Fluids

Functions of body fluids

• lubricant: joints, pleural space (lungs), heart

• metabolism- solvent for chemical reactions

• transport of oxygen, nutrients, chemical messengers

• regulates body temperature

Fluid distribution in body

• total body water (60%) (weight in kg multiple by .6 to find how much water in body)

  • 33% (1/3) extracellular

    • 25% interstitial fluid: fluids between cells, lymph, GI fluids, spinal column fluid, fluid in eyes, tears, synovial fluid)

    • 8% blood plasma

  • 66% (2/3) intracellular fluid: found inside the cells of every kind of tissue, blood cells, bone, muscle, adipose, etc

Osmolality

• solute (stuff) concentration in the blood

• Sodium, a solute, is main ion of osmolality (water follows Na)

Osmosis

• water movement across a semi-permeable membrane

• from lower concentration to higher concentration

Diffusion

• movement of particles down a concentration gradient

Active Transport

• movement of particles AGAINST a concentration gradient

• requires energy

Hydrostatic pressure

• water “pushing’ pressure

• push water out of vessel

• ex: BP, measure in arteries increase BP increase hydrostatic edema

Osmotic Pressure

• water “pulling” pressure

• pull water into cells

Colloidal osmotic pressure (COP)

• Albumin- protein, is the main colloid

• large plasma protein that influences water movement

• water “pulling” pressure

Fluid homeostasis: balance of intake and output

• Intake:

  • osmolality

  • decrease circulating volume

  • dry mucous membrane

  • aldosterone: RAAS→ increase BP; hold onto Na→ hold H2O increase circulating volume

  • Antidiuretic hormone (ADH)

• Output:

  • Natriuretic peptides

  • BNP- brain natriuretic peptide

  • ANP- atrial natriuretic peptide

Fluid homeostasis: Increase

• Aldosterone

  • secreted by adrenal cortex

  • renin-angiotensin-aldosterone

  • renal tubules reabsorb Na and water

    • water follows Na

  • Excrete K

• Antidiuretic hormone (ADH)

  • Synthesized in the hypothalamus

  • stored in and released from posterior pituitary

  • Released with increased osmolality and decreased circulating volume

  • effects distal tubule and collecting ducts

    • water reabsorption

    • decrease amount of urine

    • increased concentration of urine

Fluid homeostasis: decrease

• tell kidney to get rid of water (more urine)

• Atrial natriuretic peptide (ANP)

  • released from the right atrium when heart is stretched- increased circulating volume

• B-type natriuretic peptide or N-terminal-pro-BNP (NT-pro-BNP) (BNP)

  • promotes fluid excretion

  • increased Na excretion which takes H2O (urine more dilute, urine Na level increase, kidney put out Na to get ride of H2O)

  • Diuresis

Diuresis

• Increased production of urine by the kidneys

• medications, “drugs” and other stimulation can increase diuresis

• Caffenine natural diuretic

• exercise

• increased fluid intake

  • some fluids will increase diuresis more than just plain water

Diuresis medications

• for fluid volume overload

  • helps lower excess fluid volume, which lowers BP and edema

• block reabsorption of Na in tubules (so no water absorption)

• will lose K as well as Na, hard to maintain K levels, so monitor

• Loop diuretics: furosemide

  • loop of henle, block protein channel, that normally reabsorbs Na, K, and Cl back into body

  • by stopping reabsorption medicine keeps salt (Na) and water inside the kidney tubes to be flushed out by urine, which reduce fluid build up and lowers blood volume

• Thiazide: Hydrochlorothiazide

  • blocks Na and Cl cotransporter in the distal convoluted tubules of kidneys

  • prevents reabsorption of Na and Cl causing body to excrete more salt and water into urine

• Potassium-sparing: Spironolactone

  • helps to hold onto K while getting rid of Na and H2O

• Osmotic: Mannitol

  • IV increases osmololity in blood vessel, pull fluid in from tissue

Tonicity

• related to the osmotic pressure of a solution- how much it influences the movement of water

• refers to how “osmotically” similar a solution is to our intravascular fluid (or plasma)

• Tonicity of the blood

• 2 (Na) + Gluc/18 = tonicity

Isotonic solutions

• concentration of stuff ‘equal” to intravascular plasma

• concentration=plasma no movement of fluid

• Ex: 0.9% saline, lactated ringer’s, D5W ( isotonic in the bag but becomes hypotonic in body as cells consume the sugar)

Hypotonic

• has lower concentration of solutes (like salt, sugar) than inside the cell

• Water naturally moves through a cell membrane to balance concentrations. In a hypotonic environment, water rushes into the cell. (so fluid moves out of vascular space, into cell, bloodstream → cell)

• 0.45% saline

• EX: give to patients with dehyrdation, hypernatremia

Hypertonic

• higher concentration of solute (salt, sugar) and higher osmotic pressure outside the cell than inside ( water moves out of cell and into surrounding solution, fluid moves to vascular space)

• 3% saline, D5W, 0.9% saline

• EX: give to patients Hypovolemia (increased blood volume), increased cranial pressure/ brain swelling, hyponatermia

Fluid imbalances 2 major categories

• imbalance of volume (too much or too little)

• imbalance of concentration (too many or too few)

What are some causes of fluid deficit

• hypovolemia

  • lose more than intake

  • results in dehydration decrease blood volume

• gatrointestinal loss (vomitting, diarrehea)

• fever, hemorrage, diruretics, decrease oral intake, sweating

Fluid imbalance: volume deficit hypovolemia

• isotonic hypovolemia

• equal decrease water and Na (too much out, not enough in)

• loss of body fluid that contains similar concentration of Na and H2O as the blood plasma

