Topic 2 - Volume quantification of fluid compartments

Question 1

Words to include

Answer 1

• Distribution in EC space
  
  • Quick equilibrating space
    
    • Blood
    • Interstitium of soft tissues
    • Lymph
  • Slowly equilibrating space
    
    • Bone
    • Transcellular space
• Stewart dilution principle
  
  • Quantify volume
  • Indicator (=S)
  • V=S/C

Question 2

Topics to include in the essay

Answer 2

1. Distribution in EC space
2. Stewart dilution principle
   
   1. Stewart principle in living organsim
3. Extrapolation
4. Assessment of total body water
   
   1. Assessing density
   2. Fat content
5. Quantification of EC compartment
   
   1. Intravascular compartment
   2. Intersitial fluid compartments
   3. Changes of water compartments
      
      1. Dehydration
      2. Hyperhydration
6. Time factors of regulation

Question 3

Distribution in the EC space

Answer 3

• Measuring the EC compartments using dilution principle:
  
  • ​2 phases are observed

1. Quickly equilibrating space
   
   • ​​Substance flow is fast
   • Blood plasma
   • Interstitium of soft tissue
   • Lymph
2. Slowly equilibrating space
   
   • Completely uniform distribution develops 8-10 hours later
   • ​Bone
   • Transcellular space

Question 4

How to quantify volume?

Answer 4

• Stewart dilution principle is used to quantify volume
• After waiting for equal distribution of the indication
  • V = S / C
  • [liter] = [mol] / [mol / liter]
  • S = indicator

Question 5

Stewart principle in living organism

Answer 5

• In the living organism the concentration of the indicator decreases constantly:
  
  • Permeates barriers
  • Metabolized
  • Excreted by the kidney, lung or skin
• The calculation should be modified:
  
  • Decrease in indicator concentration should be considered
  • Indicator concentration should be calculated at administration:
    
    • V = S / C₀
      
      • C₀: supposed original concentration at administration

Question 6

Extrapolation

Answer 6

• The indicator starts to dissociate and to eliminate from the given compartment right after its administration
• Extrapolation: where to estimate initial concentration (C₀)

1. Extrapolated
2. Outflow
3. Backflow
4. Slow excretion

Question 7

Assessment of total body water

Answer 7

• Based on dilution principle:
  
  • ³H2O
  • ²H2O
  • Antipirin
  • Urea
  • Tiourea
• Excsiccation: Desiccation till constant mass at a temperature of 105ºC
• Quantifying density in vivo
  
  • ​Assessing density:
    
    • Weigh the mass (m)
    • Quantify volume (V)
    • Calculate density (m/V)
      
      • Bone: highest
      • Soft Tissue
      • Fat: lowest

Question 8

Give the percentage of water content in:

1. Lean body mass
2. Fat

Answer 8

1. Lean body mass: 73%
2. Fat: 10%

Question 9

How to measure fat content in the body?

Answer 9

• Total Body Electrical Conductance measures the fat content of the body
• Calculating density

Question 10

Quantification ofthe EC compartments

Answer 10

• Suitable substances:
  
  • Inulin
  • Mannitol
  • Saccharose
• ​Isotopes of EC ions
  
  • ​Na⁺
  • Cl^-
  • Br^-

Question 11

Quantification of the EC compartments: fluid distribution

Answer 11

• In the EC space fluid distributes at different rates:
  
  • ​Fast distribution
    
    • Volume of soft tissues
  • Slow distribution
    
    • Volume of the soft tissues and fibrous tissues
  • Late distribution
    
    • Volume of bone tissues, fibrous tissues and soft tissues

Question 12

Quantification of intravascular compartments

Answer 12

• Suitable substances plasma:
  
  • Evans blue​
  • Iodine labelled
    
    • ​Albumin
    • Globulin
    • Fibrinogen

Question 13

Quantification of IC compartments

Answer 13

• It can only be derived:
  
  • IC compartment = Total Body Water - EC compartment​
    
    • IC = TBW - EC

Question 14

Quantification of interstitial fluid compartments

Answer 14

• ISF = EC compartment - intravasal volume

Question 15

Changes of water compartments

What are the major rules?

Answer 15

• The primary aim is to keep the IC compartment isosmotic and isovolemic
• The osmolality of the EC and IC compartment equalizes in few minutes
• Water is moved by osmotic (and hydrostatic) forces; the cell membrane is the main barrier of substance movement

Question 16

Changes of water compartments

Describe dehydration and hyperhydration

Answer 16

• Dehydration / hypovolemia​
  
  • Isoosmotic hypovolemia
    
    • Hemorrhage
    • Burn
    • Vomiting
    • Diarrhea
  • Hyperosmotic hypovolemia
    
    • Hydropenia: decreased intake → increased loss → increased evaporation → diabetes insipidus
  • Hypoosmotic hypovolemia
    
    • Decreasing salt intake → primary salt loss → intensive sweating → salt loss through the kidneys → hypoadrenocorticalismus
• Hyperhydration / hypervolemia
  
  • Isoosmotic hypervolemia
    
    • Oedema: overdosed physiological saline
  • Hyperosmotic hypervolemia
    
    • Hyperosmotic fluid intake per os or parenterally
  • Hypoosmotic hypervolemia
    
    • Exaggerated water uptake; water retention in the kidney (ADH overproduction)

Question 17

Changes of water compartments

Time factors of the regulation

Answer 17

1. IC and EC osmolality returns to balance
   
   • In a few minutes
   • By the movement of fluids and osmotically active substances
2. IC and EC isoosmosis is formed
   
   • In 30 minutes
3. Isovolemia is restored
   
   • Takes a couple of days
   • Volume shifts can be tolerated much better than shits in osmolality