1 - Body Fluid Compartments Flashcards

1
Q

Objectives: Identify the fluid compartments and relative concentrations of electrolytes within these spaces

TBW

ICF

ECF

Plasma

Interstitial Fluid

A
  • Total Body Water = ICF + ECF
  • Intracellular Fluid (ICF)
    • 2/3 TBW
    • Major Cations: K+ , Mg2+
    • Major Anions: Protein, Organic Phosphates (AT/D/MP)
  • Extracellular Fluid (ECF)
    • 1/3 TBW
    • Major Cations: Na+
    • Major anions: Cl-, HCO3-
  • Plasma (part of ECF)
    • 1/4 ECF
    • Plasma Proteins: Albumin, Globulins
  • Interstitial Fluid (part of ECF)
    • 3/4 ECF
    • Lacks Protein (ultrafiltrate of plasma)
  • 60-40-20 Rule
    • TBW = 60% bw
    • ICF = 40% bw
    • ECF = 20% bw
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2
Q

Objectives: Understand dilution methods for determining distribution of water in body compartments

TBW

ECF

Plasma

Interstitial

ICF

A
  • Main method is dilution with known quantity
  • Total Body Water (TBW)
    • Tritiated Water
  • Extracellular Fluid (ECF)
    • Inulin
  • Plasma
    • Labeled Albumin, Evan’s Blue
  • Interstitial - Indirect: ECF - Plasma
  • Intracellular Fluid (ICF) - Indirect: TBW - ECF
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3
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Isosmotic Volume Expansion (Isotonic NaCl Infusion (saline IV))

A
  • ECF Volume: Increase
  • ICF Volume: No Change
  • ECF Osmolarity: No Change
    • No change to RBC size (shrink/swell)
  • Plasma Protein / Hematocrit: Decrease
    • Addition of fluid to ECF dilutes
  • Arterial BP: Increase
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4
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Isosmotic Volume Contraction (Diarrhea)

A
  • ECF Volume: Decrease
  • ICF Volume: No Change
  • ECF Osmolarity: No Change
    • ​No change to RBC size (shrink/swell)
  • Plasma Protein / Hematocrit: Increase
    • Removal of fluid to ECF enhances concentration
  • Arterial BP: Decrease
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5
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Hyperosmotic Volume Expansion (high salt intake)

A
  • ECF Volume: Increase
  • ICF Volume: Decrease
    • RBCs shrink in size
  • ECF Osmolarity: Increase
  • ICF Osmolarity: Increase (until = ECF)
  • Plasma Protein / Hematocrit: Decrease
    • Addition of fluid to ECF dilutes
  • Arterial BP: Increase
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6
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Hyperosmotic Volume Contraction (sweating, fever, diabetis insipidus)

A
  • ECF Volume: Decrease
  • ICF Volume: Decrease
    • RBCs shrink
  • ECF Osmolarity: Increase
  • ICF Osmolarity: Increase (until = ECF)
  • Plasma Protein / Hematocrit:
    • Plasma Protein: Increase
    • Hematocrit: Unchanged - water shifts into RBCs, increasing size
  • Arterial BP: Decrease
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7
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Hyposmotic Volume Expansion (SIADH, postoperative patient)

A
  • ECF Volume: Increase
  • ICF Volume: Increase
    • RBCs swell
  • ECF Osmolarity: Decrease
  • ICF Osmolarity: Decrease
  • Plasma Protein / Hematocrit:
    • Plasma Protein: Decrease
    • Hematocrit: Unchanged - water shifts into RBCs, increasing size
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8
Q

Objectives: Identify clinically relevant water shifts between body fluid compartments (6-total)

Hyposmotic Volume Contraction (Adrenal Insufficiency)

A
  • ECF Volume: Decrease
  • ICF Volume: Increase
    • RBCs swell
  • ECF Osmolarity: Decrease
  • ICF Osmolarity: Decrease (until = ECF)
  • Plasma Protein / Hematocrit:
    • Plasma Protein: Increase
    • Hematocrit: Increase
  • Arterial BP: Decrease - decrease in ECF volume
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9
Q

How do you calculate volume of distribution?

A
  • Volume = Amount / Concentration
    • Volume = Volume of Distribution or Volume of Compatment
    • Amount = Injected - Excreted
    • Concentration = (Q/V)
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10
Q

How do you estimate POSM (Plasma Osmolarity)

A
  • POSM = 2 x Na+ + Glucose/18 + BUN/2.8
    • BUN = Blood urear Nitrogen Concentration
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11
Q

What are assumptions for fluid movement from different body compartments?

A
  1. At steady state, ECF osmolarity = ICF osmolarity
  2. Water Shifts between compartments
  3. Solutes (NaCl, inulin, etc) do not cross cell membranes are are confined to ECF
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12
Q

How does TBW change with age and gender?

A
  • Age: Inverse
  • Gender:
    • Females: Lower (50% lean body mass)
    • Males: Higher (60% lean body mass)
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13
Q

What four organs communicate the ECF with the external environment?

A
  • GI System (+/-)
  • Skin ( - )
  • Lungs (+/-)
  • Kidneys ( - )
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14
Q

What are the major ions (or other solutes) in the impotant compartments?

A

ECF - Na / Cl

ICF - K

Plasma - Protein

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15
Q

Define Osmolarity and Osmolality

A
  • Osmolarity: Solute particles per 1L water
    • Ex: 150 mmol/L solution NaCl has osmolarity of 300 mOsm/L because NaCl idssociates into Na/Cl ions
  • Osmolality: Solute particles per 1K water
    • Prefered term for biological systems
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16
Q

Tonicity and Cell Size Changes

A
  • Isotonic: No change
  • Hypotonic: Cell Swell
  • Hypertonic: Cell Shrink
17
Q
A