Fluid , Electrolyte Balance

1. Zehra Eren,M.D. Fluid, ElectrolyteBalance

2. LEARNING OBJECTIVES • explain generalprinciples of disorders of water balance • explaingeneral principles of disorders ofsodiumbalance • explain general principles of disorders of potassium balance • recognize hyponatremia, hypernatremia • recognize hyperkalemia, hypokalemia

3. Assesment of thepatient • carefulhistory • physical examination and assessment of total body water and its distribution • serum electrolyteconcentrations • urineelectrolyteconcentrations • serum osmolality

4. Definitions • Total body water • Extracellularfluidvolume • Intracellularfluidvolume • Effectivearterialbloodvolume: part of theintravascularvolumethat is in thearterialsystemandeffectivelyperfusingtissues (700ml/70kg, men)

6. Definitions • Total body water • Extracellularfluidvolume • Intracellularfluidvolume • Effectivearterialbloodvolume: part of theintravascularvolumethat is in thearterialsystemandeffectivelyperfusingtissues (700ml/70kg, men)

7. Solute Composition of Body Water • Predominant solutes in ECF: Sodium (Na+) Chloride (Cl−) Bicarbonate (HCO3−) • Predominant solutes in ICF: Potassium (K+) Protein− Phosphate−

8. Plasma osmolality • Posm= 2 x [Na] + [glucose]/18 + bloodureanitrogen/2.8 • Normal ECF osmolality: 275-290mOsm/kgH2O

9. Plasmatonicity • also called the effective plasma osmolality • reflects the concentration of solutes that do not easily cross cell membranes (mostly sodium salts) and therefore affect the distribution of water between the cells and the ECF • Plasma tonicity= 2 x[Na] + [glucose]/18 (if glucose is measured in mg/dL) • 270-285 mosm/kg • ECF and ICF are in osmotic equilibrium, at steady state

11. Dehydration • reduction in TBW below the normal level without a proportional reduction in sodium and potassium, resulting in a rise in the plasma sodiumconcentration • primary loss of free water (as with unreplaced insensible losses or water loss in diabetes insipidus) • the major biochemical manifestation is hypernatremia

12. Regulatıon of water and sodium balance • The kidney regulates water and sodium balance independently since water can be taken in without salt and salt can be taken in without water • Regulation of plasma tonicity and of the effective arterial blood volume involve different hormones • areas of overlap, such as the hypovolemic stimulus to the release of antidiuretic hormone (ADH)

16. Dısorders of water and sodium balance • Hyponatremia(toomuchwater) • Hypernatremia(toolittlewater) • Hypovolemia(toolittlesodium, the main extracellularsolute) • Edema(toomuchsodiumwithassociatedwaterretention)

17. Hyponatremia  • Serum Na <135 mEq/L

18. 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

19. Hyponatremia  • major causes of persistent ADH secretion: -syndromeof inappropriate ADH secretion (SIADH) -reduced effective arterial blood volume

25. Manifestations of 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

26. Hypernatremia  • Serum Na>145 mEq/L

28. Causes of Hypernatremia • Hypovolemic hypernatremia 1.Extrarenal losses (urine Na <20 mEq/L): -insensible and perspiratory -gastrointestinal 2.Renal losses(urine Na >20 mEq/L) -osmotic diuresis • Ovolemic hypernatremia Diabetes insipidus (dilute urine, urine Na variable)

30. Causes of Hypernatremia • Hypervolemic hypernatremia -Hypertonic infusion (eg, NaHCO3) -Tube feeding

31. Manifestation of Hypernatremia • Rise in plasmaNaandosmolality →watermovementout of thebrain →rupture of thecerebralveins →focalintracerebralandsubarachnoidalhemorrages→possibleireversibleneurologicdamage • Lethargy, weaknees, irritability, twitching, seuzures, coma, • Osmoticdemyelination

32. DISORDERS OF POTASSIUM (K) • Total body K determined by internal and externalK balance • Internal balance

34. DISORDERS OF POTASSIUM (K) • Total body K determined by internal and externalK balance • Internal balance • External balance -K freelyfiltered -Filtered K reabsorbed in proximal tubule -K secretion mediated by Na reabsorption -K secretion regulated by aldosterone secretion

35. Hypokalemia  • Serum K+ less than 3.5 mEq/L (mmol/L)

37. Clinical manifestations  • Cardiovascular: -Arrhythmias -Digitalis toxicity • Neuromuscular: 1.Smooth muscle: -Ileus 2.Skeletal muscle: -Weakness -Paralysis -Rhabdomyolysis

38. Clinical manifestations • Endocrine: -Glucose intolerance • Renal/electrolyte: -Vasopressin resistance -Increased ammonia production -Metabolic alkalosis Structural changes: Renal cysts Interstitial changes PT dilation, vacuolization

39. Hyperkalemia  • Serum K ≥5.0 mEq/L (mmol/L)

42. Psodohyperkalemia • Thrombocytosis • Leukocytosis • Ischemic blood draw

44. Causes of Hyperkalemia • GFR <20 mL/min -Endogenous or exogenous K -Drugs that impair K excretion

46. Clinical manifestations  • Cardiovascular -T-wave abnormalities -Bradyarrhythmias • Neuromuscular -Ileus -Paresthesias -Weakness -Paralysis

47. Clinical manifestations  • Renal/electrolyte -Decreased ammonia production -Metabolic acidosis

49. SUGGESTED READING • Goldman's Cecile Medicine, GoldmanL, SchaferAI • Case files Internal Medicine, Toy Patlan • CurrentMedicalDiagnosisandTreatment,Maxine A. Papadakis, Stephen J. McPhee, Eds. Michael W. Rabow, Associate Ed. • CurrentDiagnosis & Treatment: Nephrology & HypertensionEdgar V. Lerma, Jeffrey S. Berns, Allen R. Nissenson