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DISORDERS OF SODIUM BALANCE
Melvin Bonilla Félix, MD
Professor & Chair,
Department of Pediatrics
University of Puerto Rico-Medical Sciences Campus
Objectives
• Review normal sodium-water balance
• Learn how to diagnose disorders in Na+ balance
• Discuss a therapeutic approach to hyponatremia and hypernatremia
• Review the most common complications of hyponatremia and hypernatremia and how to avoid them
• Practice calculation of Sodium and Free Water Deficit and how to correct them
Movement of Body Fluids: Osmotic Equilibrium
• A: Control
• B: Addition of 210 mM NaCl to ECF
• C: Addition of 1.5 L water to ECF
• D: Addition of 1.5 L isotonic saline to ECFWt: 70 Kg
Regulation of Body WaterAVP
Basal Antidiuretic hormone (Arginine vasopressin) is low
AVP is stimulated by
• ↑ plasma osmolality
o > 280
• ↓ circulating blood volume
• Nausea
• Pain
• Stress
• Drugs
Sodium
Sodium
• About 90% ECF cations
• 60 mEq/Kg of body weight
• 24% is nonexchangeable
• Crystalline phase of bone
• Of exchangeable
• 85% ECF/15% ICF
• Normal range = 135 - 145 mEq/L in ECF
• Pairs with Cl-, HCO3- to neutralize charge
• Low in ICF (~10 mEq/L)
• Most important ion in regulating water balance
Na+ Transport
http://what-when-how.com/wp-content/uploads/2012/04/tmp1426.jpg
Sodium Imbalances
Hyponatremia
• Decreased [Na+ ] in ECF
o Depletional: Too little Na+
o Dilutional: Too much water
Most common cause
Most disorders in Na+ balance are disorders in water balance
Etiology
Berry PL et. al. Pediatr Clin North Am 1990; 37: 351 - 363
Dilutional Hyponatremia
Edematous states
• CKD/AKI
• Nephrosis/Nephritis
• Liver disease
• Heart failure
Syndrome of Inappropriate ADH (SIADH)
• Impaired renal excretion of water
SIADH
Inability to excrete free water
• Clinical Characteristics
o Plasma hypo-osmolality (< 275)
o Less than maximally dilute urine (Usually > Plasma Osmo)
o Euvolemia
o Natriuresis
o Normal GFR
o No other hormonal disorder (thyroid or cortisol)
o No need to measure AVP
10 – 20% do not have elevated AVP
Depletional Hyponatremia
Na+ lost out of body or insufficient intake
• Diuretics
• Chronic vomiting
• Chronic diarrhea
• Deficiency or resistance to aldosterone
• Decreased Na+ intake
Cerebral Salt Wasting
Presence of intracranial pathology
Clinical Characteristics
• Plasma hypo-osmolality (< 275)
• Less than maximally dilute urine (< Plasma Osmo)
• Natriuresis
• Volume contraction
Clinical Presentation
Neurological symptoms
• Improper [Na+] outside cell improper depolarization/action potential/neuron conduction
• Lethargy
• Headaches
• Confusion
• Seizures possible
• Coma
Laboratory Evaluation
Urinalysis
Simultaneous serum and urine electrolytes (Na, Creat) and Osmolality
Treatment
Treat underlying disease
• Infection, D/C offending drug, CNS pathology
Restrict water (Dilutional)
Consider adding diuretic if severe volume expansion
Administer Na+ (Depletional)
Slowly (If > 48 hrs)
• Rapid correction - Central Pontine Myelinosis (CPM)
o Osmotic Demyelination Syndrome
Correction of Hyponatremia
Calculation of Na deficit
• Nadef = (135 – Naobs ) x TBW
o TBW = BW (Kg) x 0.6
Neonates K = 0.75
> 1 y/o K = 0.6
• Vol of Saline Solution = Nadef /[Na+] in solution
o 3%SS = 513 meq/L
o 0.9SS = 154 meq/L
• Give 50% in first 8 hrs, remaining 50 % in 24 – 72 hrs
o Do not increase [Na+] > 10 – 12 meq/L in 24 hrs
o Or 18 meq/L in 48 hrs
ComplicationsOsmotic Demyelination Syndrome
Correction of Hyponatremia
Symptomatic Hyponatremia
• Correct using 3%SS up to 120 - 125 meq/L or ↑ [Na+] 5 meq/L over few hours
o Symptoms will resolve ↑ [Na+] 5 meq/L, regardless of severity
• Then, correct to 135 slowly over 48 – 72hrs
