Fluid & Electrolyte Balance Flashcards
What do nurses need to know about fluid and electrolyte imbalance to provide safe and competent nursing care?
Fundamental question because many disease & clinical conditions result in alterations
Homeostasis
- a state of equilibrium within the body
- naturally maintained within certain limits
- when we measure potassium or sodium in the blood there is a normal parameter
- people fall outside those boundaries sometimes (clinical manifestations)
- self-regulated process to maintain fluid balance, electrolyte balance, and acid base balance
fluid balance
- hypovolemia
- hypervolemia
- third spacing
- fluid follows electrolytes
when homeostasis is lost we need to:
help the body return to its normal state
what percent of normal body weight is taken up by water
55-60%
newborn
80%
Toddler
70%
Child
65%
adult man
60%
Adult woman
55%
Seniors
50-55%
Body Fluid Compartments
Intracellular
Extracellular
Transcellular
Intracellular (ICF)
- 70%
- low in Na+
- High in K+
- Fluid located within the cells
Extracellular (ECF)
- 2 components
- 30%
1. plasma (intravascular)
2. Interstitial (between cells & lymph) - Transcellular - CFS, GI tract & pleural, synovial and peritoneal spaces (can become a third space)
- high in Na+
- low in K+
Electrolytes
- substances whose molecules dissociate into ions (charged particles) when placed in water
Cations
positively charged
Anions
negatively charged
Electrolyte Composition of Fluid Compartments ICF
- Prevalent cation is K+
- Prevalent anion is PO4
Electrolyte Composition of Fluid Compartments ECF
- Prevalent cation is Na+
- Prevalent anion is Cl-
Mechanisms Controlling Fluid and Electrolyte Movement
- Diffusion
- Facilitated diffusion
- Active transport
- Osmosis
- Hydrostatic pressure
- Oncotic pressure
Diffusion
movement of molecules from high to low concentrations
- occurs in liquids, solids, and gases
- membrane separating two areas must be permeable to diffusing substances.
- requires no energy
Facilitated Diffusion
- the movement of molecules from high to low concentration without energy
- uses specific carrier molecules to accelerate diffusion across the cell membrane
- passive; requires no energy
Active Transport
- process in which molecules move against a concentration gradient (sodium-potassium pump)
- external energy needed
Osmosis
- movement of water between two compartments by a membrane permeable to water but not to solute
- movement from low solute to high solute concentration
- requires no energy
Osmotic Pressure
- amount of pressure required to stop osmotic flow of water - determined by concentration of solutes in solution
Hydrostatic Pressure
Force within a fluid compartment
- BP generated by contraction of the heart
Major force that pushes water out of vascular system at capillary level
Oncotic Pressure
osmotic pressure exerted by colloids in solution (colloidal osmotic pressure)
- albumin is the pull pressure, pulling fluid back into the venous system to return back to the heart. If there is a low level of colloid osmotic pressure because of low amounts of albumin, there wont be that pull and the fluid will stay in the extracellular space and the patient will present with edema.
