This is Foundations of Nursing, Topic 6, Chapter 42, Fluid, Electrolyte, and Acid-Based Balance. Fluid is internal to and surrounds all the cells in the body. Cellular fluids contain electrolytes such as sodium and potassium and also have a degree of acidity.
Fluid, electrolyte, and acid-based balances within the body maintain the health and function of all body systems. The characteristics of body fluids influence body system function because of their effects on cell function. These characteristics include the fluid amount, volume, concentration, which is osmolality, composition, or electrolyte concentration, and degree of acidity, or pH. All of these characteristics have regulatory mechanisms that keep them in balance for normal cellular function. It is important to understand how the body normally maintains fluid, electrolyte, and acid-base balance.
You also need to understand how imbalances develop, how various fluids, electrolyte, and acid-base imbalances affect patients, and ways to help patients maintain or restore balance safely. Fluid in the body compartments contains mineral salts known technically as electrolytes. An electrolyte is a compound that separates into ions or charged particles, when it dissolves in water. Ions that are positively charged are called cations. Ions that are negatively charged are called anions.
Cations and body fluids are sodium, potassium, calcium, and magnesium ions. Anions and body fluids are chloride and bicarbonate. Anions and cations combine to make salts.
If you put table salt in water, it separates into sodium and chloride. Other combinations of anions and cations do the same. Water comprises a substantial proportion of body weight.
In fact, about 60% of the body weight of an adult man is water. This proportion decreases with age. Approximately 50% of an older man's weight is water. Women typically have less water content than men.
People who are obese have less water in their bodies than people who are lean because fat contains less water than muscle. The term fluid means water that contains dissolved or suspended substances such as glucose, mineral salts, and proteins. Body fluids are located in two distinct compartments, extracellular fluid, or ECF, outside the cells, and intracellular fluid, ICF, inside the cells. In adults, ICF comprises approximately two-thirds of total body water.
ECF makes up approximately one-third of total body water. ECF has two major divisions, intravascular fluid and interstitial fluid, and a minor division, which is transcellular fluids. Intravascular fluid is the liquid part of the blood or the plasma. Interstitial fluid is located between the cells and outside the blood vessels. Transcellular fluids such as cerebrospinal, pleural, peritoneal, and synovial fluids are secreted by epithelial cells.
There are specific processes that move water and electrolytes between body compartments. These processes maintain equal osmolality in all compartments while allowing for different electrolyte concentrations. The first process we will talk about is active transport.
Fluids in different body compartments have different concentrations of electrolytes that are necessary for normal function. Cells maintain their high intracellular electrolyte concentration by active transport. Active transport requires energy in the form of adenosine triphosphate or ATP to move electrolytes across cell membranes against the concentration gradient from areas of lower concentration to areas of higher concentration.
One example of active transport is the sodium-potassium pump, which moves sodium out of a cell and potassium into it, keeping the ICF lower in sodium and higher in potassium than the ECF. The next process is diffusion. Diffusion is passive movement of electrolytes or other particles down a concentration gradient from areas of higher concentration to areas of lower concentration.
Within a body compartment, electrolytes diffuse easily by random movements until the concentration is the same in all areas. However, diffusion of electrolytes across cell membranes requires proteins that serve as ion channels. For example, when a sodium channel in a cell membrane is open, sodium diffuses passively across the cell membrane into the ICF because concentration is lower in the ICF.
Opening of ion channels is tightly controlled and plays an important part in muscle and nerve function. The next process is osmosis. Water moves across cell membranes by osmosis, a process by which water moves through a membrane that separates fluids with different particle concentrations. Cell membranes are semi-permeable, which means the water crosses them easily, but they are not freely permeable to many types of particles, including electrolytes such as sodium and potassium.
These semipermeable cell membranes separate interstitial fluid from ICF. The fluid in each of these compartments exerts osmotic pressure, an inward pulling force caused by particles in the fluid. The particles already inside the cell exert ICF osmotic pressure, which tends to pull water into the cell.
The particles in the interstitial fluid exert interstitial fluid osmotic pressure, which tends to pull water out of the cell. Water moves into the compartment that has a higher osmotic pressure, or inward pulling force, until the particle concentration is equal in the two compartments. Finally, we have filtration.
