6- Physiology III - Hypo and Hypernatremia

omarys's version from 2017-05-27 23:32

Section 1

Question Answer
Most common electrolyte imbalanceHYPOnatremia
Mild hyponatremia (common in hospitalized patients) [Na+] not normal but still above 130 mEq/L
Severe hyponatremia< 130 mEq/L
Hyponatremia occurs in approx. 30% of people on SSRI
Vast majority of hyponatremias due toexcess ADH
Clinical manifestations of hyponatremia aremostly neurologic, cells enlarge due to hypo-osmolality and water influx

Section 2

Question Answer
All cases of hypervolemic hypon. are characterized bylow ECV (except in CRF)
Hypervolemic hypon. occurs in _______ patients.CHF, cirrhosis, nephrotic syndrome, CRF
What happens in low ECV?Kidney tries to raise plasma volume, so it retains sodium - unrelated to hypon.
How the hell does hypon. develop in low ECV? Accidentally - if ECV is severely low, you have a VOLEMIC trigger for ADH release whose purpose is vasoconstriction to raise BP. The hypon. is collateral damage.
Two CHF patients, one with hypon. and one with normonatremia. What say you?Hypon. loses - worse prognosis.
Plasma lab results in hypervolemic hypon.?Low [Na+] and osmolality (because water retention)
Urine lab results in hypervolemic hypon.?High osmolality (water retention) BUT LOW [Na+] - because kidney is going sodium retention to fix low ECV - NOT related to hypon. The cause of hypon. is water retention.

Section 3

Question Answer
______ does not cause hypon.Fusid (loop diuretic - works on NKCC2 in AL)
_______ does cause hypon. (side effect).HCTZ (acts on DCT, reduces Na+ absorption there, causing water loss in urine)
How is water reabsorbed from the lumen of the collecting duct to the blood (after ADH put those aquaporins there)?passively - because the medulla is very concentrated (thanks to NKCC of the LOH)
Fusid ___ ___ cause hypon. because fusid damages ____ ____ from the ___ ___ by interfering with the _____ saltiness.does not ; water absorption ; collecting duct ; medulla's (Fusid blocks NKCC = no concentrated medulla)
Plasma lab results in HYPOvolemic hypon.?Same as hypervolemic: [Na+] and osmolality are low (because water retention)
Urine lab results in HYPOvolemic hypon.?High osmolality (water retention) BUT LOW [Na+] CUZ KIDNEY TRYINA FIX THAT LOW ECV (in dehydration-induced hypon.)
2 causes of hypovolemic hypon.1- Side effect of thiazide (reduces Na+ abs. in DCT) ; 2- Dehydration (DUE TO LOW ECV --> VOLEMIC TRIGGER OF ADH)
Usually, in dehydration, there is _______.HYPERnatremia, due to loss of hypotonic fluids (but in extreme cases, ECV is low enough so that there's hypon.)
Hypovolemic hypon. occurs inMarathon runners (SEVERE dehydration)
The mechanism of _____-induced hypov. hpon. _____ ____ the mechanism of _____-induced hypov. hypon.dehydration ; differs from ; HCTZIn dehydration, hypon. occurs due to low ECV and a volemic ADH trigger, so there's water retention and dilution of Na+. In thiazide use, there is direct damage to Na+ absorption in the DCT, so less Na+ returns to the blood.

Section 4

Question Answer
How to differentiate bwn hyperv. hypon. and hypov. hypon.?The name says it all - by observing volume overload or depletion (respectively).
In both hyperv. and hypov. hyponatremia, ADH secretion is ______.(increased but) Appropriate (trying to fix low ECV)

