* Homeostasis, for the purpose of fluid and electrolytes, is defined as the mechanism for maintaining a steady state in the body.

FLUID AND ELECTROLYTES

Physiology

A. Basic concepts of body fluid.

I. Water is a primary body fluid. It is used to transport nutrients as well as to remove waste products.

a. Infant: 70% to 80% of body weight is water.

b. Adult: 50% to 60% of body weight is water.

c. Elderly adult: 45% to 55% of body weight is water.

2. Electrolytes: electrically charged particles.

a. Anion: carries a negative charge.

b. Cation: carries a positive charge.

c. Electrolytes found in intracellular fluid and in extracellular fluid are essentially the same: however, the concentrations differ.

3. Intracellular fluid: provides the cell with internal fluid necessary for cellular function.

a. Approximately 40% to 50% of total body fluid.

b. Electrolytes.

(1) Potassium (primary).

(2) Magnesium.

(3) Phosphate.

4. Extracellular fluids: transport system for cellular waste, oxygen, electrolytes, and nutrients; assists to regulate body temperature, lubricates and cushions joints.

a. Approximately 30% to 40% of total body water.

b. An infant maintains a larger percentage of extra-cellular fluids than does an older child or adult.

c. Vascular: circulating plasma volume.

d. Interstitial: fluid surrounding tissue cells.

e. Electrolytes.

(1) Sodium (primary)

(2) Chloride.

(3) Calcium.

B. Dynamic transport of fluid and electrolytes

a. Diffusion: movement Hof molecules from an area of high concentration to an area of low concentration.

b. Osmosis: movement of water through a semi-permeable membrane from an area of low electrolyte concentration to an area of high concentration.

(1) Oncotic pressure: the osmotic pressure created by plasma proteins.

(2) Osmotic pressure: term used to describe osmosis (water goes where the salt is).

c. Filtration: the movement of water and electrolytes through a semi-permeable membrane from an area of high pressure to an area of low pressure: hydrostatic pressure is a term used to describe the force of filtration.

2. Active transport: movement of substances from an area of low concentration to an area of high concentration with the expenditure of energy.

3. Hydrostatic pressure: the pressure created by the fluid volume in the vascular bed.

4. Filtration occurs in the arterial end of the capillaries because the hydrostatic pressure is higher than the oncotic pressure. Fluid then moves out of the vascular bed into the tissue.

5. At the venous end of the capillaries, the oncotic pressure is greater and the fluid moves back into the vascular volume.

6. Osmolarity refers to the concentration of the dissolved particles in a solution: osmolarity controls the

movement of fluid in each of the compartments.

a. Hyperosmolar: increased concentration of particles or solutes in a solution: fluid will move into this space to dilute the concentration.

b. Hypo-osmolar: decreased concentration of particles, more water and less solutes: fluid will move out of this space to increase the concentration of solutes.

c. Iso-osmolar (isotonic): normal distribution of solutes and water in body fluid.

C. Fluid shifts.

1. Plasma to interstitial fluid shift.

a. Edema: accumulation of fluid in interstitial spaces.

(1) Increase in hydrostatic pressure. as in a client with fluid overload (congestive heart failure).

(2) Decrease in oncotic pressure, as in a client with excessive protein loss (renal disease).

(3) Break in the integrity of vessel walls, as in a client experiencing burns and trauma.

b. Hypovolemia may occur as a result of excessive fluid shift into the interstitial spaces, resulting in circulatory collapse (client with burns).

2. Interstitial to plasma fluid shift: movement of fluid back into the circulatory volume, as in client with mobilization of burn edema: or in the case of excessive administration of hypertonic solution, causing the interstitial water to be returned to the plasma; client may demonstrate symptoms of circulatory overload.

3. Fluid spacing: third spacing occurs in tissue injury from an increase in capillary permeability and from an increase in vascular fluid volume.

a. Ascites.

b. Burn edema.

c. Sequestration of fluid in the bowel.

d. Homeostatic mechanisms.

1. Endocrine system.

a. Hypothalamus secretes antidiuretic hormone, which regulates the water reabsorption by the kidneys.

b. Adrenal cortex secretes aldosterone, which promotes sodium retention and potassium excretion, thereby causing an increase in plasma volume.

2. Lymphatic system: assists in the return of excessive protein and fluid, which escapes into the tissue, to the plasma volume.

