Electrolyte homeostasis Flashcards
What is measured by U&Es?
Sodium
Potassium
(Chloride)
(Bicarbonate)
Urea
Creatinine
Why might a person have abnormal electrolytes?
Primary disease state
Secondary consequence of a multitude of diseases
Iatrogenic problems are very common
What is important in the correction of abnormal electrolytes?
Maintenance of cellular homeostasis
Cardiovascular physiology - BP
Renal physiology - GFR
Electrophysiology - heart, CNS
What are the physiological water electrolyte homeostasis mechanisms?
Thirst
ADH
Renin / Angiotensin system
What therapeutic interventions are available?
Intravenous therapy
Diuretics
Dialysis
Where is ADH produced?
Produced by median eminence and release increases when plasma solute concentration rises.
What are the actions of ADH?
Decreases renal water loss
Increases thirst
What tests may be used to ascertain ADH status?
Measure plasma & urine solute concentration
- urine > plasma suggests ADH is active
Measure plasma & urine urea
- urine >> plasma suggests water retention (ADH active)
What are possible triggers for the renin-angiotensin system?
Na depletion
Haemorrhage
What are the actions of the renin-angiotensin system?
Renal Na retention
What test can be used to ascertain renin-angiotensin status?
Measure plasma & urine Na
- If urine < 10 mmol/L suggests R/A/A active
What is hyponatremia?
Too little Na in ECF
Excess water in ECF
What is hypernatremia?
Too little water in ECF
Too much Na in ECF
What is dehydration?
Water deficiency
Fluid (Na and water) depletion
What potassium serum values are dangerous?
Values 6.0 mmol/L are potentially dangerous
- Cardiac conduction defects
- Abnormal neuromuscular excitability
What is the relationship between potassium and hydrogen ions?
Changes in pH cause shifts in the equilibrium
- acidosis - potassium moves out of cells -> hyperkalaemia
- alkalosis - potassium moves into cells -> hypokalaemia
What are the possible causes of hyperkalaemia?
Artefactual
- Delay in sample analysis
- Haemolysis
- Drug therapy
- Excess intake
Renal
- Acute Renal Failure
- Chronic Renal Failure Acidosis (intracellular exchange)
Mineralocorticoid Dysfunction
- Adrenocortical failure
- Mineralocorticoid resistance - eg spironolactone
Cell Death
- Cytoxic therapy
What treatment is given for hyperkalaemia?
Correct acidosis if this is cause
Stop unnecessary supplements / intake
Give glucose & insulin - Drives potassium into cells
Ion exchange resins - GIT potassium binding
Dialysis - short and long-term
What are the possible causes of potassium depletion?
Low intake Increased urine loss
- diuretics / osmotic diuresis
- tubular dysfunction
- mineralocorticoid excess
GIT losses
- vomiting/diarrhoea/laxatives
- fistulae Hypokalaemia without depletion
- alkalosis
- insulin / glucose therapy.
What is the effect of acute potassium depletion?
Acute changes in ICF/ECF ratios
Neuromuscular:
- lethargy, muscle weakness, heart arrhythmias
What is the effect of chronic potassium depletion?
Chronic losses from the ICF:
Neuromuscular:
- lethargy, muscle weakness, heart arrhythmias
Kidney:
- polyuria
- alkalosis
- increase renal HCO3 production
What is the treatment for potassium depletion?
Prevention
- Adequate supplementation
Replacement of deficit
- oral - 48 mmol/day + diet
- IV - < 20 mmol/L
When is is appropriate to monitor potassium levels?
Diuretic therapy
Digoxin use
Compromised renal function
In support of IV resuscitation (eg DM Ketacidosis)
