Fluids and Electrolytes Chapter18 P107-123 Flashcards
What are the two major body fluid compartments?
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- Intracellular
2. Extracellular
What are the two subcompartments of extracellular fluid?
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- Interstitial fluid (in between cells)
2. Intravascular fluid (plasma)
What percentage of body weight is in fluid?
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60%
What percentage of body fluid is intracellular?
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66%
What percentage of body fluid is extracellular?
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33%
What is the composition of body fluid?
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Fluids = 60% total body weight:
Intracellular = 40% total body weight
Extracellular = 20% total body weight
(Think: 60, 40, 20)
How can body fluid distribution by weight be remembered?
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“TIE”:
T = Total body fluid = 60% of body weight
I = Intracellular = 40% of body weight
E = Extracellular = 20% of body weight
On average, what percentage of body weight does blood
account for in adults?
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≈7%
How many liters of blood
are in a 70-kg man?
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0.07 x 70 = 5 liters
What are the fluid requirements every 24 hours for each of the following substances:
1. Water
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≈30 to 35 mL/kg
What are the fluid requirements every 24 hours for each of the following substances:
2. Potassium
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≈1 mEq/kg
What are the fluid requirements every 24 hours for each of the following substances:
3. Chloride
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≈1.5 mEq/kg
What are the fluid requirements every 24 hours for each of the following substances:
4. Sodium
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≈1–2 mEq/kg
What are the levels and sources of normal daily water loss?
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Urine—1200 to 1500 mL (25–30 mL/kg)
Sweat—200 to 400 mL
Respiratory losses—500 to 700 mL
Feces—100 to 200 mL
What are the levels and sources of normal daily electrolyte loss?
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Sodium and potassium = 100 mEq
Chloride = 150 mEq
What are the levels of sodium and chloride in sweat?
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≈40 mEq/L
What is the major electrolyte in colonic feculent fluid?
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Potassium—65 mEq/L
What is the physiologic response to hypovolemia?
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Sodium/H2O retention via renin → aldosterone, water retention via ADH, vasoconstriction via angiotensin II and
sympathetics, low urine output and tachycardia (early), hypotension (late)
THIRD SPACING
What is it?
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Fluid accumulation in the interstitium of tissues, as in edema, e.g., loss of fluid into the interstitium and lumen of a paralytic bowel following surgery (think of the intravascular and intracellular spaces as the first two spaces)
THIRD SPACING
When does “third-spacing” occur postoperatively?
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Third-spaced fluid tends to mobilize back into the intravascular space around POD #3 (Note: Beware of fluid overload once the fluid begins to return to the intravascular
space); switch to hypotonic fluid and decrease IV rate
THIRD SPACING
What are the classic signs of third spacing?
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Tachycardia
Decreased urine output
THIRD SPACING
What is the treatment?
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IV hydration with isotonic fluids
THIRD SPACING
What are the surgical causes of the following conditions:
Metabolic acidosis
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- Loss of bicarbonate: diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors
- Increase in acids: lactic acidosis (ischemia), ketoacidosis, renal failure, necrotic tissue
THIRD SPACING
What are the surgical causes of the following conditions:
Hypochloremic alkalosis
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NGT suction, loss of gastric HCl through vomiting/NGT
THIRD SPACING
What are the surgical causes of the following conditions:
Metabolic alkalosis
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Vomiting, NG suction, diuretics, alkali ingestion, mineralocorticoid excess
THIRD SPACING
What are the surgical causes of the following conditions:
Respiratory acidosis
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Hypoventilation (e.g., CNS depression), drugs (e.g., morphine), PTX, pleural effusion, parenchymal lung disease,
acute airway obstruction
THIRD SPACING
What are the surgical causes of the following conditions:
Respiratory alkalosis
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Hyperventilation (e.g., anxiety, pain, fever, wrong ventilator settings)
THIRD SPACING
What is the “classic” acidbase finding with significant
vomiting or NGT suctioning?
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Hypokalemic hypochloremic metabolic alkalosis
THIRD SPACING
Why hypokalemia with NGT suctioning?
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Loss in gastric fluid—loss of HCl causes
alkalosis, driving K⁺ into cells
THIRD SPACING
What is the treatment for hypokalemic hypochloremic
metabolic alkalosis?
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IVF, Cl⁻/K⁺ replacement
THIRD SPACING
What is paradoxic alkalotic aciduria?
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Seen in severe hypokalemic, hypovolemic, hypochloremic metabolic alkalosis with paradoxic metabolic alkalosis of serum and acidic urine
THIRD SPACING
How does paradoxic alkalotic aciduria occur?
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H⁺ is lost in the urine in exchange for Na⁺ in an attempt to restore volume
THIRD SPACING
With paradoxic alkalotic aciduria, why is H⁺ preferentially lost?
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H⁺ is exchanged preferentially into the
urine instead of K⁺ because of the low
concentration of K⁺
THIRD SPACING
What can be followed to assess fluid status?
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Urine output, base deficit, lactic acid, vital signs, weight changes, skin turgor, jugular venous distention (JVD), mucosal membranes, rales (crackles), central venous
pressure, PCWP, chest x-ray findings
THIRD SPACING
With hypovolemia, what changes occur in vital signs?
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Tachycardia, tachypnea, initial rise in diastolic blood pressure because of clamping down (peripheral vasoconstriction) with subsequent decrease in both
systolic and diastolic blood pressures
THIRD SPACING
What are the insensible fluid losses?