Fluid moves into and out of capillaries between the vascular and interstitial compartments by the process of filtration. Filtration is the net effect of four forces, two that tend to move fluid out of capillaries and small venules. and two that tend to move fluid back into them. Hydrostatic pressure is the force of the fluid pressing outward against a surface. Similarly, capillary hydrostatic pressure is a relatively strong outward pushing force that helps move fluid from capillaries into the interstitial area.
Interstitial fluid hydrostatic pressure is a weaker opposing force that tends to push fluid back into capillaries. Blood contains albumin and other proteins known as colloids. These proteins are much larger than electrolytes, glucose, and other molecules that dissolve easily. Most colloids are too large to leave capillaries in the fluid that is filtered.
Therefore, they remain in the blood. Because they are particles, colloids exert osmotic pressure. Blood colloid osmotic pressure, also called oncotic pressure, is an inward pulling force caused by blood proteins that helps move fluid from the interstitial area back into capillaries.
Interstitial fluid-colyte osmotic pressure normally is a very small opposing force. Capillary hydrostatic pressure is strongest at the arterial end of a normal capillary. Fluid moves from the capillary into the interstitial area, bringing nutrients into cells. At the venous end, capillary hydrostatic pressure is weaker and the colloid osmotic pressure of the blood is stronger.
Thus, fluid moves into the capillary at the venous end, removing waste products from cellular metabolism. Disease processes and other factors that alter these forces may cause accumulation of excess fluid in the interstitial space, known as edema. For example, people with heart failure often develop edema. In this situation, venous congestion from a weakened heart that no longer pumps effectively increases capillary hydrostatic pressure, causing edema by moving excessive fluid into the interstitial space.
Inflammation is another cause of edema. It increases capillary blood flow and allows capillaries to leak colloids into the interstitial space. The resulting increased capillary hydrostatic pressure and increased interstitial colloid osmotic pressure produce localized edema in the inflamed tissues. Fluid intake occurs orally through drinking but also through eating because most foods contain some water. Food metabolism creates additional water.
Average fluid intake from these routes for healthy adults is about 2300 milliliters, although this amount can vary widely depending on exercise habits, preferences, and the environment. Other routes of fluid intake include IV, rectal such as enemas, and irrigation of body cavities that can absorb fluid. Although you might think that the major regulator of oral fluid intake is thirst, habit and social reasons also play major roles in fluid intake. Thirst, the conscious desire for water, is an important regulator of fluid intake when plasma osmolality increases or the blood volume decreases. The thirst control mechanism is located within the hypothalamus in the brain.
Osmoreceptors continually monitor plasma osmolality. When it increases, they cause thirst by stimulating neurons in the hypothalamus. People who are alert can obtain fluid or communicate their thirst to others, and fluid intake restores fluid balance. Infants, patients with neurological or psychological problems, and some older adults who are unable to perceive or communicate their thirst are at risk for dehydration. The term fluid distribution means the movement of fluid among its various compartments.
Fluid distribution between the extracellular and intracellular compartments occurs by osmosis. Fluid distribution between the vascular and interstitial parts of the ECF occurs by filtration. Fluid output normally occurs through four organs, the skin, lungs, GI tract, and kidneys. Examples of abnormal fluid output include vomiting, wound drainage, or hemorrhage.
Table 42.2 in your textbook shows average amounts of fluid excretion for healthy adults, although urine output varies greatly depending on fluid intake. Insensible, which is not visible, water loss through the skin and lungs is continuous. It increases when a person has a fever or a recent burn to the skin. Sweat, which is visible and contains sodium, occurs intermittently and increases fluid output substantially.
The GI tract plays a vital role in fluid balance. Approximately 3-6 liters of fluid moves into the GI tract daily and returns to the ECF. The average adult normally excretes only 100 mL of fluid each day through feces. However, diarrhea causes a large fluid output from the GI tract.
The kidneys are the major regulator of fluid output because they respond to hormones that influence urine production. When healthy adults drink more water, they increase urine production to maintain fluid balance. If they drink less water, sweat a lot, or lose fluid by vomiting, their urine volume decreases to maintain fluid balance.
These adjustments primarily are caused by the actions of antidiuretic hormones. hormone or ADH, the renin-angiotensin-aldosterone system or ROS, and atrial natriuretic peptides or ANPs. Antidiuretic hormone or ADH regulates the osmolality of the body fluids by influencing how much water is excreted in urine.
ADH circulates in the blood to the kidneys where it acts on the collecting ducts. Its name, antidiuretic hormone, tells you what it does. It causes renal cells to resorb water, taking water from the renal tubular fluid and putting it back in the blood.
