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Sodium, Potassium and H20 Disorders
Maria E. Ferris, MD, MPH
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
Answer
• C) Dilutional Hyponatremia
• Must investigate the IVF that were hung during surgery (D5W)
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
Answer
• c) 63 mEq/ day
Na Transport along the nephron
ANPNa Channels3%Late Distal Tubule & CCT
AldosteroneNaCl symport4 %Distal Tubule
Aldosterone1 Na-1K-2Cl symport
25 %Loop of Henle
Angiotensin II, Epinephrine, Norepinephrine & Dopamine
Na-H exchange, NA co-transport w/ a.a. & org. solutes, Na/H/Cl/anion exchange
67 %Proximal Tubule
HormonesMechanism of Na Reabsorption
Filtered load reabsorbed
Segment
ADH & ANP
Passive8-17%Late Distal Tubule & CCT
NoneNone0 %Distal Tubule
NoneDescending Thin Limb
15 %L.of Henle
NonePassive67 %Prox. Tubule
HormonesMechanism of H2O Reabsorption
Filtered load reabsorbed
Segment
H2O Transport along the nephron
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.
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
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
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
Answer
• e) fluid restriction
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
Answer
• c) Glucose
Hypernatremia
Case Presentation
• 2 Wk old, + PNC, nl delivery w/ GTC Sz
• Wt. 2.5 Kg (200 gm < birth wt) male, BP 70/40,P:140, R:50
• 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
Answer
• d) Intracraneal hemorrhage due to hypernatremia
Case Presentation
• 2 y.o. with Cong. heart Dz 1 day Hx of resp. distress & LE’s 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
Answer
• B) FENa
Potassium Disorders
K+ Homeostasis
Diet:100 mEq/d
Int. Abs: 90 mEq/d
ECF: 65mEq/dTissue Stores
Plasma K,Aldo &
ADH
Insulin, Epi &Aldosterone
Feces: 10 mEq/d
Urine 90 mEq/d
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
3Na+
2K+ATPase
Transcellular K+ Distribution
K+cell = 140-160 mEq/L
K+e = 4-5 mEq/L
Relationship Between [K+]serum and Total Body Potassium in 70 kg Adult
Serum[K+]mEq/L
Total Body Potassium
Normal-150 mEq +150 mEq
2
3
4
5
6
Potassium Distribution
ECF
ICF3920 mEq
80 mEq
98%
2%
Potassium Content in Fruits and Vegetables
Amount of PotassiumMilligrams 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
Renal Tubular Potassium Handling
Filtered load600-700 mEq
per day
K+ Reabsorption60-70%
K+ Reabsorption20-30% K+ Secretion
Urinary Excretion90mEq/day
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.
Cortical Collecting Duct - Principle Cells
Na+
K+
3Na+
2K+
AldosteroneR-Aldo
Cl-
Peritubularcapillary
Tubular lumen
ATPase
Na+
Cortical Collecting Duct
ATPase
ATPase
ATPase
Tubular lumen PeritubularCapillary
Principle Cell
Intercalated Cell
K+
H+
OH- + CO2 HCO3-
T
Cl-
H2O
H+ 3Na+
2K+
Cl-
K+
Na+
ATPase
3Na+
2K+
R-Aldo
NH3NH3H+ +
NH4+
Na+
Aldosterone
Mechanisms Leading to Hyperkalemia
• Impaired entry into cells
• Increased release from cells
• Decreased urinary excretion
3Na+
2K+ATPase
K+
H+
GlucoseInsulinDigoxinβ-blockersCell injury
Hyperkalemia – Redistribution: ICFECF
Factors that Impair Urinary K+ Excretion
• Collecting duct lumen relatively more electropositive
Flow and sodium delivery to the CCD Aldosterone production or activity
Effect of Amiloride
Predict changes in the following:
• Relative lumen charge• Renal K+ excretion• Serum potassium• Renal H+ excretion• Arterial pH ATPase
ATPase
PeritubularCapillary
OH- + CO2 HCO3-
T
Cl-
H2O
H+ 3Na+
2K+
K+
ATPase
3Na+
2K+
R-Aldo
AmilorideNa+ Channel
Amiloride
Aldosterone
Tubular lumen
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
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
ECG Changes due to Hyperkalemia
Treatment of Hyperkalemia
Therapy Mechanism of Action
Calcium Stabilization of Membrane Potential
Insulin Increased K+ entry into CellsBeta-2 AgonistsBicarbonate (if pHa<7.2 in setting of
acidosis)
Dialysis Potassium removalCation Exchange Resin (sodium polystyrene = Kayexalate)
Differential Diagnosis of Hypokalemia
• Increased entry into cells
• Inadequate intake or GI losses
• Urinary losses
3Na+
2K+ATPase
K+
Hypokalemia: Redistribution: ECFICF
Insulinβ-2 agonistsAlkalosis
Barium poisoningHypokalemic periodic paralysis
Factors that Enhance Urinary K+ Excretion
• Lumen of CCD more electronegative
• Enhanced flow and sodium delivery to the CCD
• Increased aldosterone
Thiazide Diuretics
Loop diuretics
Na+K+2Cl--
BloodLumen
Loop diuretics
Na+Cl-
Thiazide diuretics
Sites of Action of Diuretics
Lumen Blood(Defect = Bartter’s)
(Defect = Gitelman’s)
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 < 20 mEq > 30 mEq
FeK < 6 % > 10 %
Ser
um [
HC
O3-
]U
pHU
[Cl- ]35
30
25
20
7.0
5.5
4.0503010
Generation Phase Late Maintenance Phase
Volume Depletion
Metabolic Alkalosis in Vomiting
Early Maintenance Phase
Effect of Gastric Loss of HCl, Na+/H2O (Volume)
Predict changes in the following:
1. Relative lumen charge2. Renal K+ excretion3. Serum potassium4. Renal H+ excretion5. Arterial pH
ATPaseATPase
Tubular lumenPeritubularCapillary
OH- + CO2 HCO3-
T
Cl-
H2O
H+ 3Na+
2K+
K+
Na+
ATPase
3Na+
2K+
R-Aldo Aldosterone
Na+
HCO3-
Urine Na+ and Cl- in the Differential Diagnosis of Metabolic
Alkalosis and Hypokalemia
Urine ElectrolytesNa+ Cl-
Condition (meq/L)
VomitingAlkaline urine >15 <15Acidic urine <15 <15
DiureticDrug active >15 >15Remote use <15 <15
Hyperaldosteronism >15 >15
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
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
Answer
• d) Metabolic alkalosis with hypokalemia
Case Presentation
• After gaining 150 yards and 28 carries a football player becomes disoriented, gross hematuria & LOC
• T:106.7,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
Answer
• a) Heat stroke and Rhabdomyolysis
Chloride disorders
Answer
• a) Urinary Cl
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
Answer
• b) Hypochloremic metabolic alkalosis likely 2o. To pyloric stenosis