3. Cardiovascular system maintains blood pressure to ensure adequate renal perfusion.

4. Kidneys maintain fluid volume and concentration of urine via the glomeruli filtration rate.

Fluid Imbalances

A. Fluid deficit: extracellular fluid volume deficit (dehydration); hypovolemia results from vascular fluid volume loss.

1. Sensible fluid loss: fluid loss of which an individual is aware, as in urine.

2. Insensible fluid loss: fluid loss of which an individual is not aware (approximately 1000 ml of fluid is lost every 24 hours through the skin and lungs in a healthy adult).

3. Causes of fluid deficit (all result from loss of both water and sodium).

a. Decreased fluid intake.

b. Failure to absorb or reabsorb water, as in diarrhea and intestinal disorders.

c. Loss of fluid through the gastrointestinal tract, as in vomiting, nasogastric suctioning.

d. Excessive renal excretion due to renal disease and inappropriate antidiuretic hormone secretion.

e. latrogenic loss due to overuse of diuretics or inadequate replacement of fluid loss.

f. Excessive fluid loss through skin and lungs due to febrile state.

g. Impaired integrity of the skin as in burns, wounds, and hemorrhage.

NURSING PRIORITY: Sodium is the major electrolyte that affects fluid balance. "Where goes the sodium, so goes the water."

4. Clinical manifestations.

a. Thirst, longitudinal tongue furrows.

b. Dry skin and dry mucous membranes.

c. Poor skin turgor (assess skin on the abdomen or the inner thigh in children: skin turgor is a poor indicator in elderly clients).

d. Weight loss.

e. Oliguria.

f. Decreased blood pressure.

g. Decreased central venous pressure.

h. Postural hypotension.

i. Mottled skin color changes in infants and children.

j. Weakness, confusion, speech difficulty in elderly.

5. Laboratory findings.

a. Increased specific gravity.

b. Increased blood urea nitrogen (>25 mg/dl) with increase in creatinine.

c. Increased hematocrit (the normal ratio of hematocrit to hemoglobin is 3:1); for example, 12 grams hemoglobin to 36% hematocrit.

ALERT. Monitor client's hydration status (intake and output, edema, signs and symptoms

of dehydration).

B. Extracellular fluid volume excess (circulatory overload): the retention of sodium and water in the intravascular and interstitial spaces.

I. Causes of fluid excess.

a. Excessive oral fluid intake.

b. Failure to excrete fluids, as in renal disease and cardiac failure.

c. latrogenic: fluid increase due to excessive infusion of hypotonic fluids.

d. Excess intake of sodium.

2. Clinical manifestations.

a. Pitting edema, sacral edema.

b. Pulmonary edema (dyspnea).

c. Bounding pulse, bradycardia.

d. Weight gain.

e. Lethargy.

f. Variable urine volume.

g. Changes in level of consciousness.

h. Increased central venous pressure.

i. Jugular vein distention.

j. Increased blood pressure.

3. Laboratory findings: based on the area of the body in which the shift occurs.

a. Decreased specific gravity of urine (<1.010).

b. Decreased hematocrit.

c. Decreased serum sodium.

C. Extracellular fluid volume shift (third spacing): shift in the location of the extracellular fluid between the intravascular and interstitial spaces.

1. Causes of fluid shift.

a. Vascular to interstitial space shift due to tissue damage such as blisters, sprains.

b. Large fluid shifts occur in severe injuries, burns, intestinal perforations and obstruction, and lymphatic obstruction.

2. Clinical manifestations.

a. Decreased circulating volume, resulting in symptoms of hypovolemia.

b. Localized symptoms when the fluid is obstructing an organ, as in the intestinal tract.

D. Nursing management of client with fluid imbalances.

1. Assessment.

a. Evaluate client's history and predisposing factors contributing to the problem.

b. Assess for direction of fluid problem: fluid excess or deficit.

c. Evaluate appropriate lab data.

d. Evaluate client's ability to tolerate and correct the problem.

e. Elderly clients are more likely to develop extracellular fluid volume excess due to chronic diseases (renal, cardiac).

2. Nursing intervention.

a. Maintain accurate intake and output records.

b. Obtain accurate daily weight.

NURSING PRIORITY: Daily weight is the most reliable indicator of fluid loss or gain in all clients, regardless of age. Accurate daily weight: same time each day, preferably before breakfast, same scales, same clothing.

c. Evaluate for presence of edema.

d. Maintain intravenous (IV) replacement fluids at prescribed flow rate.

e. Monitor central venous pressure.

f. Monitor vital signs (blood pressure is not a reliable indicator of problems of fluid balance in young children).

g. Maintain good skin care to prevent breakdown.

h. Assess lab data for changes in the problem.

i. Carefully monitor elderly and pediatric clients and clients with cardiac disease for tolerance of fluid replacement.

