IV Fluids

Question 1

What are diff fluid and lyte disorders in a surgical pt?

Answer 1

- disorders of volume:
depletion
excess
- disorders of lyte concentrations:
sodium
potassium
chloride
calcium
Mg
phosphate

Question 2

What is the sequelae of inapprop fluid and lyte management?

Answer 2

• increased length of stay
• increased cost
• wound infection
• delayed wound healing
• anastomotic failure
• tachyarrhythmias
• cerebral edema, seizures, death
• pulm edema, CHF, renal failure

Question 3

What are you trying to accomplish w/ IV fluids?

Answer 3

• maintenance therapy:
  if pt isn’t expected to eat or drink for a period of time
• replacement therapy:
  correct abnormalities in volume and/or lytes
• volume resuscitation: hypotension, hemorrhage

Question 4

Total body water in diff pop groups?

Answer 4

• directly proportional to muscle mass: muscle mass is about 70% water
• inversely proportional to fat: fat is about 10% water
• neonates: 75-80% body wt is water
• young healthy fit female:
  on avg 55% of body wt is water
• young healthy fit male: 60% of body wt is water
• total body water decreases in:
  morbidly obese, elderly, or low muscle mass due to disease or injury
  may be as little as 35%

Question 5

Total body water consists of what 2 main compartments?

Answer 5

• intracellular fluid:
• fluid w/in cells
  2/3 TBW, in 70 kg man - 28 L
• extracellular fluid: 1/3 TBW, 14 L (70 kg man)

Question 6

Components of ECF?

Answer 6

• the fluid outside of cells
• plasma (vascular space):
  Na+ main cation, other cations: K+, Ca++, Mg++
  anions: Cl-, HCO3-, proteins, sulfates, organic acids
• interstitial space:
  same as plasma but lower concentration of protein

Question 7

Components of ICF?

Answer 7

• K+ and Mg++ main cations

- main anions: phosphates, sulfates and proteins

Question 8

Diffusion of proteins and ions?

Answer 8

• free diffusion is limited
• Na+ stays mainly outside of cell
• K+ stays mainly inside cell
• water may diffuse freely among all compartments

Question 9

Movement of water?

Answer 9

• passive
• exchange of water b/t intracellular and interstitial compartments is determined by osmotic gradients
• ex: if ECF is hypo-osmolar: water will go into cells where the osmolarity is higher until equilibrium is reached

Question 10

Normal body osmolarity? When will hyperosmolarity occur?

Answer 10

• normal = 285 osmol/L
• hyperosmolarity will occur in both ECF and ICF if extracellular osmolartiy is increased: fluid will move from ICF to ECF and leave the ICF more concentrated from loss of water so becomes hyperosmolar
• fluid constantly moves among intracellular, interstitial and vascular spaces to maintain balance

Question 11

What are the crystalloids?

Answer 11

• dextrose in water: D5W, D10W, D50W
• saline: isotonic (.9%), hypotonic (0.45% or 0.225%), hypertonic (3% or 5%)
• combo:
  D5 1/2 NS, D5 NS, D10 NS
• LR (K, HCO3, Mg, Ca)
• these solns contain small molecules and are able to pass through semipermeable membranes
• soln transfers easily across cell membrane of blood vessels

Question 12

What are the colloids?

Answer 12

• albumin: 5% in NS, 25% (salt poor)
• dextran
• hetastarch
• blood
• FFP
• solns that contain high MW proteins (like albumin) or starch
• don’t cross capillary semipermeable membrane
• remain in intravascular space (pulling fluid out of intracellular and interstitial space) for several days

Question 13

Crystalloids vs Colloids use?

Answer 13

• crystalloids are generally adequate for most situations needing fluid management
• colloids may be indicated when more rapid hemodynamic equilibration is reqd
• composition of soln and rate of admin are impt when addressing a specific situation

Question 14

Diff b/t iso/hypo/hyper-tonic?

Answer 14

• isotonic: given to expand ECF volume
• hypotonic: given to reverse dehydration
• hypertonic: given to increase ECF vol and decrease cellular swelling

Question 15

How do isotonic fluids work?

Answer 15

• have same osmolality as plasma so fluids remain primarily in ECF
• Isotonic IV fluids are used to replace ECF losses and to expand vascular volume quickly

Question 16

Diff isotonic fluids used?

Answer 16

• normal saline: provides Na and Cl in water w/ same osmolality as serum, no calories or free water
• Ringers soln: contains Na, K, Ca in similar concentrations to plasma but no dextrose, Mg, or bicarb, no calories or free water
• LR: contain Na, Cl, K, Ca, and lactate in concentrations similar to normal plasma, no dextrose, Mg or free water

Question 17

How do hypotonic solns work? When are these CI?

