Fluid And Electrolyte Balance Flashcards by Joe Reel

What is the most abundant cation in the ECF?

Sodium

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How is sodium measured?

Sodium is typically measured using an ion-selective electrode (ISE) method, which measures the activity of sodium ions in a patient’s blood sample.
This method is fast, accurate, and reliable, making it a common and widely used test in clinical laboratories.

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What does the prefix hypo- mean?

Low

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What does the prefix hyper- mean?

High

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What are causes of hyponatraemia? (3)

1.Increased sodium loss
⬇️ Aldosterone production, diuretics or nephropathy in renal disorders
Low K+
2.Increased water retention
Dilution of Na+
⬇️ Plasma proteins
3.Water imbalance
SIADH

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What are causes of hypernatraemia?

1. Excess water loss
Not usually caused by an excess of Na+ but relative deficit of water so often coincides with dehydration.

2. Decreased water intake
Older persons 👵

3.Increased intake or retention
Hyperaldosteronism

Measurement of urine required to evaluate the causes of hyponatraemia.

Severity:
Diabetes insipidus < Osmotic diuresis < loss of thirst

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Describe causes of hypokalaemia

1. GI loss
Vomiting

2. Renal Loss
Nephritis

3. Cellular shift
Alkalosis

4. Decreased intake

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Causes of hyperkalaemia

1. Decreased renal excretion
Acute or chronic renal failure

2. Cellular shift
Acidosis

3. Increased intake
Oral orIV replacement therapy

4. Artifactual
Sample haemolysis

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Describe the features of pseudohyperkalaemia

Pseudohyperkalaemia is a false elevation of potassium levels that can occur due to certain pre-analytical factors, such as prolonged tourniquet application during blood collection or high-speed centrifugation.
Pseudohyperkalaemia is not a true indication of elevated potassium levels in the body and should be confirmed using other tests.

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Symptoms of severe hypokalaemia

Muscle weakness; paralysis; Heart rhythm abnormalities

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Name two pathological processes involving electrolytes

Volume and osmotic regulation (Na+, Cl- and K+)
Myocardium rhythm and contractility (K+, Mg2+)

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__________ is the number of solute particles in 1 kg of solvent.

Osmolality

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__________ is the concentration of solutes per litre of solvent - can be inaccurate due to temp and pressure.

Osmolarity

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__________ is the difference between the measured __________ and the calculated _________. Due to differences in the way blood solutes are measured and their calculation methods in the laboratory.

Osmolar gap
Osmolality
Osmolarity

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What is the controller of Osmolality?

Arginine vasopressin hormone (AVH) (ADH)

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Where is ADH released from?

Posterior pituitary

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Define Polydipsia

The feeling of extreme thirstiness.

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ADH release is stimulated by (4)

⬆️Plasma Osmolality
⬇️Blood volume
⬇️BP
Stress

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Where is ADH produced?

Hypothalamus

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What is the primary function of ADH?

Primary function is ↓water loss in the kidneys which reduces the concentration of electrolytes.

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High ADH conc means

•↑ H2O permeability in distal tubules and collecting ducts of the kidney.
•↑ H2O reabsorption, ↓ H2O excretion.
•Establishes a negative feedback loop.

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Define hypovolemia

Loss of water & Na+ without replacement.
Total body water declines but osmolarity remains normal.
Haemorrhage, sever burns, vomiting, diarrhoea.

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_________ _____ are a major factor in estimating glomerular filtration rate - the gold standard marker of kidney health.

Creatinine levels

Direct ISE

Requires larger undiluted samples

Indirect ISE

Requires smaller, diluted sample but can be prone to **dilution error**

**Dilution error**

The dilution & calculations to produce ISE results depend on the assumption that the sample contains normal fat levels. In very lipidaemic samples, this will result in apparent hyponatraemia even when the biologically-active Na+ concentration in the aqueous phase is normal.

Pseudo-hyponatraemia

When serum sodium concentration is actually normal but erroneously reported as low due to presence of either hyper-lipidemia or hyper-proteinemia.

Symptoms of true hyponatraemia

Nausea; Confusion; Headache; Impaired consciousness

Treatment of hyponatraemia

Correction of condition causing H2O or Na+ in excess of H2O, loss Fluid management Vasopressin receptor antagonists (conivaptan)

Symptoms of hypernatraemia

Altered mental status; Lethargy; Irritability

Treatment for hypernatraemia

IV fluids to reduce Na+ with careful monitoring

What happens in rapid reduction of Na+?

Cerebral oedema, convulsions and permanent brain injury

Sources of Potassium

Beans🫘 Green veg 🥦 Bananas🍌

Hypokalaemia is linked to ________.

Alkalosis

Hyperkalaemia is linked to ________.

Acidosis

What is he hormonal regulator of K+?

Aldosterone

Where is aldosterone produced?

Produced by the cells of the adrenal cortex in the adrenal gland

What is the action of aldosterone on K+?

Release through the renin-angiotensin mechanisms or though direct release stimulates secretion into the tubular lumen; stimulates Na+ and water reabsorption from the gut, salivary and sweat glands in exchange for K+

Plasma volume decreases => ?

Increase in plasma angiotensin II

Increased plasma angiotensin II => ?

Increased aldosterone secretion in adrenal cortex

Increased plasma potassium => ?

Increased aldosterone secretion in the adrenal cortex

Renin-angiotensin system

1️⃣ Drop in blood pressure and fluid volume 2️⃣ Renin released form the kidney acts on angiotensin released from the liver 3️⃣ ACE is released from the lungs acts on angiotensin I to form angiotensin II

Effects of angiotensin II

Acts on adrenal gland to stimulate release of aldosterone Acts on blood vessels stimulating vasoconstriction

Name the two mechanisms for potassium transport

1.Electrical potential gradient (Na+K+ pump) 2.Acid base balance (K+H+ pump)

What is the effect of excercise on potassium levels?

K+ is released during exercise, changes reversed after several minutes of rest

What is the effect of hyperosmolality?

Causes H2O carrying K+ to diffuse into cells

What is the effect of cellular breakdown on potassium?

Release K+ into the ECF

What membrane is used for potassium ISE?

Valinomycin

Reasons for artefactual hyperkalaemia (4)

Haemolysis Delayed processing Exposure to cold Abnormal cells

Symptoms of hyperkalaemia

Muscle weakness; Irritability; Decreased BP

Treatment of hyperkalaemia

Calcium glauconite to stabilise heart muscle Intravenous insulin and dextrose to promote potassium entry into cells

Symptoms of hypokalaemia

Muscle weakness; Fatigue; Constipation

Treatment of hypokalaemia

Oral replacement IV K replacement Dietary correction

Hyponatraemia medical emergency

<120mmol/L for >48hours

Hypernatraemia level >160mmol/L has…

Mortality rate of 60-75%

Phone ward if potassium levels are…

<2.5mmol/L >6.5mmol/L