Fluid Therapy Flashcards
Special Features of Water
Polarity = responsible for many of chemical, physical properties
High surface tension, high specific heat, high heat of
vaporization, low vapor pressure, high boiling point
Water ionizes in nature, substances dissolved in water segregate into individual components
Also exists as a negatively charged hydroxyl ion (OH-), positively charged protonated ion (H3O+)
How much water in adult animal?
60%
How much water in neonate?
80%
Separation of ECF, ICF
separated by cell membranes
Freely permeable to water with use of carrier proteins, active
transport, passive transfusion
Governed by osmotic gradient
Separation of ISF, IVF
Endothelium
Freely permeable to water, various ionic solutes
Major cation in ECF
Na, 142mEq/L (plasma)
Major anion in ECF
Cl, 104mEq/L; HCO3 24mEq/L (plasma)
Major cation in ICF
K 140, Mg 34mEq/L (intracellular)
Major anions in ICF
OPs (40), proteins (50)
Osmolality
Determined btw different solute pressures
Solutes that cannot cross cell membrane contribute to effective osmolality = effective osmoses
Depends on NUMBER of particles in solution
Osmolality
Determined btw different solute pressures
Solutes that cannot cross cell membrane contribute to effective osmolality = effective osmoses
Ineffective Osmoses
Solutes that can readily diffuse across cell membrane, do not contribute to fluid shifts
In equilibrium on both sides of semi-permeable membrane
Osmolality of plasma, ISF
-Ions: K, Na, Cl, HCO3, glucose, urea
-Larger molecules (eg albumin) = important component in colloid oncotic pressure, contribute to little osmolality
ECF Osmolality
Mainly governed by Na, also glucose
Plasma Osmolality
Plasma osmolality (mOsm/kg)= 2 [(Na+) + (K+)] + [(Glucose)/18] + ([BUN] /2.8)
Normal = 300mOsm/L
Extracellular loss of Free Water
concentration of ECF concentrates increases causing osmotic pull (osmosis) of water through cell membrane to ECF
Movement of Fluid btw IVS, ISF
Occurs at level of capillaries, Starling’s Equation
Endothelial glycocalyx
glycocalyx model of transvascular fluid exchange and modification of starling’s equation
Filtration properties of capillary wall reside in endothelial glycocalyx layer (EGL)
Matrix covers the intracellular clefts
Glycocalyx COP replaces oncotic pressure of interstitum
Crystalloids
Classified based on tonicity relative to plasma
Isotonic crystalloids
Similar tonicity/osmolality vs plasma
Stay within ECF, no alteration in ICF volume
Fluids in ECF redistribute to IVF, ISF
Shock patients: up to one blood volume, start with 1/4-1/3 dose
LRS
–Racemic mixture of L and D lactate or just L lactate
–Ca ions: not recommended with blood products, may antagonize common anticoagulants -> production of micro emboli
Acetate Containing Solutions
–Maybe have more profound alkalinizing effect
–Large quantities (Norm R, Plasmalyte) rapidly bolused: VD DT release of adenosine from muscles = hypertension, esp in hypovolemic patients
Hypertonic Crystaloids
–Increased tonicity, osmolality vs plasma
–Increased osmotic pressure in IVF –> pulls water from ISF, ICF (ICF > ISF) –> immediate plasma expansion
–Follow with crystalloids
–Most common: 7.5% HSS
Components of 0.9% NaCl
154 Na, 154 Cl - hypertonic to plasma
LRS
Na 130
Cl 109
K 4
Ca 3
272mOsm/L
Plasmalyte
Na 148
Cl 98
K 5
Mg 3
294 mOsm/L - about isotonic to plasma
HSS
–Contraindicated with preexisting dehydration
–Effects can be prolonged with a colloid
–Cardiac arrhythmias, bradycardia, hypotension
–Dosing: 4-6mL/kg no faster than 1mL/kg/min
HSS Potential Clinopathologic Changes
hypernatremia, hypochloremic metabolic acidosis,
hyperosmolar renal failure, and hypokalemia
What equilibrium is responsible for maintaining slightly different concentrations of anions, cations in ICF vs ECF?
Gibbs Donnan Equilibrium
Filtration under normal conditions
Net filtration pressure responsible for movement out of capillaries into interstitum
Some of fluid normally returned to circulation via lymphatic system
