24 Drugs Used to Treat Fluid and Electrolyte Balances

Figure 24-1 The urinary system.

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

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

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

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

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.

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

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

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

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

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

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

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.

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

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

Figure 24-4 Electrolyte balance Figure 24-4 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.

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

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.

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.

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.

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.

Table 24-1 Normal Water Gains and Losses*

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

Table 24-2 The Main Electrolytes in the Body

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

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

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

Table 24-3 Osmotic Diuretics

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

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

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

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

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

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

Table 24-4 Carbonic Anhydrase Inhibitors

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

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

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

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

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

Table 24-5 Thiazides and Thiazide-like Diuretics

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

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

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

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

Table 24-6 Loop Diuretics

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

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

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.

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

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

Table 24-7 Potassium-Sparing Diuretics

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

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

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

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.