Chapter 14

1. Chapter 14 Fluids and Electrolytes

2. Homeostasis Maintaining relatively constant conditions as in fluid compartments To maintain internal balance, body must be able to regulate fluids All organs and structures of the body involved in homeostasis

3. Homeostasis cont’d Intracellular fluid Fluid within a cell Most of the body’s fluids found within the cell Extracellular fluid Fluid outside the cell Intravascular fluid In blood vessels in the form of plasma or serum Interstitial fluid In fluid surrounding cells, including lymph

4. Water Largest portion of body weight Percentage affected by age, sex, body fat Percentage of body water decreases with age Females have a lower percentage of body water than males throughout adult years because women have more fat than men and fat cells contain less water than other cells Obese have a lower percentage of body water because of the increased number of fat cells

5. Solutes Electrolyte Substance that develops an electrical charge when dissolved in water Examples: sodium, potassium, calcium, chloride, bicarbonate, and magnesium Maintain balance between positive and negative charges For every positively charged cation, there is a negatively charged anion Cations and anions combine to balance one another

6. Solutes cont’d Sodium (Na) Most abundant electrolyte; primary electrolyte in extracellular fluid Major role in regulating body fluid volumes, muscular activity, nerve impulse conduction, and acid-base balance

7. Solutes cont’d Potassium (K) Found mainly in the intracellular fluid; the major intracellular cation Important in maintaining fluid osmolarity and volume within the cell Essential for normal membrane excitability—a critical factor in transmitting nerve impulses Needed for protein synthesis, for the synthesis and breakdown of glycogen, and to maintain plasma acid-base balance

8. Solutes cont’d Chloride (Cl) An extracellular anion that is usually bound with other ions, especially sodium or potassium Functions are to regulate osmotic pressure between fluid compartments and assist in regulating acid-base balance

9. Solutes cont’d Calcium (Ca) Usually combined with phosphorus to form the mineral salts of the bones and teeth Of total body calcium, 99% concentrated in the bones and teeth; 1% is in the extracellular fluid Ingested through the diet and absorbed through the intestine Promotes transmission of nerve impulses; helps regulate muscle contraction and relaxation

10. Solutes cont’d Magnesium (Mg2+) A cation found in bone (50% to 60%), intracellular fluid (39% to 49%), and extracellular fluid (1%) Plays a role in the metabolism of carbohydrates and proteins, the storage and use of intracellular energy, and neural transmission Important in heart, nerve, and muscle function

11. Solutes cont’d Nonelectrolytes Other substances dissolved in the body fluids Urea, protein, glucose, creatinine, and bilirubin These solutes do not carry an electrical charge

12. Transport of Water and Electrolytes Membranes Selectively permeable membranes Separate fluid compartments and control movement of water and certain solutes Maintain unique composition of each compartment of the body while allowing transport of nutrients and wastes to and from cells Some solutes cross membranes more easily than others

13. Transport Processes Diffusion The random movement of particles in all directions is for a substance to move from an area of higher natural tendency concentration to an area of lower concentration Facilitated diffusion A carrier protein transports the molecules through membranes toward an area of lower concentration

14. Transport Processes cont’d Active transport Carrier proteins transport substances from an area of lower concentration to an area of equal or greater concentration Requires expenditure of energy Many solutes, such as sodium, potassium, glucose, and hydrogen, are actively transported across cell membranes

15. Transport Processes cont’d Filtration Transfer of water and solutes through a membrane from an area of high pressure to an area of low pressure Hydraulic pressure A combination of pressures from the force of gravity on the fluid and the pumping action of the heart Needed to move fluid out of capillaries into tissues and filter plasma through the kidneys

16. Transport Processes cont’d Osmosis Movement across a membrane from a less concentrated to a more concentrated solution Involves movement of water only; sometimes force of movement across membrane carries solutes along If a fluid compartment has less water and more sodium, water from another compartment moves to the more concentrated compartment by osmosis to create a better fluid balance

17. Osmolality Concentration of solution determined by number of dissolved particles per kg water Controls water movement and distribution by regulating the concentration of fluid in each body fluid compartment The osmolality of intracellular fluid and extracellular fluid tends to equalize because of the constant shifting of water

18. Regulatory Mechanisms

19. Kidneys Main regulators of fluid balance Control extracellular fluid by adjusting the concentration of specific electrolytes, osmolality of body fluids, the volume of extracellular fluid, blood volume, and pH The nephron is the functioning unit of the kidney Glomerulus is the filtering portion of the nephron, and the tubule is responsible for secretion and reabsorption Nephrons conduct work of the kidney through filtration, reabsorption, and secretion

20. Kidneys cont’d Filtration Blood plasma entering the kidney via the renal artery is delivered to the glomerulus About 20% of plasma filtered into glomerular capsule Most remaining plasma leaves kidney through the renal vein Filtrate then moves through the tubules, where it is transformed into urine by tubular reabsorption and secretion