Answer 17

• lower osmolality than normal plasma
• increases cell water by pulling water out of vessels into cells: results in decreased vascular vol and increased cell water
• used to prevent and tx cellular dehydration by providing free water to cells
• CI in acute brain injuries b/c cerebral cells are very sensitive to free water, absorbing it rapidly and leading to cerebral cellular edema

Question 18

Diff hypotonic fluids used?

Answer 18

• D5W: although isotonic in IV bag, has hypotonic effect in body as dextrose is quickly metabolized: leaving free water that shifts osmosis from vessels into cells, dextrose content doesn’t meet daily nutritional caloric requirements but it does prevent starvation
• 1/2 NS or 1/4 NS: these fluids provide free water to cells as well as small amts of Na and Cl often used as maintenance fluids

Question 19

When are hypertonic fluids used?

Answer 19

• these have higher osmolality than normal plasma: causes water to be pulled from cells into vessels, resulting in increased vascular volume and decreased cell water
• used to tx very specific problems: admin in carefully controlled, limited doses to avoid vascular volume overload and cell dehydration - pulls excess fluid from cells and to promote osmotic diuresis
  ex:
  saline solns that are more than 0.9% - these are used infrequently

Question 20

diff b/t isotonic, hypotonic and hypertonic fluids?

Answer 20

• isotonic: stays inside bloodstream or intravascular compartment (0.9% NS, LR)
• hypotonic: will shift and flow into a more concentrated soln (drays fluid from vessels and into cells - D5W, 0.45% NS)
• hypertonic: will pull a less concentrated soln into itself (tx severe low Na levels - 3% or 5% NS)

Question 21

Where will D5W end up in the body?

Answer 21

• if given 1 L:
  it is just handled like free water - 700 ml would move into ICF, and other 300 ml will stay in ECF (75 ml of this will stay intravascular)

Question 22

Where will 1 L of NS end up in the body?

Answer 22

• just distributed in the ECF since cell membrane isn’t permeable to sodium
  so - 1 L = ECF (3/4 - in interstitial, and other 1/4 stays intravascular)

Question 23

If given 1 L of 5% albumin and PRBCs where will it end up?

Answer 23

• will stay in the intravascular compartment

Question 24

Adverse effects of IV fluids?

Answer 24

- NS: 
fluid overload
metabolic acidosis
hypernatremia
- LRs:
fluid overload
hyponatremia
hyperkalemia
- D5W:
hyponatremia

Question 25

What are the diff types of volume deficits?

Answer 25

- total body water: water loss (diabetes insipidus, osmotic diarrhea) - extracellular: salt and water loss (secretory diarrhea, ascites, edema), GI tract losses: V/D, NG sx, enteric fistulas, third spacing - Intravascular: acute hemorrhage

Question 26

What is the "third space? Causes of this?

Answer 26

- acute sequestration in body compartment that isn't in equilibrium w/ ECF (isotonic) - causes: intestinal obstruction severe pancreatitis peritonitis major venous obstruction capillary leak syndrome burns - this situation isn't normal and fluid is derived from ECF - need IV fluids to prevent ECF vol depletion - not interstitial and not intravascular - non-contributory space

Question 27

What is extracellular space volume loss?

Answer 27

- loss occurs more rapidly than from intracellular space | - no formula to accurately est total fluid deficit

Question 28

What are causes of increased states of fluid loss?

Answer 28

- fever - burns - sepsis - gastric fistulas - surgical drains (may or may not have high output) - or other states of increased metabolic activity

Question 29

What are signs of ECF depletion?

