Urinary alkalinisation

For chlorophenoxy herbicide poisoning, consider urinary alkalinisation¹:

following deliberate ingestion
in symptomatic patients
in metabolic acidosis.

If urinary alkalinisation is indicated, for adults and children, use:

sodium bicarbonate 8.4% 1 mL/kg up to 100 mL (1 mmol/kg up to 100 mmol) intravenously over 30 to 60 minutes, as an initial dose chlorophenoxy herbicide poisoning

FOLLOWED BY

sodium bicarbonate 25 mmol/hour (child: 0.5 mmol/kg/hour up to 25 mmol/hour) by intravenous infusion. To administer 25 mmol/hour of sodium bicarbonate, add 150 mL of sodium bicarbonate 8.4% to 850 mL glucose 5% (ie remove 150 mL from a 1000 mL bag of glucose 5%) and infuse at a rate of 166 mL/hour².

In patients treated with intravenous sodium bicarbonate, monitor serum pH every 2 hours. Do not exceed a serum pH of 7.5—stop sodium bicarbonate if this occurs. Consider catheterising patients to also monitor urinary pH³ every 2 hours. Aim for a urinary pH of 7.5 to 8.0 and a urine output of 1 to 2 mL/kg/hour.

Hypokalaemia impedes the ability of the kidney to alkalinise the urine⁴. Correct hypokalaemia before starting sodium bicarbonate and maintain the serum potassium concentration between 3.5 and 4.0 mmol/L.

If patients can tolerate and absorb oral potassium, use:

potassium chloride 14 to 16 mmol (child: 0.25 mmol/kg up to 16 mmol) orally, every 2 to 4 hours as required⁵. chlorophenoxy herbicide poisoning potassium chloride

If patients cannot tolerate or absorb oral potassium, use:

potassium chloride 10 to 20 mmol (child: 0.4 mmol/kg up to 20 mmol) intravenously over 1 to 2 hours with ECG monitoring, every 2 to 4 hours as required. Use a premixed solution of the appropriate intravenous fluid⁶.

Higher doses of potassium chloride may be required for severe hypokalaemia.

Monitor serum electrolyte concentrations (especially potassium, sodium and bicarbonate), and serum urea and creatinine concentrations every 2 to 4 hours. Repeat blood glucose concentration every 2 hours.

Continue urinary alkalinisation for 12 to 18 hours. After this time, if there is progressive or severe metabolic acidosis, consider haemodialysis in consultation with a clinical toxicologist.

¹ Be aware that urinary alkalinisation and serum alkalinisation are different treatments with different indications and therapeutic regimens. Urinary alkalinisation aims to enhance elimination of a toxin, while serum alkalinisation aims to shift the poison from where it exerts its main toxic effects.Return

² In children, the volume of intravenous fluid must be adjusted for the child's weight and age to avoid fluid overload.Return

³ Accurate measurement of urinary pH is best achieved by catheterising the patient and checking the pH of a fresh urine sample from the catheter tubing, not the reservoir bag or a pan specimen.Return

⁴ Hyperkalaemia is a more common effect of chlorophenoxy herbicide poisoning than hypokalaemia.Return

⁵ Effervescent immediate-release tablets of potassium contain 14 mmol of potassium per tablet, and modified-release tablets contain 8 mmol of potassium per tablet. The modified-release preparations of potassium are almost completely absorbed within 1 hour.Return

⁶ Potassium chloride should only be given using premixed infusion bags. Extemporaneously adding ampoules of potassium chloride to intravenous fluids is not safe; inadequate mixing may result in potassium being delivered at a lethal concentration. Premixed infusion bags are available in varying concentrations and volumes; the most common is potassium chloride in 1000 mL of compatible fluid. Premixed potassium chloride is also available in a smaller volume at a high concentration (10 mmol/100 mL). Choice of preparation depends on the amount of potassium required and how much fluid the patient will tolerate.Return