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Fractional Excretion of Bicarbonate

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101. Metabolic Acidosis (Overview)

. Comparison of Types 1, 2, and 4 RTA Characteristics Proximal (Type 2) Distal (Type 1) Type 4 Primary defect Proximal HCO 3 - reabsorption Diminished distal H+ secretion Diminished ammoniagenesis Urine pH < 5.5 when serum HCO 3 - is low >5.5 < 5.5 Serum HCO 3 - >15 mEq/L Can be < 10 mEq/L >15 mEq/L Fractional excretion of HCO 3 - (FEHCO 3 ) >15-20% during HCO 3 - load < 5% (can be as high as 10% in children) < 5% Serum K + Normal or mild decrease Mild-to-severe decrease* High Associated features Fanconi (...) concentrations. On the basis of this law, the addition of H + or bicarbonate (HCO 3 - ) drives the reaction shown below to the left. H 2 CO 3 (acid)↔H + + HCO 3 - (base) In body fluids, the concentration of hydrogen ions ([H + ]) is maintained within very narrow limits, with the normal physiologic concentration being 40 nEq/L. The concentration of HCO 3 - (24 mEq/L) is 600,000 times that of [H + ]. The tight regulation of [H + ] at this low concentration is crucial for normal cellular activities because H

2014 eMedicine.com

102. Hyperchloremic Acidosis (Overview)

, urinary loss of glucose, amino acids, phosphate, uric acid, and other organic anions, such as citrate, can also occur (Fanconi syndrome). A distinctive feature of type II pRTA is that it is nonprogressing, and when the serum bicarbonate is reduced to approximately 15 mEq/L, a new transport maximum for bicarbonate is established and the proximal tubule is able to reabsorb all of the filtered bicarbonate. A fractional excretion of bicarbonate (FE[HCO 3 - ]) greater than 15% when the plasma bicarbonate (...) is normal after bicarbonate loading is diagnostic of pRTA. In contrast, the fractional excretion of bicarbonate in low and normal bicarbonate levels is always less than 5% in distal RTA (dRTA). Another feature of pRTA is that the urine pH can be lowered to less than 5.5 with acid loading. The pathogenic mechanisms responsible for the tubular defect in persons with pRTA are not completely understood. Defective pump secretion or function, namely aberrations in the function of the proton pump ([H

2014 eMedicine.com

103. Hyperkalemia (Overview)

(eg, increased intake or inhibited excretion) In patients with severe hyperkalemia, treatment is as follows: IV calcium to ameliorate cardiac toxicity, if present Identify and remove sources of potassium intake IV glucose and insulin infusion to enhance potassium uptake by cells Correct severe metabolic acidosis with sodium bicarbonate Consider beta-adrenergic agonist therapy (eg, nebulized albuterol, 10 mg, administered by a respiratory therapist); preferred over alkali therapy in patients (...) delivery to the distal tubule (eg, diuretics) High urine flow (eg, osmotic diuresis) High serum potassium level Delivery of negatively charged ions to the distal tubule (eg, bicarbonate) Renal potassium excretion is decreased by the following: Absence, or very low levels, of aldosterone WNK1 and WNK4 mutations Low sodium delivery to the distal tubule Low urine flow Low serum potassium level Kidneys adapt to acute and chronic alterations in potassium intake. When potassium intake is chronically high

2014 eMedicine.com

104. Cystinuria (Treatment)

range of 7-7.5. Acetazolamide inhibits the brush-border carbonic anhydrase of the proximal convoluted tubule, thereby increasing urinary bicarbonate excretion. Acetazolamide is not widely used as a first-line drug and is of questionable efficacy. Sodium bicarbonate was used in the past for alkalinizatoinbut is no longer recommended as a first-line agent. The sodium ion may actually increase the amount of cystine excreted. Chelating agents Cystine-binding and cystine-reducing agents share the ability (...) is important for decision-making processes, and stone site and size also influence further management. See the treatment algorithm image below. Treatment algorithm for cystinuria. Hydration The average homozygous patient with cystinuria excretes 600-1400 mg of cystine per day. The solubility of cystine at a pH level of 7 is 250-300 mg/L. Therefore, one of the oldest and most effective cystine stone–prevention techniques is hyperdiuresis to decrease urinary cystine concentration. Early studies by Dent et al

