Electrolyte Disorders 👩🏼🔬 Flashcards
What are the 6 measured electrolytes?
- sodium
- potassium
- (chloride)
- (bicarbonate)
- urea
- creatinine
What are the estimated electrolytes in the body?
water
Why are abnormal electrolytes so clinically important?
- it can be a primary disease state
- it can be a secondary consequence of many diseases
- iatrogenic problems are common
What are the 4 main important functions of electrolytes?
- maintenance of cellular homeostasis
- cardiovascular physiology - BP
- renal physiology - GFR
- electrophysiology - heart & CNS
What are the most common clinical examples of electrolyte disorders?
- haemorrhage
- poor intake in the elderly
- diabetes insipidus
- diabetes mellitus
- diuretic therapy
- endocrine disorders involving ADH, aldosterone
What five interconnecting concepts are measured in the lab?
What is the main one that is measured?
- concentrations
- compartments
- contents
- volumes
- rates of gain and loss
In the lab, concentration is measured
The other factors are deduced
What are the missing components of this important concept?
What is the normal intracellular fluid (ICF) and extracellular fluid (ECF) volume?
ICF - 23 L
ECF - plasma + interstitial 19 L
What is normal cellular sodium concentration?
How can a change in the body affect this?
Normal Na conc is 140 mmol/L
Normally the system is maintained in equilibrium
changing any factor causes a new steady state to be reached
How does decreasing the volume of fluid in the body affect ECF, ICF and Na concentration?
Decreasing the volume will raise the concentration of any solute
ICF - 20L
ECF - plasma + interstitial 18 L
Na - 148 mmol/L
How does increasing the excretion of a solute affect solute concentration?
Increasing excretion decreases solute concentration
Fill in the body fluid distribution table
How does haemorrhage affect electrolyte concentrations?
it leads to loss of isotonic solutions
If 2 L of isotonic fluid is lost from the body, how does this affect ECF, ICF and [Na]?
Why?
ECF = plasma and interstitial 17 L
ICF = 23 L
Na - 140 mmol/L
the loss is from the ECF ONLY
there is no change in [Na} and no fluid redistribution
What is the difference between isotonic and hypotonic?
an isotonic solution has the same particulate concentration as the blood
a hypotonic solution is less concentrated than the blood
What tends to lead to loss of hypotonic solutions?
dehydration
How would loss of 3L of hypotonic fluid affect ECF, ICF and [Na]?
Why?
ECF = plasma + interstitial 18 L
ICF = 21 L
[Na] = 148 mmol/L
Greater loss from ICF than ECF
Small increase in [Na]
Fluid redistribution between ECF and ICF
How can isotonic solutions be gained?
through administration of saline
How does gain of 2L of isotonic fluid through saline drip affect ECF, ICF and [Na]?
ECF = plasma + interstitial 21 L
ICF = 23 L
[Na] = 140 mmol/L
Gain is to ECF ONLY
There is no change in [Na] and no fluid redistribution
How may hypotonic solutions be gained?
through giving water
What would happen to ECF, ICF and [Na} if there was gain of 3L of hypotonic fluid?
ECF = plasma + interstitial 20L
ICF - 25L
[Na] = 133 mmol/L
greater gain to ICF than to ECF
small decrease in [Na}
fluid redistribution between ECF and ICF
What are examples of physiological compensatory mechanisms?
- thirst
- ADH
- renin/angiotensin system
What are examples of therapeutic compensatory mechanisms?
- intravenous therapy
- diuretics
- dialysis
Where is ADH produced and when is it released?
What effects does it have?
it is produced by the median eminence
it increases when osmolality rises
it decreases renal water loss and increases thirst
What is the median eminence?
a part of the hypothalamus from which regulatory hormones are released
What are the 2 simple tests to ascertain ADH status?
What do the results show?
measure plasma & urine osmolality:
if urine > plasma, this suggests that ADH is active
measure plasma & urine urea:
if urine is much greater than plasma, this suggests water retention
What activates the renin-angiotensin system?
What does it cause?
it is activated by reduced IVV caused by Na depletion or haemorrhage
it causes renal Na retention
What is the simple test to ascertain renin-angiotensin status?
measure plasma and urine [Na]
if urine [Na] < 10 mmol/L, this suggests that RAAS is active
What will happen to ECF, ICF and [Na] if 2L of isotonic fluid loss is replaced by isotonic and hypotonic fluids?
isotonic fluid:
ECF = plasma + interstitial 19L
ICF = 23 L
Na = 140 mmol/L
This is NORMAL - no change in [Na] and no fluid redistribution
hypotonic fluid:
ECF = plasma + interstitial 18 L
ICF = 24 L
[Na] = 132 mmol/L
There is a fall in [Na] and fluid redistribution
What will happen to ECF, ICF and [Na] if loss of 3 L of hypotonic fluid is replaced by isotonic and hypotonic fluid?
isotonic fluid:
ECF = plasma + interstitial 21L
ICF = 21L
[Na] = 146 mmol/L
[Na] is slightly increased but there is NO fluid redistribution
hypotonic fluid:
ECF = plasma + interstitial 19L
ICF = 23L
[Na] = 140 mmol/L
[Na is restored and there is fluid redistribution
What 2 factors can lead to hyponatraemia?
