Fluids, Electrolytes, and Acid-Base Disorders Flashcards
What factors affect the percentage of total body water (TBW)?
Weight, age, sex, and relative amount of body fat
Equation for calculating Free Water Deficit
Free Water Deficit = TBW x [1 - (140/Serum Sodium in mEq/L)]
Which body tissue is the least hydrated?
Adipose tissue
What are the 3 compartments of TBW distribution?
Intracellular fluid, extracellular fluid, and transcellular fluid
Which fluid compartment is the most clinically important?
Extracellular fluid because it contains the intravascular and interstitial spaces
What is osmotic pressure and why is it of clinical importance?
The pressure required to maintain equilibrium with no net movement of solvent. Prime importance in determining the distribution of water between the extracellular and intracellular spaces
Equation for calculating lean body weight (LBW) for males and females
LBW (women) = 1.07 x weight (kg) - 148 x [weigh (kg)/height (cm)]^2
LBW (men) = 1.1 x weight (kg) - 128 x [weight (kg)/height (cm)]^2
Describe the composition of D5W (5% dextrose) including its tonicity
Provides 50 g dextrose per liter
Hypotonic
No electrolytes
1000 ml/L free water
Describe the composition of 0.225% NaCl (1/4 normal saline) including its tonicity
Hypotonic
Provides 38.5 mEq/L Na, 38.5 mEq/L Chloride
Describe the composition of 0.45% NaCl (1/2 normal saline) including its tonicity
Hypotonic
Provides 77 mEq/L Na, 77 mEq/L Chloride
500 ml/L free water
Describe the composition of 0.9% NaCl (normal saline) including its tonicity
Isotonic
Provides 154 mEq/L Na, 154 mEq/L Chloride
0 ml/L free water
Describe the composition of 3% NaCl (hypertonic saline) including its tonicity
Hypertonic
Provides 513 mEq/L Na, 513 mEq/L Chloride
-2331 ml/L free water
Describe the composition of Lactated Ringers (LR) including its tonicity
Isotonic
Provides 130 mEq/L Na, 109 mEq/L Chloride, 4 mEq/L K+, 3 mEq/L Calcium
0 ml/L free water
Describe the composition Albumin in 0.9% NaCl including its tonicity
Isotonic
Provides 154 mEq/L Na and 154 mEq/L Chloride
Describe the water distribution of 1 L IV Dextrose in water to extracellular fluid and intracellular fluid
333 mL ECF (250 mL interstitial fluid + 83 mL intravascular fluid)
667 mL ICF
Describe the water distribution of 1 L IV 0.9% NaCl (normal saline) to extracellular fluid and intracellular fluid
1000 mL ECF (750 mL interstitial fluid + 250 mL intravascular fluid)
0 mL intracellular fluid
What fluid requirement calculations are recommended in individuals age 65 years or older to prevent dehydration?
- An adjusted Holliday-Segar formula (1500 mL for the first 20 kg body weight + 15 mL/kg for remaining body weight)
- 30 mL/kg with a minimum of 1500 mL
- 1500-2000 mL/day
List some clinical conditions which would require the addition of fluid
Patients with severe diarrhea or emesis; large draining wounds; excessive diaphoresis; constant drooling; paracentesis losses; drains; high gastric fistula and ostomy outputs; persistent fevers; lactation
Explain the 2 equations some clinicians have success using for fluid requirements when the average between the 2 formulas is used
Equation 1 (based on body weight and age):
Age 18-55: 35 mL x body weight (kg)
Age 56-75: 30 mL x body weight (kg)
Age >75: 25 mL x body weight (kg)
Fluid-restricted adults (kidney/cardia disease or fluid overload states) </= 25 mL x body weight (kg)
Equation 2 (Holliday-Segar formula adjusted for age)
Age </=50 years: 1500 mL for first 20 kg body weight + [20 mL x remaining body weight (kg)]
Age >50 years: 1500 mL for first 20 kg body weight + [15 mL x remaining body weight (kg)]
What is the calculation for obesity-adjusted weight?
Obesity-Adjusted Body Weight (lb) = [(Actual Weight - IBW) x 0.25] + IBW
When is an obesity-adjusted weight often used?
When an individual’s weight is equal to or greater than 125% IBW unless the excess weight is due to muscle mass
Calculate the fluid requirements for a 61 year old woman who is 5’4” tall and weighs 160 lb
BMI is 27.5, patient is 133% IBW
1. Calculate IBW: 100 lb + (5x4 lb) = 120 lb
2. Calculate obesity-adjusted weight: [(160-120)] x 0.25] + 120 = 130 lb (59 kg)
3. Calculate fluid requirements using Equation 1: 30 mL x 59 kg = 1770 mL/day
4. Calculate fluid requirements using Equation 2: 1500 mL + [15 x (59kg - 20kg)] = 2085 mL/day
5. Calculate the mean of the results from steps 3 and 4: (1770 + 2085)/2 = ~1900 mL/day
How would you manage maintenance fluids for a patient with heart failure?
Patient info: 65 y/o male, current weight 75 kg (IBW 66 kg), admit w/ 3+ pitting edema BLE receiving 8L/min O2, given 0.9% NaCl at 125 ml/hr, O2 requirements subsequently increased
Heart failure pt with evidence of fluid overload should be treated with loop diuretics and sodium and fluid restrictions. Start this patient on IV furosemide and change IV fluids to 0.45% NaCl at 10 mL/hr to maintain IV access. For pt with heart failure, fluid intake should be approximately 20-25 mL per kg estimated dry weight and clinical symptoms of fluid overload should be taken into account. Sodium intake restricted to <2000 mg/day (87 mEq). This patient received 3 L maintenance IV fluids which contributed to further respiratory decompensation requiring aggressive diuresis
List the volume and average electrolyte composition of saliva
1.5 L/day, 10 mEq/L Na, 26 mEq/L K+, 10 mEq/L Chloride, 30 mEq/L bicarbonate (HCO3-)