Fluid and Electrolytic imbalances

Question 1

The normal plasma level for sodium is

Answer 1

142mmol/L,

Question 2

The normal plasma level for potassium is

Answer 2

4.5mmol/L,

Question 3

The normal plasma level fo bicarbonate is

Answer 3

26mmol/L,

Question 4

The normal plasma level for chloride is

Answer 4

103mmol/L

Question 5

The normal plasma level for calcium is

Answer 5

2.5mmol/L.

Question 6

Oral potassium

Answer 6

Compensation for potassium loss is especially necessary:
• In those taking digoxin or anti-arrhythmic drugs, where potassium depletion may induce arrhythmias
• In patients with kidney problems, liver cirrhosis and severe heart failure.
• In patients with excessive losses of potassium in the faeces e.g. chronic diarrhoea associated with intestinal malabsorption or laxative abuse.

They may also be required in the elderly since they frequently consume inadequate amounts of potassium in the diet. Measures may also be required during long-term administration of drugs known to induce potassium loss (e.g. corticosteroids). Potassium supplements are rarely required with small doses of diuretics given to treat hypertension.
 potassium-sparing diuretics are recommended for prevention of hypokalaemia due to diuretics such as furosemide or thiazides.
I.V. potassium is required for severe hypokalaemia and when sufficient potassium cannot be taken by mouth.
Important safety information
- Potassium overdose can be fatal. Ready-mixed infusion solutions containing potassium should be used.

Question 7

Management of hyperkalaemia

Answer 7

Acute severe hyperkalaemia is serum potassium >6.5mmol/L. Potassium levels may be upset by drugs… promoting cellular movement of potassium, impairing excretion in kidneys or increasing supply of K+.

• It is treated with Calcium gluconate 10% by slow I.V. injection to protect the heart.
• I.V. soluble insulin (5-10 units) with 50mL of glucose 50% given over 5-15 minutes also reduces serum-potassium concentration.

Question 8

Drugs which may cause hyperkalaemia include:

Answer 8

• Enalapril
• Ramipril
• Losartan
• Ciclosporin

Question 9

Calcium imbalance

Answer 9

• Calcium supplements are usually only required when dietary calcium intake is deficient. Dietary requirement is greater in childhood, pregnancy, lactation. Also in elderly (due to impaired absorption)
• In osteoporosis… calcium recommended intake is doubled which reduces the rate of bone loss.
• In severe acute hypocalcaemia, give an initial slow I.V. injection of Calcium Gluconate 10%
• Oral supplements of calcium and Vitamin D may also be required in persistent hypocalcaemia. Concurrent hypomagnesaemia should be corrected with magnesium sulphate.

Question 10

MHRA: calcium gluconate

Answer 10

MHRA: Repeated or prolonged administration of calcium gluconate packaged in 10ml glass containers is CI in <18y + in renal impairment (risk of aluminium accumulation). Use plastic containers instead

Question 11

Management of severe hypercalcaemia

Answer 11

1. Dehydration is corrected first with an I.V. infusion of Sodium Chloride 0.9%
2. Drugs (such as thiazides + vitamin D compounds) which promote hypercalcaemia should be discontinued and dietary calcium restricted.
3. If severe hypercalcaemia persists… drugs which inhibit mobilisation of calcium from the skeleton are used. Bisphosphonates are useful and Pamidronate sodium is the most effective. Corticosteroids are widely given but often take several days to achieve the desired effect.

Question 12

Hyperparathyroidism

Answer 12

 Paricalcitol is licensed for prevention + treatment associated with chronic kidney disease

Question 13

Hypercalciuria

Answer 13

 increase fluid intake + give bendroflumethiazide + reduce dietary calcium

Question 14

Magnesium imbalance

Answer 14

Magnesium is an essential constituent of many enzyme systems, particularly energy generation.
• Magnesium salts are not well absorbed from G.I. tract… which explains the use of magnesium sulphate as an osmotic laxative.
• Magnesium is excreted mainly by the kidneys and is therefore retained in renal failure, but significant hypermagnesemia (causing muscle weakness + arrythmias) is rare.

