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NUR 200 chapter 38 Fluids, Electrolytes, and Acid- Base Balance
Terms in this set (32)
Water is the primary body fluid.
Water content varies with age, sex, and adipose tissue.
Water contains solutes.
Body Fluid Compartments
Within the cells
is contained within the cells. Essential for cell function and metabolism, it accounts for approximately 40% of body weight.
is outside the cells. ECF carries water, electrolytes, nutrients, and oxygen to the cells and removes the waste products of cellular metabolism. ECF accounts for 20% of body weight. ECF exists in three main locations in the body:
Interstitial fluid lies in the spaces between the body cells. Excess fluid within the interstitial space is called edema.
Intravascular fluid is the plasma within the blood. Its main function is to transport blood cells.
Transcellular fluid includes specialized fluids, such as cerebrospinal, pleural, peritoneal, and synovial fluid; and digestive juices.
Movement of Fluids and Electrolytes
involves movement of water (or other pure solute) across a membrane from an area of a less concentrated solution to an area of more concentrated solution. Water moves across the membrane to dilute the higher concentration of solutes. Recall that a solute is a substance dissolved in body fluid. Solutes may be crystalloids or colloids.
is the movement of both water and smaller particles from an area of high pressure to one of low pressure (Fig. 38-4). Hydrostatic pressure is the force created by fluid within a closed system; it is responsible for normal circulation of blood. In other words, blood flows from the high-pressure arterial system to the lower pressure capillaries and veins.
occurs when molecules (e.g., electrolytes) move across cell membranes from an area of low concentration to an area of high concentration. Active transport requires energy expenditure for the movement to occur against a concentration gradient. Adenosine triphosphate (ATP) is released from the cell to enable certain substances to acquire the energy needed to pass through the cell membrane.
Primarily through drinking fluids
IOM recommendation: 2700 mL/day women, 3500 mL/day men
20% from food/metabolism of food
Fluid intake regulated by thirst
Change in plasma osmolality
Urine: 1500 mL/day
Feces: 100 to 200 mL/day
Antidiuretic hormone (ADH)
Brain naturetic factor
antidiuretic hormone (ADH)
Pressure sensors in the vascular system stimulate or inhibit the release of antidiuretic hormone (ADH) from the pituitary gland. ADH causes the kidneys to retain fluid. If fluid volume within the vascular system is low, fluid pressures within the system decrease, and more ADH is released. If fluid volume (and therefore pressure) increases, less ADH is released, and the kidneys eliminate more fluid. ADH is also produced in response to a rise in serum osmolality, fever, pain, stress, and some opioids.
When extracellular (i.e., intravascular) fluid volume is decreased, receptors in the glomeruli respond to the decreased perfusion of the kidneys by releasing renin. Renin is an enzyme responsible for the chain of reactions that converts angiotensinogen to angiotensin II. Angiotensin II acts on the nephrons to retain sodium and water and directs the adrenal cortex to release aldosterone.
This stimulates the distal tubules of the kidneys to reabsorb sodium and excrete potassium. Sodium reabsorption results in passive reabsorption of water, thereby increasing plasma volume and improving kidney perfusion. When fluid excess is present, renin is not released, and this process stops.
This affects fluid volume by influencing cardiac output. An increase in thyroid hormone causes an increase in cardiac output, thereby increasing glomerular filtration rate and urine output. A decrease has the opposite effect.
Hypovolemia occurs when there is a proportional loss of fluid and electrolytes from the ECF. Loss of blood volume is called hypovolemia.
Dehydration describes a state of negative fluid balance in which there is a loss of water (hydro water) from the intracellular, extracellular, or intravascular spaces.
Weight loss of a sudden 5% loss of body weight is considered clinically significant. When loss approaches 8%, fluid loss is severe. A sudden loss of 15% of body weight due to fluid loss is usually fatal.
The patient with fluid volume deficit usually has elevated blood urea nitrogen (BUN)-to-creatinine ratio and elevated hematocrit. Both values increase because there is less water in proportion to the solid substances being measured.
Hypervolemia: This involves excessive retention of sodium and water in the ECF. Fluid volume excess can result from excessive salt intake, disease affecting kidney or liver function, or poor pumping action of the heart. The retained sodium increases osmotic pressure in the ECF. This pressure pulls fluid from the cells into the ECF.
Overhydration: The blood pressure is elevated, pulse is bounding, and respirations are increased and shallow. The neck veins may become distended. Along with increased intravascular volume, excess ECF may accumulate in the tissues, especially in dependent areas, as edema. The skin is pale and cool. Urine output becomes dilute, and volume increases. The patient rapidly gains weight. In severe fluid overload, the patient develops moist crackles in the lungs, dyspnea, and ascites (excess peritoneal fluid). Hemodilution causes BUN, hematocrit, and the specific gravity of the urine to decrease.