• 5 ml/Kg of 3% SS = ↑ [Na+] 5 meq/L
Clinical Case
5 y/o male admitted with severe diarrhea x 3 days, no vomiting, no fever
Has been tolerating oral fluids (apple juice and water), but refusing solids
Phys Exam: Wt: 25 Kg, BP: 85/50, no clinical signs of dehydration
Labs: Na: 118mEq/L, K: 4 mEq/L, Cl: 90 mEq/L, HCO3: 22 mEq/L, Alb: 3.5g/dL, BUN: 4 mg/dL, Creat: 0.3 mg/dL, Glucose: 80 mg/dL
Clinical Case
Calculate Na deficit
• (135 – 118) x 0.6 x 25 Kg = 255 meq
Calculate correction with 3%SS
• 255 meq/513 meq/L = 497 mL of 3% SS
Write your orders
• 250 mL of 3%SS to run i.v over 8 hrs at 31 mL/hr, then 250 mL of 3%SS to run i.v. over 40 hrs at 6 mL/hr
• In addition, should receive maintenance fluids and ongoing losses
Clinical Case
Check serum electrolytes 2 - 4 hrs after beginning correction
then q 4 – 8 hrs during correction
Alternatively, give 125 mL of 3%SS over 2 – 4 hrs (5 mL/Kg)
Once [Na+] 120 – 125 meq/L correct to 135 over 48 hrs
Hypernatremia
• Hypernatremia (hypertonic imbalance)
• Plasma Na+ > 145 mEq/L
• Too much Na+ or too little water
• Most commonly caused by water deficit
• “Tonicity”: # of solute particles in solution
• Hypertonic - high amount of solute
• Hypotonic - dilute
• Characteristics of hypernatremia:
• movement of water from ICF to ECF
• Cells dehydrate
• Overall increase in ECF (at expense of the cell volume)
Hypernatremia
• Primarily a hospital-acquired condition
• High risk children
• Debilitated by acute or chronic illness
• Neurologic impairment
• Critically ill
• Premature newborns
Causes of HypernatremiaPrimary water deficit
Reduced water intake for days
Lack of water/access Defective thirst/mental disorder
Loss of Pure Water
Renal loss: diabetes insipidus, osmotic diuresis GI loss: vomiting, diarrhea Cutaneous loss: excessive sweating, burns Respiratory loss: hyperventilation
Shift of water into cells
Gain of “effective” osmoles in the ICF (seizures, rhabdomyolysis)
Primary gain of Na+
Administration of hypertonic saline/NaHCO3Adding NaCl to feeding formula, ingestion of seawaterHyperaldosteronism
Causes hypervolemia and hypertension, but rarely hypernatremia, unless fluid restriction
Hypernatremia
• Clinical Features
• Usually asymptomatic until Na+ > 155 meq/L
• Magnitude and rate of rise of PNa determine severity of symptoms
• Thirst
• Lethargy
• Neurological dysfunction (dehydration of brain cells)
•Confusion, twitching, seizures, stupor, coma at >160 mM
• Blood pressure and skin turgor usually preserved
Brain and Hypernatremia
Hypernatremia
• Treatment
• Fluid resuscitation
• Lower serum [Na+]
• Use hypotonic (salt-free (5% glucose) or low-salt IV Fluids to replace body water; returns Na+ concentration to normal levels
•Slowly (If chronic)
•Rapid correction – Cerebral edema, ICH, pulmonary edema
Avoid D5W if hyperglycemia
Infusion of pure water into peripheral vein - hemolysis
Correction of Hypernatremia
Free Water Deficit = 4 mL x BW x ([Na]measured – 140)
FWD = TBW x
Complications of Correction of Hypernatremia
Clinical Case
• A 20 Kg boy with vomiting with diarrhea has been receiving home-made “rice water” for hydration
• Normal vital signs
• Serum [Na+] = 160 meq/L
Clinical CaseCalculate Free Water Deficit
• 20 x 0.6 ((160-140)/140) = 1.7 L
• 20 x 0.6 ((160/140)-1)) = 1.7 L
• 4 x 20 (160-140) = 1.6 L
Write your orders
• 800 mL of 0.2% NS to run i.v over 8 hrs at 100 mL/hr, then 900 mL of 0.2%NS to run i.v. over 40 hrs at 22 mL/hr
• In addition, should receive maintenance fluids
• You might bneed to start with a bolus of 0.9NS
• Check Serum [Na+] 2 – 4 hrs after beginning correction, then q 4 – 8 hrs
• Check blood glucose and [Ca++]