Sodium, Potassium and H20 Disorders

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Sodium, Potassium and H20 Disorders

• Maria E. Ferris, MD, MPH

2
Case Presentation

• 14 y.o male ? chronic illnesses is admitted for
  knee surgery 12 hr. post ? Sz (GTC)
• Labs Na 128, K 4.5, Cl 98, CO2 20, Ca 9, Mg 2,
  glucose 130 U.Na 35
• a) CHF, b) ? total body Na, c) dilutional
  ?Natremia, d) Renal Na wasting e) third spacing
  of fluid

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Answer

• C) Dilutional Hyponatremia
• Must investigate the IVF that were hung during
  surgery (D5W)

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Question

• Maintenance daily Na requirements for a 50 Kg, 12
  y.o. boy?
• a) 150 mEq, b) 100 mEq, c) 63 mEq,
• d) 50 mEq and e) 45 mEq

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Answer

• c) 63 mEq/ day

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Na Transport along the nephron
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H2O Transport along the nephron
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Na and Cl Reabsorption

• In the Proximal Tubule, 17,000 mEq of the 25,200
  mEq (67) of NaCl filtered per day is absorbed by
  para-cellular and trans-cellular pathways.
• Auto regulation of the GFR, glomerular-tubular
  balance, load dependency by the L.of H. the DT,
  maintain a constant fraction of the filtered Na
  load to the beginning of the collecting duct.

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Hyponatremia

• In .95 of the cases it is due to impairment of
  H2O excretion
• Factors that affect this excretion are
• Fluid intake
• Ability to deliver NaCl to diluting segment and
  its reabsorption
• ADH suppression

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Hyponatremia

• In renal dysfunction, a 1-2 fold change in SCr
  will ? volume excretion of free H2O by 4-fold
• This in great part due to ? delivery

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Case Presentation

• 6y.o c/o VP shunt malfunction, afebrile and
  lethargic
• BUN 3, SCr 0.5, NA 125,Cl 90, Urine Osmolality
  300, UNa 60. Best next step?
• a) Demeclocycline b) diuretics, c) IV Normal
  Saline, d) Immediate VP shunt removal e) fluid
  restriction

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Answer

• e) fluid restriction

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Case Presentation

• 4 y.o. with severe DH due to NV, (-) PMHx
• Labs Na 125, Serum Osm 315. Findings are most
  likely due to an increase in
• a) Cl, b) SCr c) glucose, d) P e) K

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Answer

• c) Glucose

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• Hypernatremia

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Case Presentation

• 2 Wk old, PNC, nl delivery w/ GTC Sz
• Wt. 2.5 Kg (200 gm lt birth wt) male, BP
  70/40,P140, R50
• Glu 120, BUN 50, NA 170, CO2 12, Ca 9 Mg 1.5.
  The Sz is likely due to
• a) ? Ca, b)? glycemia, c) ?Mg,
  d) intracraneal hge. e) meningitis

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Answer

• d) Intracraneal hemorrhage due to hypernatremia

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Case Presentation

• 2 y.o. with Cong. heart Dz ? 1 day Hx of resp.
  distress LEs edema
• BUN 40, SCr 1.5, NA 125, K 4, Cl 95,
• CO2 20. Most appropriate next test?
• a) Serum Osmolality b) Urine FENa, c)
  Urine pH, d) Urine S.G, e) venous pH

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Answer

• B) FENa

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Potassium Disorders
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K Homeostasis
Diet100 mEq/d
Feces 10 mEq/d
Int. Abs 90 mEq/d
Insulin, Epi Aldosterone
ECF 65mEq/d
Tissue Stores
Plasma K, Aldo ADH
Urine 90 mEq/d
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K Homeostasis

• K is one of the most abundant cations in the
  body and a major determinant of the resting
  membrane potential, which is crucial for cell
  growth/division excitability of nerve muscle.
• Homeostasis is maintained by hormones the
  kidneys, which adjust K excretion to match PO
  intake.
• K excretion is determined by the rate of K
  secretion by the distal tubule CCD

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Transcellular K Distribution
3Na
ATPase
2K
Kcell 140-160 mEq/L
Ke 4-5 mEq/L
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Relationship Between Kserum and Total Body
Potassium in 70 kg Adult
6
5
Serum K mEq/L
4
3
2
Normal
-150 mEq
150 mEq
Total Body Potassium
25
Potassium Distribution
ECF
80 mEq
2
ICF
3920 mEq
98
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Potassium Content in Fruits and Vegetables

• Amount of Potassium Milligrams mEq
• Potato with skin 844 mg 20
• 3 Oz. Dried Fruit 796 mg 20
• 10 Dried Prunes 626 mg 16
• 1 Banana 451 mg 11
• Tomato 254 mg 6.5
• 1 Kiwi 252 mg 6.5
• 8 Oz. Glass of 250 mg 6.5
• Orange Juice
• 1Grapefruit 158 mg 4

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Renal Tubular Potassium Handling
Filtered load 600-700 mEq per day
K Reabsorption 20-30
K Secretion
K Reabsorption 60-70
Urinary Excretion 90mEq/day
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Urinary Potassium Excretion

• Normal kidneys have the capacity to excrete
  500-600 mEq per day (average K excretion 40-100
  mEq/day).
• The key site of renal potassium excretion
  regulation occurs at the cortical collecting
  duct.