- too little Na in ECF
- excess water in ECF
What 2 factors can lead to hypernatraemia?
- too little water in ECF
- too much Na in ECF
What 2 factors can lead to dehydration?
- water deficiency
- fluid (Na and water) depletion
Fill in the blanks in the tree for diagnosing hyponatraemia
How will the following features change in hyponatraemia due to diuretics?
How are the following factors changed in hyponatraemia due to Syndrome of inappropriate antidiuretic hormone secretion (SIADH)?
How are the following factors changed in hypernatraemia due to decreased water intake?
How do the following factors change in hypernatraemia due to osmotic diuresis?
What is the potassium reference range?
Which values are dangerous and why?
3.6 - 5.0 mmol/L
Values < 3.0 or > 6.0 are potentially dangerous
They can cause cardiac conduction defects or abnormal neuromuscular excitability
How is potassium measured?
How is this used to calculate total body potassium?
serum potassium concentration is measured
this is a small proportion of the total potassium in the plasma
total body potassium is determined by total cell mass
What conditions can significantly affect plasma [K] and why?
- acidosis
- insulin/glucose therapy
- adrenaline
- rapid cellular incorportation - TPN, leukaemia
This is because exchange between ICF and ECF significantly affects plasma [K]
Fill in the potassium distribution table
What is the effect of K+ redistribution?
What is the relationship between K+ and H+ ions?
They exchange across the cell membrane
They both bind to negatively charged proteins (e.g. Hb)
How do changes in pH affect the K+ and H+ equilibrium?
acidosis:
potassium moves out of cells, leading to hyperkalaemia
alkalosis:
potassium moves into cells, leading to hypokalaemia
What is the movement of H+ and K+ like in acidosis?
H+ moves into cells
K+ moves out of cells
this leads to hyperkalaemia
What are the 5 causes of hyperkalaemia?
- artefactual
- renal
- acidosis (intracellular exchange)
- mineralocorticoid dysfunction
- cell death
What are examples of artefactual causes of hyperkalaemia?
- delay in sample analysis
- haemolysis
- drug therapy - excess intake
What are examples of renal and ‘cell death’ causes of hyperkalaemia?
renal:
- acute renal failure
- chronic renal failure
cell death:
- cytotoxic therapy
What are examples of mineralocorticoid dysfunction causes of hyperkalaemia?
- adrenocortical failure
- mineralocorticoid resistance - e.g. spironolactone
What are the 5 treatments for hyperkalaemia?
- correct acidosis if this is the cause
- stop unnecessary supplements/intake
- give glucose and insulin to drive K into cells
- ion exchange resins encourage GIT K binding
- short and long-term dialysis
What are the 4 causes of potassium depletion?
- low intake
- increased urine loss
- gastrointestinal losses
- hypokalaemia without depletion
What may cause increased urine loss leading to potassium depletion?
- diuretics/osmotic diuresis
- tubular dysfunction
- mineralocorticoid excess
What may cause gastrointestinal losses leading to potassium depletion?
- vomiting
- diarrhoea
- fistulae
What may cause hypokalaemia without depletion?
- alkalosis
- insulin/glucose therapy
What concentration must there be for it to be classified as potassium depletion?
< 2.5 mmol/L
What are the effects of potassium depletion due to acute changes in ICF/ECF ratios?
neuromuscular changes:
- lethargy
- muscle weakness
- heart arrhythmias
what are the effects of potassium depletion due to chronic losses from the ICF?
neuromuscular:
- lethargy
- muscle weakness
- heart arrhythmias
kidney
- polyuria
- alkalosis due to increase in renal bicarbonate production
also affects vasculature and the gut
How may potassium depletion be detected when taking a history from a patient?
- diarrhoea, vomiting, drugs (diuretics, digoxin)
- symptoms of lethargy/weakness
- cardiac arrthymias
What electrolyte tests would be done in potassium depletion and what results obtained?
- hypokalaemia
- alkalosis due to raised bicarbonate
How can potassium depletion be prevented?
through giving adequate supplementation
How can potassium depletion be treated through replacement of deficit?
oral:
46 mmol/day + diet
IV
< 20 mmol/L
In what conditions should plasma potassium be monitored regularly?
- diuretic therapy
- digoxin use
- compromised renal function
- in support of IV resuscitation
How will the following factors be changed in hypernatraemia due to aldosterone?
