1. 24
Drugs Used to Treat Fluid and Electrolyte Balances

2. Figure 24-1 The urinary system.

3. Kidney Structure Inner medulla and outer cortex
Nephrons: functional units located in renal cortex
Renal corpuscle: filtering unit with glomerulus and glomerular capsule
Renal tubule: proximal convoluted tubule, loop of Henle, distal convoluted tubule

4. Figure 24-2 The kidney with an expanded view of the nephron.

5. Renal Physiology
Urine production promotes homeostasis by regulating volume and composition of blood.
Three organic waste products:
Urea: most abundant waste
Creatinine: produced in skeletal muscle tissue
Uric acid: formed by recycling nitrogenous base from RNA molecules

6. Diuresis in Elderly People
Older adults have:
Decreased ability to concentrate urine
Decreased ability to tolerate dehydration or water loads
Fewer nephrons
Reduce drug elimination
More drug accumulation in plasma, causing possible toxic reactions

7. Urine Formation
Begins with filtration of plasma by glomerular capillaries (glomerular filtration)
Glomerular filtration produces 180 L of fluid each 24 hours.
Kidneys return filtered fluid to internal environment through tubular reabsorption.

8. Urine Formation Waste products are excreted in urine.
Tubular secretion removes hydrogen ions and toxins faster than through filtration.

9. Figure 24-3 Sites of resorption and secretion in a nephron.

10. Homeostasis Glomerular filtration + Tubular secretion
− Tubular reabsorption
____________________
Urinary excretion

11. Fluid Imbalances in Children
The urine of infants and children is more dilute than that of adults because of:
Higher blood flow
Shorter loops of Henle

12. Fluid Imbalances in Children
Pediatric patients are more affected by fluid imbalances resulting from:
Diarrhea
Infection
Improper feeding

13. Fluid Imbalances in Children
Pediatric patients have limited ability to quickly regulate change in: pH
Osmotic pressure

14. Control of Urine Volume
Urine volume regulated by reabsorption of water:
By osmosis in proximal convoluted tubule and descending loop of Henle
Antidiuretic hormone (ADH) needed to increase water permeability of tubules.
Absence of ADH can cause diabetes insipidus.

15. Medications and Urine Retention
Several medications cause urine retention:
Anticholinergics and antispasmodics
Antidepressants and antipsychotics
Antihistamines
Antihypertensives
Beta-adrenergic blockers
Opioids

16. Fluid and Electrolyte Balance
Levels of water and electrolytes in body are interdependent:
Electrolytes are dissolved in water of body fluids.

17. Figure 24-4 Electrolyte balance
Figure Electrolyte balance. Electrolyte intake occurs through the ingestion of foods and fluids through metabolic reactions. Electrolyte output occurs through the excretion of feces, sweat, and urine.

18. Dehydration in Infants
At birth, total body water (TBW) represents about 75 to 80% of total body weight.
Decreases to 67% during first year of life

19. Dehydration in Infants
Infants are particularly susceptible to significant changes in TBW because of high metabolic rate and greater body surface area.
Dehydration may occur.

20. Water Deficit Can indicate both sodium and water loss
Pure water deficits are rare.
Comatose or paralyzed patients have insensible water loss through the skin and lungs.

21. Water Balance Water intake = water output
Water balance regulated by secretion of ADH and perception of thirst.
ADH is secreted when plasma osmolality increases or circulating blood volume decreases and blood pressure drops.
Increase plasma osmolality occurs with water deficit.

22. Fluctuating TBW in Elderly Patients
Decreased TBW in elderly patients results in part from increased body fat, decreased muscle, and the kidneys’ reduced ability to regulate sodium and water balance.
With stress or illness, this decreased TBW can become life threatening.

23. Table 24-1 Normal Water Gains and Losses*

24. Electrolytes
Electrolytes: conduct electricity (cations) or are decomposed by electricity (anions)
Electrolytes of greatest importance: sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, hydrogen

25. Table 24-2 The Main Electrolytes in the Body

26. Electrolyte Imbalances
Elderly people are at higher risk for fluid and electrolyte imbalance because of:
Decreased thirst sensation
Decreased ability of kidneys to concentrate urine
Decreased intracellular fluid and TBW

27. Electrolyte Imbalances
Elderly people are at higher risk for fluid and electrolyte imbalance because of:
Decreased response to body hormones that regulate fluid and electrolytes
Increased use of diuretics
Decreased fluid and food intake

28. Diuretics Group of drugs that promote water loss from body into urine
Principal action at level of nephrons
Remove excess extracellular fluid into interstitial tissue which would otherwise result in edema
5 classes: carbonic anhydrase inhibitors and osmotic, thiazide, loop, and potassium-sparing diuretics

29. Table 24-3 Osmotic Diuretics

30. Osmotic Diuretics: Uses
Primarily work by decreasing solute content resulting in less water reabsorption by loop of Henle and collecting duct and less sodium reabsorption in proximal tubule
Highly effective in cerebral edema

31. Osmotics: Adverse Effects
Common adverse effects of osmotics include:
Headache
Tremor or convulsions
Dizziness
Hypotension or hypertension

32. Osmotics: Adverse Effects
Common adverse effects of osmotics include:
Thrombophlebitis
Blurred vision
Dry mouth
Nausea and vomiting

33. Osmotics: Contraindications
Osmotics are contraindicated in the following:
Anuria
Pulmonary congestion or edema
Severe congestive heart failure
Metabolic edema
Intracranial bleeding

34. Osmotics: Contraindications
Osmotics are contraindicated in the following:
Shock
Severe dehydration
Pregnancy and lactation

35. Osmotics: Patient Information
Advise patients to report thirst, muscle cramps or weakness, paresthesia, dyspnea, or headache.
Instruct female patients to avoid breastfeeding.

