Fluid Balance

Question 1

Fluid balance physiologic concept

Answer 1

Fluid balance is the balance between the amount of fluid in the ICF and the ECF, if more fluid than is necessary is in either compartment, edema, or too much pressure will occur. Fluid balance also pertains to the amount of fluid taken in should equal the amount excreted

Question 2

Intracellular fluid (ICF)

Answer 2

fluid within the tissue cells. Contain 60% of fluid in the body

Question 3

Extracellular fluid (ECF)

Answer 3

the interstitial fluid and the plasma

Question 4

plasma (intravascular fluid)

Answer 4

extracellular fluid that is within the blood vessels

Question 5

Interstitial fluid

Answer 5

the fluid in spaces between the tissue cells

Question 6

Normal daily water intake and output (NONE)

Answer 6

Average urine output 1.5 L/day
Intake should equal output
Intake varies between people 
Averages: 
Beverage 1200 mL = urine 1500
Food 1000mL = feces 100
Metabolic 350 mL = sweat 50
skin and lungs 900
Total: 2550 in = 2550 out

Question 7

Thirst mechanism (NONE)

Answer 7

• HYPOosmolality (low solute concentration) -> the brain downregulates ADH and thirst -> increased renal water excretion and decreased water intake -> dilute urine and normalized plasma Osm
• HYPERosmolality (high solute concentration) -> the brain upregulates ADH and thirst -> decreased renal water excretion and increased water intake -> concentrated urine and normalized plasma Osm
  Hypotension or a low intravascular fluid volume are sensed by baroreceptors in the Aorta and Carotid arteries, and cause the release of ADH in the Hypothalamus (upregulates thirst).
  Hyperosmolarity is sensed by chemoreceptors in the hypothalamus (release ADH, upregulates thirst).

Question 8

Third spacing

Answer 8

Fluid in the body is normally limited to:
1st the intracellular space (cytoplasm) and
2nd the extracellular space of blood/lymph vessels and the interstitium.
“Third spacing” is the abnormal movement of substantial amounts of ECF to the non-functional, transcellular areas such as the eye, CNS, pleural and peritoneal cavities (ascites).

Question 9

Ascites

Answer 9

Peritoneal cavity = filled with ECF

Question 10

Interstitial edema

Answer 10

second-spacing: excess volume going to areas where there normally is fluid. Both conditions (&ascites), however, are the result of increased hydrostatic pressure on the vascular side of the capillary wall.

Question 11

Osmosis

Answer 11

Movement of a solvent (H2O) across a membrane, driven by differences in osmolality (low to high)

Question 12

Osmolality

Answer 12

concentration of a solution in number of particles of a solute per liter

Question 13

Tonicity

Answer 13

relative account of osmolality which determines the direction of diffusion (osmosis)

Question 14

Isotonic

Answer 14

concentration of solutes is equal inside and outside the cell

Question 15

Hypertonic

Answer 15

concentration of solution is greater outside than inside (water leaves cell, cell shrinks)

Question 16

Hypotonic

Answer 16

concentration of solution is greater inside than outside (water enters the cell, cells swell)

Question 17

Distribution of salt water in the body and general process of volume homeostasis (NONE)

Answer 17

A small change in sodium can make big differences. Sodium content is related to total fluid volume (evaluated by a PE), sodium concentration is related to osmolality (evaluated by a blood test).
Sodium is the most abundant ion in the ECF, and its balance determines ECF volume in the body: water osmotically follows sodium:
- Hypervolemia reflects sodium (and water) retention, kidneys will excrete more (ADH DOWN).
- Hypovolemia reflects sodium (and water) deficit, kidneys will conserve more (ADH UP).

Question 18

Sodium

Answer 18

Function: primary extracellular cation. moves water to control BP and total fluid volume
Regulation: excreted or retained by kidneys depending on tonicity. Renal absorption at multiple points

Question 19

Potassium

Answer 19

Function: primary intracellular cation. Key for cell membrane excitability (electrical conduction)
Regulation: Ingested through food, regulated by aldosterone, acidosis/alkalosis mechanisms. Renal excretion at multiple points

Question 20

Bicarbonate

Answer 20

Function: primary extracellular anion. Predominant buffer system in body
Regulation: By lungs and kidneys, acid/base balance. Absorbed as H+ in proximal tubule

Question 21

Chloride

Answer 21

Function: important extracellular anion. Electroneutrality and acid/base
Regulation: By kidneys, coupled with Na absorption (salt NaCl)

Question 22

Calcium

Answer 22

Function: predominantly inside cells, 99% stored in bones. Cell cycle, membrane excitability, bone formation, coagulation
Regulation: By parathyroid hormone, calcitriol, calcitonin, in Kidney, GI tract, bone. Reabsorption at multiple points

Question 23

Hydrogen

Answer 23

Function: Low concentration in the body, determines pH (body function)
Regulation: By intracellular pH, aldosterone, and K+ concentration. Some excretion, but mostly is involved in formation of bicarb.

Question 24

Phosphate

Answer 24

Function: Predominately in bones 86%, less than 1% in ECF. Vital component for ATP, DNA, RNA. Urinary buffer
Regulation: By PTH and calcitriol in GI tract, Kidney, bone (similar to CA++). Affected by ECV. Reabsorption at multiple points

Question 25

Patient with a fluid/electrolyte disorder (NONE)

Answer 25

• Important to have an understanding of the basic fluid and electrolyte concepts.
• Important to know when to call for help.
• Perform a thorough history and physical exam
• Be aware that patient will usually present with non-specific symptoms
• Obtain a chemistry panel and other lab work or urine sample to determine the severity
• Know how to distinguish a chronic or an acute imbalance that may be life-threatening.

Question 26

Electrolyte imbalances (4 questions)

Answer 26

see table