3.1 Fluid Balance and Fluid Shift

Question 1

Total Body Water (TBW)

Answer 1

Sum of all body fluids contained in all compartments

Newborns - Water is 75-80% of body weight
Young Children - Water is 67% of body weight
Adult - 60% in Males, 50% in Females

Question 2

Extracellular Fluid (ECF)

Answer 2

• Fluid outside of cells (20% of bodyweight)

Question 3

Intravascular Fluid (IVF)

Answer 3

• Blood Plasma (15% of bodyweight)

Question 4

Interstitial Fluid (ISF)

Answer 4

• Fluid between cells (5% of bodyweight)

Question 5

Intracellular Fluid (ICF)

Answer 5

All fluid within cells (40% of bodyweight)

Question 6

Transcellular Fluid

Answer 6

All other fluid in body. Fluid that fills spaces or potential spaces of chambers formed in the linings of epithelial cells.
Examples
Pericardial Sac, Pleural Space, Peritoneal Cavity, Intraocular Fluid, Synovial Fluid, Biliary Fluid, Cerebrospinal Fluid, Lymph Fluid

Question 7

Factors that affect Total Body Water

Answer 7

Age
- Infants have more body water due to immature kidneys, decreased ability to concentrate urine
- Older adults have less body water (50% after age 60) due to diminishing renal functions and inability to retain water.
Body Composition
- Greater muscle mass more water
- Greater fat content less water

Question 8

Average Gains of Body Fluid

Answer 8

Drinking - 1500mL
Water From Food - 1000mL
Oxidative Metabolism - 400mL
Total - 2900mL

Question 9

Average Losses of Body Fluid

Answer 9

Urine - 1500mL
Stool - 100mL
Skin - 500mL
Lungs - 800mL
Total - 2900mL

Question 10

Distribution of Water

Answer 10

• Movement of water occurs in the ECF such as water going from IVF to ISF
• Also occurs between ECF and ICF like when ISF goes to ICF

Question 11

Mechanisms of Fluid Exchange

Answer 11

Passive Transport - Does not require ATP
Diffusion - Moving from high concentration to low
Filtration - Movement of water and dissolved substances across semi-permeable membrane over pressure gradient
Osmosis - Water moves from low concentration of solute to high concentration of solute

Question 12

Factors That Affect Movement of Fluid

Answer 12

• Semi-Permeable Membranes
• Electric Charge
• Hydrophobic/Hydrophilic Substance
• Balance Between Fluids and Electrolytes
• Concentration Gradient (Osmosis)
• Pressure Gradient (Hydrostatic Pressure)

Question 13

Hydrostatic Pressure Gradient

Answer 13

• Driving force for filtration across membrane/capillary

- The higher the pressure the more water sent across the semi-permeable membrane

Question 14

Osmotic Pressure Gradient

Answer 14

• Water always moves from area of low solute to areas of high solute
• Requires membrane to be more permeable to water than to solutes

Question 15

Osmotic Pressure

Answer 15

• Drawing power of solute for water
• Crystalloid Osmotic Pressure - Solution consisting of non-protein substances (sodium, potassium)
• Colloid (oncotic) pressure - Consists of protein like Albumin, RBC’s. Intravascular Osmotic (oncotic) Pressure is controlled by Albumin.
• Intracellular Osmotic Pressure is primarily Potassium and Extracellular Osmotic Pressure is primarily Sodium

Question 16

Extracellular/Intravascular/Intracellular Compartment

Answer 16

ECF - (ISF+IVF) Sodium most abundant Cation. Regulates Volume Distribution
IVF - Plasma Proteins Provide Oncotic Pressure Within Capillary and Balanced by Hydrostatic Pressure
ICF - Potassium most abundant Cation and regulates Volume Distribution

Question 17

Net Filtration

Answer 17

Force Favoring Filtration - Water moves out of capillaries when hydrostatic pressure is greater than pressure drawing water back into capillaries.

Force Opposing Filtration - Oncotic Pressure Drawing Water Back Into Capillary via Osmotic Pressure

Question 18

Fluid Shifts (ICF and ECF)

Answer 18

• If you add sodium to ECF water moves from ICF to ISF to restore equilibrium (Cells can become dehydrated)
• If you remove sodium from ECF water moves into ICF causing cell swelling

Question 19

Fluid Shifts (ISF and IVF)

Answer 19

• Adding protein (albumin) to IVF water will shift from ISF to IVF. (Tissues can become dehydrated and plasma expands)
• Losing protein shifts from water from IVF to ISF.

Question 20

Edema

Answer 20

• Accumulation of excess water in Interstitial or Intracellular spaces

Question 21

Pathology of Edema

Answer 21

• Increased capillary hydrostatic pressure, like hypervolemia or venous (lymphatic) congestion (heart failure). Obstruction of veins (deep vein thrombosis)
• Increased tissue oncotic pressure (hypoproteinemia)
• Decreased plasma oncotic pressure (hypoalbuminemia)
• Decreased crystalloid osmotic pressure
• Increased capillary membrane permeability
• Obstruction of lymphatic vessels

Question 22

Edema (cont)

Answer 22

• Can be localized (deep vein thrombosis)
• Can also be general (Renal Failure)
• Dependent (Related to gravity forces)
• Independent (Not related to gravity)
• Pitting (Due to excess fluid)
• Non Pitting (Lymphedema)

Question 23

Treatment of Edema

Answer 23

Depends on etiology but includes diuretics to decrease hydrostatic pressure, and administration of albumin to increase colloid oncotic pressure.

