Chapter 8 Disorders of Fluid, Electrolyte, and Acid-Base Balance

1. Essentials of Pathophysiology Chapter 8Disorders of Fluid, Electrolyte, and Acid-Base Balance

2. The extracellular compartment contains approximately two thirds of the body water in healthy adults, and is the larger of the two compartments. Potassium is the most abundant cation in the body. Edema of the brain, larynx, or lungs is not an acute, life-threatening condition. Polydipsia is a term that means “excessive thirst.” Decreased vascular volume would yield manifestations such as full and bounding pulses, venous distention, and signs and symptoms of pulmonary edema, such as shortness of breath, crackles, dyspnea, and cough. PRE LECTURE QUIZ (TRUE/FALSE) F F F T F

3. Diabetes insipidus is a condition that is caused by a deficiency or a decreased response to __________, also known as vasopressin. The most serious side effect of hyperkalemia is on ______________ function. Serum _______________ is directly or indirectly regulated by parathyroid hormone (PTH) and vitamin D. Respiratory acidosis is characterized by a decrease in __________, reflecting a decrease in ventilation and an increase in PCO2. Vomiting, removal of gastric secretions through the use of nasogastric suction, and low potassium levels resulting from diuretic therapy are the most common causes of _________________ alkalosis in hospitalized patients. PRE LECTURE QUIZ ADH Calcium Cardiac Metabolic pH

4. Intracellular compartment • Extracellular compartment • Interstitial spaces • Plasma (vascular) compartment • Transcellular compartment Fluid Distribution

5. Distribution of Water • Intracellular • Extracellular • Interstitial • Plasma • 3rd Space

6. An athlete ran a marathon even though he felt ill… • After the race he collapsed. He was pale with a low blood pressure and sunken eyes. One knee and ankle were badly swollen, and his abdomen was distended with fluid. The doctor diagnosed appendicitis and dehydration. Question: • What has happened to his: • Blood osmolarity? • Cell size? • Transcellular fluid volume? • Vascular compartment volume? Scenario

7. Forces Moving Fluid In and Out of Capillaries and Cells Osmosis: Which Way Will Water Move? Blood: (ECF) Few solutes Lots of water Cell: (ICF) Many solutes Less water Water Follows Solutes

8. Hydrostatic pressure Pressure created by the Heart i.e. Blood Presssure Forces water out of capillaries Forces Moving Fluid In and Out of Capillaries

9. Forces Moving Fluid In and Out of Capillaries Greatly reduced Hydrostatic pressure due to capillary resistance Hydrostatic pressure generated by the heart

10. What forces work to keep blood in the capillary? • Capillary colloid osmotic pressure (COP) & tissue COP • Capillary hydrostatic pressure & tissue COP • Capillary hydrostatic pressure & tissue hydrostatic pressure • Capillary COP & tissue hydrostatic pressure Question

11. Capillary COP & tissue hydrostatic pressure Hydrostatic pressure can be thought of as “pushing pressure,” and osmotic pressure can be thought of as “pulling” pressure. Pressure in the capillary that pulled/kept fluid in (capillary COP) and pressure pushing fluid out of the tissue (tissue hydrostatic pressure) would result in more fluid in the capillary. Answer

12. Normal level is 135–145 mEq/L • Regulates extracellular fluid volume and osmolarity Question: • Why would “retaining sodium” cause high blood pressure? Sodium

13. It’s a very hot day and you fall down the stairs on the way to see the doctor about your hepatitis and renal disease • Explain why you have edema in your sprained ankle and foot Scenario

14. High osmolarity causes: (Hypothalamic detection) • Thirst  • ADH release  • Low osmolarity causes: • Lack of thirst  • Decreased ADH release  Controlling Blood Osmolarity increased water intake water reabsorbed from urine decreased water intake water lost in the urine Negative _________________ Feedback

15. True or False: Increased levels of ADH decrease urine output. Question

16. True ADH prevents diuresis by causing more water to be absorbed in the kidney tubules. If more water is absorbed, there is less water left to eliminate as waste, decreasing urine output. Answer

17. A common problem in elderly people Scenario: • Dr. Bob thinks it could be treated with ADH given in a nasal spray • Dr. Bill thinks renin injections would be better Question: • What is your evaluation of these two theories? Dehydration Due to Hypodipsia

18. Diabetes insipidus (DI) • Neurogenic • Nephrogenic • Syndrome of inappropriate ADH (SIADH) • Which will cause hyponatremia? ADH Imbalances

19. Hyponatremia (<135 mEq/L) • Hypertonic • Hypotonic (dilutional) • Hypernatremia (>145 mEq/L) • Water deficit • Na+ administration Sodium Imbalances

20. A man with hypernatremia was severely confused. Question: • The doctor said this was due to a change in the size of his brain cells. Why would this happen? • A medical student suggested giving him a hypotonic IV. Why? • The doctor said that might worsen the change in his brain cell size, and that his blood osmolarity should be corrected very slowly. Why? Scenario

21. Normal level is 3.5–5.0 mEq/L Maintains intracellular osmolarity Controls cell resting potential Needed for Na+/K+ pump Exchanged for H+ to buffer changes in blood pH Potassium

22. Hyperaldosteronism? Alkalosis? An injection of epinephrine? Convulsions? Loop diuretics? What Will Happen to Blood K+ Levels When the Client Has:

23. Cells begin with a negative charge— resting membrane potential Stimulus causes some Na+ channels to open Na+ diffuses in, making the cell less negative, i.e. more positive The Basics of Cell Firing Threshold potential Resting membrane potential stimulus

24. At threshold potential, more Na+ channels open Na+ rushes in, making the cell positive: depolarization Action potential: the cell responds (e.g., by contracting) The Basics of Cell Firing (cont.) Action potential Threshold potential Resting membrane potential stimulus

