Week 5: IV Fluids Flashcards
What is the O2 dissociation curve of blood?
Relationship between PaO2 and Sa O2
Amount of O2 dissolved in blood (PaO2), compared to O2 saturation
PaO2 80 or above does not increase SaO2 much (>95%), however below 60-70 causes a precipitous drop
What is the function of water in the body?
Transport: nutrients, O2, CO2, electrolytes, metabolic waste, etc between fluid compartments, cells, organs Blood plasma (main component) Temperature regulation Lubrication Shock absorption
What are cations?
Positively charged ions
Na+, K+, Ca+2
What are anions?
Negatively charged ions
HCO3-, Cl-
How do electrolytes move between cells?
Diffusion
Facilitated diffusion
Active transport
What is diffusion?
Movement of molecules from an area of high to low concentration
What is facilitated diffusion?
Movement of a molecule down its concentration gradient assisted by a protein carrier (e.g insulin and glucose)
What is active transport?
Movement of molecules against its concentration gradient. This process requires energy (ATP) e.g. sodium/potassium pump
How does water move between fluid compartments?
Osmosis
Filtration
What is osmolality?
Osmolality is a measure of the concentration of particles in plasma
What is the normal serum osmolality?
275 –295 mOsm/kg
What is osmosis?
Osmosis is the movement of water across a semi permeable membrane from an area of high water concentration to an area of lower water concentration
How does protein relate to osmosis?
Albumin found in intravascular space
Major determinant for movement of water from interstitial space to intravascular compartment
Low albumin –> water moves into interstitial space (oedema)
What is an isotonic solution?
Concentration inside and outside cell is the same
No net movement of fluid inside or outside cell
Osmolarity: 270 -300 mOsm/L
What is a hypotonic solution?
Higher soluter concentration inside cell
Water moves form IVS to ICS
Cell swells
Osmolarity: < 270 mOsm/L
What is a hypertonic solution?
Higher solute concentration outside cell
Fluid shifts from ICS to IVS
Cell shrinks
Osmolarity: >300 mOsm/L
What is hydrostatic pressure?
Water moves between compartments by filtration
Filtration: water moves from areas of high pressure to low
Arterial end of capillaries: water moves out of capillary into interstitial and intracellular compartment
How does hydrostatic pressure cause pulmonary oedema?
HF –> build up of blood in pulmonary capillaries –> increased hydrostatic pressure –> fluid forced into interstitial compartment –> PO
How does hydrostatic pressure cause peripheral oedema?
Venous insufficiency in lower limbs –> increased hydrostatic pressure –> fluid forced into interstitial compartment –> peripheral oedema
What is oncotic pressure/colloid osmotic pressure?
Protein molecules attract water, pulling fluid into vascular space
What is net filtration pressure?
The added up pressure of net hydrostatic pressure and net oncotic pressure. Can be positive (arterial) or negative (venous)
How is water balance controlled?
Water homeostasis: balance between fluid intake and excretion
Controlled by neurohormonal systems: ADH, RAAS system, ANF
What are types of crystalloid IV fluids?
0.9% NaCl 5% dextrose Glucose 4% in 0.18% NaCl Hartmann's Plasmalyte
What are crystalloids?
Water with electrolytes
