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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 Osmolality
Useful 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 540Posm 275-290 259
Urine OsmolalitySerum
OsmolalityUrine
Osmolality Clinical Significance Normal or
increased Increased Fluid volume deficit
Decreased Decreased Fluid volume excess
Normal Decreased Increased 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