Amount and duration of movement in capillaries is determined by: (4)
- capillary hydrostatic pressure
- Plasma oncotic pressure
- interstitial hydrostatic pressure
- interstitial oncotic pressure
Fluid shifts: plasma to interstitial fluid shift results in edema + causes
- elevation of hydrostatic pressure
- decrease in plasma oncotic pressure
- elevation of interstitial oncotic pressure
Cause: any kind of change in pressure or proteins
Fluid shifts: interstitial fluid to plasma
- fluid drawn into plasma space with an increase in plasma osmotic or oncotic pressure
- compression stockings decrease peripheral edema by increasing tissue hydrostatic pressure
Water Deficit
- increased ECF osmolaltiy
- dehydration
- associated with symptoms that result from cell shrinkage as water is pulled into vascular system (dry wrinkled skin, sunken eyes, thirst, dry mouth)
Water excess
- decreased ECF osmolality (more diluted)
- develops from gain or retention of excess water
Third Spacing: Phase 1
- fluid moves out of intravascular space –> lymphatic system is unable to compensate sufficiently -> fluid gets trapped in body space -> risk for intravascular FVD with S&S of dehydration
Third Spacing: Phase 2
- fluid moves back into intravascular space -> risk for intravascular FVE, may lead to heart failure
Hypothalamic Regulation
- osmoreceptors in hypothalamus sense fluid deficit or increase
- stimulates thirst and antidiuretic hormone (ADH) release by the posterior pituitary
- result in increased free water and decreased plasma osmolality
- when plasma osmolality normalizes secretion of ADH is suppressed and urinary excretion restored
Pituitary Regulation
- under control of hypothalamus
- posterior pituitary releases ADH
- Stress, nausea, nicotine, and morphine also stimulates ADH release
Adrenal Cortical Regulation
- releases hormones to regulate water and electrolytes
Glucocorticoids (cortisol) - anti-inflammatory effect; increase glucose
Mineralcorticoids (aldosterone) - enhance Na+ retention, enhance K+ excretion
Renal Regulation
- kidneys are primary organ for regulating fluid and electrolyte balance
- adjust urine volume
- selective reabsorption of water and electrolytes
- renal tubules are sites of action of ADH and aldosterone
What are the two hormones that help regulate tubular reabsorption and secretion
Antidiuretic Hormone (ADH) Aldosterone
Antidiuretic Hormone (ADH)
- decreased blood volume stimulates release by the pituitary gland which makes the distal tubule and collecting ducts permeable to water allowing it to be absorbed by capillaries and returned to circulation (INCREASES BLOOD AND FLUID VOLUME)
Aldosterone
released by the adrenal cortex acts in the distal tubule to reabsorb water and sodium and potassium ions are excreted (INCREASES FLUID AND BLOOD VOLUME)
Kidney Function and BP regulation
- if volume is depleted, then renin-angiotensin-aldosterone system maintains BP
- kidneys secrete renin
- reninforms angiotensin I
- angiotensin I converts to angiotensin II which stimulates aldosterone production. aldosterone causes an increase in salt and water reabsorption in the bloodstream from the kidneys increasing BV
Caridac Regulation
atrial natriuretic factor (ANF)
- hormone released by cardiac atria in response to increased atrial pressure (increased BV)
- primary action of ANF are vasodilation and increase urinary excretion of sodium and water with decreased BV
Gastrointestinal Regulation
- small amounts of water are eliminated by the gastrointestinal tract in feces
- diarrhea and vomiting can lead to significant fluid and electrolyte loss
Insensible Water Loss
Invisible vaporization from lungs and skin to regulate body temperature
- approx: 900 ml/day is lost
- no electrolytes are lost
Sodium is a cation that plays a major role in:
- generation and transmission of nerve impulses and muscle contractions
- maintains fluid balance
- regulates blood pressure
Hypernatremia
- elevated serum sodium occuring with water loss or sodium gain
- causes hyperosmolality leading to cellular dehydration
- primary protection is thirst from hypothalamus
- sodium intake in excess or inadequate water intake can lead to hypernatremia
Manifestations of Hypernatremia (WAITLSC)
W - weight loss related to water loss A - agitation I - Impaired LOC T - thirst L - lethargy S - seizures C - coma
Why do you need to reduce serum sodium levels gradually?
Serum sodium levels must be reduced gradually to avoid cerebral edema (because the water is more dilute and will move easier into the brain cells)
pressures for fluid exchange in capillary
- interstitial fluid also has oncotic and hydrostatic pressure
- arterial end of capillary will have higher hydrostatic pressure and will move fluid out of the capillary
- venous end will have lower hydrostatic pressure and greater oncotic pressure and fluid will be pulled into the capillary
Third Spacing
- when fluid leaves intravascular and leak into another compartment (mostly transcellular - which is any place where large amounts of fluid are not supposed to accumulate)
- can cause hypovolemic shock because the fluid is not being kept in the vascular system it is leaking out
Nursing Intervention for Third-Spacing (6)
- assess for S&S of shock & intravascular FVD (Tachycardia, hypotension, postural vitals)
- monitor urine output
- monitor electrolyte imbalance
- monitor fluid balance (daily weights, abdominal girth for ascites)
- provide fluids and/or IV albumin as ordered
- Assess for intravascular hypervolemia and hypokalemia when third space fluids decreased