Question 15

Hypomagnesemia

Answer 15

Excessive losses of magnesium in diarrhoea, stoma or fistula are the most common causes of hypomagnesaemia. Deficiency may also occur in alcoholism or as a result of certain drugs.
• Magnesium is given initially by I.V. infusion or I.M. injection of Magnesium Sulphate (I.M is painful).
• Magnesium sulfate injection has also been recommended for emergency treatment of serious arrhythmias, especially in presence of hypokalaemia (as hypomagnesaemia may also be present)
• Magnesium sulfate injection is the drug of choice to treat seizures + prevent recurrent seizures in women with eclampsia. Regimens may vary between hospitals. Calcium gluconate injection is used for the management of magnesium toxicity.
• Magnesium sulfate injection is also of benefit in women with pre-eclampsia in whom there is concern about developing eclampsia. The patient should be monitored carefully – excessive doses in 3rd trimester can cause neonatal respiratory depression

Question 16

Hypermagnesemia Symptoms:

Answer 16

N&V, flushing thirst, hypotension, drowsiness, confusion, reflexes absent, respiratory depression, speech slurred, diplopia, muscle weakness, arrythmias, coma + cardiac arrest

Question 17

Phosphate Imbalance

Answer 17

Oral phosphate supplements may be required in addition to vitamin D in a small minority of patients with hypophosphataemic vitamin D-resistant rickets.

Phosphate infusion is occasionally needed in alcohol dependence or phosphate deficiency arising from use of parenteral nutrition deficient in phosphate supplements; phosphate depletion also occurs in severe DKA

Question 18

Phosphate-binding agents

Answer 18

• Calcium-containing preparations are used as phosphate- binding agents in the management of hyperphosphataemia complicating renal failure. Aluminium-containing preparations are rarely used as phosphate binding agents and can cause aluminium accumulation.
• Sevelamer is licensed to treat hyperphosphataemia in patients on haemodialysis or peritoneal dialysis. Also used in CKD patients not on dialysis who have a serum-phosphate conc. >1.78 mmol/L
• Lanthanum is licensed for hyperphosphataemia in patients with chronic renal failure on haemodialysis or continuous ambulatory peritoneal dialysis (CAPD) + in CKD patients as above.
• Sucroferric oxyhydroxide p. 1054 is licensed for the control of hyperphosphataemia

Question 19

Hypernatremia

Answer 19

Hypernatremia (sodium conc. >145mmol/L)

Symptoms: Convulsions, hypovolemia, thirst
Drug causes: Corticosteroids, Androgens / Oestrogens, Sodium chloride / bicarbonate

Question 20

Hyponatraemia

Answer 20

Hyponatraemia (sodium conc. <135mmol/L)

Symptoms: nausea + vomiting, drowsiness, headache, seizures,
Drug causes: Thiazide diuretic, SSRIs, Antipsychotics (haloperidol, phenothiazines), NSAIDs, carbamazepine

Question 21

ORT should:

Answer 21

ORT should:

• enhance the absorption of water and electrolytes;
• replace the electrolyte deficit adequately and safely;
• contain an alkalinising agent to counter acidosis;
• be slightly hypo-osmolar (about 250 mmol/litre) to prevent possible induction of osmotic diarrhoea
• be simple to use in hospital and at home; be palatable and acceptable, especially to children;
• be readily available.

Question 22

ORT - Rehydration should be

Answer 22

rapid over 3 to 4 hours (except in hypernatraemic dehydration in which case rehydration should occur more slowly over 12 hours). The patient should be reassessed after initial rehydration and if still dehydrated rapid fluid replacement should continue.

Question 23

Oral Bicarbonate

Answer 23

Sodium bicarbonate is given by mouth for chronic acidotic states such as uraemic acidosis or renal tubular acidosis. The dose for correction of metabolic acidosis is not predictable and response must be assessed. For severe metabolic acidosis, sodium bicarbonate can be given IV. Sodium bicarbonate may also be used to increase the pH of the urine; it is also used in dyspepsia. Sodium supplements may increase BP or cause fluid retention + pulmonary oedema in those at risk; hypokalaemia may be exacerbated.