Focus topic: Fluid and Electrolyte and Acid/Base Balance

Cells maintain a balance, or homeostasis, by transference of fluid and electrolytes in and out of the cell. This fluid constantly bathes the cell. Although fluid and electrolyte balance and acid/base balance are separate entities, they directly relate to one another.

For example, dehydration results in a decrease in the pH or metabolic acidosis, whereas overhydration results in an increase in the pH or metabolic alkalosis. To understand how this happens, let’s review the basics of fluid movement across the cell membrane.

Water and small particles constantly move in and out of the semipermeable membrane in the cell through active transport and osmosis. This process transports nutrients, hormones, proteins, and other molecules into the cell. It also aids in the movement of waste products out of the cell for excretion from the body.

Along with other functions, fluid also assists with body temperature regulation. When the client has an infection resulting in an elevated temperature, he tends to perspire. This loss of body fluid can lead to dehydration. Dehydration occurs when there is more fluid output than fluid intake.

Other body fluids exist in the form of pericardial fluid, pleural fluid, and spinal fluid. These fluids are compartmentalized into two types:

• Intracellular fluid (fluid that is within the cell): Two-thirds of the body’s fluid is intracellular.
• Extracellular fluid (fluid that is outside the cell): One-third of the body’s fluid is extracellular. These fluids are divided between the intravascular and interstitial spaces.

Fluid and Electrolyte and Acid/Base Balance: Total Body Water Calculation

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The distribution of body fluid is dependent on age and muscle mass. Total body water in an adult equals approximately 60% of total body weight in kilograms. Infants and the elderly have a higher percentage of body fluid averaging 70%–80%. Fatty tissue contains less water than muscle. For that reason, the elderly and infants lose fluid more quickly than adults and become dehydrated at a more rapid rate, as noted below:

 

Diffusion is the process whereby molecules move from an area of higher concentration to an area of lower concentration. Diffusion is affected by the amount and type of molecular particles. These molecular particles are removed from body fluid as they pass through semipermeable membranes in a process known as filtration.

Molecular particles can also pass from an area of lower concentration to one of higher concentration by a process known as active transport. Diffusion and active transport allow positively charged particles, called cations, and negatively charged particles, called anions, to pass in and out of the cell. These particles are also known as electrolytes because they are positively or negatively charged. As cations and anions concentrate, they result in changes in the pH. Some examples of anions are bicarb (HCO3–), chloride (Cl–), proteins, phosphates, and sulfates. Examples of cations are sodium (Na+), potassium (K+), magnesium (Mg++), and calcium (Ca++).

Positive and negatively charged particles are either acidic or alkaline in nature. An acid is a substance that releases a hydrogen (H+) ion when dissolved in water, and a base is a substance that binds with a hydrogen ion when released in water. Therefore, when there is a decrease in bicarbonate hydrogen ions (HCO3–) or an accumulation of carbonic acid, acidosis exists; when there is an increase in bicarbonate hydrogen ions (HCO3–) or a loss of carbonic acid, alkalosis exists.

This chapter discusses how these factors affect acid/base balance (pH) and the regulation of fluid and electrolytes. You will also discover the disease processes that contribute to these alterations.

The sections that follow cover the alteration in acid/base balance as it affects electrolytes and pH.

Fluid and Electrolyte and Acid/Base Balance: Management of the Client with Imbalances in Fluid and Electrolytes

Focus topic: Fluid and Electrolyte and Acid/Base Balance

All body fluid compartments contain water and solutes or electrolytes. The concentra- tion of electrolytes depends on the fluid volume and the body’s ability to regulate the fluid:solvent ratio. The electrolytes are as follows:

• Sodium (Na+)
• Potassium (K+)
• Chloride (Cl–)
• Calcium (Ca+)
• Magnesium (Mg+)
• Phosphorus (P–)
• Hydrogen (H+)
• Bicarbonate (HCO3–

The major intracellular electrolytes are potassium and magnesium. The major extracel- lular electrolytes are sodium and chloride. The majority of these electrolytes come from our food and fluid intake. Other sources that can affect electrolytes are medications, blood administration, hyperalimentation, and intravenous fluids.

Fluid and Electrolyte and Acid/Base Balance: Types of Intravenous Fluids

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Intravenous fluid replacement changes the serum by adding electrolytes and/or fluid. There are several indications for the use of intravenous fluid replacement. When the client is unable to maintain a state of fluid and electrolytes within normal limits, the physician might need to institute fluid and electrolyte replacement.

