Fluid and Electrolyte Balance Flashcards
What is the normal serum range for sodium?
135-145mmol/L.
Sodium excretion is regulated by what 3 things?
Renin-angiotensin system. Natriuretic peptides. Intrinsic renal mechanisms.
What makes up extracellular fluid?
Interstitial fluid. Plasma.
What organ produces angiotensinogen?
Liver.
What organ produces renin?
Kidneys.
Where is Angiotensin converting enzyme (ACE) found?
Lungs.
Give 2 effects of Atrial Natriuretic Peptide (ANP).
Reduction in release of renin. Dilatation of afferent arteriole (more filtrate forced out). Increased loss of sodium ion in urine.
Give 2 symptoms of hypovolaemia.
GI losses. Thirst. Lethargy. Dizziness. Confusion. Reduced urine volume.
Give 2 symptoms of hypervolaemia.
Breathlessness. Peripheral oedema. Weight gain. Abdominal floating.
What characterizes a patients as being hyponatraemic?
Na less than 135mmol/L.
What are the three types of hyponatraemia?
Hypovolaemia hyponatraemia. Euvolaemia hyponatraemia. Hypervolaemia hyponatraemia.
Give 2 causes of Hypervolaemia hyponatraemia?
Congestive heart disease. Cirrhosis. Nephrotic syndrome.
Give 2 causes of Hypovolaemia hyponatraemia?
GI losses e.g. vomiting, diarrhoea. Medications e.g. diuretics. Cerebral salt wasting.
What is Hypovolemic hyponatremia?
Small total body water, large sodium ↓.
What is Hypervolemic hyponatremia?
Total body water ↑, small sodium ↑.
What is Euvolemic hyponatremia?
↑ body water, no body sodium change.
Give 2 causes of Euvolemic hyponatremia?
Diluted urine - adrenal insufficiency, hypothyroidism, drinking too much (polydipsia). Undiluted - syndrome of inappropiate Anti-diuretic hormone (SIADH).
How is Euvolemic hyponatremia seprated?
Diiluted urine. Concentrated urine.
Give 2 symptoms of hyponatraemia.
Muscle cramps. Vomiting. Nausea.
What is a severe complication of hyponatraemia?
Cerebral oedema - confusion, death, coma. Respiratory failure.
What percentage of our body is water?
60%.
1/3 of our body water is intracellular or extracellular?
Extracellular.
What treatment is recommended for a euvolaemic hyponatraemia patient?
Fluid restriction.
Why is excessive sodium level correction dangerous?
Can lead to cerebral pontine myelinolysis (rapid sodium, water shifts → myelin-loss in pons).
What characterizes hypernatraemia?
Sodium greater than 145mmol/L.
What causes of hypernatraemia?
Water loss greater than sodium loss. Sodium increases.
What can cause un-replaced water losse resulting in hypernatraemia?
Insensible sweat losses. Nephrogenic diabetes (receptors in kidneys don’t respond to ADH). Central diabetes insipidus (damage to hypothalamus therefore less ADH produced). Damage to thirst centre.
What can cause sodium overload resulting in hypernatraemia?
Administration of high salt load.
Give 2 symptoms of hypernatraemia.
Thirst. Weakness. Seizures. Coma.
What characterizes hypokalaemia?
Low potassium levels in the blood < 3.5mEq/L
Give 3 causes of hypokalaemia?
Decreased K intake. Increased entry into cells from blood. Increased losses e.g. GI (vomiting), urine.
What is responsible for the decrease in serum K in hypokalaemia?
Increased kidney excretion (urine losses) - hyperaldosteronism, drugs (e.g. loop diuretic), renal tubular defects. Increased sweat production (e.g. exercise). Increased gastrointestinal production e.g. vomiting, diarrhoea. Insulin overdose in Type I diabetes; excess insulin → increases sodium/potassium pump action.
What is the effect of hypokalaemia on an ECG?
Flattening of T waves. Depression of ST segment. Development of U wave. Widening QRS complex.
Give 2 symptoms of hypokalaemia.
Muscle weakness. Arrhythmia. Constipation.
What characterizes hyperkalaemia?
High potassium levels in blood > 5.5 milliequivalents/liter (mEq/L).
Give 2 causes underlying hyperkalaemia.
Increased potassium released from cells. Reduced urinary excretion.
What causes increased potassium release from cells?
Uncontrolled Type I diabetes - Lack of insulin→ decreases sodium/potassium pump action. Acidosis - excess hydrogen ions move into cells via ion transporters that exchange hydrogen ions for potassium ions. Massive cell lysis e.g. tumor lysis syndrome, rhabdomyolysis, massive hemolysis. Drugs e.g. Beta2-adrenergic antagonists, digoxin toxicity. Exercise - Cellular ATP consumed → potassium channels open.
What decreases potassium excretion from kidneys?
Adrenal insufficiency → primary hypoaldosteronism, so principal cells secrete less potassium. Drugs - Renin inhibitors, angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor antagonists, potassium-sparing diuretics, nonsteroidal anti-infl ammatory drugs (NSAIDs), cyclosporine, trimethoprim-sulfamethoxazole.
Give 2 symptoms of hyperkalaemia.
Paraesthesiae (pins and needles). Muscle weakness - paralysis. Arrhythmias.
What is the effect of hyperkalaemia on an ECG?
Tall peaked T waves. Loss of p waves. Widened QRS complex. Depressed ST segment.
Give 2 treatments for hyperkalaemia.
Calcium to stabilize myocardial cell membranes. Insulin with dextrose - increase potassium shift into cells. Loop diuretics - increase potassium excretion in kidneys.