Extracellular fluid (ECF): regulates fluid volume
Intracellular fluid (ICF): muscle contraction; cardiac conduction
Bone health; neuromuscular function; cardiac function
Insufficiency leads to osteoporosis
ICF; bone; many cellular functions
Alcoholism leads to low levels
ECF; bound to other ions
Bound with calcium in teeth and bones; inverse relationship
ICF and ECF; acid-base balance
Regulated by kidneys
Produced by body to act as buffer
Acid: compound that contains hydrogen (H+) ions
Base: compound that accepts hydrogen ions
Amounts in solution reflected by pH
Acceptable range for serum: 7.35 to 7.45
Measured by arterial blood gases (ABGs)
They prevent wide swings in pH. A buffer system consists of a weak acid and a weak base. Buffer molecules keep strong acids or bases from altering the pH either by absorbing or releasing free hydrogen ions.
The lungs are the second line of defense to restore normal pH. They control the body's carbonic acid supply via carbon dioxide retention or removal. When the serum pH is too acidic (pH is low), the lungs remove carbon dioxide through rapid, deep breathing. This reduces the amount of carbon dioxide available to make carbonic acid. If the serum pH is too alkaline (pH is high), the lungs try to conserve carbon dioxide through shallow respirations. This system works with the carbonic acid-sodium bicarbonate buffer system to maintain the 20:1 ratio of base to acid.
The last line of defense is the kidneys, which regulate the concentration of plasma bicarbonate. They can neutralize more acid or base than either the respiratory system or the chemical buffers. If the serum pH is too acidic, the kidneys conserve additional bicarbonate to neutralize the acid. If the serum pH is too alkaline, the kidneys excrete additional bicarbonate to lower the amount of base and thereby decrease the pH. The kidneys also buffer pH by forming acids and ammonium (a base). Although the renal system is very effective at altering pH, it is slow. It may take up to 3 days to return the pH to normal limits. This process is known as compensation. The pH returns to normal, but the carbon dioxide or bicarbonate level is abnormal.
Serum pH below 7.35
Respiratory cause: retention of CO2
Metabolic cause: loss of bicarbonate
Serum pH above 7.45
Respiratory cause: blowing off CO2
Metabolic cause: increase in bicarbonate
Nursing Assessment: Fluid, Electrolyte, Acid-Base Imbalances
Head-to-toe physical assessment
Vital signs: temperature, pulse, respirations, blood pressure
Oral electrolyte supplements
Limiting or facilitating oral fluid intake
Parenteral replacement of fluids and/or electrolytes
Administer prescribed IV fluids based on patient's condition
To promote fluid and electrolyte balance, most people need to limit their sodium intake and increase their dietary potassium and calcium. As previously discussed, most Americans consume more sodium than they should and not enough potassium and calcium. Teach clients to eat foods rich in potassium and calcium every day and to avoid sodium-rich foods. For example, instruct clients to read food labels, particularly when trying to limit sodium intake.
oral electrolyce supplements
Encourage clients to take potassium supplements with juice to mask the taste. Teach clients to take supplements as prescribed to maintain electrolyte balance. Remind clients that supplements are medications and should be viewed as part of the treatment plan. If the client's medications are altered, review the continued need for supplements. Caution clients that salt substitutes contain potassium. If the client has been advised to use salt substitutes, review the need for potassium supplements.
Parenteral replacement of fluids and/ or electrolytes
When fluid loss is severe or the client cannot tolerate oral or tube feedings, fluid volume is replaced parenterally. IV therapy is the administration of fluids, electrolytes, medications, or nutrients by the venous route.
remain inside the blood vessels. As a result, they are useful for clients with hypotension or hypovolemia. Clients at risk for fluid volume excess must be closely monitored when they receive isotonic fluid replacement, because they may easily develop fluid overload.
The osmolality of a ------- solution is less than that of serum. Therefore, when infused, these solutions pull body water from the intravascular compartment into the interstitial fluid compartment.------------fluid is used to correct cellular dehydration.
Never give ------- solutions to patients at risk for increased ICP because they can cause/exacerbate cerebral edema.
The osmolality of ----------- fluids is higher than that of serum. When administered, they pull fluids and electrolytes from the intracellular and interstitial compartments into the intravascular compartment. ---------- fluids can help stabilize blood pressure, increase urine output, and reduce edema.
Replacement of blood and blood products
Obtain a set of vital signs
Ensure patient IV
Remain with patient for 15 min after infusion starts
Monitor for transfusion reaction (allergic, bacterial, febrile, hemolytic, circulatory overload)
STOP THE BLOOD TRANSFUSION
Assess patient and notify the provider
It is critical to identify the patient and the blood product when transfusing blood. Before beginning a transfusion, verify the written prescription for the blood product, and obtain a set of vital signs 5 to 15 min before initiating the infusion. If the patient's temperature is elevated, inform the primary care provider before hanging the transfusion. Most patients experience a minor elevation in temperature after a transfusion is given. A preexisting elevated temperature may exacerbate this response. As a result, the premedication may be prescribed.
To help prevent transfusion reactions, be extremely careful in identifying the patient and the blood, start the transfusion slowly, remain with the patient for the first 5 min of the transfusion, and assess again at 15 min.
If a transfusion reaction occurs, stop the transfusion, assess the patient, and keep the vein open with normal saline. Notify the provider. Return the blood and tubing in a biohazard bag to the blood bank.
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