Thomas: Disorders of Na and water balance
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| What controls total body water and Na? | TBW - ADH
: Na - Aldosterone
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| What lab values do you need when assessing a pt for Na disorders? | Serum chemistry, Uosm, Sosm, Una, Ucr
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| What Na level defines hyponatremia? | Na <135
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| What is one area of concern with hyponatremia? | The potential of edema in the skull, as there is limited room for expansion.
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| Name symptoms associated with acute hyponatremia. | Nausea, vomiting, lethargy, confusion, seizures, coma
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| Why is it that typically, only people with acute hypo/hypernatremia have neurological symptoms? | The brain doesn't have a chance to shoot out ions to pull water out.
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| What does an acute increase in ADH do to ECF? | It causes an acute decrease in ECF osmolality leading to the movement of water into the brain cells
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| Why isn't the increase in brain water as high as expected? | There is a prompt loss of electrolytes and organic osmolytes.
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| What is pseudohyponatremia? | Where calculated Na on lab work is low when Sosm is hypertonic (>280) due to other effective osmoles
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| Name some of the osmoles/ conditions leading to pseudohypo. | Mannitol, post transurethral resection of the prostate, and hyperglycemia
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| How does hyperglycemia cause pseudohypo? | If blood glucose is >400, the higher Sosm will pull water out of the cells with no increase in Sna.
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| For every 100 mg/dL in glucose above 100, how much with the serum Na appear to decrease? | 1.6 meq lower that the actual value.
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| What is the formula for corrected Na? | =1.6[(Pt glucose-100)/100]+pt Na
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| What is the normal response to hypovolemia? | Increase ADH release and increase thirst
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| What does the proportion of water to Na uptake look like? | Water reuptake > Na reuptake
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| Why do we use the Fractional Excretion of Sodium (FeNa)? | To determine the amount of Na lost in the urine and determine the likely source.
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| What is the formula? | FeNa(%)= (Una*Pcr)/(Ucr*Pna) *100
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| What are the two subtypes of hypo hypo? | Extrarenal and Renal
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| List some Extrarenal causes of hypo hypo. | GI losses (vomiting, diarrhea, NG suction, high output ostomy)
: Skin (burns)
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| What lab values would you expect to see with extrarenal hypo hypo? | Una <=20, FeNa <=1%, FeUr <=35%
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| List some Renal causes of hypo hypo. | Diuretics, salt-wasting nephropathy, Mineralocorticoid deficiency.
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| What lab values would you expect to see with renal hypo hypo? | Una >=20, FeNa >=2%, FeUr >=50%
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| What's the mechanism of hyponatremia in mineralocorticoid deficiency? | Decreased volume -> insufficient Aldosterone release -> Insufficient Na and water reuptake -> insufficient volume expansion
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| How and where does aldosterone work? | Increases reabsorption of Na and water while increasing the secretion of K in the DCT and CD
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| What is the Tx for hypo hypo? | Volume resusciation and treat offending cause if possible.
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| How do you calculate a pts Na deficit? | Na deficit = TBW (kg)*(desired Na-pt Na)
: TBW = 0.6 male or 0.5 female/elderly
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| What is the maximum amount you correct a pts Na in a 24 hour period? | No more than 10 meq/L
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| What occurs in Central Pontine Myelinlysis? | Relative glial dehydration and myelin degradation and/or oligodendroglial apoptosis
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| What clinical syndrome can result from CPM? | "Locked in" syndrome, quadriparesis and/or speech disturbances
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| True/False: for every 100mg/dL in glucose above 100, serum Na will appear 1.6 meq higher than the actual value. | False, it will appear 1.6 meq LOWER.
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| What body response is seen with Hypervolemic hyponatremia? | ADH release to increase thirst as well as activating RAAS, but ADH effect >> aldosterone effect
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| Una <20, FeNa <1%
: water reuptake >>Na reuptake
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| What diseases is this seen associated with? | CHF, Liver failure, nephrotic syndrome
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| What is the Tx for hyper hypo? | Fluid restriction, Na restriction, loop diuretics
: body wants to increase water and Na, we want to decrease water and Na
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| a 66 y/o male presents with CHF. What ADH action will help to increase blood volume and maintain blood pressure? | Increase in ADH
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| How is the excess ADH affecting the water in his ECF compartment and ICF compartment? | Increase wating in ECF and it shifts from ECF to ICF
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| Would you expect this patient to be symptomatic from his hyponatremia? | No
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| In this pt, how fast will the hyponatremia develop? | Over weeks to months
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| True/False: Pts with hypervolemic hyponatremia are volume overloaded in both intravascular and extravascular spaces. | False
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| How is the diagnosis of euvolemic hyponatremia made? | It's a Dx of exclusion
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| What will the pts Uosm look like? | It depends on the cause of the euvolemic hypo.
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| Name some situations where euvolemic hypo presents with a Uosm <100 | Primary polydipsia, beer potomania, tea and toast diet.
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| Name some situations where euvolemic hypo presents with a Uosm >100 | SIADH, hypothyroidism, glucocorticoid deficiency
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| Under what conditions can primary polydipsia be seen? | Psychiatric disorder, pts drink massive amount of fluid (>12L/day), max urine is about 12L/day, so excess water is retained.
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| Describe what's going on with beer potomania / tea toast diet. | Relatively large volume ingested in face of low solute load.
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| What is the underlying mechanism in euvolemic hyponatremic disorders with Usom >100? | ADH
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| What happens with hypothyroidism | Decreased CO= decreased BP = increased ADH
: If suspected, check TSH
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| What about in glucocorticoid deficiency? | CRH crossreacts and activated ADH.
: Associated NV = decreased BP = increased ADH
: If suspected, check random cortisol
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| And in SIADH? | Uosm > Sosm
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| What can cause SIADH? | Head injuries, post surgery, small cell lung cancers
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| Define hypernatremia. | Serum Na >145
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| What kind of patients do you see hypernatremia in? | Pts that lack access to water or whose water losses exceed the ability of pt to keep up
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| What are the 4 categories of hypernatrmia? | GI losses, renal losses, central causes, lack of access to water
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| What happens with GI Losses? | Water loss exceeds electrolyte loss (diarrhea, malabsorption)
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| What situations are seen with Renal Losses? | Nephrogenic Diabetes Insipidus (ADH ineffective at V2 receptors), Osmotic diuretics (hyperglycemia)
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| What situations are seen with Central causes? | Central Diabetes insipidus, Tumor invasion of thirst center, stroke in thirst center
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| What situations are seen with lack of access to water? | Elderly in NH, demented, physically impaired, intubated pts, excessive exercise, burns (depending on mechanism)
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| What is the Tx for hypernatremia? | address underlying causees (desmo for CDI, Thiazides for NDI, stop iatrogenic causes)
: calculate free water deficit and replace as appropriate
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| How do you calculate the free water deficit? | Free water= TBW(kg)*[(pt Na/desired Na)-1]
:TBW = 0.6 males and 0.5 females/elderly
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| What is the max you can correct in a day? | Do not correct Na more than 10-12 meq in 24 hours
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| True/False: Hypernatremia is always corrected by calculating the free water deficit and replacing it. | False. You need to first address the underlying cause.
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| True/False: Central diabetes insipidus is treated with Loop Diuretics. | False. Treated with desmopressin
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