Fluids and Electrolytes Flashcards
What proportion of body weight is water?
45-65%
____________ ________ comprises two-thirds of water weight.
Intracellular fluid
Extracellular fluid makes up ____-______ of water weight.
One-third
_________ is one quarter, and interstitial fluid is three quarters of the extracellular fluid.
Plasma
Extracellular fluid loss may be due to acute ______ _____, vomiting, and diarrhoea.
Blood loss
State two ways by which extracellular fluid can be gained.
IV fluid overload and heart failure
What is the homeostatic response of changes in extracellular fluid?
Changes in plasma volume, or osmotic concentrations
The concentration of solutes per kilogram of solvent (mOsm/kg H2O) is ____________.
Osmolality
‘Normal’ plasma osmolality is 2__ - 295 mOsm/kg.
85
__________ osmolality is from 300 - 900 mOsm/kg.
Urine
_________, and its associated anions, account for most of the osmotic activity of plasma.
Sodium
___________ is regulated by changes in water balance.
Sodium
___________ is regulated by changes in sodium balance.
Volume
Measurement of osmolality is done by osmometer, and based on freezing point or ___________ ______________.
Vapour depression
State the formula for calculated osmolality.
2 x [Na+] + [urea] + [glucose]
__________ _____ are caused by the difference between measured and calculated osmolality.
Osmolal gaps
Osmolality - ___________ ___________ = osmolal gap
Calculated osmolality
GFR Increases with volume expansion, and decreases with volume ___________.
Depletion
What is the role of atrial natriuretic peptide?
Promotes sodium excretion by the kidney
True or false: in water excess, ADH secretion and thirst are suppressed.
True
Hypernatraemia occurs during _______ ___________.
Water depletion
___________ dehydration can be caused by GI losses, inadequate fluid intake, etc..
Isotonic
___________ dehydration results from diuretic drugs, osmotic diuresis, etc..
Hypertonic
__________ dehydration can be derived from GI losses, and high-sodium sweat (as seen in cystic fibrosis).
Hypotonic
Give two causes of high osmolality.
Hyperglycaemia and increased urea
______________ are ions that are capable of carrying an electric charge, and may be positive or negative.
Electrolytes
List four functions of electrolytes.
Volume and osmotic regulation (Na, K, and Cl)
Acid-base balance (HCO3, K, Cl)
Neuromuscular excitability (K, Ca, and Mg)
Myocardial rhythm and contractility (K, Mg, and Ca)
True or false: electrolytes are often measured in conjunction with sodium and urea.
True
What is the plasma reference range for sodium?
135 - 145 mmol/L
Hyponatraemia is decreased plasma _________.
Sodium
Increased sodium loss may be due to _______________, potassium deficiency, diuretic use, ketonuria, prolonged D&V, or salt-losing nephropathy.
Hypoadrenalism
__________________ may be due to hyperlipidaemia, or hyperproteinaemia.
Pseudohyponatraemia
_______________ hyponatraemia may be attributed to sodium loss and water retention.
Hypoosmotic
Isosmotic hyponatraemia is due to increased non-__________ cations, and may be observed in pseudohyponatraemia.
Sodium
______________ hyponatraemia involves increased amounts of other solutes in the plasma.
Hyperosmotic
_________________ is increased plasma sodium (>146 mmol/L).
Hypernatraemia
True or false: hypernatraemia is always hyperosmolar.
True
Increased intake or retention, such as _________________, or sodium bicarbonate excess, is also a factor of hypernatraemia.
Hyperaldosteronism
<300 mOsm/kg may be observed in ____________ ____________.
Diabetes insipidus
300 - 700 mOsm/kg indicates a ________ defect in ADH, osmotic diuresis, etc..
Partial
> 700 mOsm/kg indicates a loss of thirst, insensible loss of water, GI loss of ____________ fluid, and excess intake of sodium.
Hypotonic
__________ syndrome involves excessive aldosterone.
Conn’s
Cushing’s syndrome involves __________________.
Hypercortisolism
True or false: lipaemia interferes with flame emission spectrophotometry.
True
True or false: heparinised samples are not suitable for use in sodium measurement.
False
Name a common electrochemical method of measuring electrolytes.
Iron selective electrodes (ISE)
Outline the principle of iron selective electrodes.
Measures activity of electrolytes, in a defined volume of water. Charges are produced by having different ion concentrations on either side of the membrane. Two electrodes, a reference electrode and measuring electrode, are used. The difference in potential between electrodes is a reflection of the difference in ion activity, and is used to calculate a concentration, in mmol/L. Direct ISE uses an undiluted sample; indirect ISE used a diluted sample
___________ ISE measurement is more accurate in pseudohyponatraemia, when hyperproteinaemia or hyperlipidaemia displace plasma water.
Direct
State the principle of flame emission spectrophotometry.
When atoms of many metallic elements, especially Na and K, are given sufficient energy, they emit this energy at wavelengths; the energy comes from a flame, which excites the element, and they emit characteristic spectra
Potassium is a major intracellular _________ in the body.
Cation
lThe ___________ reference range of potassium is 3.5-5.0 mmol/L.
Serum
What is the urine reference range for potassium?
30-100 mmol/day
Potassium has major effects on contraction of skeletal and cardiac muscles, together with ________ ___________ ____________.
Resting membrane potential
True or false: H+ concentration is not affected by potassium.
False
______________ increases K+ excretion.
Aldosterone
List two features, other than aldosterone, which regulate potassium secretion.
Insulin and pH
True or false: hyperkalaemia is the most common electrolyte disturbance detected.
True
List three symptoms of hyperkalaemia.
Mental confusion, bradycardia, and weakness
Outline the first-used treatment for hyperkaelamia.
Infusion of insulin and glucose, to move potassium into cells
State three causes of hyperkalaemia.
Renal failure, hypoaldosteronism, and use of diuretics.
Sample haemolysis or _______________ may cause artifacts to appear in hyperkalaemia investigation.
Thrombocytosis
Define hypokalaemia.
Serum potassium concentration of <3.5 mmol/L
Symptoms of _____________ involve muscle weakness, irritability, and paralysis.
Hypokalaemia
Pseudohypokalaemia may be observed in acute ______________.
Leukaemia
List two causes of true potassium deficit.
Cushing’s disease and acute tubular necrosis
What is the treatment for hypokalaemia?
Potassium salts, and occasionally IV potassium
True or false: serum levels of potassium tend to be lower than those of plasma.
False
What is the method of choice in measuring potassium?
Iron selective electrodes
____________ is the most abundant anion in extracellular fluid.
Chloride
What is the serum (and plasma) reference range for chloride?
97-107 mmol/L
What is the urine reference range for chloride?
110-250 mmol/day
Changes in chloride concentration usually follow those of ______________.
Sodium
If an _______-_______ ______________ is present, chloride can differentially diagnose.
Acid-base disturbance
What specimen is used in testing the chloride of cystic fibrosis patients?
Sweat
State a method of chloride quantification, other than iron selective electrodes.
Mercurimetric titration
What is the chemical formula for bicarbonate?
HCO3-
Bicarbonate is the second-most common _______ in extracellular fluid.
Anion
What is the reference range (for serum and plasma) for bicarbonate?
24-27 mmol/L
True or false: bicarbonate is most accurately quantified when the sample has been incubated at room temperature for one hour.
False
To measure total CO2 (and thus bicarbonate), if the sample is _____________, CO2 is converted to HCO3-, followed by an enzymatic reaction.
Alkalinised
CO2
converted to HCO3
-
followed by an enzymatic reaction
