16b Electrolyte homeostasis Flashcards
What is the extracellular concentration of Na+?
140 mmol/L.
What is the intracellular concentration of Na+?
10 mmol/L.
What is the intracellular concentration of K+?
150 mmol/L.
What is the extracellular concentration of K+?
5 mmol/L.
Give two examples of isotonic fluid loss:
Blood.
Fistula fluid.
What is the effect of isotonic fluid loss?
Loss from extracellular fluid.
No [Na+] change or fluid redistribution.
Give an example of hypotonic fluid loss:
Insensible water loss.
What is the effect of hypotonic fluid loss?
Greater loss form ICF than ECF.
Small increase in [Na]. Fluid redistribution.
Give an example of isotonic fluid gain:
Saline drip.
What is the effect of isotonic fluid gain?
Gain to ECF.
No [Na] change or fluid redistribution.
Give an example of hypotonic fluid gain.
Water.
Dextrose.
What is the effect of hypotonic fluid gain?
Greater gain in ICF than ECF.
Small decrease in [Na]. Fluid redistribution.
What are the effects of ADH?
Decreases renal water loss.
Increases thirst.
How is ADH status ascertained?
Osmolality measurement.
Urine greater than plasma then ADH active.
Urine much greater plasma then water retention present.
What effect does RAAS have on renal Na retention?
Increases it.
How is RAAS activation ascertained?
If urine osmolality is less than 10mmol/l, then RAAS is active.
What are the causes of hyponatraemia? (11).
Diuretics. Addison's. Na losing nephritis. SIADH (inappropriate ADH). Drugs. CRF. D+V. Skin loss. Stress. Post surgery. Hypothyroid.
What is the normal range for plasma [Na]?
135-145 mmol/L.
What is the normal range for plasma [urea]?
3-8 mmol/L.
What is the normal range for plasma [glucose]?
3.5 - 5.5 mmol/L.
Name two causes of hypernatraemia:
Decreased water intake.
Osmotic diuresis.
What is the normal range for plasma [K]?
3.6 to 5.0 mmol/L.
Which values of plasma [K] are dangerous?
Why?
less than 3 mmol/L, more than 6 mmol/L.
Cardiac conduction defects, abnormal neuromuscular excitability.
Why does serum potassium not represent body potassium?
Small proportion in plasma, very affected by ICF-ECF exchange. Dependant on total body mass.
ICF-ECF exchange significantly affects plasma [K]. Name the four factors that may change the exchange.
Acidosis.
Insulin/glucose therapy.
Adrenaline.
Rapid cellular incorporation - TPN, leukaemia.
How are potassium and hydrogen ions related?
Exchanged across cell membrane.
Both bind to same negatively charged proteins e.g. Hb.
What effect does acidosis and alkalosis have on potassium levels?
Acidosis - K out of cells - hyperkalaemia.
Alkalosis - K into cells - hypokalaemia.
What are the causes of hyperkalaemia? (4).
Renal failure.
Acidosis.
Mineralocorticoid dysfunction: adrenocortical failure, minerocorticoid resistance (spironolactone).
Cell death during cytotoxic therapy.
How is hyperkalaemia treated? (4)
Correct acidosis.
Give glucose and insulin.
Ion exchange resins.
Dialysis.
What are the causes of hypokalaemia? (5)
Low intake. Increased urine loss (diuretics, dysfunction). GIT losses (D+V, fistulae). Alkalosis. Insulin/glucose therapy.
What are the effects of a [K] less than 2.5mmol/l?
Lethargy, muscle weakness, heart arrhythmias.
Polyuria.
Alkalosis (increased renal HCO3- production).
What is the treatment of hypokalaemia?
Supplementation orally or IV.
When should potassium levels be routinely monitored? (4)
Diuretic therapy.
Digoxin use.
Compromised renal function.
In support of IV resuscitation.