Some of the reasons that the physician might choose to use intravenous fluid replacement are surgery, trauma, gastrointestinal loss of fluid, nothing-by-mouth status, burn injuries, and bleeding. Intravenous fluids are categorized by their composition. Types of IV fluids include isotonic, hypotonic, hypertonic, and colloid.

 

Intravenous Fluid Solutions

 

Fluid and Electrolyte and Acid/Base Balance: How the Body Regulates Electrolytes

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The body’s electrolytes are regulated by

• The kidneys: The kidneys regulate several electrolytes either directly or indi- rectly. In the kidneys, the glomeruli filter the small particles and water but retain the large particles. Therefore, the waste as well as potassium and sodium are filtered out as needed and the protein—a large particle—is retained.
• The endocrine system: The endocrine system helps by stimulation of an antidi- uretic hormone that helps keep sodium and potassium within a normal range.
• The gastrointestinal system: The gastrointestinal system helps by regulating gastric juices in the stomach and across the small bowel.
• The vascular system: The heart transports electrolytes in the blood.

Fluid and Electrolytes Values

If there is an alteration in electrolytes, the client experiences a state of disequilibrium. The following sections discuss alterations in electrolytes.

Fluid and Electrolyte and Acid/Base Balance: Potassium

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Potassium is the most abundant cation in the body. If damage occurs to the cell, potas- sium leaves the cell. This can result in hyperkalemia or hypokalemia, depending on renal function.

Hypokalemia and Hyperkalemia: Causes, Symptoms, and Treatments

Fluid and Electrolyte and Acid/Base Balance: Sodium

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Sodium is the major extracellular fluid cation. The major source of sodium is dietary with a minimum sodium requirement for adults of 2 grams per day. Most adults consume more than the necessary amount. Sodium along with potassium facilitates impulse transmission in nerves and muscle fibers.

Hyponatremia and Hypernatremia: Causes, Symptoms and Treatments

 

 

A: Presence of U waves (hypokalemia); B: Fusion of T and U waves with hypokalemia.

 

Hyperkalemia and the presence of peaked T waves.

Fluid and Electrolyte and Acid/Base Balance: Chloride

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Chloride is taken in through the diet, especially from foods rich in salt. It is found in combination with sodium in the blood as sodium chloride (NaCl) and is found in the stomach as a hydrogen chloride ion. The function of chloride is to assist sodium with maintaining serum osmolarity. Chloride is regulated primarily by the kidneys and the gastrointestinal system.

 

 

Most of the total body calcium is found in bone. Calcium not found in the bone is bound to plasma protein. Most of the calcium found and used by the body is taken in through the diet with a recommended daily calcium intake of 800mg. For calcium to be used, vitamin D must be present.

Several systems help in the regulation of calcium. The gastrointestinal system absorbs calcium, and the renal system filters calcium in the glomerulus and absorbs it in the tubules. Calcitonin (a thyroid hormone) helps to regulate calcium by moving it from plasma to bone. The parathyroid gland responds to low plasma levels by releasing parathyroid hormone.

Hypocalcemia and Hypercalcemia: Causes, Symptoms, and Treatments

 

Trousseau’s sign.

 

Chvostek’s sign.

Prolonged Q-T intervals if calcium levels drop below 5.4 mg/dl.

Shortened Q-T intervals.

Fluid and Electrolyte and Acid/Base Balance: Phosphorus

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Phosphorus is the major anion in the intracellular fluid. Its concentration inside the cell is approximately 100 mEq/L. Normal sources of phosphorus intake include almost all foods, especially dairy products. When the phosphorus level is elevated, the calcium level is low, and vice versa. Phosphorus acts as the critical component of the phosphate buffer system that aids renal regulation of acids and bases.

Phosphorus is also a major factor in bone and teeth development; cell integrity; and the function of red blood cells, muscles, and the neurologic system. It is also a component of DNA and RNA. Phosphorus is reabsorbed in the proximal end of the renal tubule along with sodium. The parathyroid gland secretes parathyroid hormone in response to serum calcium levels.

Hypophospatemia and Hyperphospatemia: Causes, Symptoms, and Treatments

Fluid and Electrolyte and Acid/Base Balance: Magnesium

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Magnesium is taken in through the diet and eliminated through the kidneys and gastrointestinal system. It exerts effects on the myoneural junction affecting neuromuscular irritability. Magnesium assists with cardiac and skeletal muscle cells and contributes to vasodilation. Magnesium also activates intracellular enzymes in carbohy- drate and protein synthesis.

