Fluids and Electrolytes (Intro)

exam 1

50-70% of body weight

total body water makes up

80%

percent water in infants

60%

percent water in males

50%

percent water females

45% decreasing with age

percent water in adults 60 and older

intracellular fluid (ICF) and extracellular fluid (ECF)

total body water (TBW) is divided into

2/3 of TBW

ICF is

1/3 of TBW

ECF is

interstitial fluid (ISF) and intravascular fluid (IVF/plasma)

ECF is further divided into

80% of ECF

ISF is

20% of ECF

IVF is

sodium

major determinant of ECF volume and accounts for 90% of osmotic activity in the ECF

potassium

major determinant of ICF volume

isotonic fluids (0.9% NaCl)

• no change in ECF osmolality

• increase in ECF volume

• no change in ICF volume

hypotonic fluids (D5W)

• decrease in ECF osmolality

• increase in ECF volume

• water shifts into ICF → increases in ICF volume

hypertonic fluids (3% NaCl)

• increase in ECF osmolality

• increase in ECF volume

• water shifts out of ICF→ decrease in ICF volume

ADH

• increase free water reabsorption

• increases collecting duct permeability to water

• stimulated by hyperosmolarity and hypovolemia

Angiotensin II

• causes renal retention of sodium and water

• vasoconstricts efferent arterioles

• stimulates aldosterone release

aldosterone

• stimulates sodium and water reabsorption

• increases potassium and H+ excretion

• regulated by potassium levels, RAAS, sodium levels, and ACTH

cortisol

• has mineralcorticoid activity

• increases sodium and water retention→ increases blood pressure

catecholamines (NE, epinephrine)

• increases sodium and water reabsorption

• reduces renal blood flow

• activate RAAS

• shift potassium intracellularly

atrial natriuretic peptide (ANP)

• opposes RAAS

• increase sodium and water excretion

• causes vasodilation and increased vascular permeability

2000mL/day

average daily requirement of fluids

maintenance therapy (manage fluid)

replaces normal daily losses from urine, sweat, respiration, and stool

increased osmolarity and thirst

<700mL/day of fluids =

decreased osmolarity

2.5L/day fluids

replacement fluid therapy

• corrects existing fluid or electrolyte deficits

• used for GI, urinary, skin losses, bleeding, or third spacing

acute fluid restriction

• indicated with signs or intravascular volume depletion (tachycardia, hypotension, dry mucous membranes, decreased urine output)

crystalloids (0.9% NaCl or LR)

first line therapy for acute fluid restriction

Colloids

considered for acute fluid restriction only after failure of 4-6L crystalloids or significant edema