Section 5

Question Answer
Majority of hypon. cases areeuvolemic
Is ADH involved in euv. hypon.?Always Mostly. It's involved in 3/4 of the causes (sparing primary polydipsia)
3 ADH-RELATED causes of euv. hypon. in descending order of prevalence?SIADH >>>>>>>> Addison's (low cortisol = no neg. fb on ADH release, also low aldosterone = no Na+ absorption in CD) ; hypothyroidism
Why is urine [Na+] normal in euv. hypon.?Because there's no interference with the kidney's Na+ secretion mechanism (i.e. no sodium retention). This is also why there's no edema etc.
To create edema/ascites, _____ ______ and _____ must ____ _____; reabsorption of ______ _____ does not cause ________.both water ; salt ; be reabsorbed ; water alone ; edema (reabs. of pure water will raise TBW slightly, but not enough to affect ECV and stuff)
Other than idiopathic and genetic SIADH, what are the possible etiologies? (5)Severe nausea and pain ; CNS pathologies ; neoplasms (neuroendocrine) ; drugs (SSRI, carbamazepine) ; lung diseases
Plasma lab results in euv. hypon.?Same as other hypon., but here there might also be low uric acid (due to elevated TBW)
Urine lab results in euv. hypon.?Osmolality is > 100 mEq/L, NORMAL [Na+]
normal urine sodium values (generally)?20 mEq/L (in random sample). Over 40 mEq/L w/ western diet
How does hypothyroidism cause hyponatremia?Unclear how, but hypothyroidism has to be CRAZY LOW for that to happen - so pretty rare
To dx SIADH, assess-TSH and (morning) coritsol levels - to eliminate other 2 causes of euv. hypon.

Section 6

Question Answer
CKD (or CRF) =Chronic kidney disease (chronic renal failure)
Calculated osmolarity (CO) =2 Na + 2 K + Glucose + Urea (all in mmol/L)K is negligible
Calculated osmolarity (different units) =2 Na + Glucose/18 + BUN/2.8
ineffective osmoles areosmoles that don't contribute to tonicity
What's a BUN test, precious?Blood urea nitrogen - if high, kidney disease (e.g. BUN high in CKD)
What's isosthenuria, precious?urine whose concentration is neither greater nor less than that of protein-free plasma - it reflects renal tubular damage/failure of renal medullary function.
AMOUNT of excreted Na+ in urine isdependent on diet - whatever Na+ in intake will be excreted (in steady state). The [Na+] however may change.

Section 7

Question Answer
In both primary polydipsia and CKD, serum [Na+] is ______, and EFFECTIVE plasma osmolality is _____.low (as both are causes of hyponatremia) ; low (but all in all plasma osmolality in CKD is HIGH - there's a lot of urea in the blood)
Urine osmolality in primary polydipsia?LOW - urine is dilute because they drink a lot of water and (some of) the excess goes to the urine
In CKD, urine osmolality isthe same as the blood's, i.e. ~300 mEq/L
In both primary polydipsia and CKD, urine [Na+] isnormal (> 40 mEq/L) - because problem is not in sodium absorption/secretion, nor is there underlying low ECV
Why are polydipsia patients euvolemic?Because they drink water, not saline (for hypervolemia/edema to develop, there needs to be BOTH water AND SALT retention/intake)
Kidney can secrete up to ____ water/day, while polydipsia patients may drink as much as ____/day.12 L ; 20 L (despite this excess, polydipsia patients will have elevated TBW but not hypervolemia)
Why are CKD patients ____volemic?HYPER - because their kidneys are losers mostly or idk

Section 8: "This is irregular." "I suppose life is irregular?"

Question Answer
Hypon. in 99% of cases is synonymous withhypo-osmolality (plasma)
If hypon. but normal plasma osmolalitypseudohyponatremia
About 91% of the plasma is ______, the other 9% are ______ (7%) and _____ (2%).water ; proteins ; nutrients (glucose, fatty acids, etc.)
Serum [Na+] is calculated in the lab asAMOUNT of Na+ (normally there is 154 mmol of sodium) divided by the WHOLE plasma volume (although, ideally, it should be divided by 91% of the plasma volume- the water part)
In saline, what is [Na+]?154 mEq/L
If the percentage of the non-water components of plasma (proteins and nutrients) RISES, what happens to [Na+]?REDUCED, because the gap/"mistake" the lab does is more significant here (since even less than 91% of plasma is water now)
Causes of pseudohyponatremia?Hypergammag. (in MM) ; hypertriglyceridemia ; lipoprotein X (in obstructive jaundice) - BUT DON'T FORGET, pseudohyponatremia is essentially a MISTAKE = amount of sodium in plasma IS NOT actually low
How to verify pseudonatremia?Measure (NOT CALCULATE) plasma osmolality - e.g. if [Na+] is 125 but osmolality is 285 then this is pseudohyponatremia

