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Renal 04 Na/H2O bal
Thomas: Disorders of Na and water balance
| Question | Answer |
|---|---|
| What controls total body water and Na? | TBW - ADH : Na - Aldosterone |
| What lab values do you need when assessing a pt for Na disorders? | Serum chemistry, Uosm, Sosm, Una, Ucr |
| What Na level defines hyponatremia? | Na <135 |
| What is one area of concern with hyponatremia? | The potential of edema in the skull, as there is limited room for expansion. |
| Name symptoms associated with acute hyponatremia. | Nausea, vomiting, lethargy, confusion, seizures, coma |
| 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. |
| 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 |
| Why isn't the increase in brain water as high as expected? | There is a prompt loss of electrolytes and organic osmolytes. |
| What is pseudohyponatremia? | Where calculated Na on lab work is low when Sosm is hypertonic (>280) due to other effective osmoles |
| Name some of the osmoles/ conditions leading to pseudohypo. | Mannitol, post transurethral resection of the prostate, and hyperglycemia |
| 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. |
| 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. |
| What is the formula for corrected Na? | =1.6[(Pt glucose-100)/100]+pt Na |
| What is the normal response to hypovolemia? | Increase ADH release and increase thirst |
| What does the proportion of water to Na uptake look like? | Water reuptake > Na reuptake |
| 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. |
| What is the formula? | FeNa(%)= (Una*Pcr)/(Ucr*Pna) *100 |
| What are the two subtypes of hypo hypo? | Extrarenal and Renal |
| List some Extrarenal causes of hypo hypo. | GI losses (vomiting, diarrhea, NG suction, high output ostomy) : Skin (burns) |
| What lab values would you expect to see with extrarenal hypo hypo? | Una <=20, FeNa <=1%, FeUr <=35% |
| List some Renal causes of hypo hypo. | Diuretics, salt-wasting nephropathy, Mineralocorticoid deficiency. |
| What lab values would you expect to see with renal hypo hypo? | Una >=20, FeNa >=2%, FeUr >=50% |
| What's the mechanism of hyponatremia in mineralocorticoid deficiency? | Decreased volume -> insufficient Aldosterone release -> Insufficient Na and water reuptake -> insufficient volume expansion |
| How and where does aldosterone work? | Increases reabsorption of Na and water while increasing the secretion of K in the DCT and CD |
| What is the Tx for hypo hypo? | Volume resusciation and treat offending cause if possible. |
| 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 |
| What is the maximum amount you correct a pts Na in a 24 hour period? | No more than 10 meq/L |
| What occurs in Central Pontine Myelinlysis? | Relative glial dehydration and myelin degradation and/or oligodendroglial apoptosis |
| What clinical syndrome can result from CPM? | "Locked in" syndrome, quadriparesis and/or speech disturbances |
| 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. |
| What body response is seen with Hypervolemic hyponatremia? | ADH release to increase thirst as well as activating RAAS, but ADH effect >> aldosterone effect |
| Una <20, FeNa <1% : water reuptake >>Na reuptake | |
| What diseases is this seen associated with? | CHF, Liver failure, nephrotic syndrome |
| 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 |
| a 66 y/o male presents with CHF. What ADH action will help to increase blood volume and maintain blood pressure? | Increase in ADH |
| 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 |
| Would you expect this patient to be symptomatic from his hyponatremia? | No |
| In this pt, how fast will the hyponatremia develop? | Over weeks to months |
| True/False: Pts with hypervolemic hyponatremia are volume overloaded in both intravascular and extravascular spaces. | False |
| How is the diagnosis of euvolemic hyponatremia made? | It's a Dx of exclusion |
| What will the pts Uosm look like? | It depends on the cause of the euvolemic hypo. |
| Name some situations where euvolemic hypo presents with a Uosm <100 | Primary polydipsia, beer potomania, tea and toast diet. |
| Name some situations where euvolemic hypo presents with a Uosm >100 | SIADH, hypothyroidism, glucocorticoid deficiency |
| 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. |
| Describe what's going on with beer potomania / tea toast diet. | Relatively large volume ingested in face of low solute load. |
| What is the underlying mechanism in euvolemic hyponatremic disorders with Usom >100? | ADH |
| What happens with hypothyroidism | Decreased CO= decreased BP = increased ADH : If suspected, check TSH |
| What about in glucocorticoid deficiency? | CRH crossreacts and activated ADH. : Associated NV = decreased BP = increased ADH : If suspected, check random cortisol |
| And in SIADH? | Uosm > Sosm |
| What can cause SIADH? | Head injuries, post surgery, small cell lung cancers |
| Define hypernatremia. | Serum Na >145 |
| 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 |
| What are the 4 categories of hypernatrmia? | GI losses, renal losses, central causes, lack of access to water |
| What happens with GI Losses? | Water loss exceeds electrolyte loss (diarrhea, malabsorption) |
| What situations are seen with Renal Losses? | Nephrogenic Diabetes Insipidus (ADH ineffective at V2 receptors), Osmotic diuretics (hyperglycemia) |
| What situations are seen with Central causes? | Central Diabetes insipidus, Tumor invasion of thirst center, stroke in thirst center |
| What situations are seen with lack of access to water? | Elderly in NH, demented, physically impaired, intubated pts, excessive exercise, burns (depending on mechanism) |
| 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 |
| 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 |
| What is the max you can correct in a day? | Do not correct Na more than 10-12 meq in 24 hours |
| True/False: Hypernatremia is always corrected by calculating the free water deficit and replacing it. | False. You need to first address the underlying cause. |
| True/False: Central diabetes insipidus is treated with Loop Diuretics. | False. Treated with desmopressin |
Created by:
bcriss
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