This action decreases urine volume, concentrating the urine while diluting the blood by adding water to it. People normally have some ADH released to maintain fluid balance. More ADH is released if body fluids become more concentrated. Factors that increase ADH levels include severely decreased blood volume, for example dehydration or hemorrhage, pain, stressors, and some medications.
ADH levels decrease if body fluids become too dilute. This allows more water to be excreted in the urine creating a larger volume of dilute urine and concentrating the body fluids back to normal osmolality. The renin-angiotensin-aldosterone system or ROS regulates ECF volume by influencing how much sodium and water are excreted in urine.
It also contributes to regulation of blood pressure. Specialized cells in the kidneys release the enzyme renin, which acts on angiotensinogen, an inactive protein secreted by the liver that circulates in the blood. Renin converts angiotensinogen to angiotensin-1, which is converted to angiotensin-2 by other enzymes in the lung capillaries.
Angiotensin II has several functions, one of which is vasoconstriction in some vascular beds. The important fluid homeostasis functions of angiotensin II include stimulation of aldosterone release from the adrenal cortex. Aldosterone circulates to the kidneys where it causes resorption of sodium and water in isotonic proportion in the distal renal tubules. Removing sodium and water from the renal tubules and returning it to the blood increases the volume of the ECF. To maintain fluid balance, normally some action of the ROS occurs.
Certain stimuli increase or decrease the activity of the system to restore fluid balance. For example, if hemorrhage or vomiting decreases the extracellular fluid volume, or ECV, blood flow decreases through the renal arteries and more renin is released. This increased RAS activity causes more sodium and water retention by helping to restore ECV.
Atrial natriuretic peptide, or ANP, also regulates ECV by influencing how much sodium and water are excreted in urine. Cells in the atria of the heart release ANP when they are stretched, for example by an increased ECV. ANP is a weak hormone that increases the loss of sodium and water in the urine. Thus, ANP opposes the effect of aldosterone.
If disease processes, medications, or other factors disrupt fluid intake or output, imbalances sometimes occur. There are two major types of fluid imbalances, volume imbalances and osmolality imbalances. Volume imbalances are disturbances of the amount of fluid in the extracellular compartment.
Osmolality imbalances are disturbances of the concentration of body fluids. Volume and osmolality imbalances occur separately or in combination. In an ECV imbalance there is either too little or too much of isotonic fluid. Extracellular volume deficit is present when there is insufficient isotonic fluid in the extracellular compartment.
Remember that there is a lot of sodium in normal ECF. With ECV deficit, output of isotonic fluid exceeds intake of sodium-containing fluid. Because ECF is both vascular and interstitial, signs and symptoms arise from lack of volume in both of these compartments.
Table 42.3 lists specific causes and signs and symptoms of ECV deficit. The term hypovolemia means decreased vascular volume and is often used when discussing ECV deficit. In an osmolality imbalance, body fluid becomes hypertonic or hypotonic, which causes osmotic shifts of water across cell membranes. The osmolality imbalances are called hypernatremia and hyponatremia.
Hypernatremia, also called water deficit, is a hypertonic condition. Two general causes make body fluids too concentrated. The loss of relatively more water than salt or a gain of relatively more salt than water. Table 42.3 lists specific causes under these categories. When the interstitial fluid becomes hypertonic, water leaves cells by osmosis and they shrivel.
Signs and symptoms of hypernatremia are those of cerebral dysfunction, which arise when brain cells shrivel. Hypernatremia may occur in combination with ECV deficit. This combined disorder is called clinical dehydration. Hyponatremia, also called water excess or water intoxication, is a hypotonic condition.
It arises from the gain of relatively more water than salt or loss of relatively more salt than water. The excessively dilute condition of interstitial fluid causes water to enter cells by osmosis, causing the cells to swell. Signs and symptoms of cerebral dysfunction occur when brain cells swell. ECV deficit and hypernatremia often occur at the same time. This combination is called clinical dehydration.
The ECV is too low and the body fluids are too concentrated. Clinical dehydration is common with gastroenteritis or other causes of severe vomiting and diarrhea when people are unable to replace their fluid output with enough intake of dilute sodium-containing fluids. Signs and symptoms of clinical dehydration are those of both ECV deficit and hypernatremia.
