Electrolyte Disorders

Question 1

What is a U&E test?

Answer 1

Blood test for urea and electrolytes when assessing renal function.

Question 2

What is measured in U&E test?

Answer 2

• Sodium - Potassium - (Chloride) - (Bicarbonate) - Urea - Creatinine Water is estimated

Question 3

What are common causes of electrolyte imbalance?

Answer 3

• Kidney disease - Illnesses with symptoms that cause fluid loss/dehydration (e.g. vomiting, diarrhoea, sweating) - Intestinal/digestive issues - Hormone imbalance - Medications like antibiotics, diuretics and those used to treat cancer and heart disease - Haemorrhage

Question 4

In terms of body functioning, what 6 electrolytes are the most important?

Answer 4

• Sodium - Potassium - Chloride - Bicarbonate - Calcium - Phosphate

Question 5

How does excretion of ions usually occur?

Answer 5

• Excretion of ions occurs mainly through the kidneys, with lesser amounts lost in sweat and in faeces. - Excessive sweating may cause a significant loss, especially of sodium and chloride. - Severe vomiting or diarrhoea will cause a loss of chloride and bicarbonate ions.

Question 6

What 2 components make up the ECF?

Answer 6

Plasma + Interstitial Fluid

Question 7

What is the typical volume of sodium inside and outside cell?

Answer 7

ECF: 140 mmol/L

ICF: 10 mmol/L

Question 8

What is the typical ECF volume? ICF volume?

Answer 8

The major division is into Intracellular Fluid (ICF: about 23 litres) and Extracellular Fluid (ECF: about 19 litres) based on which side of the cell membrane the fluid lies.

Question 9

What is the major cation of ECF?

Answer 9

Sodium - is responsible for one-half of the osmotic pressure gradient that exists between the interior of cells and their surrounding environment

Question 10

How is sodium excreted?

Answer 10

Mainly by the kidneys:

• Sodium is freely filtered through the glomerular capillaries of the kidneys
• Much of the filtered sodium is reabsorbed in the proximal convoluted tubule
• Some remains in the filtrate and urine, and is normally excreted

Question 11

How does decreasing blood volume affect the conc of any solute?

Answer 11

This will raise the conc of any solute

Question 12

After a huge water loss (e.g. dehydration), how does this affect ECF and ICF?

Answer 12

Water lost first from ECF (this is where most of the water is) and there is a redistribution

Question 13

Sodium and potassium body distribution:

Answer 13

Question 14

What is an isotonic solution?

Answer 14

In an isotonic solution—iso means the same—the extracellular fluid has the same osmolarity as the cell, and there will be no net movement of water into or out of the cell.

Question 15

How does a loss of isotonic fluid from the body affect sodium?

Answer 15

• Loss is from ECF
• No change in [Na]
• No fluid redistribution

Question 16

What is a hypotonic solution?

Answer 16

If the extracellular fluid has lower osmolarity than the fluid inside the cell, it’s said to be hypotonic—hypo means less than—to the cell, and the net flow of water will be into the cell.

Question 17

What is the effect of a loss of hypotonic fluid?

Answer 17

• Greater loss from ICF than ECF
• Small increase in [Na]
• Fluid redistribution between ECF and ICF

Question 18

What is the effect of a gain of isotonic fluid e.g. saline drip

Answer 18

• Gain is to ECF
• No change in [Na]
• No fluid redistribution

Question 19

How does a gain of isotonic fluid (e.g. saline drip) affect blood pressure?

Answer 19

Increases blood pressure

Question 20

What is the effect of a gain of hypotonic fluid e.g. water, dextrose?

Answer 20

• Greater gain to ICF than ECF
• Small decrease in [Na]
• Fluid redistribution between ECF and ICF

Question 21

What is hyponatraemia? What is it usually associated with?

Answer 21

• A lower-than-normal concentration of sodium
• Usually associated with excess water accumulation in the body, which dilutes the sodium
• Also due to loss of sodium from the body

Question 22

What can cause a loss of sodium?

Answer 22

• A decreased intake of the ion coupled with its continual excretion in the urine.
• Several conditions, including excessive sweating, vomiting, or diarrhea; the use of diuretics; excessive production of urine, which can occur in diabetes; and acidosis, either metabolic acidosis or diabetic ketoacidosis.

Question 23

What can cause a relative decrease in blood sodium?

Answer 23

An imbalance of sodium in one of the body’s other fluid compartments, like IF, or from a dilution of sodium due to water retention related to edema or congestive heart failure.

Question 24

At the cellular level, what is the effect of hyponatraemia?

Answer 24

• Increased entry of water into cells by osmosis, because the concentration of solutes within the cell exceeds the concentration of solutes in the now-diluted ECF
• The excess water causes swelling of the cells; the swelling of red blood cells—decreasing their oxygen-carrying efficiency and making them potentially too large to fit through capillaries—along with the swelling of neurons in the brain can result in brain damage or even death.

Question 25

What is hypernatraemia? What can it result from?

Answer 25

* Hypernatremia is an abnormal increase of blood sodium. * It can result from water loss from the blood, resulting in the hemoconcentration of all blood constituents. * Hormonal imbalances involving ADH and aldosterone may also result in higher-than-normal sodium values.

Question 26

What is the effect of ADH?

Answer 26

Stimulates water reabsorption: * Released when osmolarity rises * Increases thirst * Decreases renal water loss

Question 27

What tests can be done to ascertain ADH status?

Answer 27

* Measure plasma and urine osmolality * Urine \> plasma suggests ADH is active * Urine is very conc as water has been reabsorbed OR * Measure plasma and urine urea * Urine \>\> plasma suggests water retention

Question 28

What does a lower osmolality mean?

