3.1 Fluid Balance and Fluid Shift Flashcards
Total Body Water (TBW)
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
Extracellular Fluid (ECF)
- Fluid outside of cells (20% of bodyweight)
Intravascular Fluid (IVF)
- Blood Plasma (15% of bodyweight)
Interstitial Fluid (ISF)
- Fluid between cells (5% of bodyweight)
Intracellular Fluid (ICF)
All fluid within cells (40% of bodyweight)
Transcellular Fluid
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
Factors that affect Total Body Water
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
Average Gains of Body Fluid
Drinking - 1500mL
Water From Food - 1000mL
Oxidative Metabolism - 400mL
Total - 2900mL
Average Losses of Body Fluid
Urine - 1500mL Stool - 100mL Skin - 500mL Lungs - 800mL Total - 2900mL
Distribution of Water
- 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
Mechanisms of Fluid Exchange
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
Factors That Affect Movement of Fluid
- Semi-Permeable Membranes
- Electric Charge
- Hydrophobic/Hydrophilic Substance
- Balance Between Fluids and Electrolytes
- Concentration Gradient (Osmosis)
- Pressure Gradient (Hydrostatic Pressure)
Hydrostatic Pressure Gradient
- Driving force for filtration across membrane/capillary
- The higher the pressure the more water sent across the semi-permeable membrane
Osmotic Pressure Gradient
- Water always moves from area of low solute to areas of high solute
- Requires membrane to be more permeable to water than to solutes
Osmotic Pressure
- 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
Extracellular/Intravascular/Intracellular Compartment
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
Net Filtration
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
Fluid Shifts (ICF and ECF)
- 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
Fluid Shifts (ISF and IVF)
- 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.
Edema
- Accumulation of excess water in Interstitial or Intracellular spaces
Pathology of Edema
- 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
Edema (cont)
- 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)
Treatment of Edema
Depends on etiology but includes diuretics to decrease hydrostatic pressure, and administration of albumin to increase colloid oncotic pressure.
Fluids into Potential Spaces
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)
Osmolarity
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)
Osmoreceptors
Neurons in the hypothalamus that sense osmolarity concentration of plasma.
- Increased osmolarity triggers release of ADH and sensation of thirst.
BaroReceptors
- Neurons in left atrium, carotids and aorta that sense decreased volume
Renin
- 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)
Angiotensin II
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.
Aldosterone (Salt Hormone)
- 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.
Antidiuretic Hormone
- 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.
Renal Response
Conservation of free water (ADH)
Conservation of Sodium (Aldosterone)
As Urine Specific Gravity Increases (SG) so does Serum Osmolarity, and vice-versa.
Isotonic/Hypotonic/Hypertonic
Isotonic - Solute is equal between cell and solution
Hypotonic - Solute is less in solution
Hypertonic - Solute is more in solution
Serum Osmolarity (Important)
- Measures number of osmotically active particles dissolved in the serum/plasma
- Normal 275-279 mOsm/Kg
Urine Specific Gravity
- 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)
Urine Osmolarity
- Kidneys ability to produce concentrated or diluted urine
Normal Range 300 - 800
Total Body Water Excess
- 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
Total Body Water Deficit
- 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.
