fluids and electrolytes

TBW is __% of lean body weight in females

50

TBW is __% of lean body weight in males

60

what does TBW depend on

age and body muscle/fat content

ECF is __% of TBW

33

ICF is __% of TBW

66

water in ICF is rich in ____________

electrolytes and proteins

water in ECF is rich in ___________

electrolytes and bicarbonate

what are some ways to asess ECF

BP, mucous membranes, skin turgor, cardiopulmonary examination, LOC

where are serum electrolytes routinely measured from

ECF (plasma)

plasma is __% of TBW

8

interstitial fluid is __% of TBW

25

what is plasma

intravascular fluid, represents fluid within blood vessels

what is interstitial fluid

fluid between cells

what is transcellular fluid

includes viscous components of peritoneum, pleural space, and pericardium as well as CSF, joint space fluid and GI digestive juices

transcellular fluid is _% of TBW

1

third spacing

accumulation of fluid in transcellular space

sensible H20 intake

water intake

insensible H2O intake

food, metabolism

sensible H2O loss

kidney, GIT

insensible H2O loss

skin, resp

ECF depletion tends to occur acutely or chronically

acutely

ECF depletion cause (what type of fluid is lost and what causes the loss)

loss of isotonic fluid (proportional losses of sodium and water)

external fluid losses (burns, hemorrhage, diuresis, GI losses)

third spacing of fluids (septic shock, abdominal ascites)

does ECF depletion cause disturbances of plasma osmolality

not usually

signs and symptoms of ECF depletion

diziness, orthostasis, tachycardia, decreased urine output, decreased central venous pressure and/or hypovolemic shock

TBW depletion is acute or chronic

usually more gradual/chronic

what type of fluid loss happens in TBW depletion (isotonic, hypertonic, hypotonic)

hypotonic fluid (more water than sodium is lost) from all body compartments

does TBW depletion cause osmolality disturbance

yes

TBW depletion signs and symptoms

CNS disturbances (mental status change, seizures, coma), excessive thirst, dry mucous membranes, decreased skin turgor, elevated serum sodium, increased plasma osmolality, concentrated urine, acute weight loss

common causes of TBW depletion

insufficient oral intake, excessive insensible losses, diabetes insipidus, excessive osmotic diuresis, impaired renal concentrating mechanisms

classic indications for IV fluid

maintenance of BP, restoring of ICF volume, replacing ongoing renal or insensible losses when oral intake is inadequate, glucose administration (need for brain function)

crystalloid solutions composition/characteristics

composed of water and electrolytes, all which pass thru semipermeable membranes and remain in the plasma space for shorter periods of time

what happens to ICF/ECF when you give a crystalloid isotonic solution

same tonicity as ICF -does not shift fluids between ECF/ICF

what happens to ICF/ECF when you give hypertonic crystalloid solution

draw water from ICF to ECF

what happens to ICF/ECF when you give hypotonic crystalloid solution

draw water from ECF to ICF

5% dextrose in water tonicity

isotonic

5% dextrose in water uses

raises TBW, helpful in rehydration for fluid loss and dehydration, treatment of hypernatremia

0.9% NaCl (normal saline) tonicity

isotonic

0.9% NaCl uses

ECF volume expander (increases circulating plasma volume when red cells are adequate)

shock/resuscitation

fluid replacement in pts with DKA

hyponatremia

concurrent w/ blood transfusions

metabolic alkalosis

hypercalcemia

0.45% NaCl tonicity

hypotonic

0.45% NaCl uses

water replacement (free water)- raises total fluid volume

DKA after normal saline solution and before dextrose infusion

hypertonic dehydration

sodium and chloride depleiton

gastric fluid loss from nasogastric sunctioning or vomiting

3% NaCl tonicity

hypertonic

3% NaCl uses

treatment of severe hyponatremia

lactated ringers (LR) tonicity

isotonic

lactated ringers uses

ECF volume expander- replaces fluid and buffers pH

hypovolemia due to third space shifting

dehydration

burns

lower GI tract fluid loss

acute blood loss

D5NS (dextrose 5% in 0.9% saline) tonicity

hypertonic

D5NS uses

hypotonic dehydration

replaces fluid sodium, chloride, calories

temporary treatment of circulatory insufficiency and shock if plasma expanders aren’t available
SIADH (or use 3% sodium chloride)

addison’s disease crisis

D5 ½ NS (dextrose 5% in 0.45% saline) tonicity

hypertonic

D5 ½ NS (dextrose 5% in 0.45% saline) uses

DKA after initial treatment with normal saline solution and half normal saline solution- prevents hypoglycemia and cerebral edema (occurs when serum osmolality is reduced rapidly)

most common post op fluid

useful for daily maintenance of body fluids and nutrition, and for rehydration

D5LR (dextrose 5% in lactated ringer’s) tonicity

hypertonic

D5LR (dextrose in lactated ringer’s) use

same as LR plus provides about 180 calories per 1000mLs

indicated as a source of water, electrolytes and calories or as an alkalinizing agent

colloidal solutions

do not dissolve into true solutions and do not readily pass across semipermable membranes. remain in plasma and increase the oncotic pressure (shifts fluids into the plasma compartment), however effect is short lived

more expensive than crystalloids

plasma volume expanders

risks with colloidal solutions

risk of fluid overload, dilution of plasma proteins, decrease in hemoglobin concentration

where is albumin produced

liver

where is albumin located

40-50% in intravascular space, distributes throughout ECF

commercial albumin solutions

5% albumin, iso-oncotic, 25% albumin, hyperoncotic

risks of albumin

anaphylactic reactions with commercial solutions, human product therefore risk of disease transmission (RARE)

dextrans; hydroxyethyl starches (pentastarch, hetastarch) characteristics

synthetic products, persists 18-24hr, less expensive than albumin, risk of allergic rxn

