Fluids and Electrolytes Flashcards
Homeostasis
State of equilibrium within the body; naturally maintained by adaptive responses. Body fluids and electrolytes are maintained within narrow limits.
What fraction of body water is intracellular fluid
2/3 of body water
What fraction of body water is extracellular fluid
1/3 of body water; interstitial fluid, intravascular fluid (plasma), and cerebral spinal fluid
Sodium (cation) ranges
ECF: 135-145 mEq/L
ICF: 10-14 mEq/L
Chloride (anion) ranges
ECF: 98-106 mEq/L
ICF: 3-4 mEq/L
Potassium (cation) ranges
ECF: 3.5-5.0 mEq/L
ICF: 140-150 mEq/L
Bicarbonate (anion) ranges
ECF: 24-31 mEq/L
ICF: 7-10 mEq/L
Calcium (cation) ranges
ECF: 8.5-10.5 mg/dL
ICF: <1 mEq/L
Phosphate (anion) ranges
ECF: 2.5-4.5 mg/dL
ICF: Variable
Magnesium (cation) ranges
ECF: 1.8-3.0 mg/dL
ICF: 40 mEq/Kg
Diffusion
Movement of charges or uncharged particles along a concentration gradient. Collision of particles provides energy; passive transport
Osmosis
Movement of water across a semipermeable membrane along a concentration gradient; passive transport
Facilitated diffusion
Allows water or ion molecules (Na+) to move through channel proteins; porins. Uses specific carrier molecules to accelerate diffusion. Movement of molecules from high to low concentration; passive transport
Active transport
Molecules move against concentration gradient; sodium potassium pump. External energy required; important concept to know during acidosis; increased extracellular K+
Serum osmolality
Normal 275 to 295 mOsm/kg; fluid overload <275 mOsm/kg, dehydration >295 mOsm/kg
Urine specific gravity
Normal 1.005 to 1.030; fluid overload <1.005; dehydration >1.030
Urine/serum osmolality ratios
Normal=1:1
Difficulty concentrating urine<1:1
Overnight fluid deprivation= 3:1
Dehydration= 4:1
Fluid overload= 1:4
Intracellular fluid
Regulated by proteins and organic compounds. Water moves through permeable cell membranes, while proteins and organic compounds cannot.
Intracellular proteins are…
negatively charged; attract cations ions (K+)
Sodium enters the by…
diffusion! Pulls water into the cell; risk of cellular rupture. Na+/K+ -ATPase removes Na x3 out of cell, moves K+ x2 into the cell.
ECF
Vascular compartment (serum/blood); systematically transports electrolytes, gases, nutrients, waste.
Interstitial space: Moves substances between vascular compartment and body cells. Tissue gel sponge material composed of proteoglycan filaments; reservoir for lost vascular fluid; prevents free water accumulation; this is where peripheral edema occurs.
What are the four forces that control movement of water between vascular and interstitial compartments?
- Capillary filtration pressure: Pushes water out of capillary into interstitial tissue
- Capillary colloid osmotic pressure: Pulls water back into capillary
- Interstitial tissue hydrostatic pressure: Opposes water movement out of capillary
- Interstitial tissue colloid osmotic pressure: Pulls water out of capillary
Edema
Palpable swelling produced by expansion of interstitial fluid volume
Anasarca
Simultaneous generalized edema
Third spacing
Loss or trapping of ECF into transcellular space.
Causes: Excess fluid in pleural space; pleural effusion, excess fluid in peritoneal cavity; aseity, abdominal compartmental syndrome, pancreatitis; hypoalbuminemia (general edema) burn injuries, liver failure
Tonicity
Tension that effects osmotic pressure of solutions; when impermeable solutes exerts on cell size because of water movement
Hypotonic fluid
<280 mOsm/L; cell swelling
Isotonic fluid
280 mOsm/L; no cellular change
Hypertonic fluid
> 280 mOsm/L; cellular shrinkage
Hematocrit
Normal range: 37-50%
Increased hematocrit (concentrated): Dehydration
Decreased hematocrit (diluted): Fluid overload
Urine specific gravity
Normal range: 1.010-1.025
Increased USG (concentrated): Dehydration
Decreased USG (diluted): Fluid overload
Characteristics of measurement for normal urine analysis
Adult urine output: 30 ml/hr, 600-2,500 ml/24 hrs, Average=1,200/24 hrs. Amber in color, clear to hazy, SG (1.010-1.025), pH 4.5-8.0; average 5-6
Chemical determinations of normal urine analysis
Bilirubin negative, urobilinogen 0.5-4.0 mg/day, nitrate for bacteria negative, leukocyte esterase negative, glucose, ketones, blood, and protein negative
Microscopic examination of sediment of normal urine analysis
Few epithelial cells, hyaline casts 0 to 1/1 pf (low power field), cast negative w/ occasional hyaline casts, RBC negative or rare, crystals negative (none), white blood cells negative or rare
What are the two physiologic mechanisms that regulate water body levels?
Thirst (oral water intake) and ADH (controls output of water by kidneys).
What is hypothalamic regulation?
Osmo-receptors in the hypothalamus sense fluid deficit or excess stimulates thirst and ADH release. Results in increase in free water and decreased plasma osmolality
When does the posterior pituitary release ADH?
Decreased BP, dehydration, increased serum osmolality (hypernatremia)
Sympathetic nervous system
Compensatory response to decreased CO. Stimulates alpha and beta1/2 adrenergic receptors. Tachycardia increases demand for oxygen. Vasoconstriction, bronchodilation (adenylate cyclase).
Renin-angiotensin-aldosterone mechanism
Increase in renin by kidneys. Angiotensin I is converted to angiotensin II by the lungs. Increase in angiotensin II and aldosterone means kidneys absorb water and sodium.
ADH
Angiotensin II stimulates posterior pituitary gland secretes ADH. ADH is a vasoconstrictor; retains water
Syndrome of inappropriate ADH (SIADH)
Too much ADH (decreases serum osmolality and increases water retention). Transient pain and chronic neurogenic conditions, carcinomas.
Clinical manifestations: Decreased urine output, dark urine, irritability, nausea
Diagnosis: Decreased serum osmolality, increased urine osmolality, low hematocrit
Interventions for SIADH
Plan is to increase urine output. Fluid constriction for mild conditions. Diuretics, and ADA (lithium and demeclocycline) inhibition for moderate conditions. 3% sodium chloride for severe conditions.
Diabetes insipidus (DI)
Not enough ADH; decreased renal response to ADH; unable to concentrate urine during water restriction.
Two types, neurogenic (central), where there is a deficit in the synthesis or release of ADH, and nephrogenic, where kidneys do not respond to ADH or vasopressin.
Clinical manifestations: Increased urine output (3-20 L/day), clear urine, intensive thirst & crave ice water.
Diagnosis: Increased serum osmolality and hematocrit, decreased urine osmolality
DI interventions
Plan is to decrease urine output. Desmopressin acetate (DDAVP) stimulates release of ADH. Thiazide increased sodium and water.
Natriuretic peptides
Antagonists to RAAS. Decrease BP and blood volume. Aldosterone, renin, ADH involved in cardiac regulation.
Losses in gastrointestinal regulation
GI tract: Small amounts of water
Diarrhea: Bicarbonate loss creates metabolic acidosis
Nasal/oral gastric tube/vomiting: Acid loss creates metabolic alkalosis
Insensible water loss
Regulates body temperature. Approximately 600-900 ml/day is lost, no electrolytes are lost.
ECF volume deficit (hypovolemia)
Diarrhea, hemorrhage, dehydration, edema.
Intervention: Replace water and electrolytes (oral or IV); isotonic for intravascular volume, hypotonic for ECF replacement.
ECF volume excess (hypervolemia)
Excessive fluid intake, congestive heart failure, interstitial to plasma fluid shift.
Intervention: Fluid restriction, diuretics, dialysis
What are the roles of sodium?
ECF volume and concentration, generation and transmission of nerve impulses, acid-base balance
Hypernatremia
EXCESS fluid loss or sodium intake; DI; near drowning.
Clinical manifestations: Thirst, lethargy, agitation
Diagnosis: Med hx & assessment, serum Na+>145 mEq/L
Plan: Correct underlying cause
Hypernatremia interventions and evaluation
Administer hypotonic IV fluid (0.45 NaCl/5% dextrose in water), decrease sodium intake, promote oral water intake, strict intake & output (daily weight). Evaluate serum Na+ levels 135-145 mEq/L
Hyponatremia
LOSS of sodium or water excess.
Clinical manifestations: Headache, hypotension, tachycardia, adventitious breath sounds, muscle twitching
Diagnosis: Increase in intracranial pressure; cerebral edema. Serum Na+ <135 mEq/L
Hyponatremia interventions and evaluation
LAST RESORT: DIURETICS
Oral administration of sodium-rich foods (beef broth or tomato juice). Hypertonic or isotonic IV fluid (3% saline, 0.9% normal saline IVF). Water restriction, strict intake & output (daily weight). Evaluate serum Na+ levels 135-145 mEq/L
Potassium
Normal serum level: 3.5-5.0 mmol/L
MAJOR ICF CATION!
What is potassium required for and what are its sources?
Required for: Transmission and conduction of nerve/muscle impulses, cellular growth, maintenance of cardiac rhythms, acid-base balance.
Sources: Fruits and vegetables (bananas & citrus), salt substitutes, medications that contain K+, stored blood (RBC lysis –> increased potassium)
Hyperkalemia
Excessive salt intake. Shift from ICF to ECF; exchange between K+ and Na+. Comes from crush injury or renal failure.