Question 24

Fluids into Potential Spaces

Answer 24

Transudative - Related to pressure
Exudative - Related to inflammation
Pleural Effusion - Fluid in Pleural Space (Lungs)
Pericardial Effusion - Fluid in Pericardial Space (Heart)
Peritoneal Effusion - Fluid in Peritoneal Space (Abdomen)

Question 25

Osmolarity

Answer 25

Osmotic Concentration - Measure of solute concentration by volume. - Affected by Hydration Status, Intravascular Volume, Renal Blood Flow, and Hormonal Influence Osmolarity - Solution in a liter Osmolality - Solution in a Kilogram (Interchangeable)

Question 26

Osmoreceptors

Answer 26

Neurons in the hypothalamus that sense osmolarity concentration of plasma. - Increased osmolarity triggers release of ADH and sensation of thirst.

Question 27

BaroReceptors

Answer 27

- Neurons in left atrium, carotids and aorta that sense decreased volume

Question 28

Renin

Answer 28

- Released in the kidney when perfusion is reduced (decreased blood volume) - Stimulates release of Angiotensin I, produced in the liver. - Converted to Angiotensin II in the lungs via ACE (Angiotensin Converting Factor)

Question 29

Angiotensin II

Answer 29

Vasoconstrictor which increases blood pressure and decreases renal flow. - This stimulates release of aldosterone from the adrenal cortex (kidneys) resulting in reabsorption of water. - Once sodium and water are regulated renal perfusion inhibits further release of renin.

Question 30

Aldosterone (Salt Hormone)

Answer 30

- Secreted by adrenal cortex in response to decreased sodium levels, increased potassium levels, or hypotension. - Increase sodium retention, potassium and hydrogen loss in the distal tubules, expand plasma and ECF volume, and increase secretion of potassium.

Question 31

Antidiuretic Hormone

Answer 31

- Secreted in Posterior Pituitary in response to increased plasma osmolarity (dehydration) - Increases permeability of renal-collecting ducts to increase reabsorption of free water. - Decreases serum osmolarity and increases urine concentration.

Question 32

Renal Response

Answer 32

Conservation of free water (ADH) Conservation of Sodium (Aldosterone) As Urine Specific Gravity Increases (SG) so does Serum Osmolarity, and vice-versa.

Question 33

Isotonic/Hypotonic/Hypertonic

Answer 33

Isotonic - Solute is equal between cell and solution Hypotonic - Solute is less in solution Hypertonic - Solute is more in solution

Question 34

Serum Osmolarity (Important)

Answer 34

- Measures number of osmotically active particles dissolved in the serum/plasma - Normal 275-279 mOsm/Kg

Question 35

Urine Specific Gravity

Answer 35

- Reflects renal tubular response to hormonal influence. Measures relative concentration of solute to water in urine and changes to maintain serum osmolarity. - Normal Ranges 1. 010 - 1.020 1. 036 (increased - dehydration) 1. 006 (decreased - fluid overload)

Question 36

Urine Osmolarity

Answer 36

- Kidneys ability to produce concentrated or diluted urine | Normal Range 300 - 800

Question 37

Total Body Water Excess

Answer 37

- Overhydration with water both ECF and ICF Pathogenesis Hypotonic (Compulsive Drinking of Water, SIADH) Isotonic (Acute Renal Failure) Pathophysiology - Hyponatremia leads to hypoosmolality which causes water to diffuse across concentration gradient into ISF and ICF causing edema and rupture of cell organelles. Clinical Presentation - Weakness, Nausea, Weight Gain, Hemodilution, Interstitial Edema, Muscle Twitch, CNS Headache, cerebral edema, confusion, convulsion Treatment - Treat underlying cause. Water Restriction, Diuretics with sodium replacement, with CNS administer IV hypertonic saline solution

Question 38

Total Body Water Deficit

Answer 38

- Dehydration with water loss affecting both ECF and ICF Pathogenesis - Hypertonic (Loss of water in excess of electrolytes, HHNK) - Isotonic: proportional loss of water and electrolytes (vomiting, diarrhea, excessive diaphoresis) Pathophysiology Fluid loss without adequate replacement causes hyperosmolarity. Diffusion of water across concentration gradient from ICF to ECF results in tissue dehydration. Clinical Presentation Decreased tissue turgor (dry, shrunken fontanels), Oliguria, Hypotension, Tachycardia, Increased Temperature, Hemoconcentration, decreased consciousness/coma Treatment - Treat underlying cause, rehydration, D5W if free water needed, NSS if isotonic solution needed, Sugar and salts in oral solution.