Ch 6 Electrolytes and Fluid Balance

what are the functions of water

• -Transports nutrients

• -Transports and excretes metabolic waste

• -Supports cell shape and structure

• -Lubricates friction-generating surfaces

• -Sustains normal body temperature

electrolyte balance is significantly integrated with

fluid balance

aprox % of water in males and females

• males: 60%

• females: 50%

what influences total body water

proportion of lean body mass to body fat, and age

what are the 3 fluid compartments in the body

ICF, ECF, third space

Extracellular fluid (ECF) includes what

interstitial, intravascular, and transcellular

what does third space fluid include

• -Peritoneal, pericardial, and thoracic cavities

• -Joints and bursae

2/3 rule?

interstitial fluid makes up 2/3 of extracellular volume

PRESSURES

what is osmosis

movement of fluids across a semipermeable membrane from an area of low concentration (of solutes) to an area of high concentration (more solutes)

what is filtration

movement of fluids and solutes

what are the 2 types of pressure

osmotic pressure and hydrostatic pressure

what is osmotic pressure

force that pulls fluid across membrane (pulling force of solutes like salt and proteins that draws water toward higher concentration, aka pulling water towards the solutes)

In our vessels, this tends to be the force that pulls water into the blood vessel (higher concentration of molecules like albumin protein)

what is hydrostatic pressure

pressure exerted by fluid on membrane (physical push exerted by a fluid against a containing wall, aka weight of water/fluid pressing on our blood vessel walls)

In our vessels, this tends to be the blood pressure pushing water out of the blood vessel

osmotic pressure can be expressed as _____ and _______

osmolarity (osmole/L) or osmolality (osmole/kg)

what type of fluids may result in cellular dehydration?

hypertonic

what type of fluids may result in cellular swelling?

hypotonic

what is normal serum osmolality?

285-295 mOsm

what is normal GI tract osmolality?

300 mOsm

INTAKE ESTIMATIONS

what is considered part of fluid intake

Anything fluid at room temperature

metabolic water is what and is it good for intake estimation?

• -estimated from using intakes of carbs, protein, and fat as variables

• -contributes little in a practical sense

what is part of fluid outake?

sensible and insensible losses

what are sensible losses?

 those that are visible and measurable

• -Ex: urine and feces

what are insensible losses?

 usually not seen or measured

• -Through respiration or through skin by evaporation

what is obligatory losses? what is another name for it?

minimum amount needed to remove waste in urine

aka: renal solute load

total urine output is the sum of ___________ and _____________

obligatory urine and facultative urine

what is facultative urine

variable amount of urine adjusted by the body depending on water intake

solute concentration in urine is determined by measuring what?

specific gravity

what two lab findings are best to determine hydration status

1.specific gravity

2.osmolarity

what are the different methods for fluid requirement?

• -RDA method

• - Holiday-Seger

• - ml/kg

• - BSA method

RDA method for fluid intake

1ml/kcal

-not best for caloric restriction… would be okay for maintenance and surplus

Holiday-Seger method (peds)

• -1-10kg

• -11-20kg

• -≥ 21kg

1-10 kg: 100-150 mL/kg (OR 4 mL/kg/hr)

11-20kg: 1000 mL + 50 mL/kg for each kg over 10 kg (OR 40 mL/hr + 2 mL/kg for weight >10kg)

≥ 21kg: 1500 mL + 25 mL/kg for each kg over 20kg (OR 60 mL/hr + 1 ml/kg for weight >20kg)

Holiday-Seger method adult

≥ 31kg: 1700 mL + 30 mL/kg for every kg over 30 kg

ml/kg method

• adolescents

• young adults (16-30)

• average adult

• 55-65

• ≥65

• Adolescents: 40-60mL/kg

• Young adults 16-30 years old: 35-40 mL/kg

• Average adult: 30-35 mL/kg

• Adult, 55-65 years: 30ml/kg

• Adult ≥ 65 years: 25 ml/kg

BODY SOLUTES

what are the types of body solutes?

electrolytes and other (glucose, proteins, urea, lactate, and organic acids)

electrolytes include which (8)

sodium, chloride, magnesium, potassium, calcium, phosphate, bicarbonate, sulfate

electrolytes do what in water

dissociate in fluids to form charged particles/ions

other solutes include (5)

• Glucose, protein, urea, lactate, and organic acids

Glucose, protein, urea, lactate, and organic acids do what in solutions

remain stable

distribution of electrolytes: relationship between cations and anions

Sum of cations must be equal to sum of anions within a given compartment

what factors influence movement of solutes (4)

• Molecular size

• Electrical charge of the molecule

• Hydrostatic pressure

• Method of solute transport

plasma, interstitial fluid, and intracellular fluid compartment components

**extracellular has large sodium and chloride compartment

**intracellular has large potassium and phosphate compartment

ECF and ICF normally are in ________equilibrium

osmotic

ECF volume regulated by

sodium balance

refers to plasma and interstitial (high Na and Cl)

ICF volume regulated by

osmolality and partially by Na/K membrane pump

refers to inside the cell (high K and phosphate)

for osmolality, Equal to blood/body fluids means

isotonic

for osmolality, greater than blood/body fluids means

hypertonic

for osmolality, less than blood/body fluids means

hypotonic

which 3 electrolytes have AIs set?

sodium, potassium, and chloride

Serum levels are _______ to maintain electroneutrality

altered

what are the 4 major electrolytes?