2014 eMedicine.com

105. Hypocitraturia (Overview)

filtration rate (GFR) decreases, there is a stepwise decrease in the amount of citrate that is filtered; however, in the early stages of CKD, the increased fractional excretion of citrate prevents an abrupt decline in urinary citrate, such that overt hypocitraturia is not usually observed until advanced stages of CKD. [ ] Primary Hyperaldosteronism In this disease entity, both hypercalciuria and hypocitraturia occur via Na-dependent volume expansion and chronic hypokalemia. [ ] Previous Next: US (...) . Urol Res . 2006 Aug. 34(4):231-8. . Kessler T, Hesse A. Cross-over study of the influence of bicarbonate-rich mineral water on urinary composition in comparison with sodium potassium citrate in healthy male subjects. Br J Nutr . 2000 Dec. 84(6):865-71. . Pinheiro VB, Baxmann AC, Tiselius HG, Heilberg IP. The effect of sodium bicarbonate upon urinary citrate excretion in calcium stone formers. Urology . 2013 Jul. 82(1):33-7. . Seltzer MA, Low RK, McDonald M. Dietary manipulation with lemonade

2014 eMedicine.com

106. Hypocalcemia (Overview)

: Pathophysiology Ionized calcium is the necessary plasma fraction for normal physiologic processes. In the neuromuscular system, ionized calcium facilitates nerve conduction, muscle contraction, and muscle relaxation. Calcium is necessary for bone mineralization and is an important cofactor for hormonal secretion in endocrine organs. At the cellular level, calcium is an important regulator of ion transport and membrane integrity. Calcium turnover is estimated to be 10-20 mEq/day. Approximately 500 mg (...) of calcium is removed from the bones daily and replaced by an equal amount. Normally, the amount of calcium absorbed by the intestines is matched by urinary calcium excretion. Despite these enormous fluxes of calcium, the levels of ionized calcium remain stable because of the rigid control maintained by parathyroid hormone (PTH), vitamin D, and calcitonin through complex feedback loops. These compounds act primarily at bone, renal, and GI sites. Calcium levels are also affected by magnesium

2014 eMedicine.com

107. Syndrome of Inappropriate Secretion of Antidiuretic Hormone (Overview)

, the nonphysiological secretion of AVP results in enhanced water reabsorption, leading to dilutional hyponatremia. While a large fraction of this water is intracellular, the extracellular fraction causes volume expansion. Volume receptors are activated and natriuretic peptides are secreted, which causes natriuresis and some degree of accompanying potassium excretion (kaliuresis). Eventually, a steady state is reached and the amount of Na + excreted in the urine matches Na intake. Ingestion of water is an essential (...) of the antidiuretic hormone arginine vasopressin (AVP) despite normal or increased plasma volume, which results in impaired water excretion. [ ] The key to understanding the pathophysiology, signs, symptoms, and treatment of SIADH is the awareness that the results from an excess of water rather than a deficiency of sodium. Signs and symptoms Depending on the magnitude and rate of development, hyponatremia may or may not cause symptoms. The history should take into account the following considerations: In general

2014 eMedicine.com

108. Acute Tubular Necrosis (Treatment)

(red arrow). Finally, intratubular obstruction due to the denuded epithelium and cellular debris is evident (green arrow); note that the denuded tubular epithelial cells clump together because of rearrangement of intercellular adhesion molecules. of 2 Tables Table. Laboratory Findings Used to Differentiate Prerenal Azotemia From ATN Finding Prerenal Azotemia ATN and/or Intrinsic Renal Disease Urine osmolarity (mOsm/kg) >500 < 350 Urine sodium (mmol/d) < 20 >40 Fractional excretion of sodium (FENa (...) ) (%) < 1 >2 Fractional excretion of urea (%) < 35 >50 Urine sediment Bland and/or nonspecific May show muddy brown granular casts Contributor Information and Disclosures Author Nikhil A Shah, MBBS, DNB(Neph) Clinical Research Fellow in Home Dialysis, Nephrologist, University of Alberta Faculty of Medicine and Dentistry, Canada Nikhil A Shah, MBBS, DNB(Neph) is a member of the following medical societies: , , , Canadian Society of Nephrology, , Disclosure: Nothing to disclose. Coauthor(s) Mahendra