INTRAVENOUS FLUID REPLACEMENT THERAPY

Isotonic Solutions

A. Used to expand extracellular fluid volume and for intravascular dehydration.

B. Solutions.

1. D5W: 5% dextrose in water.

2. 0.9% NaCl (normal saline solution).

3. Lactated Ringer's solution.

C. May be used to dilute medications or to keep the vein open.

NURSING PRIORITY: In D5W the dextrose is metabolized rapidly, leaving free water to be absorbed. It does not replenish electrolytes; it is contraindicated for clients with head injuries and should be used with caution in children due to the potential for increase in intracranial pressure.

Hypotonic Solution

A. Solutions contain water, basic electrolytes.

B. 0.45% or half-strength NaCl (normal saline solution).

C. May be used for cellular dehydration.

D. Monitor closely for intravascular fluid loss, hypotension, and edema.

Hypertonic Solutions

A. Administered slowly: can cause intravascular volume overload: carefully monitor serum sodium.

B. Solutions.

1. D5W in 0.45% or half-strength NaCl (normal saline).

2. D5W in 0.9% NaCl (normal saline).

3. DSLR (lactated Ringer's solution).

C. Used to treat situations of hyponatremia and hypovolemia.

Nutritional Solutions

A. Contain very high percentage of dextrose.

B. Contain mixture of essential and nonessential amino acids. C. Concentrated solutions are used in total parenteral nutrition and must be administered via a central line.

D. Types of nutritional solutions.

1. 10% Dextrose solution.

2. Protein solutions (Aminosyn. FreAmine).

3. Fat emulsions.

ACID-BASE BALANCE

Basic Concepts of Acid-Base Balance

A. Terms used to describe acid-base balance.

1. pH: the chemical abbreviation for negative logarithm of hydrogen ion concentration.

2. CO2: carbon dioxide.

3. PaCO2,: pressure of dissolved CO, gas in the blood.

4.O2: oxygen.

5. PaO2,: pressure of dissolved 0, gas in the blood.

6. HCO3-: bicarbonate.

7. mm Hg: millimeters of mercury.

8. H+: hydrogen ion concentration.

B. Normal blood gas values.

1. pH 7.4 (7.35-7.45).

2. PaO2: 80 to 100 mm Hg.

3. PaCO2: 35 to 45 mm Hg.

4. HC03: 22 to 28 mEq/L.

C. The hydrogen ion (H') concentration determines the acidity or alkalinity of a solution; the higher the H' concentration, the more acidic is the solution.

D. Acid-base ratio is determined by sampling arterial blood. This provides a reliable index of overall body function.

E. The body maintains a normal or neutral state of acid-base balance. The stable concentration of H' balance is reflected in arterial blood with a relatively constant pH of 7.35 to 7.45.

F. It is necessary for the pH to remain relatively constant for the various enzyme systems of all body organs to function correctly.

G. 02 saturation levels reflected in blood gas readings do not have a direct effect on the acid-base balance.

H. A state of acid-base decompensation exists when the acid-base levels are either below 7.35 or above 7.45.

I. Compensation: The system not primarily affected is responsible for returning pH to a more normal level.

J. Correction: The problem in the system primarily affected is corrected, thereby returning the pH to a more normal level.

K. PaCO2, imbalance: The origin or primary system is respiratory, or it is compensating for a metabolic problem.

L. HCO3 imbalance: The origin or primary system is metabolic, or it is compensating for a respiratory problem.

M. The major clinical manifestations of an acid-base imbalance are indicative of central nervous system (CNS) involvement. The severity of the symptoms will depend on the length of time the imbalance exists, as well as the severity of the deviation.

1. Acidosis (metabolic or respiratory): Symptoms are indicative of depression of the CNS; this is not uncommon.

2. Alkalosis (metabolic or respiratory): Symptoms are indicative of increased stimulation of the CNS; death is a rare occurrence.

N. The normal ratio of HCO3 to PaCO2, is 20:1. If this ratio is present, the pH is normal.

Regulation of Acid-Base Balance

A. Buffer system: the most rapid-acting of the regulatory systems. The buffer system is activated when there is an excess acid or base present.

1. A buffer is a chemical that helps maintain a normal pH.

2. The buffer system chemicals are paired. The primary buffer chemicals are sodium HCO3 and carbonic acid. The buffers are capable of absorbing or releasing H' ions as indicated.