Answer 29

``` - clinical findings: thirst decreased urine output wt loss drowsiness to coma decreased skin turgor dry mucous membranes sunken eyes tachycardia orthostatic hypotension progressing to hypotension - lab findings: increased HCT elevated BUN/Creat elevated urine Na urine SG greater than 1.02 ```

Question 30

What are clinical signs to monitor for ECF depletion?

Answer 30

- watch hemodynamic parameters - urine output: normal is over 30 ml/hr - pt daily wts - daily labs: HCT BMP: serum Na may be helpful

Question 31

Signs of hypovolemia?

Answer 31

- orthostatic hypotension - tachycardia - flat neck veins - decreased skin turgor - dry mucosa - supine hypotension - oligouria - organ failure

Question 32

Signs of hypervolemia?

Answer 32

- HTN - tachycardia - increased JVP - gallop - edema - pleural effusion - pulmonary edema - ascites - organ failure

Question 33

A pt presents w/ severe hypovolemia and hypovolemic shock - what should be done?

Answer 33

- 1-2 L of 0.9% NS bolus/rapid infusion - continue until clincial signs of hypovolemia begin to improve: low BP, low urine output, and or impaired mental status - type of replacement fluid: if bleeding use blood to get HCT up to 35%, otherwise crystalloid vs colloid

Question 34

What should be given for replacement fluid for severe hypovolemia?

Answer 34

- crystalloid saline solns are equally effective in expanding plasma volume as colloids but need to use 1.5-3x as much b/c of extravascular distribution

Question 35

What are albumin advantages over isotonic saline as replacement fluid for severe hypovolemia?

Answer 35

- more rapid plasma volume expansion (remains in intravascular space) - lesser risk of pulmonary edema due to dilutional hypoalbuminemia - studies fail to demonstrate benefit though - disadvantages: cost, not as readily available - other colloids such as hyperoncotic starches: are assoc w/ increased risk of acute kidney injury and in some studies increased mortality

Question 36

Why may you need to buffer fluid replacement therapy?

Answer 36

- large volume resuscitation w/ isotonic saline may be assoc w/ development of hyperchloremic metabolic acidosis - isotonic saline is hyperchloremic compared to plasma - if acidotic add Na bicarb to infusate

Question 37

What should be given if pt has mild to moderate hypovolemia?

Answer 37

- rapid fluid resuscitation isn't necessary in pts w/ mild to moderate hypovolemia - to avoid worsening of volume deficit: rate of fluid admin must be greater than the rate of continued fluid losses - eqaul to output plus est insensible losses (30-50 ml/hr) plus any other fluid losses (GI) that may be present - consider admin of fluid at a rate that is 50-100 ml/hr greater than est fluid losses

Question 38

What type of replacement fluid should be used in hypernatremia?

Answer 38

- hypotonic solns

Question 39

What type of replacement fluid should be used in hyponatremia?

Answer 39

- isotonic or hypertonic saline

Question 40

What type of replacement fluid should be used in pt w/ blood loss?

Answer 40

- isotonic saline and or blood

Question 41

What should be added to fluid replacement in pts w/ hypokalemia or metabolic acidosis?

Answer 41

- K+ or bicarb may need to be added

Question 42

Route of lytes loss?

Answer 42

- no sig amt are lost in sweat or exhaled water vapor, all losses are urinary - thus anuric pts have no maintenance Na or K needs - always be careful w/ renal pt

Question 43

Disorders of sodium are regulated how?

Answer 43

- regulated by thirst, ADH and renal water handling | - a disruption in water balance is manifested as an abnormality in serum Na

Question 44

Na imbalances?

Answer 44

- Na is a fxnlly impermeable solute so it contributes to tonicity and induces water movement across membranes - hypernatremia = hyperosmolar (hypertonic) dehydration - hyponatremia = hypoosmolar (hypotonic) dehydration

Question 45

What is hypernatremia usually due to?

Answer 45

- water loss - loss of free water leads to increase in ECF osmolarity - always be careful when correcting hyper or hyponatremia - can lead to cerebral edema or central pontine myelinosis

Question 46

Management of hypernatremia?

Answer 46

- slow correction: prudent in pts w/ hypernatremia of longer or unknown duration, correct Na by 0.5 mEq/L/hr or 10 mEq/L w/ goal of 145 mEq/L, others suggest adding the calculated fluid deficit to maintenance fluid requirements and giving over 48 hrs - IVF: only hypotonic fluids are appropriate unless frank circulatory collapse exits, the more hypotonic the infusate, the lower the reqd volume to correct hypertonicity and the lower the risk of cerebral edema - rate of infusion is calc using Madias formula - est change in serum Na caused by 1 L of any infusate - the reqd vol and thus rate is determined by dividing the change in serum Na desired for a given period of time by the value obtained from madias formula

Question 47

What are expected fluid losses?

Answer 47

- measurable: urine (measure hourly if possible), GI (stool, stoma, drains, tubes, fistula, N/V/D) - insensible: (500 ml a day in healthy pt) sweat, exhaled, fever (increase by 100 ml/day/degree centigrade)

Question 48

Who needs fluid maintenance therapy?

Answer 48

- unable to eat or drink normally for prolonged period of time - periop pts - ventilated pts - goal: maintain fluid and lyte balance and provide nutrition - dextrose should be enough to prevent catabolism, after 1-2 wks of being unable to eat - should have TPN or enteral nutrition

Question 49

Monitoring parameters - fluid replacement?

Answer 49

- need baseline serum Na | - need baseline wt: est net gain or loss of fluid daily

Question 50

Maintenance therapy - requirements, monitoring?

Answer 50

- need maintenance therapy in pts that not eating, physically inactive, and afebrile - actual requirement in these pts is less than 1 L/day - can begin w/ 2L of IV fluid/day - can use 0.45% NS D5 + 20 mEq K+ - giving 2L over 24 hrs - giving about 80 - 100 ml/hr - want to check daily lytes, if Na falls - want to use NS if it increases use hypotonic soln