  • causes: acute reduction in the effect of circulating blood volume, specifically the plasma volume, which directly results in decrease in tissue perfusion and inadequate O2 delivery to tissues

• Causes: loss mainyl come from inside vessels

  • emesis or gastric drainage

  • diarrhea

  • third spaciing- edema or ascites

    • intravascular hypolemia

  • burns, hemorrhage, sweating

Hypovolemia clinical manifestations

• Increased HR (tachycardia, early sign)

• decrease BP (late sign)

• postural hypotension (late sign)

• weight loss (early sign)

• flat neck veins

• prolonged cap refill

• lightheadedness or dizziness, syncope

• oliguria (low urine, want 30cc/hr or more for urine, if below that bad)

• decreased skin turgor

• dry mucous membranes

• hard stool

• soft, sunken eyeballs

• sunken fontanel in infants

Fluid imbalance: volume excess hypervolemia

• heart failure, kidney failure, liver failure (cirrhosis)

• causes:

  • excessive infusion of isotonic solutions (NS 0.95, LR)

  • renal retention of Na and water

  • increased intake

• clinical manifestations

  • weight gain (make sure measuring and monitoring regularly, 2lb/one day, 5lb/one week)

  • edema

  • bounding pulse

  • distended jugular vein

  • crackles

  • orthopnea

  • bulging fontanel

Fluid balance: sodium and water

• abnormal Na levels can cause fluid shifts (kidney and hormones regulate Na)

4 way to maintain fluid balance (pressure)

• capillary hydrostatic pressure: BP movement of H2O from capillary into interstitial space, represents force of blood pushing against capillary walls facilitating nutrient and fluid exchange

• capillary plasma oncotic pressure: osmotically attracting water from interstitial space into the capillary, osmotic pressure exerted by proteins, primarily albumin in the blood plasma

• interstitial hydrostatic pressure: inward movement of H2O from the interstitial space into the capillary it is the pressure or push excerted by the fluid located in the spaces between your cells at interstitium, against the oustide walls of the blood vessels

• interstitial oncotic pressure: osmotically, atrracting water from capillary into the interstitial space, pressure helps prevent excessive fluid accumulation in tissues, though effect less dominat than plasma, oncotic pressure

Edema: causes

• increases capillary hydrostatic pressure (accumulation of excess interstitial fluid, results from elevated capillary hydrostatic pressure)

  • increased flow or blood pressure

  • vein blockage

• increased interstitial osmtoic pressure

  • increased vascular permeability

  • leakage of protein into interstitial space

• decreased capillary osmotic pressure

  • decreased plasma proteins/ albumin

• blocakge of lymph drainage

  • lymphatic circulation carries excess interstitial fluid and protein back to the systemic circulation

  • also has a lot of lymphocytes

Edema: increased hydrostatic pressure

• swelling caused by high blood pressure inside small blood vessels, inside those capillaries

• interstitial space is elastic and expandable

• excess fluid in the interstitial space is edema

• classic sign of volume excess/ overload (renal, heart failure)

• 1l fluid= 1kg (2.2lbs)

• there can be a significant increase in ECF before you see edema

Edema: increased hydrostatic pressure

• Venous obstruction

  • thrombophlebitis

  • hepatic obstruction

  • tight clothing on extremities

  • prolonged standing

• Sodium or water retention

  • congestive heart failre

  • renal failure

Edema: decreased capillary osmotic pressure

• fluid build up caused by lack of protein

• decrease in prodcution or loss of albumin (protein decrease, fluid leaks into surrounding tissues)

• loss of plasma proteins

Loss of plasma proteins

• leakage of plasma into interstitial space

• there is increased capillary permeability

• damage to the endothelial cells

  • burns

  • inflammation

  • immune response

Edema: increased interstitial osmotic pressure

• higher than normal pulling force in tissue space

• increased protein in the interstitial space

  • immune response or inflammation

  • protein in the interstitial space

• increase the osmotic (water pulling) pressure in the interstitial space

• contributes to more fluid being lost from inside the vessels

Edema: blockage of lymph drainage

• “picks up” protein and fluid in the interstitial space and puts it back into circulation

• decreased lymph drainage

  • removed lymph nodes

• blocked lymph drainage

  • cancer

  • infection

Third spacing

• shift of fluid from the intravascular space (inside the blood vessels) to a space where it cannot be used

• usually a serous cavity

  • 3 in the body: pleural, pericardial and peritoneal

• self perpetuating process (external intervention needed to remove)

• fluid typically protein rich

• accumulates but not reabsorbed

• protein rich fluid will pull more ‘water"‘ into the space

Third spacing: ascites

Liver disease

• peritoneal fluid backup causes abdomne to be really big with fluid

Paracentesis

• treatment for ascites

• drain fluid from the abdomen

• monitor for hypotension beauce there is going to be a fluid shift

Problems with fluid accumulation and edema

• increased distabce for diffusion of nutrients, oxygen

• impaired blood flow

• slower healing

• increased risk of infection

• pressure sores over bony prominences

loop diuretics

• work in loop of henle

• decrease reabsorption of Na, Cl, K, and Ca

  • osmotic gradient

  • prevents reabsorption of water

• furosemide (Lasix)

  • 20mg-200mg

• Bumetanide

• Torsemide

• Ethacrynic acid

Loop diuretics: furosemide side effects

• risk of hypokalemia because losing K as well

• nausea or vomitting

• constipation or diarrhea

• Hypokalemia

  • craping

  • dysrhythmias

• dehydration

• tinnitus and hearing impairment

  • higher doses, IV and renal impariment

Which drug would you have to closely monitor if the patient was also taking furosemide

Digoxin