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Loss of fluid not measured:
a) Feces—100 to 200 mL/24 hours
b) Breathing—500 to 700 mL/24 hours
(Note: increases with fever and tachypnea)
c) Skin—≈300 mL/24 hours, increased with fever; thus, insensible fluid loss is not directly measured
THIRD SPACING
What are the quantities of daily secretions:
Bile
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≈1000 mL/24 hours
THIRD SPACING
What are the quantities of daily secretions:
Gastric
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≈2000 mL/ 24 hours
THIRD SPACING
What are the quantities of daily secretions:
Pancreatic
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≈600 mL/ 24 hours
THIRD SPACING
What are the quantities of daily secretions:
Small intestine
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≈3000 mL/day
THIRD SPACING
What are the quantities of daily secretions:
Saliva
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≈1500 mL/24 hours
Note: almost all secretions are reabsorbed
THIRD SPACING
How can the estimated levels of daily secretions from bile,
gastric, and small-bowel sources be remembered?
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Alphabetically and numerically: BGS and 123 or B1, G2, S3, because Bile, Gastric, and Small bowel produce roughly 1 L,
2 L, and 3 L, respectively!
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises normal saline (NS)?
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154 mEq of Cl⁻
154 mEq of Na⁺
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises 1/2 NS?
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77 mEq of Cl⁻
77 mEq of Na⁺
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises 1/4 NS?
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39 mEq of Cl⁻
39 mEq of Na⁺
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises lactated Ringer’s (LR)?
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130 mEq Na⁺ 109 mEq Cl⁻ 28 mEq lactate 4 mEq K⁺ 3 mEq Ca⁺
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises D5W?
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5% dextrose (50 g) in H(2)O
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What accounts for tonicity?
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Mainly electrolytes; thus, NS and LR are both isotonic, whereas 1/2 NS is hypotonic to serum
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What happens to the lactate in LR in the body?
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Converted into bicarbonate; thus, LR cannot be used as a maintenance fluid because patients would become alkalotic
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
IVF replacement by anatomic site:
Gastric (NGT)
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D5 1/2 NS + 20 KCl
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
IVF replacement by anatomic site:
Biliary
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LR+/-sodium bicarbonate
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
IVF replacement by anatomic site:
Pancreatic
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LR+/-sodium bicarbonate
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
IVF replacement by anatomic site:
Small bowel (ileostomy)
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LR
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
IVF replacement by anatomic site:
Colonic (diarrhea)
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LR+/-sodium bicarbonate
CALCULATION OF MAINTENANCE FLUIDS
What is the 100/50/20 rule?
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Maintenance IV fluids for a 24-hour period:
100 mL/kg for the first 10 kg
50 mL/kg for the next 10 kg
20 mL/kg for every kg over 20 (divide by 24 for hourly rate)
CALCULATION OF MAINTENANCE FLUIDS
What is the 4/2/1 rule?
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Maintenance IV fluids for hourly rate:
4 mL/kg for the first 10 kg
2 mL/kg for the next 10 kg
1 mL/kg for every kg over 20
CALCULATION OF MAINTENANCE FLUIDS
What is the maintenance for a 70-kg man?
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Using 100/50/20: 100 x 10 kg = 1000 50 x 10 kg = 500 20 x 50 kg = 1000 Total = 2500 Divided by 24 hours = 104 mL/hr maintenance rate
Using 4/2/1: 4 x 10 kg = 40 2 x 10 kg = 20 1 x 50 kg = 50 Total = 110 mL/hr maintenance rate
CALCULATION OF MAINTENANCE FLUIDS
What is the common adult maintenance fluid?
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D5 1/2 NS with 20 mEq KCl/L
CALCULATION OF MAINTENANCE FLUIDS
What is the common pediatric maintenance fluid?
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D5 1/4 NS with 20 mEq KCl/L (use 1/4 NS because of the decreased ability of children to concentrate urine)
CALCULATION OF MAINTENANCE FLUIDS
Why should sugar (dextrose) be added to maintenance
fluid?
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To inhibit muscle breakdown
CALCULATION OF MAINTENANCE FLUIDS
What is the best way to assess fluid status?
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Urine output (unless the patient has cardiac or renal dysfunction, in which case central venous pressure or wedge pressure is often used)
CALCULATION OF MAINTENANCE FLUIDS
What is the minimal urine output for an adult on
maintenance IV?
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30 mL/hr (0.5 cc/kg/hr)
CALCULATION OF MAINTENANCE FLUIDS
What is the minimal urine output for an adult trauma
patient?
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50 mL/hr
CALCULATION OF MAINTENANCE FLUIDS
How many mL are in 12 oz (beer can)?
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356 mL
CALCULATION OF MAINTENANCE FLUIDS
How many mL are in 1 oz?
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30 mL
CALCULATION OF MAINTENANCE FLUIDS
How many mL are in 1 tsp?
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5 mL
CALCULATION OF MAINTENANCE FLUIDS
What are common isotonic fluids?
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NS, LR
CALCULATION OF MAINTENANCE FLUIDS
What is a bolus?
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Volume of fluid given IV rapidly (e.g., 1 L over 1 hour); used for increasing intravascular volume, and isotonic fluids should be used (i.e., NS or LR)
CALCULATION OF MAINTENANCE FLUIDS
Why not combine bolus fluids with dextrose?
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Hyperglycemia may result
CALCULATION OF MAINTENANCE FLUIDS
What is the possible consequence of hyperglycemia in
the patient with hypovolemia?
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Osmotic diuresis