Section 9

Question Answer
Isosmotic HyponatremiaRARE AF, due to use of non-conductive irrigation solutions (sorbitol-mannitol irrigation, a nonelectrolyte urologic irrigant) - clinical
Hyperosmotic hypon. occurs in people withdiabetes (hyperglycemia raises effective plasma osmolality, causing water efflux >>> dilution of Na+)
In hyperosmotic hypon., will there be clinical (e.g. neurological) symptoms due to water influx into cells?NO! The EFFECTIVE osmolality of plasma is normal or elevated; there won't be water influx.
T or F- Since there's is no clinical manifestations of hyponatremia in hyperosmotic hyponatremia, this condition is also a lab mistake.False. [Na+] is actually low here. The reason there aren't clinical manifestations is that plasma osmolality is NORMAL or elevated, due to the sugar.
Tx of hyperosmotic hypon. isnormalizing glucose levels; DO NOT INTERFERE W/ Na+!
How to calculate "effective"/actual Na+ levels in hyperosmotic hypon.?Effective [Na+] = [Na+] + 2 X ([Glucose] - 100) / 100

Section 10: Other (rare) causes of hypon.

Question Answer
Hypothalamus secretes ADH when Na+ levels are ______, and it stops when the concentration of sodium _____.High (e.g. after salty meal) ; decrease (back to normal)
Effect of ADH?Lowers [Na+]
In pregnancy, due to HCG, the hypothalamus stops ADH secretion at LOWER [Na+] (i.e. it secretes more ADH), so in pregnancy there isLow [Na+] / hypon.
The mechanism underlying hypon. in pregnancy is termedReset of osmostat
MDMA causes hypon. by 2 mechanisms1- induces extreme thirst and 2- causes SIADH
The MDMA-induced hypon. is _____ and can be ______, unlike the hypon. in pregnancy.serious ; fatal
A patient presents w/ hypon. and some CNS pathology. Dx is likely to beSIADH
Some (minority of) people w/ SAH will developCSW (cerebral salt wasting), leading to hypon.
CSW occurssome 10 days post-neurosurgery or post-SAH
Urine and plasma lab results in CSW are _____ to those in ________.identical ; SIADH (or just euvolemic hypon.)
Important to distinguish bwn CSW and SIADH because the ____ differs radically.tx
Dx of CSW?Lab findings (in addition to plasma and urine [Na+], check hematocrit (^), uric acid (v), etc.) AND CLINICAL FINDINGS: low BP and turgor
Beer is ____ in ______.poor ; solutes/electrolytes
Potomania is a ______ condition resulting from a _______ diet. hypo-osmolality (low [Na+]) ; low-solute

Section 11

Question Answer
Urine output in SIADH?Changes with diet (the excess ADH will maintain the CONCENTRATION of the urine, so our solute intake affects the OUTPUT (no. of liters) of urine)
In the vast majority of hypon. there is excessiveADH (whether appropriate or inappropriate)
A maximally concentrated urine (1200 mOsm/kg) MUST be at least ___ in volume.0.5 L
"1200 mOsm/kg ; 0.5-0.75 L" is analogous to"60 mOsm/kg ; 10-15 L"
Daily intake/production of solutes?600-900 mOsm (this is also the amount the kidneys need to excrete in order to maintain plasma osmolality at around 300)
Amount of urine produced from 600 mOsm is _____dependent on how dilute the body needs the urine to be - if maximally dilute (e.g. to get rid of as much water as possible), then a maximum of 10 L urine can be produced.
Volume of urine produced =(# of solutes in mOsm) / (desired concentration of urine, from 60-1200)
W/o enough solutes in the diet, large ______ of _______ ______ be _______.volumes ; urine cannot ; produced

Section 12: Hypernatremia