See table 42.3. You can best understand electrolyte balance by considering the three processes involved in electrolyte homeostasis, electrolyte intake and absorption, electrolyte distribution, and electrolyte output. Review Table 42.4 in your textbook for more information about specific electrolyte intake and absorption, distribution, and output. Factors such as diarrhea, endocrine disorders, and medications that disrupt electrolyte homeostasis cause electrolyte imbalances.
Electrolyte intake greater than electrolyte output or a shift of electrolytes from cells or bone into the ECF causes plasma electrolyte excess. Electrolyte intake less than electrolyte output, or shift of electrolyte from the ECF into cells or bone, causes plasma electrolyte deficit. There are two potassium imbalances, hypokalemia and hyperkalemia.
Hypokalemia is abnormally low potassium concentration in the blood. It results from decreased potassium intake and absorption. a shift of potassium from the ECF into cells, and an increased potassium output.
Common causes of hypokalemia from increased potassium output include diarrhea, repeated vomiting, and use of potassium-wasting diuretics. People who have these conditions need to increase their potassium intake to reduce their risk of hypokalemia. Hypokalemia causes muscle weakness, which becomes life-threatening if it includes respiratory muscles.
It can also cause potentially life-threatening cardiac dysrhythmias. Hyperkalemia is abnormally high potassium ion concentration in the blood. Its general causes are increased potassium intake and absorption, shift of potassium from cells into the ECF, and decreased potassium output. People who have oliguria, or decreased urine output, are at high risk of hyperkalemia from the resultant decreased potassium output, unless their potassium intake also decreases substantially.
Understanding this principle helps you remember to check urine output before you administer IV solutions containing potassium. Hyperkalemia can cause muscle weakness, potentially life-threatening cardiac dysrhythmias, and cardiac arrest. Calcium imbalances include hypocalcemia, which is abnormally low calcium concentration in the blood.
The physiological active form of calcium in the blood is ionized calcium. Total blood calcium also contains inactive forms that are bound to plasma proteins and small anions such as citrate. Factors that cause too much ionized calcium to shift to the bound forms causes symptomatic ionized hypocalcemia. People who have acute pancreatitis frequently develop hypocalcemia because calcium binds to undigested fat in their feces and is excreted.
This process decreases absorption of dietary calcium and also increases calcium output by preventing reabsorption of calcium contained in GI fluids. Hypocalcemia increases neuromuscular excitability, the basis for its signs and symptoms. Hypercalcemia is abnormally high calcium concentration in the blood.
Hypercalcemia results from increased calcium intake and absorption, shift of calcium from bones into the ECF, and decreased calcium output. Patients with some types of cancers, such as lung and breast cancers, often develop hypercalcemia because some cancer cells secrete chemicals into the blood that are related to parathyroid hormone. When these chemicals reach the bones, they cause shift of calcium from bones into the ECF. This weakens bones and the person sometimes develops pathological fractures, that is, bone breakage caused by forces that would not break a healthy bone.
Hypercalcemia decreases neuromuscular excitability, the basis for its signs and symptoms, the most common of which is lethargy. Hypomagnesemia and hypermagnesemia are the magnesium imbalances. Hypomagnesemia is abnormally low magnesium concentration in the blood. Its general causes are decreased magnesium intake and absorption, the shift of plasma magnesium to its inactive bound form, and increased magnesium output.
Signs and symptoms are similar to those of hypocalcemia because hypomagnesemia also increases neuromuscular excitability. Hypermagnesemia is abnormally high magnesium concentration in the blood. End-stage renal diseases cause hypermagnesemia unless the person decreases magnesium intake to match the decreased output. Signs and symptoms are caused by decreased neuromuscular excitability, with lethargy and decreased deep tendon reflexes being most common. See table 42.5 for description of each of these electrolyte imbalances.
The nurse is teaching about the process of passively moving water from an area of lower particle concentration to an area of higher particle concentration. Which process is the nurse describing? A.
Osmosis B. Filtration C. Diffusion D. Active transport The correct answer is A. Osmosis. The process of passively moving water from an area of lower particle concentration to an area of higher particle concentration is called osmosis. Let's look at our case study.
Mrs. Mendoza, age 77, fell at home after having vomiting and diarrhea for 24 hours. She was admitted to the hospital for oral and intravenous or IV fluid therapy after x-rays indicated no fractured bones. Mrs. Mendoza lives alone in an apartment and has no chronic illnesses except osteoarthritis of her hands. Robert is a nursing student assigned to Mrs. Mendoza.
