Phosphates

Hypophosphataemia may lead to muscle weakness and is a cause of difficulty in weaning a patient from mechanical ventilation. Causes of hypophosphataemia in ICU include failure of supplementation (e.g. during TPN), use of insulin and high concentration glucose, use of loop diuretics and low-dose dopamine. Normal range: 0.8–1.4 mmol/l

Uses
Hypophosphataemia

Contraindications
Hypocalcaemia (further ↓ Ca2+)
Severe renal failure (risk of hyperphosphataemia)

Administration
10 ml potassium phosphate 17.42% w/v contains 10 mmol phosphate and 20 mmol potassium.Administer 1ampoule (10 ml) (10 mmol phosphate) over 6 hours.

Disodium hydrogen phosphate 21.49% w/v is an alternative to potassium phosphate (used in order to avoid potassium). 1 ampoule (10 ml) contains 6 mmol phosphate and 12 mmol sodium.Administer 2 ampoules (20 ml) (12 mmol phosphate) over 6 hours.

The recommended dilution depends on whether it is given via the central (recommended) or peripheral route. For central venous route the dilution is to make up to 50 ml with sodium chloride 0.9% or glucose 5%. For the peripheral route, the dilution is to make up to 250 ml with sodium chloride 0.9% or glucose 5%.

• IV infusion
Central IV route: 10–12 mmol phosphate made up to 50 ml with glucose 5% or sodium chloride 0.9%, given over 6 hours Peripheral IV route: 10–12 mmol phosphate made up to 250 ml with glucose 5% or sodium chloride 0.9%, given over 6 hours

Do not give at > 12 mmol over 6 hours
Repeat until plasma level is normal
Monitor serum calcium, phosphate, potassium and sodium daily

Available in ampoules of:
• Potassium hydrogen phosphate 10 ml 17.42% w/v (phosphate 10 mmol, potassium 20 mmol)
• Disodium hydrogen phosphate 10 ml 21.49% w/v (phosphate 6 mmol, sodium 12 mmol)

How not to use phosphate
Do not give at a rate > 12 mmol over 6 hours

Adverse effects
Hypocalcaemia, hypomagnesaemia, hyperkalaemia, hypernatraemia
Arrhythmias
Hypotension
Ectopic calcification

Cautions
Renal impairment
Concurrent use of potassium-sparing diuretics or ACE-I with potassium phosphate may result in hyperkalaemia
Concurrent use of corticosteroids with sodium phosphate may result in hypernatraemia

Organ failure
Renal: risk of hyperphosphataemia

Renal replacement therapy
Dialysed. Dose in all techniques is as per normal renal function
Treat hypophosphataemia only on the basis of measured serum levels