Fluid and Electrolytes Flashcards
Review body fluid compartments.
Intracellular
- Makes up 63%
- Fluid inside the cells
Extracellular
- Makes up 37%
- Fluid outside the cells
- Intravascular: within the blood vessel e.g., plasma, lymph
- Intercellular: between the cells e.g. interstitial fluid, transcellular fluid
Define fluid balance.
Fluid balance: Fluid intake should roughly equal output to maintain homeostasis.
Intake 2500 mL = Output 2500 mL
INTAKE
- 10% of water is gained from metabolism
- 30% of water is gained from moist food
- 60% (1500 mL) is gained from beverages
OUTPUT
- 12% of water is lost through feces and sweat
- 28% of water is lost through water vapour from the lungs, and through the skin
- 60% (1500 mL) of water is lost in urine
Review how the following pressures direct movement of fluid between compartments: hydrostatic pressure, osmotic pressure, oncotic pressure.
Hydrostatic pressure
- The mechanical force of water pushing against cellular membranes.
- In the vascular system, it is the BP generated in vessels by the contraction of the heart (25-30mmHg).
- This pressure pushes fluid through the capillary membranes into the interstitial space.
Osmotic pressure
- The pulling of water from an area of lower solute concentration to an area of high solute concentration.
- In the vascular system, hydrostatic pressure is lowest at the venule end of the capillary and osmotic pressure is higher. This allows water to flow through a semi-permeable membrane.
Oncotic pressure
- A form of osmotic pressure created by Albumin
- Increases osmotic pull of fluid back into capillaries
Define edema.
Edema: An excessive amount of fluid in the interstitial compartment, causing swelling or enlargement of the tissues.
Define Dehydration.
Dehydration: Insufficient body fluid caused by low fluid intake or excessive fluid loss.
Discuss the causes of edema: hypertension, loss of plasma proteins (esp. albumin), obstruction of the lymph circulation, inflammation.
Hypertension
-Increased capillary hydrostatic pressure (high BP)
- Prevents the return of fluid from the interstitial compartment to the venous end of the capillary or forces excessive amounts of fluid out of the capillaries into the tissues.
Loss of plasma proteins (especially albumin)
- Presence of fewer plasma proteins in the capillary allows more fluid to leave the capillary and less fluid to return to the venous end of the capillary
- Loss of oncotic pressure
Obstruction of the lymphatic circulation
- Localized edema because of excessive fluid and proteins are not returned to the general circulation
Inflammation
- Histamine and other chemical mediators released from cells following tissue injury cause increased capillary permeability and increased fluid movement into the interstitial area
Define pulmary edema. What are it’s manifestations?
Pulmonary Edema
- Excessive fluid in alveoli and lung interstitium which interferes with O2 diffusion and causes hypoxemia
- Interferes with surfactant can cause lungs to collapse
Manifestations:
- Dyspnea
- Cough
- Tachypnea
- Orthopnea
- Cyanosis
- Crackles
- Fatigue
Define intertitial edema. What are it’s manifestations?
Interstitial edema
- Specifically refers to excessive fluid in the interstitial spaces between cells in tissues.
Manifestations
- Swelling
- Restricted movements of area
- Pain
- Decreased circulation to area
- Weight gain
Which populations are at highest risk of dehydration? Why?
The elderly are most at risk for dehydration because:
- Lower fluid reserve (TBW)
- Decreased ability to conserve fluid quickly
- Protein-deficient diets
- Decreased sensation of thirst
- More likely to take laxatives and diuretics
Review manifestations of electrolyte imbalances.
HYPOnatremia
- Na+ less than 135 mEq/L
- May be caused by:
- Excessive loss of sodium through sweating, vomiting, diarrhea, diuretics
- Chronic renal failure
- Excessive water intake
HYPERnatremia
- Na+ greater than 145 mEq/L
- May be caused by:
- Excessive sodium intake
- Excessive water loss due to sweating, vomiting, diarrhea, low ADH
- Loss of thirst mechanism
HYPOkalemia
- K+ less than 3.5 mmol/L
- May be caused by:
- Diuretics
- Diarrhea/Vomiting
- Excessive aldosterone/glucocorticoids
- Inadequate K+ intake
HYPERkalemia
- K+ greater than 5.0
- May be caused by:
- Renal Failure
- Deficit of aldosterone
- Use of K+ sparing drugs
- Extensive tissue damage – K+ leaks from cells
- Acidosis
List normal serum levels for: sodium and potassium.
Sodium: 135 - 145 mmol/L
Potassium: 3.5 - 5.0 mmol/L
What effect do ADH and aldosterone have on fluid balance in the body?
When fluid volume is low…
Antidiuretic Hormone (ADH)
- Controls the amount of fluid leaving the body. It promotes reabsorption back into the blood.
Aldosterone
- Determines the reabsorption of Na+ and H2O from kidney tubules, aldosterone will help conserve fluid when volume is low.
