DISORDERS OF FLUIDS AND ELECTROLYTES BALANCE

Question 1

sodium makes up about_______% of total plasma solutes.

Answer 1

92%

Question 2

Sodium constitutes about_______mmol of extra cellular fluid

Answer 2

3000 mmol

Question 3

Daily intake of water and sodium are approximately____ and _____respectively

Answer 3

1.5L-2L
60-150mmol

Question 4

Water and sodium are lost through what?

Answer 4

urine (kidneys), feaces (gastrointestinal tract), sweat (skin) as well as expired air (lungs).

Question 5

The roles of Antidiuretic Hormone (ADH) in water balance

Answer 5

•It improves water reabsorption in excess of solutes at the collecting ducts, hence its stimulation by plasma osmolality and dehydration

Question 6

Aldosterone

Answer 6

•This is a mineralocorticord hormone secreted from adrenal cortex (zona glomerulosa)

•It prevents loss of sodium mainly in renal tubular cells and to some extent in feaces and sweat

•It affects the control of sodium-potassiun and sodium-hydrogen ion exchange across all cell membranes.

•It stimulates the reabsorption of sodium in distal tubular cell in exchange for potassium or hydrogen ion.

•One can conclude that the actions of Aldosterone lead to retention of sodium than water with net loss of potassium and hydrogen ion in a normal functioning system

Question 7

Angiotensin II

Answer 7

•It has vasoconstriction effect by its direct action on capillary walls.

•It helps in the production and secretion of aldosterone by its action on adrenal cortex zonal glomerulosa

•It stimulates taste centre to promote oral fluid intake

•With the functions of angiotensin II above, one can conclude that sodium secretion is not entirely dependent on plasma sodium level but also on effect of angiotensin II on aldosterone secretion.

Question 8

Atrial Natriuretic peptide

Answer 8

•This hormone is secreted in the right atrial wall and it is sensitive to stretch receptors.

•It stimulates excretion of sodium in the tubule due to it suppressive action on renin, aldosterone and increased GFR.

Question 9

Haemodilution & Hemoconcentration

Answer 9

Decrease in the concentration of plasma proteins and hemoglobin due to increase in plasma volume

Increase in the concentration of plasma proteins and hemoglobin due to a decrease in plasma volume

Question 10

Osmotic pressure

Answer 10

Osmotic pressure is the pressure exerted by a solution to prevent the flow of water molecules into it through a semipermeable membrane.

It’s a measure of the concentration of solutes in a solution and is responsible for regulating the balance of fluids within living cells.

Question 11

Measurement/calculation of plasma osmolarity

Answer 11

(Plasma osmolarity=2[Na+ + K+] + [Urea]+[glucose] in mmol/l)

Question 12

How is Sodium Status assessed?
Why isn’t it enough to measure plasma sodium only when assessing sodium balance?

Answer 12

Assessment of Sodium Status
fractional excretion of sodium (FENa%)

                      Urine [Na]             Plasma [creatinine]
  FENa% =     -----------      X        ----------------
                      Plasma [Na]         Urine [creatinine] •Assessing only plasma sodium may not completely show disturbance in sodium balance. •Measurement of urinary sodium shows whether the renal blood flow is adequate or not.

Question 13

A value of a FENa% > 1% means what and <1% means what?

Answer 13

A value of less than 1% means poor renal perfusion and value more than 1% means intrinsic renal damage.

Question 14

Hypovolaemia

Answer 14

•This can be simply defined as depletion of intravascular volume with subsequent reduction in functional ECF and ICF.

•It is as a result of reduced rate of sodium and water intake which is less than renal and extra renal loss.

Question 15

Clinical features of hypovolemia

Answer 15

Depending on the degree of loss, weakness and tachycardia
With moderate loss patients may experience hypotension and reduced urine volume

With severe loss, there is severe volume contraction with increased sympathetic activity, very low blood pressure, cold extremities and oliguria

It should be noted that these features above are worse in patients with decreased cardiovascular reserve

Question 16

Diagnosis of hypovolemia

Answer 16

Diagnosis
*Identify the cause (s) of fluid loss from the history
*Urine output measurement
*Urine specific gravity and osmolarity measurement
*Plasma and urine sodium measurements as well as plasma osmolarity
*Fractional excretion of sodium will also help to differentiate extra renal and intrinsic renal loss

Question 17

Treatment principle of hypovolaemia

Answer 17

• Treat identified cause(s) of fluid loss
• Rate of fluid loss should be calculated and replaced orally or intravenousely as the case maybe.
• Blood loss is replaced with blood, extracellular fluid loss is replaced with normal saline ( 0.9% saline) and dextrose saline is used as maintenance fluids

Question 18

What is Hypervolaemia?