21. Kidneys cont’d Tubular reabsorption A process by which most of the glomerular filtrate is returned to the circulation Water and selected solutes move from the tubules into the capillaries Waste products remain in tubules for excretion, whereas most water and sodium is reabsorbed into the bloodstream Adjusts volume and composition of the filtrate; prevents excessive fluid loss through kidneys

22. Kidneys cont’d Tubular secretion The last phase in the work of the kidneys The filtrate is transformed into urine Various substances—drugs, hydrogen ions, potassium ions, creatinine, and histamine—pass from the blood into the tubules Process eliminates some excess substances to maintain fluid and electrolyte balance, as well as metabolic waste products

23. Hormones Renin Hormone secreted when blood volume or blood pressure falls Causes the release of aldosterone with subsequent sodium and water retention Aldosterone Acts on kidney tubules to increase reabsorption of sodium and decrease reabsorption of potassium Because the retention of sodium causes water retention, aldosterone acts as a volume regulator

24. Hormones cont’d Antidiuretic hormone (ADH) Causes capillaries to reabsorb more water, so urine is more concentrated and less volume is excreted Atrialnatriuretic factor (ANF) Hormone released by the atria in response to stretching of the atria by increased blood volume Stimulates excretion of sodium and water by the kidneys, decreased synthesis of renin, decreased release of aldosterone, and vasodilation Reduces blood volume and lowers blood pressure

25. Thirst Regulates fluid intake Increased plasma osmolality stimulates osmoreceptors in the hypothalamus to trigger the sensation of thirst More sodium and less water in the body make a person thirsty Additional fluids consumed; kidneys conserve water until osmolality returns to normal

27. Fluid Gains and Losses In healthy adult, 24-hour fluid intake and output approximately equal Fluids gained by drinking and eating and lost through the kidneys, skin, lungs, and gastrointestinal tract The usual adult urine volume is between 1 and 2 L/day, or 1 ml/kg of body weight per hour In kidneys, water loss varies largely with the amount of solute excreted and with the level of antidiuretic hormone

28. Fluid Gains and Losses cont’d Losses through the skin occur by sweating Water loss through the lungs by evaporation at 300 to 400 ml/day In the gastrointestinal tract, the usual loss of fluid is about 100 to 200 ml/day

29. Age-Related Changes Affecting Fluid Balance Aging kidney slower to adjust to changes in acid-base, fluid, and electrolyte balances Older adult often has a reduced sense of thirst and therefore may be in a state of chronic dehydration Total body water declines with age; greatest loss from the intracellular fluid compartment

30. Age-Related Changes Affecting Fluid Balance cont’d Older person has limited reserves to maintain fluid balance when abnormal losses occur Antihypertensives, diuretics, and antacids can also contribute to imbalances Unless contraindicated, fluid requirements for older adults, based on ideal body weight, are 30 ml/kg for ages 55 to 65 and 25 ml/kg for 65 years and older

31. Assessment of Fluid and Electrolyte Balance Health history Determines if patient has conditions that contribute to fluid or electrolyte imbalances Vomiting, diarrhea, kidney diseases, diabetes, salicylate poisoning, burns, congestive heart failure, cerebral injuries, ulcerative colitis, and hormonal imbalances; the intake of drugs, such as diuretics and cathartics; and medical interventions, such as gastric suctioning Complaints of fatigue, palpitations, dizziness, edema, muscle weakness or cramps, dyspnea, and confusion may be associated with fluid imbalances

32. Assessment of Fluid and Electrolyte Balance cont’d Vital signs Pulse, respiration, temperature, and blood pressure can indicate changes in fluid and electrolyte balance. Temperature variations can be associated with fluid volume excess or deficit. Pulse rate and quality may change in response to blood volume alterations; electrolyte changes can affect heart rate and rhythm. Blood pressure is directly related to blood volume. Respirations are minimally affected by electrolyte changes.

33. Assessment of Fluid and Electrolyte Balance cont’d Intake and output Accurate records are essential to determine whether the patient’s intake is equal to output All fluids entering or leaving the body should be noted A changing urine output may reflect attempts by the kidneys to maintain or restore balance, or it may reflect a problem that causes fluid disturbances Urine characteristics also give clues to fluid balance Clear, pale urine in a healthy person suggests the excretion of excess water, whereas darker, concentrated urine indicates the kidneys are retaining water

34. Assessment of Fluid and Electrolyte Balance cont’d Skin Characteristics Moisture, turgor, and temperature reflect fluid balance. Dry, flushed skin—dehydration. Pale, cool, clammy skin—severe fluid volume deficit that occurs with shock. Moist, edematous tissue seen with excess fluid volume Facial characteristics Severely dehydrated patient has a pinched, drawn facial expression. Soft eyeballs and sunken eyes indicate severely deficient fluid volume. Puffy eyelids and fuller cheeks suggest excess fluid volume