3. The body buffers an acid more effectively than it neutralizes a base.

4. An effective buffer system depends on normal functioning respiratory and renal systems.

B. Respiratory system: the second most rapid response in the regulation of acid-base balance. Carbonic acid is transported to the lungs, where it is converted to CO2 and water, then excreted.

1. The amount of CO2 in the blood is directly related to the carbonic acid concentrations.

2. Increased respirations will decrease CO2 levels, thus decreasing the carbonic acid concentration and resulting in decreased H+ concentration and an increase in the pH.

3. Decreased respirations will cause retention of CO2 increasing the carbonic acid concentrations and resulting in increased H+ concentration and a decrease in the pH.

4. With excessive acid formation, the respiratory center in the medulla is stimulated, which results in an increase in the depth and rate of respirations. This causes a decrease in the CO2 levels and returns the pH to a more normal point.

5. With excessive base formation, the respiratory rate slows to promote retention of CO2 and decrease the alkalotic state. CO2, is considered an acid substance because it combines with water to form carbonic acid. The PaCO2 levels are influenced only by respiratory causes.

C. Renal system: the slowest, but most effective, mechanism of acid-base regulation.

1. The kidneys reabsorb sodium (Na) and produce and conserve sodium bicarbonate (NaHCO3-).

2. In acidosis the H+ concentration is increased; therefore the H+ ions are excreted before the potassium (K+) ions, thereby precipitating hyperkalemia. When the acidosis is corrected, the potassium will move back into the cell.

3. In alkalosis the H+ concentration is decreased; there is an augmented renal excretion of K+ ions, thereby precipitating hypokalemia.

ALERT.- Modify client's care based on results of diagnostic tests (e.g.. arterial blood gases).

Alterations in Acid-Base Balance

A. Respiratory acidosis: characterized by excessive retention of CO2 due to hypoventilation; therefore an increased carbonic acid concentration produces an increase in H' ions and a decrease in the pH (decreases below 7.35).

1. Causes.

a. Depression of the respiratory center.

(1) Head injuries.

(2) Over-sedation with sedatives and/or narcotics.

(3) Infection of CNS.

b. Conditions affecting pulmonary function.

(1) Obstructive pulmonary diseases.

(2) Pneumonia.

(3) Cystic fibrosis.

(4) Atelectasis.

(5) Occlusion of respiratory passages.

c. Conditions that interfere with chest wall excursion.

(1) Thoracic trauma.

(2) Diseases affecting innervation of thoracic muscle (Guillain-Barre syndrome, myasthenia gravis, polio).

2. Clinical manifestations.

a. Dyspnea on exertion.

b. Rapid. shallow respirations (hypoventilation).

c. Disorientation, decreased level of consciousness.

d. Tachycardia, dysrhythmias.

e. Muscle weakness.

3. Blood gas values.

a. pH decreases below 7.35.

b. PaCO2, increases above 45 mm Hg.

c. HCO3; remains normal.

4. Compensation/correction.

a. Compensation: Renal system will compensate by retaining HCO3 and excreting increased amounts of H+ ions.

b. Correction: vigorous pulmonary hygiene to improve ventilation and decrease PaCO2, levels or

mechanical ventilation in states of decreased respiratory drive.

5. Nursing management.

a. Use preventive management.

(I) Have client turn, cough, and deep breathe every 2 hours after surgery.

(2) Use narcotics judiciously in the immediate postoperative period.

(3) Maintain adequate hydration.

b. Use semi-Fowler's position to facilitate breathing.

c. Thoroughly assess client's pulmonary function.

d. Perform postural drainage and percussion, followed by suction, to remove excessive pulmonary secretions.

e. Anticipate need for mechanical ventilation if client does not respond to pulmonary hygiene.

f. Anticipate use of bronchodilator.

g. Administer 0, with caution, as it may precipitate CO2 narcosis.

h. Evaluate for hyperkalemia.

i. Support renal system to promote adequate compensation.

B. Respiratory alkalosis: characterized by a low PaCO2, due to hyperventilation. An excessive amount of CO2 is exhaled, resulting in a decrease in H- concentration and an increase in pH (above 7.45).

ALERT.- Identify changes in respiratory status. The concept of respiratory acidosis may be tested in a variety of situations.

1. Causes of respiratory alkalosis.

a. Primary stimulation of CNS.

(1) Emotional origin (hysteria, fear, apprehension).

(2) CNS infection (encephalitis).

(3) Salicylate poisoning.

b. Reflex stimulation of CNS.

(1) Hypoxia: stimulates hyperventilation.

(2) Fever.