Clinical manifestations: Lower extremity cramping/pain, muscle weakness, ventricular tachycardia, peak T-wave
Diagnosis: K+ >5.0 mmol/L, peak T-waves
Hyperkalemia interventions
Emergency: Glucose 50 mL D50 or D10 NS IVF, regular insulin 10u IVP, calcium gluconate 1 gm IVP, bicarbonate IVP, albuterol nebulizer 10 to 20 mg.
Non-urgent: Kayexalate, dialysis
Hypokalemia
Abnormal losses of K+; metabolic alkalosis; hypomagnesemia.
Clinical manifestation: Confusion, nausea/vomiting, muscle cramps, prolonged PR interval, ST segment depression
Diagnosis: K+ <3.5 mmol/L
Hypokalemia interventions
Increase potassium intake, administer K+ per MD orders; NS with 20 mEq K+ (DO NOT PUSH K+ IV)!
How does pH affect calcium?
Decreased pH (acidosis): Increases ionized and serum calcium
Increased pH (alkalosis): Decreases ionized and serum calcium
How does vitamin D affect PTH control of calcium?
Increases serum calcium level
How does calcitonin affected PTH control of calcium?
Decreases serum calcium level
Chvostek sign
Contraction of facial muscles in response to light tap over facial nerve in front of ear
Trousseau sign
Carpal spasm; induced by inflating BP cuff above systolic pressure for a few minutes
Hypercalcemia
EXCESS CALCIUM intake. Hyperparathyroidism causes 2/3 of cases. Malignancies, decreased phosphate levels, and prolonged immobilization also part of etiology.
Clinical manifestations: Stupor, weakness, muscle flaccidity
Diagnosis: Total Ca++ >10.5 mg/dL, ionized Ca++ >5.4 mg/dL
Hypercalcemia interventions and evaluation
Interventions: Isotonic IVF, diuretic (lasix), calcitonin, dialysis.
Evaluation: Total Ca++ 8-10.5 mg/dL, ionized C++ 4.4 to 5.4 mg/dL
Hypocalcemia
Dietary deficiency, decreased PTH, increased vitamin D and phosphate levels, multiple blood transfusions (citrate). Clinical manifestations: Positive Trousseau’s and Chvostek’s sign, dysphagia (laryngeal stridor), mouth/extremity tingling.
Diagnosis: Total Ca++ <8 mg/dL, Ca++ <4.4 mg/dL
Hypocalcemia interventions and evaluation
Interventions: Supplemental calcium, synthetic PTH, administer active vitamin D for clients with liver/renal failure
Evaluation: Total Ca++ 8-10.5 mg/dL, Ca++ 4.4-5.4 mg/dL
Phosphate range and roles
Primary anion in ICF normal serum value: 2.5 to 4.5 mg/dL
Roles: Muscle function, RBCs, nervous system, deposited with calcium for bone growth and tooth structure, renal function, acid-base buffering system, ATP production, cellular uptake of glucose
Hyperphosphatemia
Etiology: Excessive phosphate intake, renal failure, trauma, chemotherapy
Clinical manifestations: Related to calcium deficiency, dysphagia, mouth/extremity tingling, positive Trousseau’s and Chvostek’s sign.
Diagnosis: Phosphate > 4.5 mg/dL
Hyperphosphatemia interventions and evaluation
Interventions: Dietary management, calcium acetate (phosphate binder), calcium gluconate, dialysis
Evaluation: Phosphate 2.5-4.5 mg/dL
Hypophosphatemia
Etiology: Malnourishment, GI malabsorption, alcohol withdrawal, phosphate-binding antacids, prolong glucose infusion and hyperventilation (increased protein binding decreases ionized calcium)
Clinical manifestations: Confusion, muscle weakness and pain, dysrhythmias, cardiomyopathy
Diagnosis: Phosphate <2.5 mg/dL
Hypophosphatemia interventions and evaluation
Interventions: Diet management and phosphate supplements (oral and IVPB)
Evaluation: Phosphate 2.5-4.5 mg/dL
Magnesium range and roles
Normal serum value: 1.8-3.0 mg/dL
Roles: 50-60% contained in bone, coenzyme in metabolism of protein and carbohydrates, related to calcium, acts directly on myoneural junction, important for normal cardiac function. Ex: Brown rice, almonds, spinach, avocados
Hypermagnesemia
Etiology: Excess magnesium intake; renal insufficiency/failure, increased magnesium suppresses calcium levels (hypocalcemia)
Clinical manifestations: Confusion, hyporeflexia, muscle weakness, hypotension, prolongation of PR interval
Hypermagnesemia interventions and evaluation
Interventions: Oral supplements, increased dietary intake, IV or IM magnesium
Evaluation: Serum Mg 1.8-3.0 mg/dL
