Fluid Balance

fluid compartments

• intracellular compartment

• extracellular compartment

extracellular compartments

• intravascular fluid (plasma within BV’s)

• interstitial fluid (fluid that lies between cells/tissues)

• transcellular fluid (cerebral spinal fluid, synovial fluid)

intracellular fluids

• potassium, phosphate, protein, magnesium, and sulfate ions

• provide cells with nutrients and assist in cellular metabolism

• sodium-potassium pump

extracellular fluid

• all body fluid outside the cells

• plasma - fluid portion of blood

• transport medium between blood and body cells for nutrients, gases, waste products, and other substances

osmosis

• net diffusion or movement of water across cell membrane

• passive process requiring no expenditure of energy

osmolality

• concentration of solute in body water

• level is primarily impacted by sodium levels

• normal is ~ 275 to 295

• hypothalamus senses osmolality

• reflects pt hydration status

starling forces

• capillary hydrostatic pressure

• capillary oncotic pressure

capillary hydrostatic pressure

• force is generated by contractions of the heart

• pressure or force of a fluid inside a restricted space (highest in the arterial end of the capillary)

• hydrostatic pressure PUSHES water from the capillary into the interstitial fluid

capillary oncotic pressure

• what is a pulling force on water that is created by proteins albumin

• oncotic pressure pulls water from the interstitial fluid to the capillary

• creates oncotic pressure and helps keep blood within the capillary

thirst

awareness of desire to drink that occurs in response to stimulation of osmoreceptors in hypothalamus

arterial baroreceptors

• stretch receptors that detect pressure changes

• located in arch of aorta, carotid sinus, and pulmonary arteries

regulation of fluid balance

decrease in BP, BV, and osmolality → osmoreceptors in hypothalamus stimulates posterior pituitary to secrete ADH → increases distal tubule permeability to increase resorption of water → decrease UO, BP, BV, and blood osmolality

RAAS

• BP decreases

• renin released from kidneys and circulates in body to liver

• liver converts renin to angiotensinogin

• angiotensin 1 → angiotensin 2

• angiotensin 2 constricts BV’s and releases aldosterone and ADH → retains sodium and water

• increased BP

lab values to monitor with fluid balance

• BUN

• creatinine

• BUN:creatinine ratio

• osmolality

• serum albumin

electrolytes to monitor

• extracellular: sodium

• intracellular: potassium, mg, phosphorus

sodium

• responsible for water balance

• required for normal transmission of impulses across muscle and nerve cells thru sodium-potassium pump mechanism

• changes in sodium levels alter water balance

calcium

• located almost entirely within bone

• required for blood coagulation in coagulation cascade, neuromuscular contraction, enzymatic activities, and bone integrity

potassium

• mostly intracellular

• vital in maintaining normal cardiac and neuromuscular function

• role in normal cell membrane function

magnesium

• role in nerve cell conduction by acting as first line treatment for seizure sin preeclampsia and eclampsia

• mg sulfate works by decreasing excitability of nervous system

• required for ample absorption of potassium

phosphorus/phosphate

• essential component of bones and teeth

• required for energy in production of ATP