Fluids Flashcards
Assessing volume status
Hypovolemia: volume depletion (loss of Na and water)
-dehydration (loss of water from icf)
Accurate assessment challenging
Systematic approach to estimating blood volume
Preop -> history, exam, labs
Intraop -> visual of loss, HR, BP, UO
invasive: PVP, CVP, PCWP, TEE
Icf deficit (free water loss)
Insensible loss from skin, Resp, kidneys
- cellular dehydration, increased plasma osmolality and Na
- will not present as acute circulatory collapse -> its gradual
ECf deficit (blood loss, GI loss)
Vomitting, diarrhea, ascites, 3rd spacing
- labs: increased BUN/Cr ratio, decreased urinAry Na excretion
- rapid circulatory collapse
- txt with isotonic solutions
Expected plasma volume increment
PV = volume infused x (baseline PV/Vd of infused fluid)
Traditional approach to fluid replacement
Fluid replacement = maintenance + deficit + 3rd space + loss Maintenance: 4, 2, 1 Deficit: maintenance x hrs NPO 3rd space: 4-8 mL/kg/hr Loss: crystalloid x3, colloid X11
Crystalloids
Aqueous solution that contains salts and water soluble molecules
- low cost, hig urinary flow
- minimal hemodynamics improvement, edema
Colloids
Larger insoluble molecules
- lower volume needs to be infused, increased time in plasma, low edema, high oxygen delivery
- high cost, coagulopathy, decrease GFR, allergies
D5W
Replaces free water, isotonic to plasma but becomes free water
Lactate Ringer
Most widely used
- lactate metabolized in liver to CO2, unsuitable for patients in liver disease
- coagulant, may be better than NS for kidney transplants due to lower incidence of acidosis and hyperkalemia
Normal saline
0.9% - widely used
Useful for neurosurg because of osmolality
Large doses can lead to hyperchloremic acidosis
Hypertonic saline
3, 7.5, 23.4%
Used for 1-intravascular volume expansion in hypovolemic shock
2- reduce cerebral blood volume and ICP
Albumin
5 or 25% available
Half-life of 16 hrs, made from human blood
5%- isotonic
Unclear evidence but don’t use inTBI
Hetastarch
Hydroxylethyl starch
High molecular weight synthetic colloid, increases colloid osmotic pressure
- elevates serum amylase, anaphylaxis
Dextran
Can cause anaphylaxis, coagulopathies, pulmonary edema
Voluven
New hetastarch with low molecular weight and low degree of substitution that theoretically may be associated with lower bleeding risk
Fluid compartments
TBW- 60% in males, 50% in females - inversely proportional to adipose tissue Intracellular fluid- 2/3 Extra cellular- 1/3 - interstitial volume (2/3 of ECf) - plasma volume (1/3 ECf)
