HypoPhosphataemia

Background

Phosphate, found in dairy, grains and meat, is an element which is absorbed distal to the duodenum (aided by Vit D) and excreted via the kidneys (aided by PTH).

Essential constituent of cytoplasm
Intracellular compounds
Bone formation
Neuromuscular functioning

Normal serum levels: 0.8 - 1.3mmol/L.

Major stores of phosphate:

Bone (85%)
Intracellular (in soft tissues) (14%)
Extracellular fluid (1%)

Aetiology hypophosphataemia

↓ GI Absorption

Alcoholism (commonest)
Vitamin D deficiency
Malabsorptive disease
PO4 binders
- Ca²⁺
- Al³⁺ / Mg²⁺ antacids
TPN
Fasting states (anorexia)

↑ renal excretion

Hyperparathyroidism
Glycosuria (DKA)
Osteomalacia (tumour induced)
Renal tubular acidosis
Acute tubular necrosis
HypoMagnesaemia / HypoKalaemia
Multiple myeloma
Fanconi syndrome:
- Proximal tubular dysfxn
- Wilson's disease (children)
- Cystinosis (children)

Metabolic conditions

Resp. alkalosis
Hungry bone synd.
DKA
Starvation refeeding

Other

Medications
Anabolic steroids
Diuretics
Sever burns

Clinical

Mechanism	Early signs PO4 1-2mg/dl	Late signs PO4 <1mg/dl
Dysfunctional bone metabolism	↓ Bone Mineralisation Bone pain	Rickets (children) Osteomalacia (adults)
Intracellular ATP	↓ Myocardial contractility Proximal muscle weakness Muscle pain ↑RBC rigidity Encephalopathy	Heart Failure Arrythmias Rhabdomyolysis Haemolysis Seizures/Coma
↓ RBC 2,3 DPG	↑ affinity of Hb for O₂	Systemic ischaemia Leucocyte & platelet dysfunction

Investigations

FE PO₄^-3 = $\frac{Urine[PO4] x Plasma[Cr]}{Urine[Cr] x Plasma[PO4]}$ x100

Management ↓PO₄

Treat the underlying cause.

Oral Phosphate-Sandoz® tablets

Each effervescent tablet contains:

Phosphate – 16mmol, Sodium – 20.4mmol

Dose: 1-2 tablets (in 100mL water) q8h.

Diarrhoea is a common side effect (? ↓ dose).

Intravenous

Preparation	Sodium Phosphate (unlicensed)	Potassium Phosphate	Addiphos®
Contents	Each 20mL ampoule of sodium phosphate contains: Phosphate 12 mmol Sodium 20 mmol	Each 20mL ampoule contains: Phosphate 12 mmol POTASSIUM 20 mmol	Each 20mL ampoule contains: Phosphate 40 mmol POTASSIUM 30 mmol Sodium 30 mmol
Dose	One 20 mL ampoule	One 20 mL ampoule	10-20mL of one ampoule
Preparation	Dilute one ampoule in 250mL of NaCl 0.9% or DW 5% Sodium phosphate is incompatible with magnesium and calcium salts thus making sodium lactate (Hartmann's solution) and Ringer's injection incompatible infusion fluid	Dilute 1 ampoule in ≥500mL of NaCl 0.9% or DW5	Dilute 1 20mL ampoule in 750mL of DW5
Infusion	Give over 6 to 12 hours Max. rate of phosphate admin. peripherally is 20mmol/hour	Admin. over at least 2 hours: Max. POTASSIUM peripherally is 10mmol/hour Contains POTASSIUM BOLUS INJECTION may be FATAL	Admin. over 3 - 12 hours Max. POTASSIUM peripherally is 10mmol/hour Contains POTASSIUM BOLUS INJECTION may be FATAL

HypoPhosphataemia: Approach and management in the ED

Background

Aetiology hypophosphataemia

↓ GI Absorption

↑ renal excretion

Metabolic conditions

Other

Clinical

Mechanism

Early signs PO4 1-2mg/dl

Late signs PO4 <1mg/dl

Investigations

Management ↓PO₄

Treat the underlying cause.

Oral Phosphate-Sandoz® tablets

Intravenous

Links

References (from above CUH document)

HypoPhosphataemia: Approach and management in the ED

Background

Aetiology hypophosphataemia

↓ GI Absorption

↑ renal excretion

Metabolic conditions

Other

Clinical

Mechanism

Early signs PO4 1-2mg/dl

Late signs PO4 <1mg/dl

Investigations

Management ↓PO4

Treat the underlying cause.

Oral Phosphate-Sandoz® tablets

Intravenous

Links

References (from above CUH document)

Management ↓PO₄