Lecture 1/2 - fluid homeostasis and sodium

where is intracellular fluid predominantly found

mostly in muscle cells

H20 and Na+ movement across membranes

H20 moves freely, Na+ doesn’t

what are intracellular osmoles

mostly large proteins that don’t move

what is the dominant extracellular tonically active particle

Na+

(other prevalent ones: K+, glucose, urea, albumin)

ratio of intracellular fluid : extracellular fluid

2/3 : 1/3

ratio of interstitial water : intravascular water of extracellular fluid (1/3 of total fluid)

3/4 : 1/4

hypotonic environment

higher concentration of solute in the cell compared to extracellular environment

water moves INTO cells causing them to swell

isotonic environment

equal concentration of solute inside and outside the cell, resulting in no net movement of water.

hypertonic environment

higher concentration of solute in the extracellular environment compared to the cell, causing water to move OUT of the cells and shrink them.

what is the function of osmotic pressure

maintain distribution of fluids between compartments of fluid (i.e. intracellular, extracellular)

what is osmotic pressure influenced by

concentration of dissolved electrolytes, proteins, other large molecules (cannot move across membranes so water moves freely to maintain equilibrium)

what is intracellular fluid (ICF) needed for

volume is critical for normal cell function

what is extracellular fluid (ECF) needed for

volume is essential for tissue perfusion

what is interstitial fluid

fluid between or around tissues, e.g. plasma

What is intravascular water

fluid that crosses epithelial cells, e.g. cerebrospinal fluid, synovial fluid

s/s of dehydration (adult)

dry mucous membranes

skin tenting (pinch skin and takes long to go back to normal)

decreased urine output

postural changes (lying → standing = decreased SBP, dizziness, increased HR)

decreased capillary refill

cool extremities

decreased cognitive function

s/s of dehydration - infant/young child

dry mouth and tongue

lack of tears when crying

no wet diaper for 3 hours

sunken eyes/cheeks

sunken soft spot on top of skull

irritability

***requires immediate medical attention***

typical fluid maintenance per day

2000-3000mL

6-8 × 250 mL glasses of water

management of mild dehydration

drink - water, WHO-ORS (world health organization oral rehydration solution), water + salt, sports drink and increased fluid intake.

management of severe dehydration

depends on severity, medical attention/IV fluid replacement

IV replacements for severe dehydration

what is edema

excess fluid volume in extracellular compartment

usually caused by heart/kidney/liver failure

may occur during pregnancy or due to malnutrition

s/s of edema

swelling in feet/ankles/lower legs (gravity), pitting (push on swelled area and it leaves a pit, measure severity of edema by depth and duration of pit)

weight gain

increased jugular venous pressure

Positive hepatojugular reflux (firm pressure over the liver temporarily increases venous return of the heart) (see lecture slides for video)

s/s of pulmonary edema

increased respiratory rate

SOB sensation

crackles present using stethoscope

medications to manage edema

diuretics = increase sodium excretion and water follows

• loop diuretics (furosemide, ethacrynic acid) = strong

• thiazide diuretics (HCTZ, chlorthalidone, metolazone)

• K sparing diuretics (spironolactone, triamterene, amiloride) (depending on K levels)

loop diuretics

• furosemide, ethacrynic acid= strong

thiazide diuretics

• HCTZ, chlorthalidone, metolazone

K sparing diuretics

• spironolactone, triamterene, amiloride (depending on K levels)

what is the primary electrolyte for ECF osmolarity

Na+

What is the primary electrolyte for ICF osmolarity

K+

what is normal serum osmolarity of sodium

280-300 mOsmol/kg

what is the formula for calculating sodium serum osmolarity

what is sodium’s role in homeostasis

Na/K pump (active transport), regulating BP, cell depolarization (nerves and muscles)

what organ primarily controls sodium in body

kidney

hyponatremia may cause

decreased cognitive function

increased risk of falls, fractures, bone loss

what is the most common electrolyte abnormality

hyponatremia

what is hypernatremia associated with

hypertonicity → cause significant reduction in ICF

risk factors for hyponatremia

advancing age (independent of sex)

increased intake of hypotonic fluids (orally, tube, IV)

symptoms of mild/chronic hyponatremia

asymptomatic

impaired attention

gait changes

postural changes

increased risk of falls (elderly)

symptoms of moderate/severe hyponatremia

nausea/vomiting

headache

lethargy

altered mental status

seizures

respiratory arrest

increased risk of death

what is hypovolemic hypernatremia

Na < 135 mmol/L AND Uosm > 450 mOsm/kg

loss of sodium and water from the body, but a greater amount of sodium is lost compared to water = low blood sodium levels and a decrease in overall blood volume

what are causes of hypovolemic hyponatremia

external losses (GI, skin, lungs)