2014 eMedicine.com

109. Acute Renal Failure (Treatment)

be harmful for the patient. Maintenance of volume homeostasis and correction of biochemical abnormalities remain the primary goals of treatment and may include the following measures: Correction of fluid overload with furosemide Correction of severe acidosis with bicarbonate administration, which can be important as a bridge to dialysis Correction of hyperkalemia Correction of hematologic abnormalities (eg, anemia, uremic platelet dysfunction) with measures such as transfusions and administration (...) agents, nonsteroidal anti-inflammatory drugs [NSAIDs]) should be avoided or used with extreme caution. Similarly, all medications cleared by renal excretion should be avoided, or their doses should be adjusted appropriately. A 2013 study indicated that triple therapy using nonsteroidal anti-inflammatory drugs (NSAIDs) with 2 antihypertensive medications—a diuretic along with an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin-receptor blocker (ARB)—significantly increases the risk

2014 eMedicine.com

110. Azotemia (Treatment)

in developing countries: analysis of 2405 cases in 26 years from eastern India. Clin Kidney J . 2013 Apr. 6 (2):150-5. . . Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int . 2002 Dec. 62(6):2223-9. . . Faubel S, Patel NU, Lockhart ME, Cadnapaphornchai MA. Renal relevant radiology: use of ultrasonography in patients with AKI. Clin J Am Soc Nephrol . 2014 Feb. 9(2):382-94. . . Holmquist F, Hansson K (...) , Mele C, et al. Transvenous transjugular renal core biopsy with a redesigned biopsy set including a blunt-tipped needle. Cardiovasc Intervent Radiol . 2002 Mar-Apr. 25(2):155-7. . Fenske W, Stork S, Koschker AC, et al. Value of fractional uric acid excretion in differential diagnosis of hyponatremic patients on diuretics. J Clin Endocrinol Metab . 2008 Aug. 93(8):2991-7. . Liu KD, Matthay MA, Chertow GM. Evolving practices in critical care and potential implications for management of acute kidney

2014 eMedicine.com

111. Metabolic Acidosis (Treatment)

and well tolerated, and was associated with improvements in bone quality, suggesting a beneficial effect of both alkali treatment and restoration of acid/base balance. The researchers concluded that potassium citrate may be superior to sodium bicarbonate, because it lacks volume effects and the obligatory calcium excretion associated with sodium administration. [ ] Go to and for complete information on these topics. Next: Type 1 Renal Tubular Acidosis Administration of an alkali is the mainstay (...) with placebo followed by escalating doses of oral sodium bicarbonate at 2-week intervals (0.3, 0.6, and 1.0 mEq/d per kg ideal body weight). [ ] Sodium bicarbonate was well tolerated, even at high doses; produced a dose-dependent increase in serum bicarbonate; and was associated with an improvement in lower extremity muscle strength and reduced urinary nitrogen excretion. The authors caution, however, that the results require further study and confirmation from a large randomized placebo-controlled study

2014 eMedicine.com

112. Hypertension (Treatment)

[ , ] : (1) elevated BP, with a systolic pressure (SBP) between 120 and 129 mm Hg and diastolic pressure (DBP) less than 80 mm Hg, and (2) stage 1 hypertension, with an SBP of 130 to 139 mm Hg or a DBP of 80 to 89 mm Hg. In adults at increased risk of heart failure (HF), the optimal BP in those with hypertension should be less than 130/80 mm Hg. Adults with HFrEF (HF with reduced ejection fraction) and hypertension should be prescribed GDMT (guideline-directed management and therapy) titrated to attain

