SODIUM HOMEOSTASIS

Mohammed Almeziny BsPharm R,Ph. Msc PhD

Clinical Pharmacist

Introduction

Sodium is the principle cation of extracellular fluid

The regulation of osmolarity (80%). The acid-base balance. The membrane potential of cells.

Introduction Cont’d

The total is 4200 mmol (60mmol/kg). 40% bone 50% extracellular 10

intracellular.

Daily requirement

1-3 mmol/kg/day

1 liter of 0.9% provides 154 mmol N+

HYPONATREMIA

Definition

Serum sodium concentration less than 132 mmol/l

The sodium con.. Is a reflection of water balance rather than total body sodium.

Type of hyponatremia

Hypovolemic hyponatremia Euvolemic hyponatremia Hypervolemic hyponatremia Redistributive hyponatremia Pseudohyponatremia

Hypovolemic hyponatremia

A decrease in total body water (TBW) and a greater decrease in total body sodium (Na+) occur. The extracellular fluid (ECF) volume is decreased.

Euvolemic hyponatremia

An increase in TBW with normal total sodium occurs. The ECF volume is increased minimally to moderately, but edema is not present.

Hypervolemic hyponatremia

An increase in total body sodium and a greater increase in TBW occur. The ECF is increased markedly, and edema is present.

Redistributive hyponatremia

A shift of water from the intracellular to the extracellular compartment occurs with a resultant dilution of sodium. The TBW and total body sodium are unchanged. This condition occurs with hyperglycemia.

Pseudohyponatremia

A dilution of the aqueous phase by excessive proteins or lipids occurs. The TBW and total body sodium are unchanged. This condition is seen with hypertriglyceridemia and multiple myeloma.

Diagnostic approach to hyponatremia

Normal (280mOsm)

Elevated(>280mOsm)

Low (<280 mOsm)

Measure serum Osmolality

Isotonic hyponatremia

Hypertonichyponatremia

Clinically assesECF volume

Next slideHyperlipidemiaHyperproteinemiaIsotonic infision

HyperglycemiaHypertonic infusion

Low ( BP, HR)

poor skin turgor

Elevated (edema)

Normal

Hypovolemic Hypotonic

hyponatremia

hypervolemicHypotonic

hyponatremia

IsovolemicHypotonic

hyponatremia

Total body Na deficitGI, skin,lung kidney

Adrenal insufficiency

Total body Na excessCHF, Liver damage

Nephrosis

Total body Na normalH2O intoxication

SIADH, Renal FailureK loss

Reset Osmstat

Diagnostic approach to hyponatremia cont’d

Interpreting Lab. Data

Urinary Sodium help to distinguish between renal and nonrenal losses.

urine sodium < 20 mEq/L. e.g cirrhosis, nephrosis, congestive heart failure SIADH will have urine sodium levels in excess of

20 mEq/L.

Causes

Drugs. thiazide diuretics, amiodarone, chlorpropamide, cyclophosphamide, clofibrate, carbamazepine, oxcarbazepine, opiates, oxytocin, desmopressin, vincristine, selective serotonin reuptake inhibitors, trazodone or tolbutamide

Causes cont’d

Adrenal Insufficiency and Adrenal Crisis

Congestive Heart Failure and Pulmonary Edema Gastroenteritis Hypothyroidism and Myxedema Coma Renal Failure, Acute Renal Failure, Chronic and Dialysis Complications Syndrome of Inappropriate Antidiuretic Hormone Secretion(SIADH).

Clinical presentation

Depend on the degree and the chronicity of hyponatremia.

120 mEq/L 110 mEq/L Most abnormalities on physical exam

are neurological in origin.

Clinical presentation cont’d

Anorexia Nausea and vomiting Difficulty concentrating Confusion Lethargy Agitation Headache Seizures

Calculate adult Na deficit in hyponatremia

Na mEq.=

(140 mEq/L - patient's serum Na) x (0.5X body weight).

An increase in serum sodium of 4-6 mEq/L is generally sufficient

0.5 mEq/L/hr or 12 mEq/L/day or 18 mEq/L/2 day’s.

Hypernatremia

Definition

Serum sodium concentration More than 145 mmol/l

The sodium con.. Is a reflection of water balance rather than total body sodium.

Etiology and Pathophysiology

Hypernatremia in adults has a mortality of 40 to 60%.

The elderly are particularly susceptible, especially in warm weather, due to a reduced thirst response and underlying diseases.

Principal Causes of Hypernatremia

Extrarenal losses GI: Vomiting,

diarrhea Skin: Burns,

excessive sweating Renal losses

Intrinsic renal disease

Loop diuretics Osmotic diuresis

(glucose, urea, mannitol)

Hypernatremia with hypovolemia (decreased TBW and Na; relatively greater decrease in TBW)

Principal Causes of Hypernatremia cont’d

Extrarenal losses Respiratory:

Tachypnea Skin: Fever,

excessive sweating Renal losses Central diabetes

insipidus

Nephrogenic diabetes insipidus

Other Inability to access

water Primary hypodipsia Reset osmostat

Hypernatremia with euvolemia (decreased TBW; near-normal total body Na)

Principal Causes of Hypernatremia cont’d

Hypertonic fluid administration (hypertonic saline, NaHCO3, total parenteral nutrition)

Mineralocorticoid excess Adrenal tumors secreting deoxycorticosterone Congenital adrenal hyperplasia (caused by 11-

hydroxylase defect)

Hypernatremia with hypervolemia rare

Symptoms and Signs

The major signs of hypernatremia result from CNS dysfunction due to brain cell shrinkage. Confusion, neuromuscular excitability, seizures, or coma may result; cerebrovascular damage with subcortical or subarachnoid hemorrhage and venous thromboses are frequent in patients dying from severe hypernatremia.

Treatment

Free water deficit =

TBW × [(plasma Na/140) − 1]

TBW = body wt x 0.6 = liters if hypernatremia is chronic or of unknown duration,

it should be corrected over 48 h, and the plasma osmolality should be lowered at a rate of no more than 2 mOsm/L/h to avoid cerebral edema caused by excess brain solute.

Loop diuretics

Treatment cont’d

In patients with hypernatremia and depletion of total body Na content (ie, who have volume depletion), the free water deficit is greater than that estimated by the formula.

In patients with hypernatremia and ECF volume overload (excess total body Na content), the free water deficit can be replaced with 5% D/W, which can be supplemented with a loop diuretic.

Treatment cont’d

In patients with hypernatremia and euvolemia, free water can be replaced using either 5% D/W or 0.45% saline.