renal losses (diuretics, adrenal insufficiency)

what is the treatment for hypovolemic hyponatremia

isotonic fluid (0.9% NaCl, LR)

what is euvolemic hyponatremia

Na < 135 mmol/L AND Uosm <

normal total amount of sodium but an excess of water

what are some causes of euvolemic hyponatremia

hypothyroidism

hypocortilsolism

kidney failure

SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion)

what is the treatment for euvolemic hyponatremia

water/sodium restriction

treat underlying cayse

loop diuretic

vasopressin receptor antagonists

what is hypervolemic hyponatremia

Na < 135 mmol/L AND Uosm

too much total body water and a relatively smaller increase in total body sodium

what are causes of hypervolemic hyponatremia

heart failure

cirrhosis

nephrotic syndrome

what is the treatment for hypervolemic hyponatremia

water/sodium restriction

diuretic

vaspressin receptor antagonist

treatment for acute/severely symptomatic hypotonic hyponatremia

IV 3% NaCl (513 mEq/L (mmol/L) or

Normal saline (0.9%) until severe symptoms resolve (more common)

how to avoid osmotic demyelination syndrome when treating hypotonic hyponatremia

Na concentration should be corrected to a rate that does not exceed 6-12 mmol/L during the first 24 hours and no higher than 120mEq/L (mmol/L)

treatment for hypovolemic hyponatremia

treat underlying cause of fluid loss:

• GI (vomiting, diarrhea)

• diuretics (reassess/dosage adjustment)

admin:

• 0.9% NaCl or other isotonic solution (lactated Ringer’s)

• oral replacement: water, WHOORS, sport drink

treatment of euvolemia hyponatremia

correct the underlying cause if possible e.g. stop drug causing SIADH, hypothyroidism

fluid restriction (1000-1200 mL/day) = create negative water balance

chronic SIADH may require increased solute (NaCl tablet) intake ± loop diuretic

vasopressin receptor antagonists (tolvaptan, conivaptan)

treatment of hypervolemic hyponatremia

correct underlying cause if possible (e.g. HF, cirrhosis, nephrotic syndrome, optimize drug therapy)

fluid restriction - create negative water balance

sodium restriction

vasopressin receptor antagonists (tolvaptan, conivaptan)

symptoms of hypernatremia

mild: weakness, lethargy, restlessness, irritability

moderate: twitching

severe: seizure, coma, death

how is hypernatremia classified

based on status of extracellular fluid volume

hypovolemic/euvolemic/hypervolemic hypernatremia

what is hypovolemic hypernatremia

water loss » sodium loss

what is the cause of hypovolemic hypernatremia

renal: diuretic use, diuresis

sweating, diarrhea, vomiting, exposure to high temperature

symptoms of hypovolemic hypernatremia

hypotension, tachycardia, dry mucous membranes

hypovolemic hypernatremia treatment

if hemodynamically stable (normal BP) → oral solution

if hemodynamically unstable (low BP) → 0.9% NaCl. Once stable then 0.45% NaCl/D5W or other hypotonic fluid

what is euvolemic (isovolemic) hypernatremia

water loss only

what is the most common cause of euvolemic hypernatremia

diabetes insipidus

symptoms of euvolemic hypernatremia

depends on severity

seizures, lethargy

treatment of euvolemic hypernatremia

central: replace vasopressin (desmopressin acetate)

nephrologic: correct underlying cause (e.g. hypercalcemia), if drug induced (e.g. Li+) stop or decrease dose, limit sodium intake, add diuretic

what is diabetes insipidus

daily urine output >3L

what is the cause of diabetes insipidus

central - low levels of vasopressin

• polyuria is sudden

• unreplaced water loss from skin/lung

• medical conditions: hypodipsia, TB, head trauma, CNS malignancy

• other: ethanol ingestion (transient)

nephrogenic - renal tubules do not respond to vasopressin

• polyuria develops gradually

• medical conditions: hypokalemia, hypercalcemia, kidney disease

• drug induced: lithium, amphortericin B, demeclocycline

what is hypervolemic hypernatremia

sodium gain > water gain

What is the cause of hypervolemic hypernatremia

sodium overload (3% NaCl, NaCl tablet, NaHCO3, sodium containing medications)

symptoms of hypervolemic hypernatremia

peripheral and pulmonary edema

variable BP

treatment of hypervolemic hypernatremia

D5W + loop diuretic (furosemide 20-40mg orally or IV q6h)

which cation does chloride passively follow

sodium

what is hypochloremia and what is it associated with

low chloride

associated with:

• hyponatremia

• loss of large volumes of stomach acid (vomiting)

• diuretic use

• metabolic alkalosis

what is hyperchloremia and what is it associated wth

high chloride

associated with:

• metabolic acidosis and hypernatremia