Sodium Physiology

1. Sodium Physiology . Sodium and its anions make up about 90% of the total extracelluar osmotically active solute. . Serum osmolality (mOsm/kg H2O) = 2x (Na+ ) + (glucose)/18 + (BUN)/2.8 . For practical purposes, twice the Na+ concentration equals serum osmolality because urea and glucose are responsible for less than 5% of the osmotic pressure.

3. C/P ? mainly CNS dt cellular overhydration . Na 125-135 ? asymptomatic . 120—125 ? anorexia,vomiting . Na < 120-115 ? Cerebral edema, lethargy, confusion, coma

4. TTt of Hyponatremia . Dec ECF voulme ? a) renal (uNa . 20 meq/L) b) extrarenal (uNa,10 meq/L) - replace isotonic deficit - replace Na deficit . Normal ECF voulme ? a) Thyroid or adreanl hypofunction? cortisol or thyroid hormone + water restriction b) SIADH ? uNa >20-40meq/L ?Demecycline + water res. . Inc. ECF volume ? a) heart failure, cirrhosis, nephrotic syndrome ? uNa<20meq/L ? restrict water + loop dieuritcs b) renal failure? uNa>20 meq/L ? restrict water Required Na deficit = total body water x Na defecit Replaced by normal saline

5. Hypernatremia 1) low total body Na content (dec ECV) loss of water > loss of Na renal(osmotic dieuritics) extrarenal (diarrhea, sweat) 2) normal total body Na (ECV normal then dec.) there is loss of water only renal (DI) extrarenal (burns, fever) 3) high total body Na (inc. ECV) inc. Na intake> inc. total body water bicarb. and hypertonic saline therapy Cushing and Conn’s syndrome

6. C/P ? CNS dt cellular dehydration:Na 150-158 ? restlessness and hyperreflexia Na > 158 ? seizures and coma rapid dec. in brain volume ? Ic hge, SAH

7. Ttt of Hypernatremia 1-ttt of the cause 2- with low total body Na (dec ECV) ?replace isotonic fluid deficit then water deficit 3- with normal total body Na content (normal ECV) ?replace water deficit 4- with high total body Na (high ECV) ? first give loop diuretics then replace water deficit water deficit replaced by D5W normal total body water x normal serum Na = measured total body water x serum Na

8. Potassium balance . Normal K balance in adults : k intake 80 mmol/day k loss = 80 mmol/day ? renal loss = 70mmol/d extrarenal (mainly GIT ) = 10mmol/d . Serum K 3.5 – 5.5 meq/L . K is important for : Carbohydrate and protein synthesis maintain RMP by ICK/ECK

9. * Regulation : . Exercise . PH . Insulin . sympathetic activity (catecholamines) . Plasma osmolality . hypothermia

10. Hyperkalemia . Causes : 1- intercompartemental shift acidosis, digitalis toxicity, tissue breakdown 2- dec. renal K loss renal failure, decd. Menaralocorticoid activity (Aisson dis.) 3- inc. Intake ? K penicillin , old blood 4- pseudo hyperkalemia C/P ? ECG dt delayed ventricular depolarization : K>/= 7meq/L ? tall peaked Twave, wide QRS complex K> 10meq/L ? VF skeletal muscle weakness up to paralysis

11. Ttt of hyperkalemia 1- ttt of the cause 2- Ca IV 3- Na HCO3 if the cause is acidosis 4- glucose-insulin infusion 5- furosmide 6- nonabsorbable cation exchange resins 7- dialysis

12. Hypokalemia Causes : 1.Intercomparetemental shift (insulin, alkalosis, B2 agonist) 2.inc K losses (renal ? u K > 20 meq/L, eg. Diuretics, ketoacidosis, RTA) (extrarenal ? u K <20 meq/L, eg. Diarrhea, excessive sweating, vomiting, laxative use) 3. dec. K intake C/P-> 1) dec. myocardial contractility 2) ECG dt delayed ventricular repolarization (inverted T wave,ST segment depression, apparent U wave) 3) skeletal muscle weakness and ileus 4) renal polyuria 5) dec insulin secretion 6) –ve Nitrogen balance , encephalopahty witrh liver dis.

13. TTT of Hypokalemia 1- ttt of the cause 2- K administration oral K chloride 60-80 mmol/d IV K ? peripheral ? rate 8 mmol/hr central ? rate 10 -20 mmol/hr types : K chloride - K bicarbonate