H Y P O N A T R E M I A WORKSHOP CASE FOR FLUID AND ELECTROLYTE DISORDERS Saldana, E. * Sales, S. * Salonga, C. * San Diego, P. San Pedro, R. * Sanez, E. * Sanidad, E. * Santos, E. Santos, J. * Santos, J. * Santos, K. * Santos, E.
51 year old, female CHIEF COMPLAINT: Vomiting
H I S T O R Y Persistence of vomiting CONSULTATION
PAST MEDICAL HISTORY • Hypertensive for 10 years • Medications: • Telmisartan, 40mg • Hydrochlorthiazide 12.5 daily • Amlodipine was discontinued due to bipedal edema
PERSONAL HISTORY • No smoking • No alcohol intake REVIEW OF SYSTEMS • Unremarkable
P H Y S I C A L E X A M
L A B O R A T O R Y
SALIENT FEATURES • 51 year old, female (vomiting) • Fever, dysuria, urgency • Intake of paracetamol and antibiotic • Headache, body malaise, nausea • Vomiting: 50cc/episode • Known hypertensive • Telmisartan (40 mg) • Hydrochlorthiazide (12.5 daily) • Weak looking, wheelchair-borne • BP: 120/80 (supine), 90/60 (sitting), 130/80 (usual) • HR: 90 bpm (supine), 105 bpm (sitting) • Lost weight (53 kg 50 kg) • Poor skin turgor • Dry mouth, tongue and axillae • Normal JVP
I M P R E S S I O N HYPOVOLEMIC HYPONATREMIA SECONDARY TO THIAZIDE DIURETIC INTAKE
20% of total body weight 40% of total body weight Source: Guyton and Hall. Textbook of Medical Physiology
PATIENT’S PROFILE SIGNS OF ECF VOLUME CONTRACTION
a state of combined salt and water loss exceeding intake Hypovolemia ECF VOLUME CONTRACTION
IMPORTANCE OF SODIUM • Essential for regulation of body • fluids and blood. • Transmits nerve impulses and • controls heart activity. • Assists in metabolic functions. • Helps maintain BP levels.
HYPONATREMIA • Plasma Na+ concentration < 135 mEq/L, and is considered severe when the level is below 125 mEq/L. • Most causes of hyponatremia are associated with a low plasma osmolality.
CLINICAL FEATURES OF HYPONATREMIA The clinical manifestations of hyponatremia are related to osmotic water shift leading to increased ICF volume, specifically cerebral edema.
CLINICAL FEATURES OF HYPONATREMIA SERUM SODIUM LEVELS: • 125 mEq/L • 120 mEq/L • 115 mEq/L Nausea and malaise Headache, lethargy, obtundation Seizure and coma Patient profle: Serum Na+: 123 mEq/L Headache, body malaise, nausea, weak looking, wheelchair-borne
FACTORS WHICH CONTRIBUTED TO THE PATIENT’S HYPONATREMIA HYDROCHLOROTHIAZIDE TELMISARTAN • Inhibits reabsorption of sodium and chloride in the distal convoluted tubule, thus promoting water loss. • Leads to Na+ and K+ depletion and AVP-mediated water retention. • Angiotensin II receptor blocker
3. Compute for the plasma osmolality and effective plasma osmolality. What is the importance of computing for such?
Plasma osmolality (mOsm/kg) = 2 [ plasma Na ] + [ Glucose ] + [ BUN ] 18 2.8 http://www.merck.com/mmpe/print/sec12/ch156/ch156b.html
Plasma Osmolality Plasma osmolality (mOsm/kg) = 2 [ 123 mEq/L] + [ 98 mg/dL ] + [ 22 mg/dL ] 18 2.8 Plasma osmolality = 259.3 mOsm/kg
Effective Plasma Osmolality Effective Plasma osmolality = PlasmaOsmolality - BUN_ 2.8 = 259.3 mOsm/kg – 22 mg/dL 2.8 = 251.44 mOsm/kg http://cmbi.bjmu.edu.cn/uptodate/critical%20care/Fluid%20and%20electrolyte%20disorders/.htm
Significance of Plasma Osmolality • The osmolality of plasma is closely regulated by anti-diuretic hormone (ADH). • In response to even small increases in plasma osmolality, ADH release from the pituitary is increased causing water resorption in the distal tubules and collecting ducts of the kidney and correction of the increased osmolality. • The opposite happens in response to a low plasma osmolality with decreased ADH secretion and water loss through the kidneys.
