HYPONATREMIA

51 y/o, F CC: vomiting

HISTORY OF PRESENT ILLNESS

PAST MEDICAL/SOCIAL HISTORY Known hypertensive--- 10 years Have had bipedal edema amlodipine

was discontinued Telmisartan 40 mg daily for the past

month HCTZ 12.5 daily for the past month

PHYSICAL EXAMINATION

Weak-looking, wheelchair-borne Wt: 50 kg (usual: 53 kg) Poor skin turgor, dry mouth, tongue and

axillae BP: supne-120/80, sitting: 90/60 (usual

130/80) CR: supine-90 bpm; sitting-105 bpm JVP: <5 cm H2O at 45 degrees.

REVIEW OF SYSTEMS

UNREMARKABLE

LABORATORY TESTS Hgb=132 mg/dL WBC=12.5 Plasma Na=123

mEq/L Plasma K=3.7

mEq/L Chloride=71/mEq/L Urine

Na=100mmol/L mEq/L

Uosm=540 mosm/L

hematocrit= 0.35 Neutrophils= 0.88 Lymphocyte= 0.12 BUN= 22mg/dL Serum Crea= 0.9

mg/dL Glucose= 98 mg/dL

Urinalysis: Yellow, slightly

turbid, pH 6.0, Sp.Gr. 1.020

(-) Albumin and Sugar

Hyaline cast 5/hpf Pus cells 10-15/hpf RBC: 2-5/hpf (not

dysmorphic

ABG Ph =7.3 CO2 = 35 HCO3 = 18

Diagnosis

-vomiting

HYPOVOLEMIA

2-day history of vomiting (3 episodes, 50cc/episode)

Has been taking HCTZ daily for 1 month Orthostatic hypotension Poor skin turgor, dry mouth, yongue and

axillae patient is dehydrated Low JVP

Urinary tract infection

fever, dysuria and urgency Hyaline cast 5/hpf Pus cells 10-15/hpf RBC: 2-5/hpf (not dysmorphic

Factors that contributed to hyponatremia

Vomiting and dehydration

HCTZ (Hydrochlorothiazide)

OSMOLALITY

Count of the total number of osmotically active particles in a solution

Equal to the sum of the molalities of all the solutes present in that solution

affected by changes in water content

EFFECTIVE PLASMA OSMOLALITY Tonicity Shift of water through biomembranes produced by

osmotically active particles Effective osmolality determined by restricted solutes

Na= reflection of ECF volume K= reflection of ICF volume

In the ECF: Na+ : 145 mEq/L Major cation Cl-:105 mEq/L HCO3-:25 mEq/L Major anions

Ineffective osmoles Don’t contribute to water shifts Urea

Plasma Osmolality Serum Na+ = 123 mEq/L Glucose = 98 mg/dL BUN = 22 mg/dL

Serum Osmolality = {Serum Na (mEq/L) x 2} + {Glucose

(mg/dL)/18} + {Urea (mg/dL)/2.8} = {123 mEq/L x 2} + {98 mg/dL ÷ 18}

+ {22 mg/dL ÷ 2.8} = 259.30 mOsm/Kg H2O

Effective Plasma Osmolality Effective Plasma Osmolality = {Serum Na (mEq/L) x 2} = {123 mEq/L x 2} = 246 mOsm/Kg H2O LOW   Normal Plasma Osmolality

285 – 295 mOsm/Kg H2O

Importance

Serum OsmolalityUseful when dealing with patients with an

elevated plasma [Glucose] secondary to DM and in patients with CRF whose plasma [Urea] is increased

Investigation of Hyponatremia Identification of Osmolar gap

Hyponatremia Hypotonic Hyponatremia: < 280

ECF volume status may be: Low, Normal or High

Isotonic Hyponatremia: 280 – 295Very high blood levels of lipid or proteinPseudohyponatremia

Hypertonic Hyponatremia: > 295associated with shifts of fluid due to osmotic

pressureDiabetes Mellitus

Osmolar Gap

Measured Osmolality – Calculated Osmolality

If > 10 mmol/L presence of unmeasured osmotically active

substances in the plasma (ethanol, methanol, ethylene glycol, acetone, or isopropyl alcohol)

Urine Osmolality An important test of renal concentrating ability Identification of disorders of the ADH

mechanism Identification of causes of hyper-or

hyponatremia Reflects the total number of osmotically active

particles in the urine, without regard to the size or weight of the particles

Evaluate electrolyte and water balance Used in work-up for renal disease Normal Urine Osmolality: 50-1200 mOsm/kg