36. Table 24-4 Carbonic Anhydrase Inhibitors

37. Carbonic Anhydrase Inhibitors: Uses
Work by converting carbon dioxide into bicarbonate ions
Used to treat absence, tonic-clonic, and focal seizures; to reduce intraocular pressure in glaucoma; to treat high-altitude sickness

38. Carbonic Anhydrase Inhibitors: Adverse Effects
Common: anorexia, nausea and vomiting, weight loss, dry mouth, thirst, diarrhea, fatigue, dizziness, drowsiness, hyperglycemia
Serious: bone-marrow depression, hepatic dysfunction

39. Carbonic Anhydrase Inhibitors: Contraindications
Contraindicated in renal and hepatic dysfunction, Addison’s disease and adrenocortical insufficiency, hyponatremia, hypokalemia, hypochloremic acidosis
Safety in pregnancy and lactation not established

40. Carbonic Anhydrase Inhibitors: Contraindications
Use cautiously in diabetes mellitus, gout, obstructive pulmonary disease and respiratory acidosis, and in patients taking digitalis.

41. Carbonic Anhydrase Inhibitors: Patient Information
Instruct patients to avoid driving or hazardous activities if drowsiness or dizziness occurs.

42. Table 24-5 Thiazides and Thiazide-like Diuretics

43. Thiazide Diuretics: Uses
Increase urinary excretion of sodium and water by inhibiting sodium reabsorption; also increase excretion of chloride, potassium, and bicarbonate ions
Used to treat hypertension and as adjunctive therapy in edema associated with heart failure and cirrhosis

44. Thiazide Diuretics: Adverse Reactions
Common: anorexia, gastric irritation, nausea, vomiting, cramping, diarrhea, constipation, jaundice, hypokalemia, pancreatitis
Serious: anaphylactic reactions, respiratory distress

45. Thiazide Diuretics: Contraindications
Contraindicated in patients with diabetes, history of gout, severe renal disease and impaired liver function, and in elderly patients
Not recommended during lactation
Interactions occur with corticosteroids, lithium, probenecid, antidiabetic agents

46. Thiazide Diuretics: Patient Information
Instruct patients with diabetes to monitor blood glucose levels with care.

47. Table Loop Diuretics

48. Loop Diuretics: Uses
Act directly on loop of Henle to inhibit sodium and chloride reabsorption
Drugs of choice in acute pulmonary edema of heart failure
Also used to treat hypercalcemia and hypertension

49. Loop Diuretics: Adverse Reactions
Common: fluid/electrolyte imbalances, skin rashes, photosensitivity, hypotension
Serious: circulatory collapse, thromboemboli, hepatic encephalopathy, ototoxicity, shock, cardiac arrhythmias, bone-marrow depression

50. Loop Diuretics: Contraindications
Do not use in infants or lactating women.
Avoid in patients with severe diarrhea, dehydration, electrolyte imbalance, or hypotension.
Use cautiously in patients with hepatic cirrhosis, diabetes mellitus, pulmonary edema, pregnancy, and history of gout.

51. Loop Diuretics: Contraindications
Interact with NSAIDs, lithium, anticoagulants, aminoglycosides, and thiazide diuretics

52. Loop Diuretics: Patient Information
Instruct patients to take in the morning and not at bedtime.
Advise women to avoid during lactation.

53. Table 24-7 Potassium-Sparing Diuretics

54. Potassium-Sparing Diuretics: Uses
Prevent sodium reabsorption in distal tubule
Used to treat edema of heart failure, hepatic cirrhosis with ascites, nephrotic syndrome
Used mainly in combination with other drugs to treat hypertension

55. Potassium-Sparing Diuretics: Adverse Effects
Common: kidney stones, gynecomastia
Serious: life-threatening hyperkalemia, renal failure

56. Potassium-Sparing Diuretics: Contraindications
Contraindicated in patients with acute renal insufficiency, impaired renal function, or hyperkalemia
Use cautiously in pregnancy and lactation, or in patients with cirrhosis.
Interact with potassium supplements, NSAIDs, and lithium

57. Potassium-Sparing Diuretics: Patient Information
Teach patients about symptoms of hypokalemia, such as muscle cramps and weakness, lethargy, anorexia, irregular pulse, and confusion.
Advise patients of symptoms of hyperkalemia, including thirst, dry mouth, and drowsiness.