Answer 28

The particles are more diluted

Question 29

What activates RAAS?

Answer 29

Reduction in intravascular volume (drop in blood pressure) : * Na depletion * Haemorrhage

Question 30

What is the effect of RAAS?

Answer 30

* Renal Na retention * Water retention

Question 31

What test can be done to ascertain R/A/A status?

Answer 31

* Measure plasma and urine Na * If urine \< 10 mmol/L suggests R/A/A active * More Na has been retained as less lost in urine

Question 32

If there has been a loss of 2L of isotonic fluid, what happens when there is a 2L replacement with isotonic fluid?

Answer 32

This is **ideal** - no change in [Na] and no fluid redistribution

Question 33

If there has been a 2L loss of isotonic solution, what happens if there is a 2L replacement with hypotonic fluid?

Answer 33

This is **wrong:** fall in [Na] and fluid redistribution * Oedema * Na hasn't been replaced

Question 34

What fluid do you need to use as a replacement if there has been a loss of hypotonic fluid?

Answer 34

Replacement with hypotonic fluid: * [Na] restored * Fluid redistribution

Question 35

What happens if you replace a loss of hypotonic fluid with isotonic fluid?

Answer 35

This is **wrong** especially if patient has renal failure * [Na] increased * Fluid redistribution

Question 36

Describe the water and Na in ECF in hyponatraemia and hypernatraemia

Answer 36

Hyponatraemia: * Too little Na in ECF * Excess water in ECF Hypernatraemia * Too little water in ECF * Too much Na in ECF

Question 37

Describe Na and water levels in dehydration

Answer 37

* Water deficiency * Fluid (Na and water) depletion

Question 38

Clinical case 1: Patient is dry and has been treated for CCF. * Plasma * Na 120 (135-145 mmol/L) * Urea 15 (3.0-8.0 mmol/L) * Urine * Na 50 mmol/L * Urea 150 mmol/L

Answer 38

* Plasma: Low sodium and high urea * Patient has been **overtreated** with diuretic * Treated for CCF * Hence why patient is dry

Question 39

How can diuretics lead to hyponatraemia?

Answer 39

* Diuretics decrease Na reabsorption * This increases renal loss: Na \> water * This increases urine [Na] and decreases plasma [Na]

Question 40

How does an increase in renal loss affect IVV?

Answer 40

* Decreases IVV * This decreases GFR * This increases plasma [creat] and [urea] * This increases ADH

Question 41

What is SIADH?

Answer 41

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a condition in which the body makes too much antidiuretic hormone (ADH).

Question 42

How can SIADH lead to hyponatraemia?

Answer 42

Question 43

How can a decreased water intake lead to hypernatraemia?

Answer 43

Question 44

How can osmotic diuresis lead to hypernatraemia?

Answer 44

Osmotic diuresis is the increase of urination rate caused by the presence of certain substances in the small tubes of the kidneys.

Question 45

What is the potassium reference range?

Answer 45

3.6 to 5.0 mmol/L

Question 46

What is the major intracellular cation?

Answer 46

Potassium

Question 47

Where is the majority of potassium found?

Answer 47

Inside the cell **not** in the plasma

Question 48

What can the pump moving K+ in and out of cell be affected by?

Answer 48

* Acidosis * Insulin/glucose therapy * Adrenaline * Rapid cellular incorporation - TPN, leukamia

Question 49

What is the effect of K+ being shifted into the plasma?

Answer 49

Plasma conc is affected hugely as is originally so low

Question 50

What is the relationship of Potassium to Hydrogen ions?

Answer 50

K+ and H+ exchange across the cell membrane --\> both bind to negatively charged proteins (e.g. Hb)

Question 51

How does acidosis affect potassium?

Answer 51

Excess H+ ions causes K+ to move out of the cell --\> **hyperkalaemia** Conversely, K+ depletion and excess can affect acid-base status

Question 52

How does alkalosis affect potassium levels?

Answer 52

Causes potassium to move into cells --\> hypokalaemia

Question 53

Causes of hyperkalaemia?

Answer 53

* 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

Question 54

What is the treatment of hyperkalaemia?

Answer 54

* 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

Question 55

What are the causes of excess potassium depletion?

Answer 55

* 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.

Question 56

What can acute changes in ICF/ECF ratios of K+ cause?

Answer 56

Neuromuscular --\> lethargy, muscle weakness, heart arrhythmias

Question 57

What can chronic losses of K+ from ICF lead to?

Answer 57

* Neuromuscular: * lethargy, muscle weakness, heart arrhythmias * Kidney: * polyuria * alkalosis - increase renal HCO3 production * Vascular * Gut

Question 58

What history would indicate K+ depletion?

Answer 58

* Diarrhoea, vomiting, drugs (diuretics, digoxin) * Cardiac arythmias * Symptoms of lethargy/weakness

Question 59

What electrolytes investigations can indicate potassium depletion?

Answer 59

* Hypokalaemia * Alkalosis - raised HCO3

Question 60

How can K+ depletion be treated?

Answer 60

1. Replacement of deficit 1. Oral 2. IV 2. Monitor plasma K+ regularly

Question 61

Hypernatraemia due to alsosterone

Answer 61

Question 62

If a cell is placed in a hypotonic solution, what happens?

Answer 62

there will be a net flow of water into the cell, and the cell will gain volume

Question 63

What is the effect of blood volume (IVV) on GFR?

Answer 63

For example, increased blood volume increases arterial pressure, renal perfusion, and glomerular filtration rate. Decreased IVV --\> decreased GFR --\> increased [creat] and [urea]

Question 64

Effect of aldosterone on Na and K?

Answer 64

Na --\> reabsorption K (and H+) --\> excretion