Fluids and Electrolytes Flashcards
Intracellular Fluid (ICF)
- fluid inside cells
- 2/3 of body fluid
- primarily located in skeletal muscle mass
Extracellular Fluid (ECF)
- fluid outside cells
- 1/3 of body fluid
- transport system that carries nutrients and waste to and from cells
3 compartments:
- interstitial
- intravascular
- transcellular (synovial fluid, CSF, pleural and peritoneal fluid)
Osmolarity
concentration of particles (solutes) dissolved in a solution (solvents)
measure for evaluating concentration of plasma, urine and body fluids
*plasma osmolarity is usually between 280 and 300 mmol/kg
Tonicity
the ability of an extracellular solution to make water move into and out of a cell by osmosis
- related to its osmotic concentration (osmolarity)
a. solution with LOW osmotic concentration has FEWER solute particles per litre = LOWER TONICITY
b. solution with HIGH osmotic concentration has MORE solute particles per litre = HIGH TONICITY
Osmosis
movement of water between two compartment separated by semipermeable membrane
water moves from areas of low solute concentration to areas of high solute concentration
Hypertonic IV Fluid
fluid leaves cells
Hypotonic IV Fluid
fluid goes into cells
Isotonic IV Fluid
no osmosis, not moving in or out
Hydrostatic pressure
- force within a fluid compartment
- major force that pushes water out of the vascular system at the capillary level
Oncotic pressure
- colloid osmotic pressure
- osmotic pressure exerted by protein, such as albumin, to pull water into circulatory system
*albumin accounts for 70% of oncotic pressure
Filtration
fluid moves out of the capillary into the interstitial space
Reabsorption
fluid moves back into capillary from the interstitial space
Net filtration
Starling hypothesis
Forces favouring filtration
a. capillary hydrostatic pressure (blood pressure)
b. interstitial oncotic pressure (water pulling)
Forces opposing filtration
c. plasma oncotic pressure (water pulling)
d. interstitial hydrostatic pressure
Albumin and oncotic pressure
when albumin levels are too low, water leaves vasculature and going into interstitial space
= edema, swelling!
albumin is manufactured by the liver
Causes of edema
- increased capillary permeability
- burns, inflammation - changes in plasma protein level
- cirrhosis, malnutrition, kidney disease causing loss of plasma protein - increased capillary hydrostatic pressure
- salt and water retention, heart failure
*lymphatic system usually absorbs fluids but if lymph system is blocked, fluid gets stuck
Third spacing
fluid accumulation in part of the body where it is not easily exchanged with ECF
increased permeability causes protein to leak out, which then pulls water out as well
i.e. patient with severe infection
S/S of Third Spacing
a. decreased urine output
b. increased HR
c. decreased BP
d. increased weight
e. edema, ascites
Hypothalamic-pituitary Regulation
osmoreceptors in hypothalamus sense fluid deficit or excess
- fluid excess»_space; secretion of ADH is suppressed at posterior pituitary»_space; urinary excretion of water
- fluid deficit»_space; secretion of ADH is increased»_space; water reabsorption
**Fluid Deficit: hypothalamus stimulates thirst and ADH release
Adrenal Cortical Regulation
Fluid Deficit: hypothalamus signals anterior pituitary to secrete ACTH, which then signals
adrenal cortex to secrete
a. cortisol
b. aldosterone
which increases Na+ reabsorption and K+ excretion
Renal regulation
primary organ for regulating fluid and electrolyte balance
adjust urine volume by:
a. selective reabsorption of water and electrolytes
b. renal tubules are sites of action of ADH and aldosterone
Cardiac regulation
Natriuretic peptides are antagonists to the RAAS
- produced by cardiomyocytes in response to increased atrial pressure
**natriuretic peptides suppress secretion of aldosterone, renin, and ADH to decrease blood volume and pressure
Gastrointestinal regulation
INPUT
- oral intake
OUTPUT
- 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
- approximately 600 to 900ml/day
- no electrolytes are lost
Age related considerations
a. structural changes in kidney
b. hormonal changes
c. loss of subcutaneous tissue
d. reduced thirst mechanism
Water content across lifespan
Infant: 70-80% water
Adult: 50-60% water
Older Adult: 45-55&
most water are stored in muscle tissue!
*more fat = less water!
Hypovolemia
ECF volume deficit
- decrease capillary hydrostatic pressure and fluid transport
3 Main Causes:
- fluid loss
- reduced fluid intake
- fluid shift from intravascular space
How does the body respond to hypovolemia?
a. decreased renal blood flow triggers RAAS leading to increased ADH and aldosterone production
b. thirst response
c. increase in heart rate and vascular resistance
**When body cannot compensate anymore, hypovolemic shock occurs
S/S of Hypovolemia
- hypotension
- tachycardia, weakened pulse
- thirst
- flattened neck veins
- dry mucous membrane/skin, decreased skin turgor
- weight loss
- decreased urine output
- prolonged capillary refill
- sunken eyes
- confusion, headache, changes in LOC
Hypovolemia Assessment
a. intake and output
b. cardiovascular changes (HR, BP)
c. respiratory changes
d. daily weights
e. skin assessment
f. neurological function
- LOC, PERRLA, voluntary movement, muscle strength, reflexes
Treatment for Hypovolemia
a. oral or parenteral fluids
b. fluid resuscitation (IV infusion)
c. blood/blood product if hemorrhage
d. antidiarrheals/antiemetics as needed
*urine output is a good indicator of fluid volume returning
Why are infants more predisposed to serious, rapid fluid volume deficits?
