Patho 1016 week 11 – Fluids & Electrolytes Notes
Review Terms:
ECF: extra cellular fluid, all the fluids outside the cells including interstitial or tissue space and
blood vessels. Sodium and chloride are in higher concentrations, small amount of potassium.
Plasma is ECF
ICF: fluid within the cell, no calcium, small amount of sodium, large amounts of potassium
Diffusion: movement of uncharged particles along a concentration gradient
Edema: a palpable swelling produces by an increase in interstitial fluid volume, does not
become evident until the interstitial volume has increased by 2.5-3ltrs
Osmolality: concentration of dissolved particles in a solution
ADH: helps to regulate fluid balance, and sodium/water reabsorption
Isotonic: equal/neutral number of particles vs solutes in the fluid
Hypotonic: too little of solute’s vs the amount of fluid
Hypertonic: larger amount of concentration of solutes in the fluid
Causes of Edema:
• First cause - Increased capillary hydrostatic pressure, equivalent to high blood
pressure…prevents the return of fluid from the interstitial compartment to the venous
end of the capillary (hypervolemia)
• Second cause - Related to the loss of plasma proteins, albumin which helps regulate
plasma oncotic pressure, if there is low albumin the regulation of fluid is also decreased.
• Third cause – may also be result of obstruction of the lymphatic circulation, this kind of
obstruction can be a localized edema
• Fourth cause – increased capillary permeability such as in an inflammatory response,
usually results from infection
Balance of water & electrolytes: Maintained by:
• Thirst mechanism in hypothalamus
• Antidiuretic hormone (ADH) – controls amount of fluid leaving the body in urine
• Aldosterone – reabsorption of Na & H2O
• Natriuretic peptide hormones
Comparison of signs & symptoms of fluid excess (edema) & fluid deficit (dehydration):
Fluid Excess (Edema)
• Localized swelling (feet, hands, periorbital area, ascites)
• Pale, grey or red skin colour
• Weight gain
• Slow, bounding pulse, high blood pressure
• Lethargy, possible seizures
• Pulmonary congestion, cough, rales
•
Laboratory values: decreased hematocrit, decreased serum sodium, urine: low specific
gravity, high volume
Fluid Deficit (dehydration)
• Sunken, soft eyes
• Decreased skin turgor, dry mucous membranes
• Thirst, weight loss
• Rapid, weak thready pulse, low BP, and orthostatic hypotension
• Fatigue, weakness, dizziness, possible stupor
• Increased body temperature
• Lab Values: increased hematocrit, increased electrolytes (or variable), urine: high
specific gravity, low volume
Hormones:
ADH:
• Caused distal tubules, and collecting ducts, to help regulate water retention by
becoming more permeable to water
Aldosterone:
• Plays a part in sodium regulation by promoting the reabsorption of sodium from the
kidneys in the renal tubules
Hyponatremia:
Hypertonic:
• Results from an osmotic shift of water from ICF to ECF. In hyperglycemia the sodium in
the ECF becomes diluted as water moves outside the body cells as response to the
osmotic effects of high blood glucose
Hypotonic:
• Caused by water retention and dilutes sodium in the ECF. Happens when PT’s may have
water excess. Lesser concentration of sodium in the fluids
Hypovolemic:
• Both water and sodium are lost due to sweating/exercising
Hypervolemic:
• Caused by conditions such as congestive heart failure, when there is fluid accumulation
in the body of increased ADH hormone released
Sodium:
• The GI tract usually absorbs sodium from most of the foods
• Our typical intake far exceeds the bodies daily requirements
• Sodium leaves the body through urine, sweat, feces
• Kidneys regulate the concentration of sodium in the ECF by either excreting or retaining
water under the influence of ADH
• Antidiuretic hormone causes DCT and Collecting Ducts in kidneys to help regulate water
retention by becoming more permeable to water
•
Aldosterone plays part in sodium regulation by promoting reabsorption of sodium of the
kidneys in the renal tubules
- Hyponatremia = movement of water from ECF to ICF
- Hypernatremia = movement of water from ICF to ECF
Hyponatremia:
• A common electrolyte imbalance that describes a state where the sodium concentration
in the plasma (meaning outside the cell or ECF) is lower than normal
• Serum sodium is usually less than 135mmol
Causes of Hyponatremia:
• Hypertonic (hyperglycemia): sodium in ECF (outside cell) becomes diluted as water
moves out of the body cell as a response to the increase in blood glucose
• Hypotonic (water retention): dilutes sodium in ECF
• Hypovolemic (sweating/exercise): water and sodium are lost via sweating, water is
used to replace the loss
• Hypervolemic (accompanied by edema): causes by conditions such as congestive heart
failure, liver disease
Hypernatremia:
• Excess loss of body fluids that have a lower than normal concentration of Na+ so that
water is lost in excess of Na+
Manifestations of Hypernatremia:
• THIRST
• Decreased urine output
• Increased urine osmolarity
• Skin warm, flushed decreased turgor
• Increase serum osmolality
• Dry mucous membranes
• Decreased reflexes
• Headache, restlessness, agitation, decreased LOC
- Due to altered cellular metabolism
• Late symptom: Na+ > 155mEg/L = severe neuro changes ie. Coma, Seizures
Potassium:
• Most abundant cation in the ICF
• Role in conducting nerve impulses & excitability of cardiac, skeletal & smooth muscles
• Content of ECF of K+ = 3.5-5.0 mmol
Hypokalemia: