Week 2: Fluids and Electrolytes

solvent

water

solute

dissolved or suspended particles

ECF

fluid outside the cell; includes fluid spaces between cells (interstitial, lymph), and transcellular fluid (synovial, CSF, peritoneal fluid)

ICF

fluid within the cell; 2/3 of total body water; medium for metabolic precesses

primary ECF cation

Na+

primary ECF anion

Cl-

primary ICF cation

K+

primary ICF anion

phosphorus

filtration

movement of fluid through a cell or blood vessels; imbalance in hydrostatic pressure causes movement of fluid

diffusion

movement of particles (solute) across a permeable membrane; movement form high to low concentration; cell membranes are more selective than capillary membranes

sodium pump

moves excess sodium form the inside of the cell “uphill” against the concentration gradient back into the ECF; uses a special transport system

osmosis

movement of water form area of low solute concentration to greater solute concentration through a semipermeable membrane which only allows the movement of water; maintains both ECF and ICF

osmosis stops

when hydrostatic pressure equals and the concentration differences disappear

how solutions are characterized

tonicity (concentration, osmolarity), and pH

isotonic solutions

270-300 mOsm/L (similar to body fluid)

no fluid shift, stays in vessels; NS, LR

hypertonic solution

>300 mOsm/L; pulls water form cells into interstitial spaces and bloodstream

shifts fluids back into vessels; D5 0.45% NS, D5 0.9% NS, 3% NS, 5% NS

hypotonic solution

<270 mOsm/L; water moves into cells

shifts fluid out of blood vessels into the cells; 0.25% NS, 0.45% NS, D5W

solutions with very high or low pH

given into a central line where there is greater blood flow

cations

positive charge; potassium, magnesium, sodium, calcium

anions

negative charge; chloride, phosphorus

potassium range

3.5-5.0 mEq/L

sodium range

136-145 mEq/L

chloride range

98-106 mEq/L

calcium range

9-10.5 mg/dL

magnesium range

1.3-2.1 mg/dL

phosphate range

3.0-4.5 mEq/L

blood glucose range

70-110 mg/dL

factors in body fluids

age (elders have less total body water), gender, fat (obese patient has less water)

modes of fluid output

kidneys, skin, lungs, intestinal tract

normal urine output

400-600 mL

water loss

wound drainage, fistulas, GI suctioning, diarrhea

aldosterone secretion

by adrenal cortex when ECF sodium is low

aldosterone action

acts on kidney nephrons to reabsorb sodium and water form urine; increases blood volume and osmolarity; prevents water and sodium loss; part of RAAS

antidiuretic hormone (ADH, vasopressin) secretion

released form posterior pituitary gland if osmoreceptors detect increased sodium in plasma

antidiuretic hormone (ADH, vasopressin) action

acts in kidney to reabsorb more water; makes blood more dilute

natriuretic peptide secretion

secreted by special cells lining the atria and ventricles of the heart (ANP/BNP) when BP and blood volume increase, stretching the heart tissue and releasing the peptides

atria natriuretic peptides are from the atria, brain natriuretic peptides are from the ventricles

syndrome of inappropriate ADH (SIADH)

ADH secreted when osmolarity is low/normal, leading to water retention and fluid overload; can occur with cancer therapy, pulmonary infections, drugs such as SSRIs and opioids; water retention leads to low sodium, increasing blood volume, and inhibiting renin and aldosterone, which increases sodium loss

S&S: hyponatremia; confusion, muscle weakness, diminished deep tendon reflexes, nausea, diarrhea

most important fluids to keep in balance

blood volume and intracellular fluid; failure leads to poor organ perfusion and cellular dysfunction

kidneys

major regulator of water and sodium balance; maintain blood and perfusion pressure to all tissues/organs; secrete renin when they sense a low parameter (triggers RAAS)

activation of RAAS system

kidney senses low BP/blood volume (ECF)/blood sodium/blood O2, or increased urine sodium; releases renin into bloodstream

RAAS system

angiotensin (secreted by liver) → renin converts angiotensin to angiotensin I → ACE (angiotensin converting enzyme) converts angiotensin I to angiotensin II → angiotensin II adrenal glands to release aldosterone → aldosterone increases sodium and water retention → rapidly constricts arteries and veins to increase BP

simplified RAAS system

angiotensin → (renin) → angiotensin I → (ACE) → angiotensin II → adrenal cortex → (aldosterone) → kidney → increase sodium/water retention, ECF → increase BP

sodium body uses

muscle contraction, cardiac contraction, nerve impulses; influences water balance (where sodium goes, water follows)

sodium rich foods and intake

processed foods, preserved foods, condiments

aim for <1500 mg/day, no more than 2300 mg/day (daily average is 3400 mg/day)

sodium regulation

by kidney under the influence of aldosterone, ADH, NPs

potassium regulation

sodium potassium pump is main controller in ECF

potassium rich foods

bananas, cantaloupe, oranges, avocados, cauliflower, mushrooms, spinach, potatoes, salmon, chocolate, meat, fish, broccoli