35. Assessment of Fluid and Electrolyte Balance cont’d Skin turgor Measured by pinching the skin over the sternum, the inner aspects of the thighs, or the forehead In patients who are dehydrated, skin flattens more slowly after the pinch is released Edema Reflects water and sodium retention, which can result from excessive reabsorption or inadequate secretion of sodium, as may occur with kidney failure Pitting depression remains in the tissue after pressure is applied with a fingertip

36. Assessment of Fluid and Electrolyte Balance cont’d Mucous membranes Tongue turgor In well person, tongue has one longitudinal furrow. Fluid volume deficit causes additional longitudinal furrows, and the tongue is smaller. Sodium excess causes the tongue to appear red and swollen. Moisture of the oral cavity A dry mouth may be the result of deficient fluid volume or mouth breathing. Veins Appearance of the jugular veins in the neck and the veins in the hands can suggest either a fluid volume deficit or excess.

37. Diagnostic Tests and Procedures Urine studies Urine pH Determines if kidneys are responding appropriately to metabolic acid-base imbalances Urine specific gravity A measure of urine concentration A good indicator of fluid balance Osmolality Measures the number of dissolved particles in a solution Provides more precise measurement of kidneys’ ability to concentrate urine

38. Diagnostic Tests and Procedures cont’d Urine creatinine clearance tests Detect glomerular damage in the kidney A 24-hour specimen is required Urine sodium Sodium intake and fluid volume status Urine potassium A measure of renal tubular function

39. Diagnostic Tests and Procedures cont’d Blood studies Serum hematocrit Percentage of blood volume composed of red blood cells Serum creatinine A metabolic waste product Indicator of renal function Blood urea nitrogen (BUN) A measure of renal function

40. Diagnostic Tests and Procedures cont’d Serum albumin A plasma protein that helps maintain blood volume by creating colloid osmotic pressure Serum electrolytes Sodium, potassium, chloride, and calcium

41. Fluid Imbalances Deficient fluid volume Less water than normal in the body Isotonic extracellular fluid deficit Hypovolemia Hypertonic extracellular fluid deficit Dehydration Decreased intake, abnormal fluid losses, or both Examples: loss of water from excessive bleeding, severe vomiting/diarrhea, severe burns

42. Fluid Imbalances cont’d Excess fluid volume An increase in body water Extracellular fluid excess Isotonic fluid excess Intracellular water excess Hypotonic fluid excess From renal or cardiac failure with retention of fluid, increased production of antidiuretic hormone or aldosterone, overload with isotonic IV fluids, or administration of dextrose 5% in water (D5W) after surgery or trauma

43. Electrolyte Imbalances

44. Hyponatremia Lower than normal sodium in the blood serum Can be actual deficiency of sodium or increase in body water that dilutes the sodium excessively Assessment Symptoms: headache, muscle weakness, fatigue, apathy, confusion, abdominal cramps, and orthostatic hypotension Take blood pressures with the patient lying or sitting and then standing to determine if a significant drop

45. Hyponatremia cont’d Medical treatment The usual treatment is restriction of fluids while the kidneys excrete excess water Diuretic: furosemide (Lasix) Sodium replacement therapy Nursing care Administer prescribed medications and IV fluids Measure fluid intake and output and assess mental status

46. Hypernatremia Higher than normal concentration of sodium in the blood Very serious imbalance; can lead to death if not corrected Occurs when excessive loss of water or excessive retention of sodium Signs and symptoms Thirst, flushed skin, dry mucous membranes, low urine output, restlessness, increased heart rate, convulsions, and postural hypotension

47. Hypernatremia cont’d Medical treatment Oral or IV replacement of water to restore balance A low-sodium diet often prescribed Nursing care Encourage patients with hypernatremia to drink water Closely monitor the infusion of IV fluids Teach patient to track daily intake and output and to recognize the signs and symptoms of fluid retention or depletion

48. Hypokalemia Low serum potassium May result in gastrointestinal, renal, cardiovascular, and neurologic disturbances Can cause abnormal, potentially fatal, heart rhythm Signs and symptoms Anorexia, abdominal distention, vomiting, diarrhea, muscle cramps, weakness, dysrhythmias (abnormal cardiac rhythms), postural hypotension, dyspnea, shallow respirations, confusion, depression, polyuria (excessive urination), and nocturia

49. Hypokalemia cont’d Medical treatment Potassium replacement by the IV or oral route Nursing care Monitoring at-risk patients for decreased bowel sounds, a weak and irregular pulse, decreased reflexes, and decreased muscle tone Cardiac monitors may be used to detect dysrhythmias Administer oral or IV potassium Urine output should be no less than 30 ml/hr

50. Hyperkalemia High serum potassium Patients at risk: decreased renal function, in metabolic acidosis, taking potassium supplements A serious imbalance because of the potential for life-threatening dysrhythmias Signs and symptoms Explosive diarrhea and vomiting; muscle cramps and weakness, paresthesia, irritability, anxiety, abdominal cramps, and decreased urine output