(3) Cardiac conditions.

c. Mechanical ventilation, resulting in "overbreathing."

d. Thickened alveolar-capillary membrane: congestive heart failure, pneumonia, pulmonary emboli.

2. Clinical manifestations.

a. Deep, rapid breathing (hyperventilation).

b. CNS stimulation, resulting in confusion, syncope, seizures.

c. Hypokalemia.

d. Muscle twitching and weakness.

e. Tingling of extremities.

3. Blood gas values.

a. pH increases above 7.45.

b. PaCO2 decreases below 35 mm Hg.

c. HCO3 remains normal.

4. Compensation/correction.

a. Compensation: Renal system will compensate by increasing HCO 3 excretion and retaining H+ ions, thus returning pH to a more normal level.

b. Correction: Prevent loss of CO, from respiratory systems.

5. Nursing management.

a. Identify and eliminate (if possible) causative factor.

b. Evaluate need for sedation.

c. Use rebreathing mask to increase CO@ levels.

d. Remain with client to decrease anxiety levels.

C. Metabolic alkalosis: characterized by an increase in the HCO 3 levels in the serum, leading to a decrease in the H+ concentration and an increase in the pH (increase above 7.45).

1. Causes (either an increase in serum HCO3- or a decrease in serum H+ concentration).

a. Diuretic therapy: loss of H', chloride (Cl-), K' precipitates an increase in the HCO level in the serum.

b. Excessive loss of H' ions.

(1) Prolonged nasogastric suctioning without adequate electrolyte replacement.

(2) Excessive vomiting, resulting in loss of hydrochloric acid and K+.

c. Prolonged steroid therapy: loss of H+', Cl-, and K+ ions, leading to an increased retention of HCO3 by the kidneys.

2. Clinical manifestations.

a. Nausea, vomiting, diarrhea.

b. Increased irritability, disorientation.

c. Restlessness, muscle twitching.

d. Hypokalemia.

e. Shallow, slow respirations (hypovolemia).

f. Dysrhythmias.

3. Blood gas values.

a. pH increases above 7.45.

b. PaCO2 remains normal.

c. HCO3 increases above 26 mEq/L.

4. Compensation/correction.

a. Compensation: Respiratory system will compensate by retaining CO, (hypoventilation) to compensate for the alkalosis.

b. Correction: replacement of electrolytes and fluids lost due to excessive renal excretion or due to excessive gastric loss of acid.

5. Nursing management.

a. Preventive.

(1) Provide foods high in potassium and chloride for client receiving diuretics.

(2) Administer potassium supplement to client receiving long-term diuretic therapy.

(3) Administer IV solution with replacement electrolytes.

b. Maintain accurate intake and output records.

c. Evaluate the lab values for a decrease in serum potassium levels.

d. Acetazolamide (Diamox) may be used to increase excretion of HCO; .

D. Metabolic acidosis: characterized by a decrease in HCO3- level in the serum, leading to an increase in H+ concentration and a decrease in pH (below 7.35).

1. Causes (deficit of a base or an increase in acid).

a. Incomplete oxidation of fatty acids.

(1) Diabetic acidosis.

(2) Starvation.

(3) Salicylate poisoning.

b. Abnormal loss of alkaline substances.

(1) Deep, prolonged vomiting may cause excessive loss of base products.

(2) Severe diarrhea and loss of pancreatic secretions.

c. Renal insufficiency: Kidneys lose ability to compensate for acid overload; thus H+ ions are not

excreted, nor is HCO3 retained in normal amounts.

d. Salicylate poisoning due to accumulation of ketone bodies produced as a result of the increased metabolic rate.

2. Clinical manifestations.

a. Disorientation.

b. Deep, rapid respirations (Kussmaul).

c. Increased lethargy.

d. Dysrhythmias.

e. Hyperkalemia.

3. Blood gas values.

a. pH decreases below 7.35.

b. Pco2 remains normal.

c. HCO,- decreases below 22 in Eq/L.

4. Compensation/correction.

a. Compensation: Respiratory system compensates by increasing rate and depth of respirations to

blow off CO2 and increase the pH.

b. Correction: identification of the underlying problem and promotion of optimal function.

5. Nursing management.

a. Assist in identification of underlying problem.

b. Administer sodium HCOz intravenously to neutralize acid and return pH to normal.

c. Evaluate diabetic client for ketoacidosis and administer insulin accordingly.

d. Assess renal function and hydration status.

e. Maintain accurate intake and output records.

f. Evaluate lab values for hyperkalemia.

g. Support respiratory system to promote compensation.