Significance of Plasma Osmolality • Plasma osmolality is used in two main circumstances: • Investigation of hyponatremia • Identification of an osmolar gap
Significance of Plasma Osmolality • Serum osmolality is a useful preliminary investigation for identifying the cause of hyponatremia.
Significance of Effective Plasma Osmolality • Solutes that are restricted to the ECF or the ICF determine the effective osmolality (or tonicity) of that compartment. • In a patient with hyponatremia, normal or elevated effective serum osmolality suggests the presence of either pseudohyponatremia or increased concentrations of other osmoles, such as glucose and mannitol.
Significance of Urine Osmolality • Urine osmolality may vary between 50 and 1200 mmol/kg in a healthy individual depending on the state of hydration. • The urine osmolality is the best measure of urine concentration with high values indicating maximally concentrated urine and low values very dilute urine. • The main factor determining urine concentration is the amount of water which is resorbed in the distal tubules and collecting ducts in response to ADH.
Significance of Urine Osmolality • The test is useful in the following areas: • For determining the differential diagnosis of hyper- or hyponatraemia. • For identifying SIADH • For differentiating pre-renal from renal kidney failure (high urine osmolality is consistent with pre-renal impairment, in renal damage the urine osmolality is similar to plasma osmolality). • For identifying and diagnosing diabetes insipidus (low urine osmolality not responding to water restriction).
Significance of Urine Sodium • In patients with hyponatremia and inappropriately concentrated urine, it is particularly important to assess the effective arterial blood volume.
Sodium Deficit Sodium deficit = (desired serum Na – actual Na) x TBW = (140 mEq/L – 123 mEq/L) x (0.5 x ) = 450.5 mEq/L total needed
6. What are the basic principles in the treatment of hyponatremia?
Hyponatremia • Goals of therapy • To raise the plasma Na+ concentration by restricting water intake and promoting water loss • To correct the underlying disorder
Treatment • Mild asymptomatic hyponatremia • Generally of little clinical significance and requires no treatment • Asymptomatic hyponatremia associated with ECF volume contraction • Na+ repletion isotonic saline • Restoration of euvolemia removes the hemodynamic stimulus for AVP release
Treatment • Hyponatremia associated with edematous states • Have increased total body water that exceeds the increase in total body Na+ content • Restriction of Na+ and water intake, correction of hypokalemia, and promotion of water loss in excess of Na+
Treatment • Acute or severe hyponatremia (plasma Na+ concentration <110–115 mmol/L) • Tends to present with altered mental status and/or seizures • Requires more rapid correction • Treated with hypertonic saline
Rate of Correction • depends on the absence or presence of neurologic dysfunction
Osmotic demyelination syndrome (ODS) • Follows too-rapid correction of hyponatremia • Neurologic disorder characterized by flaccid paralysis, dysarthria, and dysphagia • Diagnosis is usually suspected clinically and can be confirmed by appropriate neuroimaging studies • No specific treatment for the disorder • Associated with significant morbidity and mortality
Osmotic demyelination syndrome (ODS) • Chronic hyponatremia • Most susceptible to ODS, since their brain cell volume has returned to near normal as a result of the osmotic adaptive mechanisms • Administration of hypertonic saline to these individuals can cause sudden osmotic shrinkage of brain cells
Osmotic demyelination syndrome (ODS) • Risk factors • Prior cerebral anoxic injury • Hypokalemia • Malnutrition, especially secondary to alcoholism