Fluids and Electrolytes, Acids and Bases

1. Fluids and Electrolytes, Acids and Bases Chapter 4

2. Distribution of Body Fluids • Total body water (TBW) • Intracellular fluid • Extracellular fluid • Interstitial fluid • Intravascular fluid • Lymph, synovial, intestinal, CSF, sweat, urine, pleural, peritoneal, pericardial, and intraocular fluids

3. Distribution of Body Fluids • Pediatrics • 75% to 80% of body weight • Susceptible to significant changes in body fluids • Dehydration • Aging • Decreased percent of total body water • Increase adipose and decrease muscle mass • Renal decline • Diminished thirst perception

4. Water Movement Between the ICF and ECF • Osmolality • Osmotic forces • Aquaporins • Starling hypothesis • Net filtration = forces favoring filtration minus forces opposing filtration

5. Net Filtration • Forces favoring filtration • Capillary hydrostatic pressure (blood pressure) • Interstitial oncotic pressure (water-pulling) • Forces favoring reabsorption • Plasma oncotic pressure (water-pulling) • Interstitial hydrostatic pressure

6. Edema • Accumulation of fluid within the interstitial spaces • Causes • Increase in capillary hydrostatic pressure • Decrease in plasma oncotic pressure • Increases in capillary permeability • Lymph obstruction

7. Edema

8. Water Balance • ADH secretion • Thirst perception • Osmolality receptors • Hyperosmolality and plasma volume depletion

9. Sodium and Chloride Balance • Sodium • Primary ECF cation • Regulates osmotic forces • Roles • Neuromuscular irritability, acid-base balance, and cellular chemical reactions and membrane transport • Chloride • Primary ECF anion • Provides electroneutrality

10. Sodium and Chloride Balance • Renin-angiotensin system • Aldosterone • Natriuretic peptides

11. Alterations in Na+, Cl–, and Water Balance • Isotonic alterations • Total body water change with proportional electrolyte and water change • Isotonic fluid loss • Isotonic fluid excess

12. Hypertonic Alterations • Hypernatremia • Serum sodium >147 mEq/L • Related to sodium gain or water loss • Water movement from the ICF to the ECF • Intracellular dehydration • Manifestations • Intracellular dehydration, convulsions, pulmonary edema, hypotension, tachycardia, etc.

13. Water Deficit • Dehydration • Pure water deficits • Renal free water clearance • Manifestations • Tachycardia, weak pulses, and postural hypotension • Elevated hematocrit and serum sodium level

14. Hyperchloremia • Occurs with hypernatremia or a bicarbonate deficit • Usually secondary to pathophysiologic processes • Managed by treating underlying disorders

15. Hypotonic Alterations • Decreased osmolality • Hyponatremia or free water excess • Hyponatremia decreases the ECF osmotic pressure, and water moves into the cell

16. Hypotonic Alterations • Water movement causes symptoms related to hypovolemia • Free water excess causes symptoms of hypervolemia and water intoxication

17. Hyponatremia • Serum sodium level <135 mEq/L • Sodium deficits cause plasma hypo-osmolality and cellular swelling • Pure sodium deficits • Low intake • Dilutional hyponatremia • Hypoosmolar hyponatremia • Hypertonic hyponatremia

18. Hyponatremia • Manifestations • Lethargy, confusion, decreased reflexes, seizures, and coma

19. Water Excess • Compulsive water drinking • Decreased urine formation • Syndrome of inappropriate ADH (SIADH) • ADH secretion in the absence of hypovolemia or hyperosmolality • Hyponatremia with hypervolemia

20. Water Excess • Manifestations: cerebral edema, muscle twitching, headache, and weight gain

21. Hypochloremia • Usually the result of hyponatremia or elevated bicarbonate concentration • Develops as a result of vomiting and the loss of HCl • Occurs in cystic fibrosis

22. Potassium • Major intracellular cation • Concentration maintained by Na+/K+pump • Regulates intracellular electrical neutrality in relation to Na+ and H+ • Essential for transmission and conduction of nerve impulses, normal cardiac rhythms, and skeletal and smooth muscle contraction

23. Potassium Levels • Changes in pH affect K+ balance • Hydrogen ions accumulate in the ICF during states of acidosis. K+ shifts out to maintain a balance of cations across the membrane. • Aldosterone, insulin, and catecholamines influence serum potassium levels

24. Hypokalemia • Potassium level <3.5 mEq/L • Potassium balance is described by changes in plasma potassium levels • Causes can be reduced intake of potassium, increased entry of potassium, and increased loss of potassium

25. Hypokalemia • Manifestations • Membrane hyperpolarization causes a decrease in neuromuscular excitability, skeletal muscle weakness, smooth muscle atony, and cardiac dysrhythmias

26. Hyperkalemia • Potassium level >5.5 mEq/L • Hyperkalemia is rare because of efficient renal excretion • Caused by increased intake, shift of K+ from ICF, decreased renal excretion, insulin deficiency, or cell trauma