Na, K, Cl, HCO3

functions od the major electrolytes (4)

• Maintenance of body fluid osmolarity

• Distribution of body fluids among fluid compartments

• Regulation of acid-base balance

• Promotion of neuromuscular irritability

sources of potassium

PHYSIOLOGICAL REGULATION OF FLUID AND ELECTROLYTES

by what organ is thirst triggered?

hypothalamus

increase in pressure in capillaries results in what for the kidneys

larger amounts of fluid moving from the capillaries into the renal tubules (excreted as urine)

what are the 2 hormonal influences in the regulation of fluid and electrolytes?

Renin-angiotensin-aldosterone system (RAAS) and arginine vasopressin

what within the blood vessels is stimulated by low hydrostatic pressure?

baroreceptors

low hydrostatic blood pressure is indicative of

decrease in blood volume

what 2 things stimulate the pituitary gland to release arginine vasopressin?

• -Increasing osmolality of the ECF

• -Detection of a decrease in hydrostatic pressure by baroreceptors in blood vessels

fluid/electrolyte regulation pathway (try to explain from memory)

Decrease Na/Cl OR ECF volume Or arterial BP will result in:

• -Liver activation to release angiotensinogen and renin release from kidney --> conversion of angiotensin 1 --> conversion to angiotensin 2 (with lung enzyme) -->

• -Angiotensin 2 will trigger:

  • Vasopressin release --> H2O reabsorption --> water conservation

  • Thirst --> increased fluid intake --> water increase to correct ECF volume

  • Vasoconstriction --> helps correct blood pressure

  • Trigger adrenal cortex to release aldosterone --> trigger kidney to reabsorb more sodium (and chloride passively) --> increase H20 in ECF --> H20 conservation

what are the 4 issues we may see with fluid/electrolyte balance?

1.decrease ECF volume

2.decrease arterial BP

3.decrease NaCl (salt)

4.increase osmolarity

Decrease Na/Cl OR ECF volume Or arterial BP will result in

the release of renin from the kidneys

renin and angiotensinogen (from liver) form

angiotensin I

what happens to angiotensin I?

converts to angiotensin II by angiotensin-converting enzyme (lung enzyme)

what does angiotensin II do (4 different possible paths)

1.triggers vasopressin release**

2.trigger thirst**

3.trigger vasoconstriction**

4.aldosterone release from adrenal cortex

**other things can also cause these

aldosterone does what for fluid balance?

increase Na reabsorption (Cl passively) which will cause more H20 to be conserved

vasopressin will do what 2 main actions?

1.increase H2O reabsorption

2.arterial vasoconstriction

increased water reabsorption will do what? (2)

increase water reabsorption by kidney tubules (so decrease urine output) will decrease plasma osmolarity and increase plasma volume

arterial vasoconstriction will do what?

increase arterial BP

increased osmolarity occurs how?

decrease in water volume makes solute concentration higher

increased thirst will to what?

increase water intake

increased water intake will do what 2 things

decrease plasma osmolarity and increase plasma volume (ECF volume)

what peptide assist in sodium control

atrial natriuretic peptide (ANP)

how is high potassium regulated (simple)

aldosterone release from adrenal glands

how are calcium and phosphorus regulated?

Dependent on intestinal absorption, exchange between ECF and bone, and renal excretion of these minerals

DISORDERS OF FLUID BALANCE

disorders of fluid balance deal with what 3 things

changes in fluid volume, concentration or osmolarity and composition

changes in fluid, electrolyte, and acid-base balance typically occur

together (rare to happen in isolation)

hypovolemia is always related to what 2 things

renal (urine excretion) or extrarenal loss of fluids

what do we mean by extrarenal loss of fluids?

when fluids are trapped in body spaces

• -like with ascites, HF, pulmonary edema and burns

excessive renal losses occurs secondary to

diuresis (increased urine production by kidneys)

hyperglycemia impacts urine output by

increasing it

skin losses contribute to hypovolemia as

fever, sweating

Signs and symptoms of hypovolemia (5)

-Poor skin turgor (skin with decreased turgor remains elevated after being pulled up and released

-Decreased moisture in oral cavity

-Decreased urine output (oliguria)

-Increased urinary specific gravity (1.003-1.035 is normal)

• -This reflects fluids conservation by the kidneys

-Disrupted BUN/Cr ratio (>10.1)

hypovolemia physical findings (6)

 tachycardia, weak pulse, dizziness, poor skin turgor, dry skin, and mucous membranes

lab findings for hypovolemia

No single lab finding will confirm hypovolemia

(Signs might include elevated urine specific gravity, elevated electrolytes)

treatment for hypovolemia is based on

 underlying cause for the fluid deficit

how do we assess weight change for fluid balance?

% weight loss

2% loss/gain:

mild fluid volume deficit or excess (+- 3lbs in a 150lb person)

5% loss/gain

moderate fluid volume deficit or excess (+- 7.5lbs in a 150lb person)

8% loss/gain

severe fluid volume deficit or excess (+- 12lbs in a 150lb person)

what is the most common cause for hypervolemia

decrease in urinary output

why may someone have decreased output (think conditions)

Compromised regulation (CHF, renal failure, cirrhosis, steroid use)

hypervolemia results in what 3 things

elevated BP, jugular venous distension, and edema

what respiratory symptoms are seen with hypervolemia

difficulty breathing (dyspnea) and the presence of rales (fine crackle sound of lungs)

signs and symptoms of hypervolemia

• Weight gain over short period of time

• Peripheral edema

• Distended neck and peripheral veins

• Slow emptying peripheral veins

• Decreased BUN, hematocrit (hemodilution)

• Polyuria if renal function is normal

• Increased RR, moist rales, rhonchi

• Can include ascites, or pleural effusion depending on underlying cause

edema categories