Chapter 41: Fluid, Electrolyte, and Acid-Base Balance

1. Chapter 41: Fluid, Electrolyte, and Acid-Base Balance Bonnie M. Wivell, MS, RN, CNS

2. Distribution of Body Fluids • Intracellular = inside the cell; 42% of body weight • Extracellular = outside the cell, 17% of body weight • Interstitial = contains lymph; fluid between cells and outside blood vessels • Intravascular = blood plasma found inside blood vessels • Transcellular = fluid that is separated by cellular barrier,

3. Body Fluid Compartments

4. Functions of Body Fluid • Major component of blood plasma • Solvent for nutrients and waste products • Necessary for hydrolysis of nutrients • Essential for metabolism • Lubricant in joints and GI tract • Cools the body through perspiration • Provides some mineral elements

5. Composition of Body Fluids • Body fluids contain Electrolytes • Anions – negative charge • Cl, HCO3, SO4 • Cations – positive charge • Na, K, Ca • Electrolytes are measured in mEq • Minerals are ingested as compounds and are constituents of all body tissues and fluids • Minerals act as catalysts

6. Electrolytes in Body Fluids • Normal Values • Sodium (Na+) 35 – 145 mEq/L • Potassium (K+) 3.5 – 5.0 mEq/L • Ionized Calcium (Ca++) 4.5 – 5.5 mg/dL • Calcium (Ca++) 8.5 – 10.5 mg/dL • Bicarbonate (HCO3) 24 – 30 mEq/L • Chloride (Cl--) 95 – 105 mEq/L • Magnesium (Mg++) 1.5 – 2.5 mEq/L • Phosphate (PO4---) 2.8 – 4.5 mg/dL

7. Movement of Body Fluids • Osmosis = movement across a semi-permeable membrane from area of lesser concentration to are of higher concentration; high solute concentration has a high osmotic pressure and draws water toward itself • Osmotic pressure = drawing power of water (Osmolality) • Osmolarity = concentration of solution

8. Movement of Body Fluids • Colloid or Oncotic pressure = keeps fluid in the intravascular compartment by pulling water from the interstitial space back into the capillaries

10. Solutions • Isotonic Solution • The same concentration as blood plasma; expand fluid volume without causing fluid shift • Hypotonic Solution • Lower concentration than blood plasma; moves fluid into the cells causing them to enlarge • Hypertonic solution • Higher concentration than blood plasma; pulls fluid from cells causing them to shrink

11. Movement of Body Fluids Cont’d. • Diffusion = Molecules move from higher concentration to lower • Concentration gradient • Filtration = water and diffusible substances move together across a membrane; moving from higher pressure to lower pressure • Edema results from accumulation of excess fluid in the interstitial space • Hydrostatic pressure causes the movement of fluids from an area of higher pressure to area of lower pressure

14. Active Transport • Requires metabolic activity and uses energy to move substances across cell membranes • Enables larger substances to move into cells • Molecules can also move to an area of higher concentration (Uphill) • Sodium-Potassium Pump • Potassium pumped in – higher concentration in ICF • Sodium pumped out – higher concentration in ECF

16. Regulation of Body Fluids • Homeostasis is maintained through • Fluid intake • Hormonal regulation • Fluid output regulation

17. Fluid Intake • Thirst control center located in the hypothalamus • Osmoreceptors monitor the serum osmotic pressure • When osmolarity increases (blood becomes more concentrated), the hypothalamus is stimulated resulting in thirst sensation • Salt increases serum osmolarity • Hypovolemia occurs when excess fluid is lost

18. Fluid Intake • Average adult intake • 2200 – 2700 mL per day • Oral intake accounts for 1100 – 1400 mL per day • Solid foods about 800 – 1000 mL per day • Oxidative metabolism – 300 mL per day • Those unable to respond to the thirst mechanism are at risk for dehydration • Infants, patients with neuro or psych problems, and older adults

