Fluids & Electrolytes Pt 1 Flashcards
Homeostasis
- State of equilibrium in body
- Naturally maintained by adaptive responses
- Body fluids and electrolytes are maintained within narrow limits
Water Content of the Body
- 50-60% of body weight in adult
> Greater in men than women as men have more lean body mass - 45-55% in older adults
- 70-80% in infants
> Varies w/gender, body mass, & age
Compartments
- Intracellular fluid (ICF) [2/3 body water]
Extracellular fluid (ECF) [1/3 body water]
- Intravascular (plasma) [1/3 of ECF]
- Interstitial [2/3 of ECF]
> Transcellular
- CSF, fluid in GI tract, pleural, synovial, peritoneal, intraocular, pericardial
Fluid Compartments of the Body
- ICF (40%)
- ECF (20%) [intravascular & interstitial]
- Solids (40%)
! Water is the key to the proper transport & delivery of nutrients, electrolytes, & other substances to organs, tissues, & cells
Therefore, if you have changes in the amounts of water and/or electrolytes, it can affect ALL of the functioning of the cells, organs, & tissues
Electrolyte Composition
ICF
Prevalent cation is ?
Prevalent anion is ?
K+
PO3-4 (phosphate)
ECF
Prevalent cation is ?
Prevalent anion is ?
Na+
Cl-
Mechanisms Controlling Fluid & Electrolyte Movement
- Filtration
- Diffusion/facilitated diffusion
- Osmosis
?
Is the movement of fluid through a cell or blood vessel membrane b/c of hydrostatic pressure differences on both sides of the membrane
If nothing stops it, water can move from a higher hydrostatic pressure space to a lower one
Filtration
?
Is reached when enough fluid leaves one space & enters the other until the hydrostatic pressure is equal
Equilibrium
?
Is the movement of molecules from high to low concentration
Liquids, solids, & gases; membrane separating 2 areas must be permeable to diffusing substance; requires no energy
Gases (O2, N, CO2) & other substances (i.e., urea) can permeate through cell membranes & are distributed throughout body
Diffusion
- Differences in concentrations and/or permeability allow or prevent these shifts
- i.e., Na+ often times has to cross an impermeable membrane & needs the Na+ pump & energy provided by ATP
- Can be facilitated diffusion, like w/glucose, needs assistance of insulin to cross
! Diffusion is important in the transport of most electrolytes & particles throughout cell membrane
Na+ K+ Pump
By active transport, Na+ moves out of the cell & K+ moves into the cell to maintain concentration difference
- Energy for this mechanism is ATP, made in cell’s mitochondria
?
Movement of H2O between 2 compartments by a membrane permeable to H2O but not to solute
- Moves from low to high concentration
- Requires no energy
Osmosis
- Stops when the concentration differences disappear, or when hydrostatic pressure builds and is sufficient to oppose any further movement of water
- The thirst mechanism is an example of how osmosis helps maintain homeostasis
- Feeling of thirst is caused by activation of cells in the brain that respond to changes in ECF osmolarity
- A rising blood osmolarity, or a decreasing blood volume triggers the sensation of thirst
Filtration: Clinical Significance: Blood Pressure
- BP is an example of hydrostatic filtering forces; moves whole blood from the heart to capillaries where filtration can occur to exchange water, nutrients, and waste products between blood & tissues
Clinical Significance: Edema
- Edema develops w/changes in normal hydrostatic pressure differences; occurs when the pressure gradients aren’t balanced & fluid ends up in the interstitial spaces
> i.e., Rt-sided HF
Effects of Water Status on RBC
- If a cell is surrounded by hypotonic fluid, water moves into the cell, causing it to swell & possibly to burst
- If a cell is surrounded by hypertonic fluid, water leaves the cell to dilute the ECF; the cell shrinks & eventually may die
Fluid Balance
- Fluid intake
- Fluid loss - minimum amount of urine needed to excrete toxic waste products is 400-600 mL; insensible water loss
?
Is the invisible vaporization from the lungs and skin that helps regulate body temperature; 600-900 mL/day
Insensible water loss
- Accelerated body metabolism that occurs with increased body temp & exercise increases the amt of water loss; insensible perspiration causes only water loss
- Excessive sweating (sensible perspiration) caused by exercise, fever, or high environmental temperatures may lead to large losses of water & electrolytes
?
Is an abnormal accumulation of interstitial fluid (i.e., edema)
Second spacing
?
Is a normal distribution of fluid in ICF and ECF
First spacing
?
Is fluid accumulation in part of body where it is not easily exchanged w/ECF (i.e., ascites, sequestration of fluid in abdominal cavity w/peritonitis, & edema assoc w/burns, trauma, or sepsis)
Third spacing
Hormonal Regulation of BP
- Aldosterone
- ADH
- Natriuretic peptides
?
Is secreted by the adrenal cortex & regulates sodium & water reabsorption by the kidneys
Aldosterone
?
Is produced by the hypothalamus to reduce diuresis & increase water retention if serum osmolarity inc or if blood volume dec
ADH (aka, vasopressin)
?
