Fluid & Electrolyte
Basics
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Homeostasis
• Body fluids are in constant
motion transporting
nutrients, electrolytes, and
oxygen to cells while
carrying away waste
products
• Many disease and
treatments affect this
balance
Water
• More important to life than any other nutrient
–
–
–
–
–
–
Carries nutrients and waste products
Participates in metabolic reactions, food digestion
Solvent for minerals, vitamins, glucose
Lubricant and cushion for the joints, eyes, spinal cord
Aids in regulation of body temp
Maintains blood volume
• 60% of an adult’s body weight (more in a child, less
in the elderly)
• Found in foods (but not in alcohol)
• Daily need is about 2000 mL
• 1 liter of water weighs 1 kg
Fluid Intake and Loss
• Intake sources
– Liquids (1500 mL/day)
– Solid foods (800 mL/day)
– Metabolism (300 mL/day)
• Fluid loss routes
– Kidney (1200-1500 mL/day)
– Skin (500-600 mL/day)
– Lungs (400 mL/day)
– GI tract (100-200 mL/day)
– Drainage from
fistulas/drains, GI suction,
salivation
Intake
Measurable
Output
Measurable
Oral fluid, tube
feedings
Urine
Parenteral fluid
Emesis
Enemas
Feces
Retained
irrigation fluid
Drainage from
body cavities
Not Measurable
Not Measurable
Solid foods
Sweating
Metabolism
Vaporization
through lungs
Electrolytes
• Chemicals dissolved in the body fluid, distribution
affects fluid balance
• Regulated by intake, output, acid-base balance,
hormones, and cell integrity
• Sodium
– Major extracellular electrolyte
– Controls and regulate water balance
• Potassium
– Major intracellular electrolyte
– Helps maintain intracellular water balance
– Transmit nerve impulses to muscles and contract skeletal
and smooth muscles
F&E Labs
• Sodium (Na) 135-145
– Determines whether water is retained, excreted, or moved
– Imbalances cause neuro problems
• Potassium (K) 3.5-5.0
– Increased with poor kidney function
– Decreased with excessive urination, diarrhea, vomiting
– Imbalances cause cardiac problems
• Chloride (Cl) 96-106
– Works with sodium to maintain osmotic pressure
– Increased with poor kidney function
– Decreased with excessive vomiting or diarrhea
F&E Labs
• Calcium (Ca) 9.0-10.5
– Transmission of nerve impulses, heart and muscle
contractions, blood clotting, formation of teeth and bone
– Requires Vit D for absorption
• Phosphate (PO4) 3.0-4.5
– Balance is intertwined with calcium
• Other tests
– BUN 6-20
– Creatinine 0.6-1.3
– Hematocrit 42-52% (males), 37-47% (females)
– Total protein, albumin
Lab Normals – Magic 4
Electrolyte
Range
Magic 4
Potassium
3.5 – 5.5
4
Chloride
98 – 106
104
Sodium
135 - 145
140
pH
7.35 – 7.45
7.4
pCO2
35 – 45
40
HCO3
22 – 26
24
FYI – Hematocrit normal is 3 times the hemoglobin (10-14 is normal)
Osmolarity and Osmolality
• Indicates the water balance of the body
• Serum osmo is 285 - 295 mOsm/kg
– High is water deficit (concentrated)
– Low is water excess (dilute)
• Urine osmo is 50-1200 mOsm/kg (avg - 500800 mOsm/kg)
• Together are used to determine what is
causing a sodium imbalance
Distribution of body fluids &
Electrolytes
• Intracellular (2/3) – K+, PO4• Extracellular (1/3) – Na+, Cl– Interstitial (lymph) and transcellular
(cerebrospinal, pleural, peritoneal, synovial fluids)
– Intravascular (blood plasma)
Regulation of Fluid & Electrolyte
Movement
Diffusion
Active
Transport
Filtration
Osmosis
Regulation of Water Balance
Kidneys
Kidneys
(JG cells)
(adrenal cortex)
• Sense low Na, low
volume
• Release renin
• Converts
angiotensinogen to
angiotensin I which
converts to
angiotensin II
• Stimulates release
of aldosterone
(RAAS)
• Senses low serum
osmo or low Na
• Releases
aldosterone
• Reabsorbs Na into
the blood,
increases K
excretion in the
urine
• Increases serum
osmo
Hypothalamus
• Senses high serum
osmo or high Na
• Stimulates thirst
• Triggers release of
ADH (vasopressin)
from posterior
pituitary
• Retains water in
the blood
• Concentrates urine
• Mildly constricts
blood vessels
• Decreases serum
osmo
Heart
• Senses high
volume through
stretch receptors in
the right atrium
• Secretes ANP, BNP
• Inhibits ADH
• Stops the RAAS
• Increases Na
excretion through
the urine
• Dilates blood
vessels
• Decreases serum
osmo
Fluid Spacing
• First spacing
– Normal
• Second spacing
– Edema
• Third spacing
– Ascites
– Burn edema
IV Fluids
• Isotonic
– NS
– D5W
– LR
• Hypertonic
– 3% NS
– D51/2NS
– D10W
• Hypotonic
– 1/2NS
• Plasma Expanders
Gerontologic considerations
• Percent of body weight of water is decreased
• Structural changes in the kidney and decreased renal
blood flow
–
–
–
–
–
•
•
•
•
•
Decreased GFR
Decreased creatinine clearance
Loss of ability to concentrate urine and thus conserve water
Decrease in renin and aldosterone
Increase in ADH and ANP
Loss of subcutaneous tissue
Decrease in thirst mechanism
Musculoskeletal changes
Mental status changes
Incontinence
Assessment Considerations
• History – nutrition, I/Os, insensible losses, use
of diuretics/laxatives, weight changes, kidney
or endocrine disorders, LOC, mental status,
depression, eating disorders, alcohol intake
• Physical – hydration status, skin turgor,
mucous membranes, I/Os
• Dx tests – electrolyte levels, BUN, glucose,
creatinine, pH, bicarb, osmolality, Hgb, Hct,
urine dipstick, urine pH, urine specific gravity
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Image Attribution
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Slide 1 – Flickr by Randy Le'Moine Photography, www.pixabay.com, no attribution
required
Slide 2 – Flickr by TipsTimes, By Anna Frodesiak (Own work) [Public domain or
CC0], via Wikimedia Commons
Slide 3 – www.pixabay.com no attribution required
Slide 10 - http://antranik.org/fluid-compartments-within-the-human-body/
Slide 13 – By James Heilman, MD (Own work) [CC-BY-SA-3.0
(http://creativecommons.org/licenses/by-sa/3.0) or GFDL
(http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Slide 14 - http://medxforum.com/vb/showthread.php?483-What-is-the-name-ofThis-sign-What-is-your-Differential-Diagnosis,
https://myspace.com/dancingsquids/photos/64974051
Slide 15 - "Photo by Chalmers Butterfield"." [CC-BY-2.5
(http://creativecommons.org/licenses/by/2.5), GFDL
(www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0
(http://creativecommons.org/licenses/by-sa/3.0/)], from Wikimedia Commons