DISORDERS OF SODIUM BALANCE

Melvin Bonilla Félix, MD

Professor & Chair,

Department of Pediatrics

University of Puerto Rico-Medical Sciences Campus

melvin.bonilla1@upr.edu

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

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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++]