1. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 39 Disorders of Fluid and Electrolyte Balance

2. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Fluids, Ions, Nonelectrolytes, and Electrolytes Body Fluids Ions Nonelectrolytes Electrolytes

3. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Functions of Body Fluids Transport gases, nutrients, and wastes Help generate the electrical activity needed to power body functions Take part in the transformation of food into energy Maintain the overall function of the body

4. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Distribution of Body Fluids Intracellular Compartment (ICF) –Consists of fluid contained within all of the billions of cells in the body –Larger of the two compartments, with approximately two thirds of the body water in healthy adults –High concentration of K + Extracellular Compartment (ECF) –Contains the remaining one third of body water –Contains all the fluids outside the cells, including that in the interstitial or tissue spaces and blood vessels –High concentration of Na +

5. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Composition of the ECF, Plasma and Interstitial Fluids Large amounts of sodium and chloride Moderate amounts of bicarbonate Small quantities of potassium, magnesium, calcium, and phosphate

6. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Composition of the ICF Almost no calcium Small amounts of sodium, chloride, bicarbonate, and phosphate Moderate amounts of magnesium Large amounts of potassium

7. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which ion is in the highest concentration in the ICF? –A. Na + –B. K + –C. Cl − –D. Ca 2+

8. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. K + Rationale: K + is the most abundant ion of the ICF and is responsible for the regulation of the resting membrane potential.

9. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Diffusion and Osmosis Concentration Gradient –Difference in concentration over a distance Diffusion –The movement of charged or uncharged particles along a concentration gradient from an area of higher concentration to one of lower concentration Osmosis –The movement of water across a semipermeable membrane from the side of the membrane with the lesser number of particles and greater concentration of water to the side with the greater number of particles and lesser concentration of water

10. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Tonicity The tension or effect that the effective osmotic pressure of a solution with impermeable solutes exerts on cell size because of water movement across the cell membrane Solutions can be classified according to whether or not they cause cells to shrink: –Isotonic: neither shrink nor swell –Hypotonic: swell –Hypertonic: shrink

11. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms Protecting Extracellular Fluid Volume Alterations in Hemodynamic Variables –Vasoconstriction and an increase in heart rate Alterations in Sodium and Water Balance –Isotonic contraction or expansion of ECF volume –Hypotonic dilution or hypertonic concentration of extracellular sodium brought about by changes in extracellular water

12. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Edema Accumulation of fluid in extracellular space –Pitting edema –Nonpitting edema –Brawny edema

13. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Edema Formation The physiologic mechanisms that contribute to edema include factors that: –Increase the capillary filtration pressure –Decrease the capillary colloidal osmotic pressure –Increase capillary permeability –Produce obstruction to lymph flow Localized edema General edema Dependent edema

14. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Methods for Assessing Edema Daily weight Visual assessment Measurement of the affected part Application of finger pressure to assess for pitting edema

15. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Physiologic Mechanisms Assisting in Regulating body Water Thirst –Primarily a regulator of water intake ADH –A regulator of water output Both mechanisms respond to changes in extracellular osmolality and volume

16. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Water and Na + Balance Baroreceptors regulate effective volume. Modulating sympathetic nervous system outflow and ADH secretion ANP RAAS –Angiotensin II –Aldosterone Gain –Water –Oral intake and metabolism of nutrients –Na + Loss –Kidneys –Skin –Lungs –Gastrointestinal tract

17. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Regulators of Sodium The kidney is the main regulator of sodium. –Monitors arterial pressure; retains sodium when arterial pressure is decreased; and eliminates it when arterial pressure is increased –The rate is coordinated by the sympathetic nervous system and the renin–angiotensin–aldosterone system (RAAS). –Atrial natriuretic peptide (ANP) may also regulate sodium excretion by the kidney.

18. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Assessment of Body Fluid Loss History of conditions that predispose to sodium and water losses, weight loss, and observations of altered physiologic function indicative of decreased fluid volume –Heart rate –Blood pressure –Venous volume/filling –Capillary refill rate

19. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Psychogenic Polydipsia Compulsive water drinking Psychiatric disorders Schizophrenia Drinking large amounts of water and excrete large amounts of urine Cigarette smoking –ADH –Interfere with water excretion by the kidneys Antipsychotic medications increase ADH levels.

20. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins ADH and Aquaporin-2 Channels ADH –V 1 receptors Vasoconstriction –V 2 receptors Control water reabsorption Aquaporins

21. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Disorders of ADH expression Diabetes insipidus –Deficiency of or a decreased response to ADH –Patients unable to concentrate urine during periods of water restriction and excrete large volumes of urine –Neurogenic diabetes insipidus –Central diabetes insipidus SIADH –Failure of the negative feedback system that regulates the release and inhibition of ADH

22. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Diabetes Insipidus Central or Neurogenic Diabetes Insipidus –Occurs because of a defect in the synthesis or release of ADH Nephrogenic Diabetes Insipidus –Occurs because the kidneys do not respond to ADH

23. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Causes of Fluid Volume Excess Inadequate sodium and water elimination Excessive sodium intake in relation to output Excessive fluid intake in relation to output

24. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Isotonic Fluid Volume Excess Isotonic expansion of the ECF compartment with increases in both interstitial and vascular volumes An increase in total body sodium that is accompanied by a proportionate increase in body water Causes of decreased sodium and water elimination –Renal function –Heart failure –Liver failure –Corticosteroid excess

25. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Potassium Distribution and Regulation Intracellular concentration of 140 to 150 mEq/L The extracellular concentration 3.5 to 5.0 mEq/L Body stores of potassium are related to body size and muscle mass. Is normally derived from dietary sources Plasma potassium is regulated through two mechanisms: –Renal mechanisms that conserve or eliminate potassium –A transcellular shift between the ICF and ICF compartments

26. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Abnormal Potassium Hypokalemia refers to a decrease in plasma potassium levels below 3.5 mEq/L 1.Inadequate intake 2.Excessive gastrointestinal, renal, and skin losses 3.Redistribution between the ICF and ECF compartments Hyperkalemia refers to an increase in plasma levels of potassium in excess of 5.0 mEq/L 1.Decreased renal elimination 2.Excessively rapid administration 3.Movement of potassium from the ICF to ECF compartment

27. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Diagnosis and Treatment of Potassium Disorders Diagnosis is based on complete history, physical examination to detect muscle weakness and signs of volume depletion, plasma potassium levels, and ECG findings. Treatment –Calcium antagonizes the potassium-induced decrease in membrane excitability. –Sodium bicarbonate will cause K + to move ICF. –Insulin will decrease ECF K + concentration. –Curtailing intake or absorption, increasing renal excretion, and increasing cellular uptake

28. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Disorders of which ion will have the greatest effect on the membrane potential? –A. Bicarbonate –B. K + –C. Cl − –D. Mg 2+

29. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. K + Rationale: Slight deviations in concentration of K + will directly change the membrane potential.

30. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Vitamin D, Calcitonin, and Parathyroid Hormone Calcium, phosphate, and magnesium are the major divalent cations in the body. Vitamin D acts to sustain normal plasma levels of calcium and phosphate by increasing their absorption from the intestine. Calcitonin acts on the kidney and bone to remove calcium from the extracellular circulation.

31. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms Regulating Calcium, Phosphate and Magnesium Balance Calcium, phosphate, and magnesium are the major divalent cations in the body. They are –Ingested in the diet –Absorbed from the intestine –Filtered in the glomerulus of the kidney –Reabsorbed in the renal tubules –Eliminated in the urine

32. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Physiological Calcium ECF calcium exists in three forms: –(1) Protein bound 40% of ECF calcium is bound to albumin. –(2) Complexed 10% is chelated with citrate, phosphate, and sulfate. –(3) Ionized 50% of ECF calcium is present in the ionized form.

33. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Calcium Gain and Loss Gains –Dietary dairy foods –PTH and vitamin D stimulate calcium reabsorption in this segment of the nephron. Losses –When dietary intake (and calcium absorption) is less than intestinal secretion

34. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Causes and Symptoms of Hypocalcemia Causes –Impaired ability to mobilize calcium from bone stores –Abnormal losses of calcium from the kidney –Increased protein binding or chelation such that greater proportions of calcium are in the nonionized form –Soft tissue sequestration Symptoms –Increased neuromuscular excitability –Cardiovascular effect –Nerve cells less sensitive to stimuli

35. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Causes and Symptoms of Hypercalcemia Increased intestinal absorption –Excessive vitamin D and calcium –Milk-alkali syndrome Increased bone resorption – Parathyroid hormone –Malignant neoplasms –Prolonged immobilization Decreased elimination –Thiazide, lithium therapy Symptoms –Changes in neural excitability –Alterations in smooth and cardiac muscle function –Exposure of the kidneys to high concentrations of calcium

36. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Alterations in ________________ may result in hypercalcemia. –A. ADH –B. Na + –C. vitamin D –D. K +

37. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer C. vitamin D Rationale: Vitamin D when increased will result in higher retention of calcium.

38. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Role of Phosphate in the Body Plays a major role in bone formation Essential to certain metabolic processes: –The formation of ATP and the enzymes needed for metabolism of glucose, fat, and protein A necessary component of several vital parts of the cell Incorporated into the nucleic acids of DNA and RNA and the phospholipids of the cell membrane

39. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Role of Phosphate in the Body (cont.) Serves as an acid–base buffer in the extracellular fluid and in the renal excretion of hydrogen ions Necessary for delivery of oxygen by the red blood cells Needed for normal function of other blood cells –White blood cells and platelets

40. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Common Causes of Hypophosphatemia and Hyperphosphatemia Hypophosphatemia –Depletion of phosphate because of insufficient intestinal absorption –Transcompartmental shifts –Increased renal losses Hyperphosphatemia –From failure of the kidneys to excrete excess phosphate –Rapid redistribution of intracellular phosphate to the ECF compartment –Excessive intake of phosphate

41. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Magnesium Balance Essential to all reactions that require ATP Regulation at the kidney level –Magnesium absorption in the thick ascending loop of Henle is the positive voltage gradient created in the tubular lumen by the Na + -K + -2Cl − cotransporter system Ingested in the diet Absorbed from the intestine Excreted by the kidneys

42. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Manifestations of Hypomagnesemia Laboratory Values –Serum magnesium level less than l.8 mg/dL Neuromuscular Manifestations –Personality change, athetoid or choreiform movements, nystagmus, tetany, positive Babinski, Chvostek, Trousseau signs Cardiovascular Manifestations –Tachycardia, hypertension, cardiac dysrhythmias

43. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Causes of Hypermagnesemia Excessive Intake –Intravenous administration of magnesium for treatment of preeclampsia –Excessive use of oral magnesium-containing medications Decreased Excretion –Kidney disease –Acute renal failure