Fluids Flashcards
Body water distribution
TBW
(60% / 42 L)
ICF ECF (40% / 28 L) (20% / 14 L)
Interstitial fluid Plasma
(15% / 11 L) (5% / 3 L)
Major ECF ions
- Na
- Ca
- Cl
- HCO3
Major ICF ions
- K
- Mg
Neonates TBW%
higher
Females, obese, elderly TBW%
lower
Starling forces
dictate passive exchange of H2O b/t capillaries & interstitial fluid
Forces that move fluid from capillary to interstitial space
- Pc = capillary hydrostatic pressure (push)
- Interstitial oncotic pressure (pull)
Forces that move fluid from interstitial space into capillary
- Pif = interstitial hydrostatic pressure (push)
- capillary oncotic pressure (pull)
endothelial glycolayx
- protective layer on interior wall of vessel
- gatekeeps what can pass from vessel to interstitial space
- disruption contributes to capillary leark
What factors disrupt glyocalyx?
- sepsis
- ischemia
- DM
- vascular surgery
Hematocrit
fraction of BV occupied by erythrocytes
Hct is increased by:
- increased # RBCs (polycythemia)
- decreased plasma volume (hypovolemia)
Hct is decreased by:
- decreased # RBCs (anemia)
- increased plasma volume (hemodilution)
Lymphatic system
- removes fluid protein, bacteria, & debris in interstitium
- propels lymph through vessel network via one way valves
- creates negative pressure
Return of lymph for systemic circulation
- returned via thoracic duct at juncture of IVC & subclavian vein
osmosis
net movement of H2O across semipermeable membrane
diffusion
net movement of substance from area of high concentration to area of lower concentration across fully permeable membrane
osmotic pressure
pressure of a solution against a semipermeable membrane that prevents H2O from diffusion across
osmolarity
- measures concentration of particles in a solution
- unit of measurement = osmoles per L of solution (mOsm/L)
osmolality
- measures concentration of particles in a solution
- unit of measurement = osmoles per kg of solvent (mOsm/kg of H2O)
plasma osmolarity formula
2 [Na+] + Glucose/18 + BUN/2.8
normal plasma osmolarity
280-290 mOsm/L
most important determinant plasma osmolarity
Na+
What 2 things can increase plasma osmolarity?
- hyperglycemia
- uremia
Hypotonic solutions
- solution hypotonic to cell
- H2O enters & cell swells
- lower osmolarity than plasma
- increases ECF & ICF volume
- decreases plasma osmolarity
isotonic solutions
- solution isotonic to cell
- no H2O transfer & cell remains same size
- osmolarity approximates plasma
- expand plasma volume & ECF
- increases ECF
- ICF & plasma osmolarity stay same
hypertonic solutions
- solution hypertonic to cell
- H2O exits cell & cell shrinks
- osmolarity exceeds plasma
- expands IV volume
- ECF & plasma osmolarity increase
- ICF decreases
Hypotonic solution examples
Crystalloids
- NaCl 0.45%
- D5W
Isotonic solution examples
Crystalloids
- NaCl 0.9%
- LR
- Plasmalyte A
Colloids
- albumin 5%
- volvuven 6%
- hespan 6%
Hypertonic solution examples
Crystalloids
- NaCl 3%
- D5 NaCl 0.9%
- D5 NaCl 0.45%
- D5 LR
Colloids
- Dextran 10%
What complication can result from large amounts of NaCl?
hyperchloremic metabolic acidosis
How long do crystalloids remain in the IV space?
~ 30 minutes
What complication can result when hypertonic saline is administered too quickly?
central pontine myelinolysis
Crystalloid advantages
- 3:1 replacement
- expands ECF
- restores 3rd space loss
Colloid advantages
- 1:1 replacement
- increases plasma vol (3-6 hr)
- smaller vol needed
- less peripheral edema
- albumin has anti-inflammatory properties
- dextran 40 reduces blood viscosity
Crystalloid disadvantages
- limited ability to expand plasma volume
~ increases for ~ 20-30 min
~ higher potential for peripheral edema - large vol NaCl –> hyperchloremic met acidosis
- dilutional effect on albumin
- dilutional effect on coagulation factors
Colloid disadvantages
- albumin binds Ca+ –> hypocalcemia
- black box warning on synthetic colloids- renal injury
- coagulopathy
Dextran > Hetastarch > Hextend (no >20 ml/kg) - anaphylactic potential- highest = dextran
What is the black box warning on synthetic colloids?
risk of renal injury
Which colloid has highest incidence of coagulopathy?
dextran > hetastarch
How does albumin affect serum calcium?
hypocalcemia
Fluid Calculation (Historical)
1: Fluid Hourly Maintenance (4:2:1)
- 4 ml/kg/hr = 1st 10 kg
- 2 ml/kg/hr = 2nd 10 kg
- 1 lm/kg/hr remaining kg
- Calculate fluid deficit
- # fasting hours x hourly maintenance - Calculate “third space” loss
- very minimal surgical trauma = 1-2 ml/kg/hr
ex: orofacial surgery
- minimal surgical trauma = 2-4 ml/kg/hr
ex: inguinal hernia repair - moderate surgical trauma = 4-6 ml/kg/hr
ex: major nonabdominal surgery - severe surgical trauma: 6-8 ml/kg/hr
ex: major abdominal surgery
- Calculate blood loss replacement
- crystalloid = 3:1 (3 ml for q 1 ml blood loss)
- colloid or blood = 1:1
Goal-directed fluid therapy
- attempts to optimize pt’s position on Starling curve
- administration of small quantities of fluid (200-250 ml) to determine difference b/t preload dependence & preload independence
Enhanced Recovery After Surgery
5 objectives to enhance postsurgical outcomes w/ ERAS
- Attenuate physiologic changes that accompany surgical trauma
- Minimize impact of fluid shifts
- Maximize nutritional impact of healing
- Improve postop pain
- Improve patient education & compliance