These hormones are secreted in response to increased blood volume & BP
They then bind to the receptor sites in nephrons of the kidney that create effects that are OPPOSITE to aldosterone; this then dec the BP by causing vasodilation & reduces fluid volume by inc excretion of sodium & water
Natriuretic peptides
i.e., ANP [atrial], BNP [brain]
! This is why 1 of the tests for HF is elevated BNP
Regulation of Water Balance
- Hypothalamic-pituitary regulation
> Osmoreceptors in hypothalamus sense fluid deficit or increase
> Deficit stimulates thirst & ADH release
> Decreased plasma osmolality (water excess) suppresses ADH release
- Renal regulation
> Primary organs for regulating fluid & electrolyte balance
> Adjusting urine volume
- Selective reabsorption of water & electrolytes
- Renal tubules are sites of action of ADH & aldosterone
- Adrenal cortical regulation
> Releases hormones to regulate water & electrolytes
> Glucocorticoids
- Cortisol
> Mineralocorticoids
- Aldosterone
Glucocorticoids primarily have an anti-inflammatory effect & increase serum glucose levels
Mineralocorticoids cause sodium retention & potassium excretion; water is retained w/sodium
Decreased renal perfusion or decreased sodium delivery to the distal portion of the renal tubule activates the ____, which results in aldosterone secretion
renin-angiotensin-aldosterone system (RAAS)
Increased serum potassium, decreased serum sodium, & release of ACTH from anterior pituitary also stimulate release of aldosterone
- Gastrointestinal regulation
- Oral intake accounts for most water
- Small amounts of water are eliminated by GI tract in feces
- Diarrhea & vomiting can lead to significant fluid & electrolyte loss
Gerontologic Considerations
- Structural changes to kidneys decrease ability to conserve water
- Hormonal changes lead to decrease in renin & aldosterone and increase in ADH & ANP
- Loss of subcutaneous tissue leads to increased loss of moisture
- Reduced thirst mechanism results in decreased fluid intake
- Functional changes affect ability to independently obtain fluids
- Nurse must assess for these changes & implement treatment accordingly
Fluid & Electrolyte Imbalances
- Directly caused by illness or disease (burns or HF)
- Result of therapeutic measures (IV fluid replacement or diuretics)
- Imbalances as deficits or excesses
- i.e., a pt w/prolonged NG suction will lose Na+, K+, H+, & Cl-
> Imbalances may result in a deficiency of both Na+ & K+, a fluid volume deficit, & a metabolic alkalosis resulting from loss of HCl
! Restoring fluid balance & preventing injury
ECF volume deficit ( ? )
hypovolemia
- Abnormal loss of normal body fluids, inadequate intake, or plasma-to-interstitial fluid shift
- Vomiting, diarrhea, fistula drainage, hemorrhage, diuresis; also 2nd to dz process like diabetes insipidus, burns, hemorrhage, & intestinal obstruction
! Do not use interchangeably w/dehydration as dehydration refers to loss of pure water alone w/o corresponding loss of sodium
- Clinical manifestations r/t loss of vascular volume as well as CNS effects
- Restlessness, drowsiness, lethargy, confusion, postural hypotension, tachycardia, tachypnea, weakness, dizziness, wt loss, seizures, coma
- Skin turgor, capillary refill, & urine output dec’d
- Treatment: replace water & electrolytes w/balanced IV solutions
- LR, isotonic (0.9%) NaCl, blood
ECF volume excess ( ? )
hypervolemia
- Excessive intake of fluids, abnormal retention of fluids (HF, renal failure), or interstitial-to-plasma fluid shift (inc intravascular volume)
- Clinical manifestations r/t excess volume
- HA, confusion, lethargy, peripheral edema, JVD, bounding pulse, HTN, dyspnea, crackles, pulmonary edema, muscle spasms, wt gain, seizures, coma
- Treatment: remove fluid w/o changing electrolyte composition or osmolality of ECF
- Diuretics & fluid restriction
?
- Excess fluid volume (r/t inc water &/or sodium retention)
- Impaired gas exchange (r/t water retention leading to pulmonary edema)
- Risk for impaired skin integrity (b/c peripheral edema)
- Activity intolerance (b/c inc water retention, fatigue, & weakness)
- Disturbed body image (d/t appearance of edema)
- Potential complications: pulmonary edema, ascites
Hypervolemia
?
- Deficient fluid volume & Decreased CO (r/t excessive ECF losses or dec fluid intake)
- Risk for deficient fluid volume
- Potential complication: hypovolemic shock (if fluid loss continues w/o replacement)
Hypovolemia
Generate Solutions & Take Action
- I&O
- Monitor cardiovascular changes (changes in BP, pulse force, JVD)
- Assess respiratory status
> Excess = pulm congestion/edema, SOB, moist crackles
> Deficit = inc RR - Neurologic changes, skin assessment
- Specific gravity <1.005 = FLUID OVERLOAD
- Water = ~1.000
- Ideal = 1.002 - 1.030
> The higher the # the more dehydrated you might be
- Closer the # is to 1.000, greater the FLUID EXCESS
Assessment of Skin Turgor
- Usual eval sites = over sternum, abdomen, & anterior forearm
! Dec skin turgor is less predictive of fluid deficit in older persons b/c loss of tissue elasticity