Answer 18

•This can be simply defined as excess of body fluid with associated increase in ECF and ICF

Question 19

Causes of hypervolemia

Answer 19

•Excessive intake of fluid
•Excessive transfusion of blood
•Inadequate sodium excretion as seen in renal and heart failures
•Mineralocorticord excess

Question 20

Clinical features, Investigations & Treatment principle of hypervolemia

Answer 20

Clinical features
Increased blood pressure as a result of sodium retention and increased intravascular volume
Oedema as a result of increased hydrostatic pressure
Dyspnoea on exertion as a result of accumulation of fluid in pulmonary instertitium

Investigations
*Plasma sodium may be normal because of compensation or hyponatreamia as a result of increased volume
*Plasma urea and creatinine are deranged if renal failure is the cause.

Treatment principle
*Primary cause should be treated
*The use of diuretics

Question 21

Hyponatraemia and types

Answer 21

This is defined as plasma concentration of sodium lower than lower reference limit of what is expected for population.

Hyponatraemia could be true or pseudo hyponatraemia

•True hyponatraemia: there are three major types of true hyponatraemia
•Hyponatraemia with hypovolaemia.
•Hyponatraemia with euvolaemia
•Hyponatraemia with hypervolaemia

Question 22

What is Hyponatraemia with hypovolemia?

Answer 22

Total body water decreases but total body sodium decreases to a larger extent. This is seen in patients with extra renal loss like vomiting, diarrhoea, excessive sweating; renal loss like in the use of diuretics and aldosterone deficiency.

Question 23

What is Hyponatraemia with euvolaemia?

Answer 23

-Hyponatraemia with euvolaemia: in this total body sodium is normal but there is increase in total body water. This is seen in patients with syndrome of inappropriate ADH secretion like in malignant neoplasm, drugs like chlorpropamide, post operative hyponatraemia

Question 24

What is Hyponatraemia with hypervolaemia?

Answer 24

Hyponatraemia with hypervolaemia:

in this the total body sodium is increased but total body water is increased to a larger extent. This is seen in oedematous state as seen in congestive cardiac failure, renal failure and nephrotic syndrome.

Question 25

What is Pseudohyponatraemia?

Answer 25

Pseudohyponatraemia: : plasma sodium is normal. Hyponatraemia is confused because of gross hyperlipidaemia or hyperoteinaemia

Question 26

Investigation of hyponatraemia

Answer 26

•Rule out artefactual cause •Request for lipid profile and plasma protein as well as plasma glucose to rule out pseudohyponatraemia •Do serum aldosterone level to exclude adrenal insufficiency . In the case of Addison’s disease, assess adrenal function • Thyroid hormone profile to rule out hypothyroidism •Renal and cardiac status are checked •Cancer survey in case of SIADH

Question 27

Principle of treatment hypovolemia

Answer 27

*Look for underlined cause and treat *Hypertonicity is treated by administration of intravenous fluid. This should be done slowly to prevent cerebral oedema *Hypovolaemia is treated with fluid replacement mainly done with isotonic saline *Total requirement is calculated thus: TBW X ( desired Na+ - current Na+) *TBW = body weight in kg X % water (children=0.6, Adult= 0.55, Elderly= 0.5)

Question 28

Hypernatraemia

Answer 28

•Plasma sodium is higher than upper reference limit for the population. •It always reflects hyperosmolality if all artefactual causes are eliminated because it is the major solute that is responsible for plasma osmolality. •It should be noted that it is usually due to predominant loss of water than sodium

Question 29

Causes and Investigations of hypernatremia

Answer 29

Causes *Artefactual causes *Poor intake of water and excessive intake of sodium *Increased renal loss of sodium and water *Increased extra renal loss like insensible loss *Administration of drugs like diuretics and drug containing sodium like carbenicillin Investigation *Remove identified cause *Hydration status of the patient should be assessed clinically *If there is hypernatraemai and hypokalaemia, consider mineralocorticord excess

Question 30

Treatment of hypernatremia

Answer 30

Treatment *If it is due to water depletion, oral water replacement is advised or if impossible intravenous fluid with low sodium is used * The aim is to lower plasma sodium at no more than 1-2mmol/l per hour *Treatment of primary hyperadosteronism and cushing’s symdrome are instituted if identified as causes

Question 31

What is the daily intake of potassium & the distribution and regualtion of it

Answer 31

The daily intake of potassium has been estimated to be between 40-200mmol. Distribution and regulation *Potassium when ingested is almost completely absorbed in the intestine *Functional extracellular potassium is a function of total body potassium and distribution in extracellular fluid and intracellular fluid. *The total body potassium balance is difference between potassium intake and its excretion. *Potassium is more abundant in the cells and this is kept intact with the help of Na+/K+ ATP pump using Na+/K+ ATPase.