2014 eMedicine.com

113. Hypocitraturia (Treatment)

filtration rate (GFR) decreases, there is a stepwise decrease in the amount of citrate that is filtered; however, in the early stages of CKD, the increased fractional excretion of citrate prevents an abrupt decline in urinary citrate, such that overt hypocitraturia is not usually observed until advanced stages of CKD. [ ] Primary Hyperaldosteronism In this disease entity, both hypercalciuria and hypocitraturia occur via Na-dependent volume expansion and chronic hypokalemia. [ ] Previous Next: US (...) . Urol Res . 2006 Aug. 34(4):231-8. . Kessler T, Hesse A. Cross-over study of the influence of bicarbonate-rich mineral water on urinary composition in comparison with sodium potassium citrate in healthy male subjects. Br J Nutr . 2000 Dec. 84(6):865-71. . Pinheiro VB, Baxmann AC, Tiselius HG, Heilberg IP. The effect of sodium bicarbonate upon urinary citrate excretion in calcium stone formers. Urology . 2013 Jul. 82(1):33-7. . Seltzer MA, Low RK, McDonald M. Dietary manipulation with lemonade

2014 eMedicine.com

114. Toxicity, Mushroom (Treatment)

), Boletus edulis (king boletus), Leccinium versipelle (brown birch boletus), and Albatrellus ovinus (sheep polypore). Many of these are identified in field guides as edible. Treatment is with aggressive IV fluid resuscitation and consideration for IV sodium bicarbonate to alkalinize the urine. In rare cases, dialysis may be needed if renal failure occurs. Agitation, commonly observed with hallucinogenic mushrooms, is treated with benzodiazepines; phenothiazines are best avoided in this setting. Other (...) of them demonstrate an important decrease in hepatic necrosis histologically. [ ] A large human case series found an association between both silibinin and NAC and higher survival rates. [ ] Corticosteroids, vitamin C, kutkin, aucubin, and thioctic acid have been used in the past but have no proven benefit and are no longer recommended. Charcoal hemoperfusion and hemodialysis are also ineffective in removing toxins because once the toxin is formed, it is rapidly excreted by the kidneys. Plasma

2014 eMedicine.com

115. Toxicity, Barbiturate (Treatment)

to be renally excreted. Urinary alkalinization is not recommended for short-acting barbiturates. Enhancement of urinary elimination may be accomplished with an initial sodium bicarbonate bolus of 1 mEq/kg followed by a constant infusion. This infusion may be made by adding 100-150 mEq of sodium bicarbonate to 850 mL of D5 and titrating to maintain a urine pH of greater than 7.5 with an arterial pH of less than 7.50. The goal should be a urine output of 150-250 mL/h. Risks include hypokalemia, fluid overload (...) it was administered at 30 minutes, 60 minutes, and 120 minutes, respectively, current guidelines in overdose management question its benefit. There is no evidence that the administration of activated charcoal improves clinical outcome. Indeed, its use has decreased to less than 5% of all reported ingestions in recent years. [ ] A single dose of activated charcoal may be given within an hour of overdose if the clinician estimates that a clinically significant fraction of the ingested substance remains in the GI

2014 eMedicine.com

116. Azotemia (Overview)

for hypothalamic production of antidiuretic hormone, which exerts its effect in the medullary collecting duct for water reabsorption. Through unknown mechanisms, activation of the sympathetic nervous system leads to enhanced proximal tubular reabsorption of salt and water, as well as BUN, creatinine, calcium, uric acid, and bicarbonate. The net result of these 4 mechanisms of salt and water retention is decreased output and decreased urinary excretion of sodium (< 20 mEq/L). Intrarenal azotemia Intrarenal (...) Failure Study Group. Kidney Int . 1996 Sep. 50 (3):811-8. . . Prakash J, Singh TB, Ghosh B, Malhotra V, Rathore SS, Vohra R, et al. Changing epidemiology of community-acquired acute kidney injury in developing countries: analysis of 2405 cases in 26 years from eastern India. Clin Kidney J . 2013 Apr. 6 (2):150-5. . . Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int . 2002 Dec. 62(6):2223-9

