
* Low urine volume
* High ADH levels
Three physiologic stimuli for ADH release
Three physiologic stimuli for ADH release
1. Increased plasma osmolality
2. Decreased ECF
3. Decreased blood pressure
If osmoreceptors sense hypotonicity while at the same time baroreceptors sense low blood pressure, ADH is (inhibited/secreted)
If osmoreceptors sense hypotonicity while at the same time baroreceptors sense low blood pressure, ADH is secreted
* Blood pressure regulation trumps tonicity
* ADH can still get released despite being in a hypotonic state
What will serum osmolality tell us about hyponatremia?
High serum osmolality ( > 295 mOsm/kg):
* Hypertonic hyponatremia: hyperglycemia
Low serum osmolality ( < 280 mOsm/kg):
* Hypotonic hyponatremia (what we should probably expect)
Normal serum osmolality (280-295 mOsm/kg):
* Hyperproteinemia, hyperlipidemia
What does it mean if you have hyponatremia and high serum osmolality?
High serum osmolality must be from something other than Na+ in the serum –> hyperglycemia for example
* High glucose in the serum pulls water out of the cell and dilutes the Na+
What does it mean if you have hyponatremia but normal serum osmolality?
What does it mean if you have hyponatremia but normal serum osmolality?
* You have a pseudohyponatremia (hyperproteinemia or hyperlipidemia)
If you have hyponatremia and low serum osmolality, what do you do next?
Most commonly hyponatremia is associated with low serum osmolality –> next we need to check the volume status
* Is the patient hypovolemic, euvolemic, or hypervolemic?
Causes of hypotonic, hypovolemic hyponatremia
Causes of hypotonic, hypovolemic hyponatremia:
* Extrarenal salt loss like dehydration, diarrhea, vomiting
* You have likely rehydrated with pure water
Causes of hypotonic, euvolemic, hyponatremia
Causes of hypotonic, euvolemic, hyponatremia:
* SIADH
* Thiazides
* Hypothyroidism
* Increased CRH
* Psychogenic polydipsia
* Endurance exercise
Causes of hypotonic, hypervolemic, hyponatremia
Causes of hypotonic, hypervolemic, hyponatremia:
* Congestive heart failure
* Liver disease
Hyponatremia with low serum osmolality (hypotonic) + low urine osmolality; ADH is (present/not present)
Hyponatremia with low serum osmolality (hypotonic) + low urine osmolality; ADH is not present
* Urine is dilute so ADH is not present
* Causes include primary polydipsia, low solute intake, beer potomania, tea and toast diet
Hyponatremia with low serum osmolality (hypotonic) + high urine osmolality; ADH is (present/not present)
Hyponatremia with low serum osmolality (hypotonic) + high urine osmolality; ADH is present
* The urine is concentrated so ADH is present
* Multiple causes including true hypovolemia (volume loss), CHF/ cirrhosis (hypervolemic), and SIADH (euvolemic)
Patient with hypotonic hyponatremia from vomiting, burns, diarrhea will have UNa+ of _
Patient with hypotonic hyponatremia from vomiting, burns, diarrhea will have UNa+ of < 20 mEq/L
Patient with hypotonic hyponatremia due to CHF, cirrhosis, nephrosis will have UNa+ of _
Patient with hypotonic hyponatremia due to CHF, cirrhosis, nephrosis will have UNa+ of < 20 mEq/L
Patient with hypotonic hyponatremia from SIADH will have UNa+ of _
Patient with hypotonic hyponatremia from SIADH will have UNa+ of > 40 mEq/L
* The concentration of Na+ in the urine will be high because water will be so low in the urine
* Volume expansion also induces pressure natriuresis which increases urine sodium
