Hyponatremia-Hypernatremia

Dr Rim Braham

Total fluid volume and distribution

Total body fluid accounts for 60% of body mass.

Intracellular fluid ( ICF) : 40% Extracellular fluid (ECF): 20%

Interstitial fluid: 15% Plasma: 5%

Solute Composition of Body Water

•Predominant solutes in ECF: Sodium (Na+)Chloride (Cl−)Bicarbonate (HCO3−)

•Predominant solutes in ICF: Potassium (K+)Protein−Phosphate−

Osmolality

•Posm=2×plasma Na+ +

Glucose/18 + BUN/2.8

Osmolality

• Normal ECF osmolality: 280-290mOsm/kgH2O

• ECF and ICF are in osmotic equilibrium, at steady state

Mechanisms of regulation of body fluid and electrolyte balance

Sensation of thirstAntidiuretic hormone (ADH)Renin-angiotensin-aldosterone

systemAtrial natriuretic peptide (ANP)

ADH •ADH synthesized in the cell bodies of

hypothalamic neurons in the supraoptic nucleus

•ADH is stored in the posterior pituitary—forms the most readily released ADH pool

ADH

Main target sites: distal tubules and collecting ducts in kidney

Function: to Promote the water reabsorption and cause increased ECF volume and decreased urinary output.

Stimulating factors:• Blood pressure↓• Plasma osmolality↑• Blood volume ↓

Renin-angiotensin-aldosterone system

Arterial pressure ↓

Plasma sodium content↓

Sympathetic nerve ↑

Glomerulus (juxtaglomerular cells)

renin

Angiotensin I Angiotensin II

Angiotensin converting enzyme

aldosterone

Renal retention of sodium

Increase potassium secretion

ECF volume ↑

Arterial pressure↑

Adrenal gland

ANP

ANP is a hormone produced by specific cells of cardiac atrim in response to blood volume expansion.

Function: ANP inhibits the reabsorption of sodium and water by the renal tubules, which in turn increases urinary excretion and helps to return blood volume back toward normal.

ANP exerts a negative regulation against ADH in the central nervous system.

Hyponatremia 

•Serum Na <135 mEq/L

Hyponatremia 

•Serum Na <135 mEq/L

Dısorders of water and sodium balance

•Hyponatremia (too much water)

•Hypernatremia (too little water)

•Hypovolemia (too little sodium, the main

extracellular solute)

•Edema (too much sodium with associated

water retention)

Hyponatremia is a disorder of water balance

Hyponatremia •almost always due to the oral or intravenous

intake of water that cannot be completely excreted

• impaired water excretion that is most often due to:

• an inability to suppress the release of antidiuretic hormone (ADH)

• or to advanced renal failure

Diagnosis

• Volume status and serum osmolality are

essential to determine etiology

Differences between SIADH and

cerebral salt wasting

Sherlock M, O’Sullivan E, et all. The incidence and pathophysiology of hyponatraemia after

subarachnoid haemorrhage. Clinical Endocrinology; 2006, 64: 250–254

Symptoms of Hyponatremia

• symptoms depends on severity and acuity hyponatremia

• the symptoms reflect neurologic dysfunction induced by cerebral edema and possible adaptive responses of brain cels to osmotic swelling

• Nausea, malaise, headache, lethargy, seizures, coma, respiratory arrest

• the physical examination should help categorize the patient's volume status into hypovolemia, euvolemia, or hypervolemia.

Classification of symptoms of hyponatraemia

Clinical practice guideline on diagnosis and treatment of hyponatraemia; Nephrol Dial Transplant (2014) 0: 1–39

Complications of hyponatraemia

Management of hyponatremia

Patients who require emergency therapy are typically treated with hypertonic saline (usually as a 100 mL bolus given over 10 to 15 minutes).

Management of hyponatremia

In patients who require non-emergency treatment in the hospital setting:- In patients with asymptomatic acute or subacute hyponatremia, hypertonic saline (either as a 50 mL bolus or slow continuous infusion) unless the hyponatremia is already autocorrecting due to a spontaneous water diuresis.

Management of hyponatremia

In patients who require non-emergency treatment in the hospital setting:- In patients with chronic severe hyponatremia who have mild to moderate symptoms (eg, dizziness, forgetfulness, gait disturbance, nausea, vomiting, confusion, and lethargy), hypertonic saline (typically as a slow infusion at 15 to 30 mL/hour, but a 50 mL bolus can be used).

Management of hyponatremia

In patients who require non-emergency treatment in the hospital setting:- In patients with chronic moderate hyponatremia who have mild to moderate symptoms, no hypertonic saline.

In patients with edematous states (such as heart failure and cirrhosis), SIADH, advanced kidney disease, or primary polydipsia, fluid restriction. In general, fluid intake should be less than 800 mL/day.

-In patients with heart failure or in patients with SIADH who also have a high urinary cation concentration, loop diuretics may be necessary. Vasopressin receptor antagonists are another option in such patients.Patients with SIADH may also be treated with oral sodium chloride tablets.

-In patients with true volume depletion, isotonic saline. With true volume depletion, the administration of saline will usually correct the hypovolemia, thereby removing the stimulus to the release of antidiuretic hormone (ADH) and allowing the excess water to be excreted in the urine.

-In patients with diuretic-induced hyponatremia or drug-induced SIADH, discontinuation of the responsible medication may be all that is required.

Hypernatremia 

•Serum Na>145 mEq/L

Symptoms and Sings of Hypernatremia

• Dehydrated patient → orthostatic hypotension

and oliguria

• Rise in plasma Na and osmolality

→water movement out of the brain

→rupture of the cerebral veins

→focal intracerebral and subarachnoidal hemorrages

→possible irreversible neurologic damage

• Lethargy, weaknees, irritability, twitching, seuzures,

coma

• Osmotic demyelination (uncommon)

Laboratory Findings

•Urine osmolality > 400 mosm/kg → renal water-conserving ability is functioning (hypotonic fluid losses from excessive sweating, the respiratory tract, or bowel movements and lactulose)

•Urine osmolality < 250 mosm/kg → characteristic of DI

-Central DI: inadequate ADH release -Nephrogenic DI: renal insensitivity to ADH(lithium, demeclocycline, relief of urinary obstruction, interstitial nephritis,

hypercalcemia, and hypokalemia)

•Water deficit ≈ body weight X 0.6 X

(plasma Na concentration/

desired plasma Na concentration) - 1