H2O

Regualtion of Osmolality Osmoreceptors

Found in anterolateral hypothalamusStimulated by tonicity, effective osmolality, ECF

volumeThreshold

○ 295 mOsm/kg H2O, thirst, suppress AVP○ 280-290 mOsm/kg H2O, enhance AVP secretion

AVP/ADHStimulates insertion of water channels in

basolateral membrane of principal cells in the collecting ducts

Passive water reabsorption

In the Patient Plasma Osmolality = {Serum Na (mEq/L) x 2} + {Glucose (mg/dL)/18} +

{Urea (mg/dL)/2.8} = {123 mEq/L x 2} + {98 mg/dL ÷ 18} + {22 mg/dL ÷

2.8} = 259 mOsm/Kg H2O

Normal Values

Patient

Uosm 50-1200 540

Posm 275-290 259

Urine Osmolality

Serum Osmolality

Urine Osmolality

Clinical Significance

Normal or increased

Increased Fluid volume deficit

Decreased Decreased Fluid volume excess

Normal DecreasedIncreased fluid intake or

diuretics

Increased or normal

Decreased (with no increase in fluid intake)

Kidneys unable to concentrate urine or lack of ADH (diabetes

insipidus)

Decreased Increased SIADH

Serum and Urine Osmolality Levels

HypoosmolalitySodium loss due to diuretic

use and a low salt diet Hyponatremia Adrenocortical insufficiency SIADH Excessive water

replacement/ overhydration/water intoxication

Serum and Urine Osmolality levelsHyperosmolality

Renal disease Congestive heart failure Addison's disease Dehydration Diabetes insipidus Hypercalcemia Diabetes mellitus/ hyperglycemia Hypernatremia Alcohol ingestion Mannitol therapy Azotemia

Normal Value of Urine Sodium:10-40 mEq/L Higher-than-normal Urine Sodium levels

may indicate: EXCESSIVE SALT INTAKE

Lower-than-normal Urine Sodium levels may indicate:

ALDOSTERONISM CONGESTIVE HEART FAILURE DIARRHEA AND DEHYDRATION STATUS RENAL FAILURE

Hyponatremia

Urine sodium <10 mmol/L may indicate Extra-renal Depletion:Dehydration (gastrointestinal or sweat loss)Congestive heart failureLiver disease Nephrotic syndromes

Patient Urine Sodium: 100 mmol/L Urine sodium >10 mmol/L may indicate:

diuretics, emesis, intrinsic renal diseases, Addison disease, hypothyroidism, or syndrome of inappropriate antidiuretic hormone (SIADH)

In SIADHUrinary Sodium is usually >20 mmol/L

Sodium Deficit

Target Sodium = 125 – 135 mEq/L (130 mEq/L)

Sodium Deficit = 0.6 x weight in kg X (desired Na

– actual Na) = 0.6 x 50 kg x (130 – 123) = 210 mEq/L

Goals of Therapy

Raise the plasma Na+ concentration by restricting water intake and promoting water loss; and

Correct the underlying disorder

Mild asymptomatic hyponatremiarequires no treatment

Asymptomatic hyponatremia associated with ECF volume contractionNa repletion, generally in the form isotonic salinerestoration of euvolemia removes the hemodynamic

stimulus for AVP release, allowing the excess free water to be excreted

Hyponatremiaassociated with edematous statesrestriction of Na and water intake, correction of

hypokalemia, and promotion of water loss in excess of Na

Hyponatremiaassociated with primary polydipsia, renal failure, and SIADHWater restriction

Osmotic Demyelination Syndrome “central pontine myelinolysis” Demyelinating lesion in the brain that

occurs with overly rapid correction of hyponatremia

Characterized by acute paralysis, dysphagia, and dysarthria

Most common in those with chronic hyponatremia (usually caused by alcoholism)

Osmotic Demyelination Syndrome

Osmotic Demyelination Syndrome

Osmotic Demyelination Syndrome Prevention: Correction rate=0.5-

1.0meq/L/hr, with not more than 12meq/l correction in 24 hrs; should receive no more than 8-10mmol of sodium per day

Management: Supportive Prognosis is poor

INTRAVENOUS FLUID 0.9% NaCl (contains 154 meq/L) Correct at a rate in which Na

concentration be raised no more than 0.5 – 1 meq/L per hour

175 meq (sodium deficit) 175 meq/154 meq/L = 1.14 L

1140 mL x 15 gtt/min = 8 gtts/min 24 hrs x 60 min/hr