ECF electrolytes (ECF, plasma, interstiital space)

Na+, HCO3-

Cl- (plasma)

K+, Ca2+, Mg2+, PO4- (interstital space)

ICF electrolytes

K+, PO4-, Mg+, Cl-, Ca2+, Na+

main cations

sodium, potassium, calcium, magnesium

main anions

chloride, bicarbonate, phosphate

ECF primary ions

sodium and chloride

ICF primary ions

potassium and phosphate

what is osmolality

number of particles per kg of water (mOsm/kg)

osmolality is determined by

number of particles in solution (not by particle size or valence)

principles of osmolality

only water, not solute may pass thru selectively permeable membranes

osmotic pressure keeps volume of 3 compartments constant

water moves downs osmotic gradient between intracellular and extracellular compartments

proteins in intravascular space, primary osmole affecting water distribution

as the body regulates water to maintain osmolality, changes in serum osmolality are used to estimate ____ stores

TBW

Posm helps determine deviations in ___ content

TBW

what is an osmolal gap and what does it indicate

if measured Posm exceeds calculated Posm by >10mOsm/kg

may indicate presence of large amount of low molecular weight substances in plasma (Ethanol, methanol, acetone, paraldehyde, ethylene glycol)

serum electrolyte concentrations reflect the stores of the ECF or ICF electrolytes?

ECF electrolytes

Na+ determines….

ECF volume and is the primary factor in establishing osmotic pressure between ICF and ECF

Na+ roles (3)

regular serum osmolality, regulate fluid balance, essential for maintaining transmembrane electric potential

what is pseudohyponatremia

hyponatremia with normal osmolality, isotonic hyponatremia

elevated serum lipids or proteins results in a larger discrepancy between the volume of the sample and serum water, which leads to a falsely low measurement of the serum sodium concentration

hypertonic hyponatremia is usually associated with significant hyper______

glycemia

_______ is an osmotically active agent that leads to an increase in TBW with little change in total body sodium

glucose

how to treat hypertonic hyponatremia

treat hyperglycemia and the sodium should normalize (less concerned about sodium bc not the underlying issue)

what is a risk when treating hyponatremia

osmotic demyelination syndrome (ODS)

who are at greatest risk with hyponatremia

pts who acutely develop moderate to severe hyponatremia and/or pts who have severe symptoms

changes in serum sodium concentration is associated with shift of…..

water into and out of body compartments

correction of hypovolemic hypotonic hyponatremia and why is this the best treatment

0.9% NaCl bc these patients have both sodium and water deficits

correction of euvolemic and hypervolemic hypotonic hyponatremia (in pts who do not require rapid correction)

water restriction is best

demeclocycline (not in canada), vasopressin receptor antagonists (VRA), urea, or loop diuretic can be used if water restriction not adequate

normal sodium range

135-145mmol/L

what does serum sodium represent

total body water

what to use to treat hyponatremia in patients with SEVERE symptoms

3% NaCl

loop diuretic can also be administered concurrently to enhance the serum sodium correction by enhancing free water excretion

who requires long term management of hyponatremia

patients whom the underlying cause that cannot be corrected

long term management of hyponatremia i those who require it

depending on cause: water restriction, increasing sodium intake and/or VRA

what is osmotic demyelination syndrome (ODS) (and how does it occur, what are symptoms)

neurologic disease caused by severe damage of the myelin sheath of nerve cells in the brainstem

ODS occurs with too rapid correction of hyponatremia

resulting in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma, death

who is particularly susceptible to ODS/ at increased risk

severe malnutrition, alcoholism, or advanced liver disease, may be particularly susceptible

hyponatremia >48hr, very low Na+ (<120), correction of Na+ >12 mmol/L during 24hr

goal of treatment for hyponatremia

reduce cerebral edema and increase serum Na+ only to the point necessary to maintain normal respiration, keep pt seizure free and alert, and prevent ODS

what is the rate and max rate to raise serum sodium at when treating hyponatremia

rate of 0.5-1mmol/L/hr initially until reach 120mmol/L, then by 0.5mmol/L/hr, max 12 mmol/L in first 24hr

characteristics of water and sodium loss/gain in hypovolemic hyponatremia

sodium loss » water loss (but both sodium and water are low, sodium is just lower)

causes of hypovolemic hyponatremia (renal and non renal)

thiazide diuretics

diarrhea, cerebral salt wasting

effect of hypovolemic hyponatremia on TBW and TBNa

decreases both (water more than sodium ?)

additional lab findings of renal vs non renal hypovolemic hyponatremia (Uosm, UNa)

renal: UOsm high, UNa high

nonrenal: UOsm high, UNa low

clinical presentation of hypovolemic hyponatremia

orthostasis, hypotension, tachycardia, dry mucous membranes, CNS changes

treatment of hypovolemic hyponatremia

0.9% NaCl until vital signs stable; maintenance fluids to continue fluid deficit replacement; sodium replacement if cerebral salt wasting

what treatment is contraindicated in hypovolemic hyponatremia

VRA

euvolemic (isovolemic) hyponatremia water and sodium loss/gain

water gain only

causes of euvolemic hyponatremia

SIADH

effect of euvolemic hyponatremia on TBW and TBNa

increased TBW, normal TBNa