magnesium imbalance

think cardiac function (arrhythmias); low potassium is correlated with low magnesium, prioritize replacing magnesium; check with use of loop diuretics (furosemide/lasix)

calcium absorption and storage

absorption requires active vitamin D; 80% is sorted in bones to maintain bone strength and density

when more calcium is needed

parathyroid hormone (PTH) is released, releasing free calcium from bone storage, stimulating vitamin D activation, inhibits kidney calcium excretion, stimulate kidney calcium reabsorption

calcium body uses

needed for clotting and nerve impulses, skeletal and cardiac muscle contraction, activation of some enzymes

magnesium storage

mostly in bones and cartilage

magnesium body uses

skeletal muscle contraction, carbohydrate metabolism, generation of energy stores, vitamin activation, blood coagulation, cell growth, responsible for transport of Na+ and K+ across the cell membrane

fluid volume deficit

especially plasma volume (fluid is lost from ECF); caused by hemorrhage, vomiting, diarrhea

reduced BP/perfusion, heart pumps harder/faster, vasoconstriction, hypovolemia, increased peripheral resistance, squeezing blood into vital organs

signs and symptoms of dehydration

increased HR, weak peripheral pulses, decreased BP, orthostatic hypotension, flat neck veins; increased RR; skin tenting, for skin turgor, dry; changes in cognition, amber color urine, strong odor

dehydration diagnostic labs

no single test is definitive; hemoconcentration, loss of plasma and blood cells; likely to have increased Hb, Hct, serum osmolarity, glue, protein, BUN, electrolytes

possible dehydration priorities

disrupted fluid and electrolyte balance due to excess fluid loss or inadequate fluid intake

potentila for injury due to poor perfusion associated with decreased fluid volume

possible dehydration interventions

fluid replacement (oral or IV), drug therapy (Antibiotics, antidiarrheal, antiemetics, antipyretics

monitor pulse rate/quality, urine output, and daily weight during rehydration

fluid overload

hypervolemia; severe cases lead to heart failure and pulmonary edema; dilution of sodium and potassium can lead to seizures, coma, death

signs and symptoms of fluid overload

increased HR, BP, CVP (central veinous pressure), bounding pulse, distended neck veins JVD; weight gain; increased RR, shallow respirations, SOB, crackles; pitting edema, pale/cool skin; altered LOC, headache, visual disturbances, skeletal muscle weakness, paresthesia; increased GI motility, enlarged liver

possible fluid overload interventions

ensure patient safety: prevent HF, pulmonary edema, electrolyte imbalance, fall risk, skin breakdown

restore fluid balance: diuretics, electrolytes

prevent future fluid overload: decrease salt intake, consider the cause

provide supportive care

hyponatremia S&S

“salt loss”

Stupor/coma, Anorexia (nausea vomiting), Lethargy (weakness/fatigue), Tachycardia (thready pulse), Limp muscles (muscle weakness), Orthostatic hypotension, Seizures/headache, Stomach cramping (hyperactive bowels)

hypernatremia S&S

“fried salt”

Flushed skin, Restless (anxious, confused, irritable), Increased BP and fluid retention, Edema (pitting), Decreased urine output, Skin flushed and dry, Agitation, Low grade fever, Thirst (dry mucous membranes)

hypokalemia S&S

generalized muscle weakness and less contraction, hyporeflexia, shallow respirations, thready/weak, irregular pulse, orthostatic hypotension, anxiety, lethargy, confusion, coma, paresthesias, constipation (hypoactive bowel), nausea, vomiting, abdominal distention, ECG (shallow/inverted T wave, ST depression, prominent U)

hyperkalemia S&S

“murder”

Muscle cramps and weakness, Urine abnormalities, Respiratory distress, Decreased cardiac contractility (decreased HR/BP), EKG changes (tall/peaked T waves, flat P, wide QRS, prolonged PR), Reflexes (increased DTR)

hypocalcemia S&S

“cats go numb”

Convulsions/seizures, Arrhythmias, Tetany, Spasms ask stridor, GO NUMB in fingers/face/limbs

positive trousseau’s signs (carpal spasm from inflating BP cuff), chovstek’s signs (contraction of facial muscle with light tap over facial nerve)

hypercalcemia S&S

“back me”

Bone pain, Arrhythmias, Cardiac arrest (bounding pulses), Kidney stones, Muscle weakness (decreased DTR), Excess urination

hypomagnesemia S&S

(high everything; not sedated) tachycardia, hypertension, hyperreflexia, shallow respirations, twitches, paresthesias, tetany and seizures, irritability and confusion

positive trousseau’s signs (carpal spasm from inflating BP cuff), chovstek’s signs (contraction of facial muscle with light tap over facial nerve)

hypermagnesemia S&S

(low everything; sedated) decreased DTR, bradycardia, hypotension, bradypnea, shallow respirations, decreased bowel sounds