Fluid Management
1.
Total body water (TBW): 60% of lean body weight in men, 50% in women
A.
2/3 Intracellular fluid (ICF), 1/3 Extracellular fluid (ECF)
B.
TBW: 0.6 x W = X
C. Intravascular compartment: 1/4 x ECF = Y
D. Interstitial compartment: 3/4 x ECF = Z
2. Disturbances in TBW change serum osmalality and electrolyte concentrations. Majority of water contained in intracellular space, the loss of water alone does not typically result in hemodynamic changes.
3.
Total body Na+: 85~90% of total body Na+ is extracellular, and constitutes predominate solute in ECF. Changes lead to contraction or expansion of ECF, manifests as volume depletion or expansion.
4.
Maintenance fluids:
A. Minimum water requirements for daily fluid balance =
U/O + Stool water loss + insensible losses + drain losses
a. Minimum urine output necessary = solute per day/(maximum amount of solute that can be excreted/L urine)
1) ~600 - 800 mOsm/d / 1, 200 mOsm/L in healthy kidneys =
> 0.5 L/d
b. Water loss in stool ~ 200 mL/d
c. Insensible water losses:
1) Skin + respiratory tract: ~400 - 500 mL/d
2) Endogenous metabolism: ~250 - 350 mL/d
B.
Total: 1400 mL/d or 60 mL/hr
C.
75 - 175 mEq Na+/d (2 g Na+ diet gives 86 mEq Na+/d)
a. 0.9%: 154 mEq/L
b. 0.45% 77 mEq/L
D.
20 - 60 mEq K+/d for normal renal function
E.
100 - 150 g/d dextrose given to minimize protein catabolism and prevent starvation keotacidosis
a. D5W 50 g dextrose/L