19. Hormonal Regulation • ADH (Antidiuretic hormone) • Stored in the posterior pituitary and released in response to serum osmolarity • Pain, stress, circulating blood volume effect the release of ADH • Increase in ADH = Decrease in urine output = Body saves water • Makes renal tubules and ducts more permeable to water

20. Hormonal Regulation Cont’d. • Renin-angiotensin-aldosterone mechanism • Changes in renal perfusion initiates this mechanism • Renin responds to decrease in renal perfusion secondary to decrease in extracellular volume • Renin acts to produce angiotensin I which converts to angiotensin II which causes vasoconstriction, increasing renal perfusion • Angiotensin II stimulates the release of aldosterone when sodium concentration is low

21. Hormonal Regulation Cont’d. • Aldosterone • Released in response to increased plasma potassium levels or as part of the renin-angiotensin-aldosterone mechanism to counteract hypovolemia • Acts on the distal portion of the renal tubules to increase the reabsorption of sodium and the secretion and excretion of potassium and hydrogen • Water is retained because sodium is retained • Volume regulator resulting in restoration of blood volume

22. Hormonal Regulation Cont’d. • Atrial Natriuretic Peptide (ANP) • ANP is a hormone secreted from atrial cells of the heart in response to atrial stretching and an increase in circulating blood volume • ANP acts like a diuretic that causes sodium loss and inhibits the thirst mechanism • Monitored in CHF

23. Fluid Output Regulation • Organs of water loss • Kidneys • Lungs • Skin • GI tract

24. Fluid Output Regulation Cont’d. • Kidneys are major regulatory organ of fluid balance • Receive about 180 liters of plasma to filter daily • 1200 – 1500 mL of urine produced daily • Urine volume changes related to variation in the amount and type of fluid ingested • Skin • Insensible Water Loss • Continuous and occurs through the skin and lungs • Can significantly increase with fever or burns • Sensible Water Loss occurs through excess perspiration • Can be sensible or insensible via diffusion or perspiration • 500 – 600 mL of insensible and sensible fluid lost through skin each day

25. Fluid Output Regulation Cont’d. • Lungs • Expire approx 500 mL of water daily • Insensible water loss increases in response to changes in resp rate and depth and oxygen administration • GI Tract • 3 – 6 liters of isotonic fluid moves into the GI tract and then returns to the ECF • 200 mL of fluid is lost in the feces each day • Diarrhea can increase this loss significantly

26. Regulation of Electrolytes • Major Cations in body fluids • Sodium (Na+) • Potassium (K+) • Calcium (Ca++) • Magnesium (Mg++)

27. Sodium Regulation • Most abundant cation in the extracellular fluid • Major contributor to maintaining water balance • Nerve transmission • Regulation of acid-base balance • Contributes to cellular chemical reactions • Sodium is taken in via food and balance is maintained through aldosterone

28. Potassium Regulation • Major electrolyte and principle cation in the extracellular fluid • Regulates metabolic activities • Required for glycogen deposits in the liver and skeletal muscle • Required for transmission of nerve impulses, normal cardiac conduction and normal smooth and skeletal muscle contraction • Regulated by dietary intake and renal excretion

29. Calcium Regulation • Stored in the bone, plasma and body cells • 99% of calcium is in the bones and teeth • 1% is in ECF • 50% of calcium in the ECF is bound to protein (albumin) • 40% is free ionized calcium • Is necessary for • Bone and teeth formation • Blood clotting • Hormone secretion • Cell membrane integrity • Cardiac conduction • Transmission of nerve impulses • Muscle contraction

30. Magnesium Regulation • Essential for enzyme activities • Neurochemical activities • Cardiac and skeletal muscle excitability • Regulation • Dietary • Renal mechanisms • Parathyroid hormone action • 50 – 60% of magnesium contained in bones • 1% in ECF • Minimal amount in cell

31. Anions • Chloride (Cl-) • Major anion in ECF • Follows sodium • Bicarbonate (HCO3-) • Is the major chemical base buffer • Is found in ECF and ICF • Regulated by kidneys