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Cortical Collecting Duct - Principle Cells
Na
Peritubular capillary
Na
3Na
ATPase
2K
Tubular lumen
K
Aldosterone
R-Aldo
Cl-
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Cortical Collecting Duct
Na
Tubular lumen
Peritubular Capillary
Na
3Na
Principle Cell
ATPase
2K
K
Aldosterone
R-Aldo
Cl-
ATPase
3Na
H
ATPase
Intercalated Cell
H2O
2K
T
HCO3-
OH- CO2
K
NH4
ATPase
Cl-
H
NH3
H
NH3
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Mechanisms Leading to Hyperkalemia

• Impaired entry into cells
• Increased release from cells
• Decreased urinary excretion

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Hyperkalemia Redistribution ICF?ECF

• H
• ?Glucose
• ?Insulin
• Digoxin
• ß-blockers
• Cell injury

3Na
ATPase
2K
K
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Factors that Impair Urinary K Excretion

• Collecting duct lumen relatively more
  electropositive
• ? Flow and sodium delivery to the CCD
• ? Aldosterone production or activity

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Effect of Amiloride
Tubular lumen

• Predict changes in the following
• Relative lumen charge
• Renal K excretion
• Serum potassium
• Renal H excretion
• Arterial pH

Aldosterone
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Hyperkalemia Decreased Renal Excretion

• Volume depletion? decreased flow in CCD
• Decreased renin-AII-aldo production
• NSAIDS ? ? renin
• ACEI ? ? AII
• Heparin ? ? aldosterone production
• Spironolactone ? ? aldosterone activity
• Inhibition of CCD Na channel
• Amiloride, triamterene, trimethoprim, pentamidine

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ECG Changes of Hyperkalemia
Serum K (mEq/L) ECG
9 Sinoventricular V-fib 8 Atrial
standstill Intraventricular block 7 Tall
T wave. Depressed ST segment 6 Tall T
wave. Shortened QT interval
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ECG Changes due to Hyperkalemia
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Treatment of Hyperkalemia

• Therapy Mechanism of Action

Calcium Stabilization of Membrane
Potential Insulin Increased K entry into
Cells Beta-2 Agonists Bicarbonate (if pHalt7.2
in setting of acidosis) Dialysis Potassi
um removal Cation Exchange Resin (sodium
polystyrene Kayexalate)
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Differential Diagnosis of Hypokalemia

• Increased entry into cells
• Inadequate intake or GI losses
• Urinary losses

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Hypokalemia Redistribution ECF?ICF

• Insulin
• ß-2 agonists
• Alkalosis
• Barium
• poisoning
• Hypokalemic
• periodic
• paralysis

3Na
ATPase
2K
K
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Factors that Enhance Urinary K Excretion

• Lumen of CCD more electronegative
• Enhanced flow and sodium delivery to the CCD
• Increased aldosterone

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Sites of Action of Diuretics
Thiazide Diuretics
Loop diuretics
Blood
Lumen
(Defect Bartters)
Na Cl-
Blood
Lumen
Na K 2Cl--
Thiazide diuretics
Loop diuretics
(Defect Gitelmans)
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Interpretation of Urinary K in the Setting of
Hypokalemia
GI Losses or prior Renal K Loss
or Diuretic Therapy Current
Diuretic Use 24o Urine K lt 20
mEq gt 30 mEq FeK lt 6
gt 10
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Metabolic Alkalosis in Vomiting
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Volume Depletion
30
Serum HCO3-
25
20
7.0
UpH
5.5
4.0
50
UCl-
30
10
Generation Phase
Late Maintenance Phase
Early Maintenance Phase
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Effect of Gastric Loss of HCl, Na/H2O (Volume)
Predict changes in the following 1. Relative
lumen charge 2. Renal K excretion 3. Serum
potassium 4. Renal H excretion 5. Arterial pH
HCO3-
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Urine Na and Cl- in the Differential Diagnosis
of Metabolic Alkalosis and Hypokalemia
Urine Electrolytes Na Cl- Condition
(meq/L)
Vomiting Alkaline urine gt15 lt15 Acidic
urine lt15 lt15 Diuretic Drug active gt15 gt15 R
emote use lt15 lt15 Hyperaldosteronism gt15 gt15
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K disequilibrium

• Acid-base disturbances
• Acute metabolic acidosis ?K
• Chronic metabolic acidosis ?K
• Metabolic alkalosis ?K
• Exercise ( ?-blockers ?K)
• Cell lysis (trauma, burns, tumor-lysis, G-I
  bleed)
• Plasma osmolality ? (? by 10 mOsm/Kg ?K)
• Changes in tubular fluid flow

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Case Presentation

• 10 month old with CHF on 2 mg/Kg lasix b.i.d. His
  most likely serum labs?
• a) pH 7.2, K 3.0, b) pH 7.2, K 3.5, c) 7.2, K
  4.5, d) pH 7.5 K 3.0, e) pH 7.5, K4.5

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Answer

• d) Metabolic alkalosis with hypokalemia

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Case Presentation

• After gaining 150 yards and 28 carries a football
  player becomes disoriented, gross hematuria LOC
• T106.7,P160,R30,100/60, BUN54, CK??? Next day
  oliguria develops despite CR and fluid support.
  Most likely Dx?
• a) Heat stroke, b) HUS, c)Hgic. shock
  encephalopathy, d)Reye Sx. e) viral Sx

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Answer

• a) Heat stroke and Rhabdomyolysis

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Chloride disorders
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Answer

• a) Urinary Cl

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Case presentation

• 6 Week old baby c/o emesis p. each feed X 2 wks.
  always hungry, emaciated, dry mucosas, ? RUQ
  abdominal mass. Labs?
• a) Hypochloremic metabolic acidosis, b)
  Hypochloremic metabolic alkalosis, c) Resp.
  alkalosis, d) Respiratory acidosis metabolic
  compensation, e) nl. electrolytes

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Answer

• b) Hypochloremic metabolic alkalosis likely 2o.
  To pyloric stenosis