27. Hyperkalemia • Mild attacks • Increased neuromuscular irritability • Tingling of lips and fingers, restlessness, intestinal cramping, and diarrhea • Severe attacks • The cell is not able to repolarize, resulting in muscle weakness, loss or muscle tone, and flaccid paralysis

28. Calcium • 99% of calcium is located in the bone as hydroxyapatite • Necessary for structure of bones and teeth, blood clotting, hormone secretion, and cell receptor function • Plasma concentration 9 to 10.5 mg/dL

29. Phosphate • Like calcium, most phosphate is also located in the bone • Necessary for high-energy bonds located in creatine phosphate and ATP and acts as an anion buffer

30. Calcium and Phosphate • Calcium and phosphate concentrations are rigidly controlled • Ca++ x HPO4– – = K+ (constant) • If the concentration of one increases, that of the other decreases • Plasma concentration 2.5 to 4.5 mg/dL

31. Hypocalcemia • Decreases the block of Na+ into the cell • Increased neuromuscular excitability (partial depolarization) • Muscle cramps

32. Hypercalcemia • Increases the block of Na+ into the cell • Decreased neuromuscular excitability • Muscle weakness • Cardiac arrest • Kidney stones • Constipation

33. Hypophosphatemia • Osteomalacia (soft bones) • Muscle weakness • Bleeding disorders (platelet impairment) • Anemia • Leukocyte alterations • Antacids bind phosphate

34. Hyperphosphatemia • See hypocalcemia • High phosphate levels are related to the low calcium levels

35. Magnesium • Intracellular cation • Plasma concentration is 1.8 to 2.4 mEq/L • Acts as a cofactor in intracellular enzymatic reactions • Increases neuromuscular excitability

36. Hypomagnesemia • Associated with hypocalcemia and hypokalemia • Neuromuscular irritability • Tetany • Convulsions • Hyperactive reflexes

37. Hypermagnesemia • Skeletal muscle depression • Muscle weakness • Hypotension • Respiratory depression • Lethargy, drowsiness • Bradycardia • Hypoactive reflexes

38. pH • Inverse logarithm of the H+ concentration • If the H+ are high in number, the pH is low (acidic). If the H+are low in number, the pH is high (alkaline).

39. pH • The pH scale ranges from 0 to 14: 0 is very acidic, 14 is very alkaline. Each number represents a factor of 10. If a solution moves from a pH of 6 to a pH of 5, the H+ have increased 10 times.

40. pH • Acids are formed as end products of protein, carbohydrate, and fat metabolism • To maintain the body’s normal pH (7.35-7.45) the H+ must be neutralized or excreted • The bones, lungs, and kidneys are the major organs involved in the regulation of acid and base balance

41. pH • Body acids exist in two forms • Volatile • H2CO3 (can be eliminated as CO2 gas) • Nonvolatile • Sulfuric, phosphoric, and other organic acids • Eliminated by the renal tubules with the regulation of HCO3–

42. Buffering Systems • A buffer is a chemical that can bind excessive H+ or OH– without a significant change in pH • A buffering pair consists of a weak acid and its conjugate base • The most important plasma buffering systems are the carbonic acid–bicarbonate system and hemoglobin

43. Carbonic Acid–Bicarbonate Pair • Operates in the lung and the kidney • The greater the partial pressure of carbon dioxide, the more carbonic acid is formed • At a pH of 7.4, the ratio of bicarbonate to carbonic acid is 20:1 • Bicarbonate and carbonic acid can increase or decrease, but the ratio must be maintained

44. Carbonic Acid–Bicarbonate Pair • If the amount of bicarbonate decreases, the pH decreases, causing a state of acidosis • The pH can be returned to normal if the amount of carbonic acid also decreases • This type of pH adjustment is referred to as compensation

45. Carbonic Acid–Bicarbonate Pair • The respiratory system compensates by increasing or decreasing ventilation • The renal system compensates by producing acidic or alkaline urine

46. Other Buffering Systems • Protein buffering • Proteins have negative charges, so they can serve as buffers for H+ • Renal buffering • Secretion of H+ in the urine and reabsorption of HCO3– • Cellular ion exchange • Exchange of K+ for H+ in acidosis and alkalosis

47. Acid-Base Imbalances • Normal arterial blood pH • 7.35 to 7.45 • Obtained by arterial blood gas (ABG) sampling • Acidosis • Systemic increase in H+ concentration • Alkalosis • Systemic decrease in H+ concentration

48. Acidosis and Alkalosis • Four categories of acid-base imbalances • Respiratory acidosis—elevation of pCO2 as a result of ventilation depression • Respiratory alkalosis—depression of pCO2 as a result of alveolar hyperventilation

49. Acidosis and Alkalosis • Four categories of acid-base imbalances • Metabolic acidosis—depression of HCO3– or an increase in noncarbonic acids • Metabolic alkalosis—elevation of HCO3– usually caused by an excessive loss of metabolic acids

50. Metabolic Acidosis