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
Nutritional Requirements:
1. Ideal Body Weight
A. Men = 106 lb + 6 lb for each inch over 5 ft
B. Women = 100 lb + 5 lb for each inch over 5 ft
2. Harris-Benedict Equation for resting kcal expenditure in healthy adults (Basal Metabolic Rate)
A. Men = 66 + (13.7 x W) + (5 x H) - (6.8 x A)
B. Women = 665 + (9.6 x W) + (1.8 x H) - (4.7 x A)
a. H: height
b. W: weight
c. A: age
3. Calorie Requirements
A. Normal: 0.8 g/kg/d
B. Metabolic stress (illness/injury): 1.0 -1.5
C. AKI (undialyzed): 0.8 - 1.0
D. Hemodialysis: 1.2-1.4
E. Peritoneal dialysis: 1.3-1.5
F. Protein delivered (g) x 4 (cal/g) = protein caloric requirement
G. Protein caloric requirement / total daily caloric reqreuiment (x100) = % total daily calorie requirement in protein
4. Tube Feeding
A. Types of tubes:
a. < 6 wks: nasogastric/nasoenteric feeding tube
b. > 6 wks: gastrostomy/jejunostomy
B. Methods of feeding:
a. Bolus feedings: given by syringe as rapidly as tolerated
b. Gravity feedings: infused over 30 - 60 minutes
C. Patient's upper body should be elevated 30 - 45 degrees during feeding and for at least 2 hrs afterward
D. Tubes should be flushed with after after each feeding
E. Patients w/ Nausea and early satiety with bolus gravity feedings may require continuous infusion at a slower rate.
a. Continuous feeding: 20 - 30 mL/hr, increased by 10 mL/hr Q6H until feeding goal reached
b. Continuous feeding should always be used when feeding directly into duodenum/jejunum to avoid distention, abdominal pain, and dumping syndrome.
F. Contraindications:
a. Persistent N/V
b. Intolerable postprandial abd. pain/diarrhea
c. Mechanical obstruction/severe hypomotility
d. Severe malabsorption
e. Presence of high-output fistula
G. Complications:
a. NG feeding tube misplacement to tracheobronchial tree
b. Erosive tissue damage
c. Tube occlusion by inspissated feedings/pulverized medications given through < 10# Fr tubes
d. Hyperglycemia in pts using insulin
e. Pulmonary aspiration
f. Diarrhea associated w/ abx/Intestinal ischemia/necrosis in critically ill pts receiving vasopressors
(Reference: The Washington Manual of Medical Therapeutics)
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