- surface area to volume - 3 times greater than adults
- ability to concentrate urine
- metabolic rate
Hypervolemia
fluid volume excess
- abnormal increase in volume circulating fluid
3 Main Causes:
- risk for sodium and water retention
- excessive sodium and water intake
- fluid shifts to the intravascular space
How does the body respond to Hypervolemia?
a. circulatory overload
b. increased cardiac contractility and increased bp
c. increased capillary hydrostatic pressure
d. shift of fluid into interstitial space
e. edema
f. increased bp inhibits ADH and aldosterone, which increases urinary elimination
**If hypervolemia is severe, CV dysfunction, heart failure and pulmonary edema may develop
S/S of Hypervolemia
- hypertension
- tachypnea, dyspnea and crackles
- cyanosis
- decreased tissue perfusion
- rapid, bounding pulse
- headache
- distended neck veins
- moist skin
- weight gain
- edema
- muscle twitching
Hypervolemia Assessment
a. intake and output
b. cardiovascular changes (HR, BP)
c. respiratory changes
d. daily weights
e. skin assessment
f. neurological function
- LOC, PERRLA, movment of extremities, muscle strength, reflexes
Treatment for Hypervolemia
a. remove fluid without changing electrolyte composition or osmolarity of ECF
b. promote output and treat underlying condition
c. restrict sodium and fluid intake
d. diuretic therapy - furosemide
e. dialysis
Electrolytes
substances which split into ions when placed in a solution
+ cations are positively charged particles
- anions are negatively charged particles
Prevalent Cations and Anions in ECF and ICF
ECF
cation: Na+
anion: Cl-
ICF
cation: K+
anion: phosphate
Sodium Reference Range
135-145 mmol/L
Regulation of sodium balance
a. ADH
increases water reabsorption in the kidneys, reduces sodium concentration
b. aldosterone
promotes sodium reabsorption in the distal nephron
c. atrial natriuretic hormone (ANH)
promotes sodium excretion
*changes in serum Na+ may reflect sodium or water imbalance, usually in ECF volume
Hypernatremia Critical Value
> 160 mmol/L
results from water loss
osmotic shift from ICF to ECF»_space; cellular dehydration
S/S of Hypernatremia
a. intense thirst (early symptom)
b. agitation, restlessness
c. water loss
dry swollen tongue, weakness, postural hypotension, decreased central venous pressure, weight loss
d. sodium gain
flushed skin, weight gain, peripheral and pulmonary edema, increased bp, increased CVP
Treatment of Hypernatremia
a. treat underlying cause
b. oral fluid or IV solution (D5W or hypotonic 0.45%NS)
c. diuretics
d. monitor sodium levels
Hyponatremia Critical Value
<120 mmol/L
results from excess sodium loss or water gain
osmotic shift from ECF to ICF»_space; intracellular edema
Dilutional Hyponatremia (water intoxication)
resulting from large intake of free water or replacement fluid loss with IV D5W
water enters into cells, coma results from swelling brain tissues
- babies under 6 months
- lethal volume around 6L in a 165lb adult
S/S of Hyponatremia
Mild: not associated with any symptoms
Moderate: lethargy, weakness, confusion, headache, nausea, vomiting, abdominal cramps
Severe: muscle twitching, seizure, coma, death
Treatment of Hyponatremia
a. treat underlying cause
b. replace lost sodium (PO or IV) SLOWLY
c. get rid of excess water (loop diuretics)
d. if primary water deficit, prevent water loss or water replacements
Potassium
- transmission and conduction of nerve and muscle impulses
- cellular growth
- maintenance of cardiac rhythms
- acid-base balance
Potassium Reference Range
3.5-5.0 mmol/L
Sources of Potassium
- fruits and vegetables
- salt substitutes
- potassium medications (PO or IV)
- stored blood
Regulation of Potassium Balance
aldosterone, insulin, epinephrine and alkalosis facilitate K+ into the cells
insulin deficiency, aldosterone deficiency, acidosis and strenuous exercise facilitate K+ out of cells
*maintained by sodium potassium pump
Hyperkalemia Critical Value
> 6.5 mmol/L
Causes of Hyperkalemia
a. massive intake
b. impaired renal excretion
c. shift from ICF to ECF
*common in renal failure
HYPEREXCITABILITY: more intense action potential»_space; longer refractory period»_space; slower movement
S/S of Hyperkalemia
Mild: no specific symptoms
Moderate: tingling of lips and fingers, restlessness, intestinal cramping and diarrhea, ECG changes
Severe: muscle weakness, loss of muscle tone, flaccid paralysis, cardiac arrest
- arrhythmia can lead to death
ECG changes and Hyperkalemia
- 5-6.5 mmol/L: tall, peaked T-wave
- 5-7.5 mmol/L: loss of P wave
7-8 mmol/L: widening of QRS complex
8-10 mmol/L: cardiac arrythmias, sine wave pattern, asystole (beepppp)
Treatment of Hyperkalemia
a. telemetry, monitoring
b. eliminate oral or parenteral K+ intake
c. increase elimination of K+ (diuretics, dialysis, kayexalate)
d. force K+ form ECF to ICF by IV insulin
e. reverse membrane effects using calcium gluconate IV
Hypokalemia Critical Value
< 2.5 mmol/L
Causes of Hypokalemia
a. abnormal losses of K+ via kidneys or GI tract
b. magnesium deficiency
c. metabolic alkalosis
S/S of Hypokalemia
Mild: no specific symptoms
Moderate: muscle weakness/spasms, fatigue, numbness, tingling, constipation, palpitations
Severe: confusion, lethargy, weak pulses, hypotension, muscle cramps and pain, cardiac arrhythmias
ECG changes and Hypokalemia
shallow T wave
ST depression
prominent U wave
Treatment of Hypokalemia
a. treat underlying cause
b. telemetry, monitoring
c. KCl supplements (PO or IV)
should not exceed 10-20 mmol/hr