32. Anions Cont’d. • Phosphate (PO4---) • Buffer ion found in ICF • Assists in acid-base regulation • Helps to develop and maintain bones and teeth • Calcium and phosphate are inversely proportional • Promotes normal neuromuscular action and participates in carbohydrate metabolism • Absorbed through GI tract • Regulated by diet, renal excretion, intestinal absorption and PTH

33. Regulation of Acid-Base Balance • Lungs and kidneys are our buffering systems • A buffer is a substance that can absorb or release H+ to correct an acid-base imbalance • Arterial pH is an indirect measure of hydrogen ion concentration • Greater concentration of H+, more acidic, lower pH

34. Regulation of Acid-Base Balance • Lower concentration of H+, more alkaline, higher pH • The pH is also a reflection of the balance between CO2 (regulated by lungs) and bicarb (regulated by kidneys) • Normal H+ level is necessary to • Maintain cell membrane integrity • Maintain speed of cellular enzymatic actions

35. Chemical Regulation • Carbonic acid-bicarbonate buffer system is the first to react to change in the pH of ECF • H+ and CO2 concentrations are directly related • ECF becomes more acidic, the pH decreases, producing acidosis • ECF receives more base substances, the pH rises, producing alkalosis • Lungs primarily control excretion of CO2 resulting from metabolism • Kidneys control excretion of hydrogen and bicarb

36. Biological Regulation Buffer actions that occur Exchange of K+ and H+ Carbon dioxide goes into RBCcarbonic acid (HCO3-) HCO3 ready to exchange with Cl- Chloride shift within RBC H+ H+ K+ K+ K+ H+ H+ H+

37. Acidosis vs Alkalosis Acidosis Acids have high H+ ions in solution Alkalosis Bases have low H+ ion concentration Acidity or Alkalinity of a solution measured by pH

38. Physiological Regulators Lungs Regulate by altering H+ ions Metabolic acidosis Metabolic alkalosis Kidneys Regulate by altering HCO3 and H+ ions H+ H+ H+ H+ HCO3 HCO3 HCO3 HCO3

39. Causes of Electrolyte Imbalances Excessive sweating Fluid loss leading to dehydration Excessive vomiting Diuretics like Lasix (K+ depletion) Massive blood loss Dehydration may go unnoticed in hot, dry climates Renal failure

40. Sodium Most abundant in extracellular space Moves among three fluid compartments Found in most body secretions Na Na Na Na Na

41. Hyponatremia – Low Sodium Seizures Personality changes Nausea/vomiting Tachycardia Convulsion Normal Na (135-145)

42. Hypernatremia Excessive Na in ECF Loss of water Diarrhea Insensible water loss Water deprivation Gain of Sodium Diabetes insipidus Heat stroke

43. Hypokalemia – Low Potassium Severe leg cramps Flaccid muscles Fatigue Irregular pulse Chest discomfort EKG changes T wave flattens Normal Potassium-3.5-5

44. Hyperkalemia CNS Nausea and vomiting Peripheral Nervous System Tremors, twitching Heart Bradycardia, peaked T wave

45. Hypocalcemia – Low Calcium Tingling of fingers Tetany Muscle cramps Positive Trousseau’s Carpal spasm Positive Chvostek’s Contraction of facial muscle when facial nerve tapped

46. Hypercalcemia Causes Prolonged immobility Osteoporosis Thiazide diuretics Acidosis Signs/symptoms N/V, weakness Hypoactive reflexes Cardiac arrest

47. Hypomagnesemia Causes Malnutrition Alcoholism Polyuria Pre-ecclampsia Signs/symptoms Muscle tremor Hyperactive deep reflexes Chvostek’s/Trousseau’s Difficulty breathing

48. Hypermagnesemia Causes Renal failure Excessive intake Signs/symptoms Low BP Muscle weakness Absent reflexes Bradycardia