2014 eMedicine.com

117. Acute Tubular Necrosis (Overview)

From ATN Finding Prerenal Azotemia ATN and/or Intrinsic Renal Disease Urine osmolarity (mOsm/kg) >500 < 350 Urine sodium (mmol/d) < 20 >40 Fractional excretion of sodium (FENa) (%) < 1 >2 Fractional excretion of urea (%) < 35 >50 Urine sediment Bland and/or nonspecific May show muddy brown granular casts Contributor Information and Disclosures Author Nikhil A Shah, MBBS, DNB(Neph) Clinical Research Fellow in Home Dialysis, Nephrologist, University of Alberta Faculty of Medicine and Dentistry (...) , but it also helps in the excretion of these toxins by glomerular filtration and tubular secretion. Exogenous nephrotoxins that cause ATN Aminoglycoside-related toxicity occurs in 10-30% of patients receiving aminoglycosides, even when blood levels are in apparently therapeutic ranges. Risk factors for ATN in these patients include the following: Preexisting liver or renal disease Concomitant use of other nephrotoxins (eg, amphotericin B, radiocontrast media, cisplatin) Shock Advanced age Female sex Higher

2014 eMedicine.com

118. Metabolic Acidosis (Follow-up)

and well tolerated, and was associated with improvements in bone quality, suggesting a beneficial effect of both alkali treatment and restoration of acid/base balance. The researchers concluded that potassium citrate may be superior to sodium bicarbonate, because it lacks volume effects and the obligatory calcium excretion associated with sodium administration. [ ] Go to and for complete information on these topics. Next: Type 1 Renal Tubular Acidosis Administration of an alkali is the mainstay (...) with placebo followed by escalating doses of oral sodium bicarbonate at 2-week intervals (0.3, 0.6, and 1.0 mEq/d per kg ideal body weight). [ ] Sodium bicarbonate was well tolerated, even at high doses; produced a dose-dependent increase in serum bicarbonate; and was associated with an improvement in lower extremity muscle strength and reduced urinary nitrogen excretion. The authors caution, however, that the results require further study and confirmation from a large randomized placebo-controlled study

2014 eMedicine.com

119. Hypocitraturia (Follow-up)

filtration rate (GFR) decreases, there is a stepwise decrease in the amount of citrate that is filtered; however, in the early stages of CKD, the increased fractional excretion of citrate prevents an abrupt decline in urinary citrate, such that overt hypocitraturia is not usually observed until advanced stages of CKD. [ ] Primary Hyperaldosteronism In this disease entity, both hypercalciuria and hypocitraturia occur via Na-dependent volume expansion and chronic hypokalemia. [ ] Previous Next: US (...) . Urol Res . 2006 Aug. 34(4):231-8. . Kessler T, Hesse A. Cross-over study of the influence of bicarbonate-rich mineral water on urinary composition in comparison with sodium potassium citrate in healthy male subjects. Br J Nutr . 2000 Dec. 84(6):865-71. . Pinheiro VB, Baxmann AC, Tiselius HG, Heilberg IP. The effect of sodium bicarbonate upon urinary citrate excretion in calcium stone formers. Urology . 2013 Jul. 82(1):33-7. . Seltzer MA, Low RK, McDonald M. Dietary manipulation with lemonade

2014 eMedicine.com

120. Hypertension (Follow-up)

[ , ] : (1) elevated BP, with a systolic pressure (SBP) between 120 and 129 mm Hg and diastolic pressure (DBP) less than 80 mm Hg, and (2) stage 1 hypertension, with an SBP of 130 to 139 mm Hg or a DBP of 80 to 89 mm Hg. In adults at increased risk of heart failure (HF), the optimal BP in those with hypertension should be less than 130/80 mm Hg. Adults with HFrEF (HF with reduced ejection fraction) and hypertension should be prescribed GDMT (guideline-directed management and therapy) titrated to attain

2014 eMedicine.com

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