Disorders of Sodium, Water and Potassium Flashcards
What is measured in U + Es? (6)
- Sodium
- Potassium
- Urea
- Creatinine
- (chloride)
- (bicarbonate)
What is estimated from U + Es?
Water.
What are electrolytes important for? (4)
- Maintain cellular homeostasis
- Cardiovascular physiology (BP)
- Renal physiology (GFR)
- Electrophysiology
What are the 5 important concepts?
- Concentrations
- Compartments
- Contents
- Volumes
- Rates of gain/loss
Which of these concepts is mainly measured by the lab?
Concentrations.
-the other factors are deduced
What is ECF composed of?
Plasma + interstitial fluid.
What is the normal volume of water in ECF and ICF?
ECF = ~19L ICF = ~ 23L
What is the approximate sodium concentration of ICF and ECF?
ICF - 10mmol/L
ECF - 140mmol/L
What is the approximate potassium concentration of ICF and ECF?
ICF - 150 mmol/L
ECF - 5 mmol/L
What effect does decreasing the volume of water in the body have (e.g. excess sweating)?
- Increased plasma concentration of electrolyte (e.g. Na)
- ICF loses more fluid than ECF
What is the total volume of water in the body?
~42 L.
19+23
Give an example of loss of isotonic fluid from the body.
Haemorrhage (bleeding).
What is the effect of 2L blood loss (isotonic)? (3)
- Loss from ECF
- No change in [Na]
- No fluid redistribution
What is the effect of 3L loss of hypotonic fluid (e.g. dehydrated)? (3)
-Greater loss from ICF than ECF
-Small increase in [Na]
-Fluid redistribution between ECF and ICF
» CELLS SHRINK
What is the effect of 2L gain of isotonic fluid (e.g. saline drip)? (3)
- Gain to ECF
- No change in [Na]
- No fluid redistribution
Does gain/loss of isotonic fluid lead to fluid redistribution?
NO.
-no change in ICF volume
What is the effect of 2L gain of hypotonic fluid (e.g. water)? (3)
-Greater gain in ICF than ECF
-Small decrease in [Na]
-Fluid redistribution between ECF and ICF
» CELLS EXPAND
What are the body’s main compensatory mechanisms?
- PHYSIOLOGICAL - thirst, ADH, RAAS
* THERAPEUTIC - IV, diuretics, dialysis
What is ADH?
Anti-diuretic hormone.
-AKA vasopressin
What is ADH produced by?
Median eminence.
What causes an increase in ADH release?
Rise in osmolality.
What are the main effects of ADH? (3)
- Decreases renal water loss (» water retention)
- Increases thirst
- Constricts blood vessels
How does measuring plasma and urine osmolality ascertain ADH status?
Urine > plasma suggests ADH is active.
How does measuring plasma and urine urea ascertain ADH status?
Urine urea > plasma urea suggests water retention.