Hypomagnesemia and Hypermagnesemia: Causes, Symptoms, and Treatments

 

Fluid and Electrolyte and Acid/Base Balance: How the Body Regulates pH

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Many organs are involved in maintaining homeostasis. They are

• Lungs
• Heart
• Pituitary
• Adrenal
• Kidneys
• Blood vessels
• Parathyroids

The body maintains its pH by keeping the ratio of HCO3 (bicarb) to H2CO3 (carbonic acid) at a proportion of 20:1. HCO3, or bicarbonate, is a base, whereas carbonic acid is acidic. This relationship constantly changes and is compensated for by the kidneys and lungs. The normal pH is 7.35–7.45, with the ideal pH being 7.40. If the carbonic acid concentration increases, acidosis occurs and the client’s pH falls below 7.40. A pH below 7.35 is considered uncompensated acidosis. If the HCO3 concentration increases, alkalosis occurs and the client’s pH rises above 7.40. A pH above 7.45 is considered uncompensated alkalosis.

 

 

Although several systems assist with the regulation of pH, there are primarily two buffer systems of the body:

• Kidneys: By retaining or excreting NaHCO3 (sodium bicarb) or by excreting acidic urine or alkaline urine. They also help by reabsorbing NaHCO3– and secreting free H+ ions.
• Lungs: By retaining carbonic acid in the form of CO2 (carbon dioxide) or by rapid respirations excreting CO2.When there is a problem with the capability of either the lungs or the kidneys to compensate, an alteration in this balance results.

Fluid and Electrolyte and Acid/Base Balance: Metabolic Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Metabolic acidosis results from a primary gain of carbonic acid or a loss of bicarbonate HCO3 with a pH below 7.40.

Causes of Metabolic Acidosis

The following is a list of some causes of metabolic acidosis:

• Certain disease states: Disease states that create excessive metabolism of fats in the absence of usable carbohydrates, leading to the accumulation of ketoacids.
• Diabetes mellitus: Lack of usable insulin, leading to hyperglycemia and ketoacidosis.
• Anorexia: Leads to cell starvation.
• Lactic acidosis: Due to muscle and cell trauma, such as myocardial infarction.
• Renal failure: Leading to waste accumulation in the body and elevated levels of creatinine, BUN, uric acid, and ammonia. All these substances are acidic.
• Diarrhea: With a loss of HCO3. This loss of HCO3 and fluid leads to dehydration. When the client is dehydrated, acidosis is likely.
• Excessive ingestion: Ingestion of aspirin or other acids.
• Overuse of diuretics: Particularly non–potassium-sparing diuretics.
• Overwhelming systemic infections: Also called sepsis. Overwhelming infections lead to cell death and nitrogenous waste accumulation.
• Terminal stages of Addison’s disease: Adrenal insufficiency results in a loss of sodium and water. This leads to a decrease in blood pressure and hypovolemic shock.

Fluid and Electrolyte and Acid/Base Balance: Symptoms of Metabolic Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The following list highlights symptoms of metabolic acidosis that a nurse needs to be aware of for both the NCLEX and for on-the-job observations:

•  Lab values: Decreased pH, decreased PaCO2, decreased serum CO2, often increased potassium
• Renal: Polyuria and increased acid in the urine
• Respiratory: Hyperventilation (due to stimulation of the hypothalamus)
• Gastrointestinal: Anorexia, nausea, vomiting, diarrhea, fruity breath
• Neurological: Headache, lethargy, drowsiness, loss of consciousness, coma, death

Fluid and Electrolyte and Acid/Base Balance: Management of the Client with Metabolic Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Metabolic acidosis is rarely present without an underlying disease process. Treatment involves early diagnosis and treatment of the causative factors:

• Monitor the potassium level (K+) and treat accordingly: Because potassium (K+) is an intracellular cation, changes in potassium levels commonly occur with metabolic acidosis. The symptoms of hyperkalemia are malaise, generalized weakness, muscle irritability, flaccid paralysis, nausea, and diarrhea. If the potassium is excreted through the kidneys, hypokalemia can result. The symptoms of hypokalemia are diminished reflexes, weak pulse, depressed U waves on the ECG exam, shallow respirations, shortness of breath, and vomiting.

 

 

• Treat diabetes: Treat with insulin for hyperglycemia; treat with glucose for hypoglycemic.
• Treat hypovolemia: Treat with a volume expander and blood transfusions, and treat shock.
• Treat renal failure: Treatment includes dialysis or transplant. The diet for renal failure clients should control protein, sodium, and fluid. Supplemental with calories and carbohydrates is suggested.
• Treat lactic acidosis: Treatment includes oxygen and NaHCO3.
• Treat Addison’s disease: Treatment includes cortisone preparations, a high sodium diet, and fluids for shock.

Nursing care of the client with metabolic acidosis includes frequent monitoring of vital signs and attention to the quality of pulses, intake and output, and oral hygiene. Clients with vomiting should be positioned on their side, with a nasogastric tube to Levin suction. Those with diabetes should be taught the importance of frequent finger sticks and urine checks for hyperglycemia.

Fluid and Electrolyte and Acid/Base Balance: Respiratory Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Respiratory acidosis occurs when there is a decrease in the rate of ventilation to the amount of carbonic acid production. Hypoventilation leads to CO2 accumulation and a pH value less than 7.35. Loss of the lungs as a buffer system causes the kidneys to compensate. In chronic respiratory acidosis, the kidneys attempt to compensate by retaining HCO3.

Fluid and Electrolyte and Acid/Base Balance: Causes of Respiratory Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The following list highlights causes of respiratory acidosis you need to know. All these involve accumulation of carbonic acid (CO2) and/or a lack of oxygenation:

• Oversedation or anesthesia.
• Head injury (particularly those affecting the respiratory center). This type of head injury leads to an increase in intracranial pressure and suppression of the respirations.
• Paralysis of the respiratory muscles (for example, Guillian-Barrè, myasthenia gravis, or spinal cord injury).
• Upper airway obstruction.
• Acute lung conditions (such as pulmonary emboli, pulmonary edema, pneumonia, or atelectasis).
• Chronic obstructive lung disease.
• Prolonged overbreathing of CO2.

Fluid and Electrolyte and Acid/Base Balance: Symptoms of Respiratory Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The following list gives the symptoms of respiratory acidosis you need to know:

• Neurological: Dull sensorium, restlessness, apprehension, hypersomnolence, coma
• Respiratory: Initially increased respiratory rate, perspiration, increased heart rate; later, slow respirations and periods of apnea or Cheyne-Stokes respirations (breathing marked by periods of apnea lasting 10–60 seconds followed gradually by hyperventilation) with resulting cyanosis

Fluid and Electrolyte and Acid/Base Balance: Caring for the Client with Respiratory Acidosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Care of the client with respiratory acidosis includes attention to signs of respiratory distress, maintaining a patent airway, encouraging fluids to thin secretions, and chest physiotherapy.

 

Fluid and Electrolyte and Acid/Base Balance: Metabolic Alkalosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Metabolic alkalosis results from a primary gain in HCO3 or a loss of acid that results in a pH level above 7.45.

Fluid and Electrolyte and Acid/Base Balance: Causes of Metabolic Alkalosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The following list highlights causes of metabolic alkalosis that you need to be aware of:

• Vomiting or nasogastric suction that might lead to loss of hydrochloric acid
• Fistulas high in the gastrointestinal tract that might lead to a loss of hydrochloric acid
• Steroid therapy or Cushing’s syndrome (hypersecretion of cortisol) that might lead to sodium, hydrogen (H+) ions, and fluid retention
• Ingestion or retention of a base (for example, calcium antacids or NaHCO3)

Fluid and Electrolyte and Acid/Base Balance: Symptoms of Metabolic

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Symptoms of metabolic alkalosis include

• Neurological: Fidgeting and twitching tremors related to hypokalemia or hyperkalemia
• Respiratory: Slow, shallow respirations in an attempt to retain CO2
• Cardiac: Atrial tachycardia and depressed T waves related to hypokalemia
• Gastrointestinal: Nausea, vomiting, and diarrhea, causing loss of hydrochloric acid
• Lab changes: pH levels above 7.45, normal or increased CO2, increased NaHCO3

Fluid and Electrolyte and Acid/Base Balance: Caring for the Client with Metabolic Alkalosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

The following items are necessary care items a nurse should know for treating clients with metabolic alkalosis:

• Administering potassium replacements
• Observing for dysrhythmias
• Observing intake and output
• Assessing for neurological changes

Fluid and Electrolyte and Acid/Base Balance: Respiratory Alkalosis

Focus topic: Fluid and Electrolyte and Acid/Base Balance

Respiratory alkalosis relates primarily to the excessive blowing off of CO2 through hyperventilation. Causes of respiratory alkalosis include

• Hypoxia
• Anxiety
• High altitudes

FURTHER READIND/STUDY:

Resources:

• NCLEX-RN: Test-Taking Strategies

• NCLEX: MUSCULOSKELETAL DISORDERS

• NCLEX: End-of-life care

• NCLEX: Obesity

• NCLEX: Cancer care

• NCLEX: Hematologic and lymphatic disorders

• NCLEX: Musculoskeletal disorders

• NCLEX: Reproductive system disorders

• NCLEX: Renal and urologic disorders

• NCLEX: Cardiovascular disorders