He has cared for other patients with gastrointestinal disorders, but none with fluid and electrolyte imbalances. Robert plans his care by reviewing Mrs. Mendoza's electronic health record or EHR and the health care providers orders. The health care provider orders include IV infusion, of normal saline at 125 milliliters per hour intake and output recordings vital signs every four hours, and daily weights.
Robert knows that Mrs. Mendoza is 77 years old and that this may put her at additional risk for fluid imbalances. He plans his assessment to incorporate how this factor may contribute to the other risks she has for fluid and electrolyte imbalance. What assessment activities do you anticipate Robert will perform?
Robert should do the following. Ask Mrs. Mendoza to describe her nausea and what accompanying signs and symptoms she is experiencing. Conduct an examination of GI and urinary function.
Assess her vital signs. Assess her skin and mucous membranes for indicators of dehydration. Evaluate her laboratory values and electrocardiogram or ECG results. Robert continues his assessment of Mrs. Mendoza using his knowledge of fluid and electrolytes to determine her hydration status with its related assessments. His assessment reveals her current vital signs, temperature 99.6 degrees Fahrenheit, pulse 110 beats per minute and regular, a supine blood pressure of 90 over 58 millimeters of mercury with no changes when standing, and respirations 18 breaths per minute.
Robert's assessments reveal that Mrs. Mendoza has had vomiting and diarrhea for the past six days, has lost weight, has dizziness and increased heart rate on standing, and has postural hypotension. Robert also notes that Mrs. Mendoza has three brown watery stools this morning, as well as hypoactive bowel sounds with abdominal cramping. He also notes decreased skin turgor.
Robert also notes Mrs. Mendoza's low potassium and low sodium. due to prolonged vomiting and diarrhea. What conclusions can Robert draw from this information?
Mrs. Mendoza's vital signs show findings of ECV deficit. What nursing diagnosis should Robert choose? As Robert analyzes these assessment findings, the data clusters provide him cues that lead him to identify dehydration as a priority nursing diagnosis for the plan of care.
Along with this diagnosis, Robert recognizes that Mrs. Mendoza is also experiencing nausea, stating that she is currently slightly nauseated, and diarrhea because of the persistent brown watery diarrhea, including more than six stools yesterday. Robert recognizes that Mrs. Mendoza has risk for impaired skin integrity because of the persistent diarrhea. The goals he sets are Mrs. Mendoza's fluid volume will return to normal by the time of discharge.
Mrs. Mendoza will achieve normal electrolyte balance by discharge. What expected outcomes would Robert establish for these goals? In the nursing care plan, Robert sets outcomes for improving Mrs. Mendoza's fluid status.
The interventions chosen for delivering care will focus on one or more outcomes. After interventions are delivered, Robert will decide if the outcomes have been met, for example by monitoring the outcome of focused assessments and INO. Each outcome needs a time frame for achievement. What additional expected outcome would be included?
Another expected outcome might be that Mrs. Mendoza will not have more than one stool a day in three days. What interventions can you anticipate? Here are some potential interventions.
What are the rationales for these interventions? Rationales include Replacement of body fluid to restore blood volume and normal serum electrolyte levels. An isotonic solution expands the body's intravascular fluid volume without causing a fluid shift from one compartment to another.
Pepto-Bismol is an antidiarrheal and is given to inhibit GI secretions, stimulate absorption of fluid and electrolytes, inhibit intestinal inflammation, and suppress the growth of Helicobacter pylori. INO documents hydration and fluid balance for directing therapy. Daily weights provide reliable data on fluid balance.
Ferrosamide or Lasix is a potassium-wasting diuretic. The body does not store potassium, thus requiring dietary supplements rich in potassium. Robert discusses sources of potassium in the diet with Mrs. Mendoza and writes this documentation note. Denies nausea and reports feeling better. No diarrheal stool since yesterday afternoon around 3 p.m.
On inspection, oral mucosa remains dry without lesions or inflammation. Skin trigger is normal. Bowel sounds are normal in all four quadrants. Abdomen soft to palpation. IV of normal saline is infusing in left cephalic vein and forearm at 40 mls per hour per MD order.
No tenderness or inflammation at IV site. Patient is able to identify 5 food sources for potassium to include in the diet. She is resting comfortably, out of the bed in a chair, and ate all of her breakfast. Will continue to monitor. This information was referenced from Potter, Perry, Stockard and Hall.
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