25. K+ channels open K+ diffuses out, making the cell negative again: repolarization Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in The Basics of Cell Firing (cont.) Action potential Threshold potential Resting membrane potential stimulus

26. Hyperkalemia raises resting potential toward threshold • Cells fire more easily • Increased K+ can move resting potential to threshold, Na+ gates open and won’t close Blood K+ Levels Control Resting Potential Threshold potential Hyperkalemia Normal resting membrane potential

27. Hypokalemia lowers resting potential away from threshold • Cells fire less easily Blood K+ Levels Control Resting Potential (cont.) Threshold potential Normal resting membrane potential Hypokalemia

28. What effect does a potassium level of 7.5 mEq/L have on resting membrane potential (RMP)? • RMP becomes less negative, and it takes a greater stimulus in order for cells to fire. • RMP becomes less negative, and it takes less of a stimulus in order for cells to fire. • RMP becomes more negative, and it takes a greater stimulus in order for cells to fire. • RMP becomes more negative, and it takes less of a stimulus in order for cells to fire. Question

29. RMP becomes less negative, and it takes less of a stimulus in order for cells to fire. A potassium level of 7.5 mEq/L is considered hyperkalemic. In hyperkalemia, RMP is moved closer to the threshold (it becomes less negative). Because RMP is nearer to the threshold, a weaker stimulus will cause the cell to fire (a lesser distance must be overcome). Answer

30. Normal level is 8.5–10.5 mg/dL Extracellular: blocks Na+ gates in nerve and muscle cells Clotting Leaks into cardiac muscle, causing it to fire Intracellular: needed for all muscle contraction Acts as second messenger in many hormone and neurotransmitter pathways Calcium

31. Calcium Regulation • Blood Ca2+ can be increased by: • Increased intestinal absorption • Release from bones

32. Calcium regulation • Blood Ca2+ can be increased by: • Increased intestinal absorption • Release from bones

33. A man with metastatic cancer complains of bone pain and sudden weakness. Question: • Why did the doctor measure: • PTH? • Calcium levels? • Vitamin D levels? Scenario:

34. Normal level is 1.8–2.7 mg/dL • Cofactor in enzymatic reactions • Involving ATP • DNA replication • mRNA production • Binds to Ca2+ receptors • Can block Ca2+ channels Magnesium

35. Hypercalcemia • Blocks more Na+ gates • Nerves are less able to fire • Hypocalcemia • Blocks fewer Na+ gates • Nerves fire more easily • Which would cause Trousseau’s & Chvostek’s sign? Extracellular Calcium Controls Nerve Firing Hypocalcemia because they indicate easy nerve firing

36. CHVOSTEK’S SIGN Elicitation: Tapping on the face at a point just anterior to the ear and just below the zygomatic bone Postitive response: Twitching of the ipsilateral facial muscles, suggestive of neuromuscular excitability caused by hypocalcemia TROUSSEAU’S SIGN Elicitation: Inflating a sphygmomanometer cuff above systolic blood pressure for several minutes Postitive response: Muscular contraction including flexion of the wrist and metacarpophalangeal joints, hyperextension of the fingers, and flexion of the thumb on the palm, suggestive of neuromuscular excitability caused by hypocalcemia CHVOSTEK’S SIGN &TROUSSEAU’S SIGN

37. True or False: Both hyperkalemia and hypercalcemia cause cells to fire more easily. Question

38. False Recall that hyperkalemia cause cells to fire more easily by moving RMP closer to the threshold. Hypercalcemia, on the other hand, blocks more sodium gates. If less sodium enters the cell, it cannot depolarize as quickly (it is less likely to fire). Hypocalcemia blocks fewer sodium gates–cells depolarize more quickly (they are more likely to fire). Answer

39. Insert fig. 6-16 Balance between blood pH, HCO3= and H2CO3 H2CO3 = .03 * PaCO2 Normal Balance Metabolic Acidosis Respiratory Alkalosis Important Relationships

40. Normal value: pH = 7.35–7.45 • Blocks Na+ gates • Controls respiratory rate • Individual acids have different functions: • Byproducts of energy metabolism (carbonic acid, lactic acid) • Digestion (hydrochloric acid) • “Food” for brain (ketoacids) Acid (H+)

41. CO2 + H2O   H2CO3 (carbonic acid) • H2CO3  H+ + HCO3- (bicarbonate ion) • An increase in CO2 will cause • Increases in CO2 (increased PCO2) • Increases in H+ (lower pH) • Increases in bicarbonate ion Respiratory or Volatile Acid

42. CO2 + H2O   H2CO3  H+ + HCO3- • (carbonic acid)  (bicarbonate ion) • Respiratory distress may be an attempt to compensate for low serum pH Respiratory Acidosis and Alkalosis

43. Tell whether the following statement is true or false: Serum levels of pH and CO2 levels are directly proportional. Question

44. False As blood levels of CO2 increase, pH becomes more acidic (decreases). Answer

45. Scenario: • A woman was given an acidic IV. Soon she began to breathe more heavily. Why? • When her blood was tested, it had: • Slightly lowered pH • Low bicarbonate • Low PCO2 • Slightly increased K+ • Her urine pH was slightly lowered • Why? Respiration and Buffers Adjust Blood pH

46. Buffer Systems

47. Metabolic acidosis • Increased levels of ketoacids, lactic acid, etc. • Decreased bicarbonate levels • Metabolic alkalosis • Decreased H+ levels • Increased bicarbonate levels Metabolic Acid Imbalances

48. Increased metabolic acids raise H+ levels • Some H+ combines with bicarbonate, decreasing it • Breathing adjusts CO2 levels to bring pH back to normal Metabolic Acidosis and Alkalosis