Question 32

Internal potassium balance

Answer 32

•This is referred to balance of potassium between ECF and ICF compartments. • This may be under the influence of physiological or pathological factors

Question 33

Physiological factors of Internal potassium balance

Answer 33

*Plasma potassium concentration in which the increase leads to movement of potassium into the cells and vise versa *Insulin : this hormone influences movement of potassium into the cell along with glucose *Catecholamine mainly beta2 adrenergic agent promotes inflow of potassium into the cell *Na+/K+ ATPase. It keeps potassium and sodium in their concentrations both in the cell and outside the cell respectively. *Exercise : this may cause hyperkalaemia as a result of potassium release from the muscular cells.

Question 34

Pathological factors of Internal potassium balance

Answer 34

*Trauma : this leads to breaking down of cells with subsequent release of potassium. *Hypertonicity : Movement of fluid from ICF to ECF with the aim of diluting tonicity of plasma, potassium may be dragged along *Acid/Base balance : with acidosis (fall in plasma PH) potassium moves into plasma from the cell resulting into hyperkalaemia and the reverse is the case with alkalosis

Question 35

Functions of potassium

Answer 35

•Regulation of protein and glycogen synthesis •It helps in normal responsiveness of renal tubular cells to ADH •It also involves in cell depolarisation

Question 36

Hypokalaemia, causes & investigations

Answer 36

Hypokalaemia This can be simply defined as plasma potassium lower than lower reference limit for the population Causes *Taking sample for the laboratory analysis from the site of intravenous fluid *Reduce intake as seen in starvation *Increase cell entry as seen in insulin therapy, alkalosis, catecholamines *Excessive loss through vomiting, diarrhoea, sweat, burns, primary hyperaldosteronism, Cushing’s syndrome or high dose corticosteroid therapy, diuretic therapy, renal tubular acidosis Investigations Plasma electrolytes, urea and creatinine Urine potassium. If less than 20mmol/l it indicates extra renal loss If urine potassium is abnormally high. Further investigations to exclude renal loss are indicated. Plasma renin and aldosterone are determined Electrocardiograme (ECG) is done . This gives idea of effect of hypokalaemia on heart

Question 37

Investigations of hypokalemia

Answer 37

•Plasma electrolytes, urea and creatinine •Urine potassium. If less than 20mmol/l it indicates extra renal loss •If urine potassium is abnormally high. Further investigations to exclude renal loss are indicated. Plasma renin and aldosterone are determined •Electrocardiograme (ECG) is done . This gives idea of effect of hypokalaemia on heart

Question 38

What is Hyperkalaemia and the causes?

Answer 38

This can be simply defined as plasma potassium concentration more than upper reference limit for the population Causes *Artefactual causes *Excessive oral supplement and blood transfusion *Insulin deficiency, metabolic acidosis, use of beta-2 adrenergic blocker, tissue damage *Decrease urine excretion

Question 39

Clinical features and investigations of hyperkalemia

Answer 39

Clinical features *Problem with neuromuscular function resulting into weakness and paralysis; Diarrhoea and abdominal distension *Cardiac arrhythmias Investigations *Any abnormal result requires immediate repeat with well taken fresh sample *Plasma electrolytes, urea and creatinine *Plasma renin and aldosterone *ECG2.5

Question 40

Investigations of hypovolaemia

Answer 40

•Plasma sodium may be normal because of compensation or hyponatreamia as a result of increased volume •Plasma urea and creatinine are deranged if renal failure is the cause.

Question 41

What is Appropriate hyponatraemia?

Answer 41

Appropriate hyponatraemia: this can also called redistributive hyponatraemia: This is hyponatraemia in the phase of hyperglycaemia, acute uraemia, infusion of amino acids and monitor. These are all osmotically active agents that have dilution effect

Question 42

What is Artefactual hyponatraemia?

Answer 42

•Artefactual hyponatraemia: this is as a result of blood sample taking from the site of infusion if fluid being given is free of sodium.