Fluid Therapy

Question 1

Indications for fluid therapy

Answer 1

to treat dehydration, hypovolemia or hypoperfusion
to maintain intravascular fluid volume and osmotic pressure
to correct electrolyte imbalances

Question 2

functions of water

Answer 2

transportation of nutrients and oxygen across cells
solvent for minerals and nutrients:> metabolic process
contributes to body temperature regulation
flushes metabolic (liver) and excretory (kidney) wastes
moistens tissues: oral cavity, eyes, airway
lubricates joints

Question 3

TBW

Answer 3

60% of BW

Question 4

ECF

Answer 4

20% BW

1/3 TBW

Question 5

ICF

Answer 5

40% BW

2/3 TBW

Question 6

IVF

Answer 6

5% BW

1/12 TBW

Question 7

ISF

Answer 7

15% BW

3/12 TBW

Question 8

What influences fluid movement

Answer 8

cell membrane: permeable to water, impermeable to ions

Capillary wall: permeable to water, permeable to ions, impermeable to proteins

Question 9

Osmosis

Answer 9

dependent on concentration gradients of ions
approx osmolality in both ECF and ICF is 300 mOsm/kg
sodium potassium pump maintains a vital concentration gradient
tonicity as determined by osmolality of solutions
isotonic: no effect on RBC size
hypotonic: RBC expands > hemolysis
Hypertonic: RBC shrinks

Question 10

Plasma proteins and oncotic pressure

Answer 10

at pH 7.4 have a net negative charge: vital for driving fluid inward, esp IVF
physiological osmotic pressure is approc 23 mmHg
Albumin is the most important determinant of colloid oncotic pressure
edema formation likely during hypoalbuminemia

Question 11

Hydrostatic pressure

Answer 11

exerted by fluid due to their molecular weight
Antagonizes osmosis (ICF, ECF) during fluid shifts
Drives fluids outwards

Question 12

Extracellular fluid movement

Answer 12

well explained by starling-landis equation
Capillaries: freely permeable to water and small solutes, but not to protein (albumin)
this results in high protein gradient in the IVF vs ISF
Opposing hydrostatic pressure exists at the arteriolar end of capillary bed
so fluid moves from IVF to ISF space
at venous end of capillary bed fluid mostly moves back to IVF space, and lymphatics are responsible for moving back the remainder of ISF to IVF space
Alterations to this balanced cause edema or dehydration

Question 13

Summary on body water compartments

Answer 13

the amount of fluid in the ICF, ECF compartments is maintained almost constant in healthy animals by various homeostatic processes that involve movement of ions across the capillary bed, and these processes are driven by such forces as osmolality, colloid oncotic pressure and hydrostatic pressure within these compartments, among others

Question 14

Crystalloids

Answer 14

contain water, electrolytes, non-electrolytes
Can enter all body fluid compartments
Replaces small blood losses at 3:1 v/v ratio
can be isotonic, hypotonic, hypertonic
Two main types: replacement (balanced) solution; maintenance solutions

Question 15

Replacement (balanced) solutions

Answer 15

Include Ringers solution, lactated ringers solution (LRS), plasmalyte R (normosol R)
used to replace body water and electrolytes; for diarrhea, vomiting, polyuria, third space losses, dehydration
These are the standard fluids used in anesthetized patients
Electrolyte composition similar to ECF
causes no change in plasma electrolytes
excessive large volume dilute proteins, avoid in hypoalbuminemia
large volumes cause rapid re-expansion of ECF but:
~1/3 remains IVF after 30 min
~1/4 remains IVF after 1 hr
normally contain alkalinizing agents: lactate, acetate, gluconate
Using these as maintenance solutions for long periods predisposes patients to hypernatremis and hypokalemia