Treatment for QRS widening and sodium channel blockade: serum alkalinisation
Assess the QRS complex on a 12-lead ECG—see Diagrammatic representation of a normal electrocardiogram (ECG) complex for the normal QRS width. If the QRS complex is wider than 120 milliseconds, commence continuous ECG monitoring and assess serial 12-lead ECGs for early detection of arrhythmias.
If QRS widening is associated with airway, breathing or circulatory compromise (eg arrhythmias, hypotension), or central nervous system (CNS) depression, immediately start serum alkalinisation (intravenous sodium bicarbonate) and concurrent hyperventilation therapy (by intubation and mechanical ventilation).
Serum alkalinisation has been extensively evaluated for the treatment of QRS widening due to poisoning, particularly tricyclic antidepressant poisoning. Intravenous boluses of sodium bicarbonate are administered to alkalinise the serum pH, but only produce transient changes. The addition of mechanical ventilation is required to maintain the change in serum pH, by controlling the partial pressure of arterial carbon dioxide (PaCO2).
Do not use an intravenous infusion of sodium bicarbonate for serum alkalinisation because the desired change in serum pH is buffered by physiological reflex changes in PaCO2 and renal bicarbonate excretion.
For QRS widening associated with airway, breathing or circulatory compromise, or CNS depression, for adults and children, use:
sodium bicarbonate 8.4% 1 to 2 mL/kg up to 100 mL (1 to 2 mmol/kg up to 100 mmol) intravenously, every 3 to 5 minutes, titrated to a narrowing of the QRS complex and aiming for a serum pH between 7.45 and 7.55. Maximum total dose is 6 mL/kg (6 mmol/kg). Urgently seek advice from a clinical toxicologist if there is inadequate response to the maximum total dose resuscitation for poisonings - QRS widening
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hyperventilation by intubation and mechanical ventilation, aiming for a serum pH between 7.45 and 7.55 (typically by maintaining partial pressure of arterial carbon dioxide [PaCO2] between 30 and 35 mmHg).
Typically serum alkalinisation causes an incremental narrowing of the QRS complex within 5 minutes, or with correction of serum pH.
Serum alkalinisation can cause hypokalaemia due to intracellular potassium shift—monitor the serum potassium concentration and replace potassium if required, aiming for the normal serum potassium concentration. Use:
potassium chloride 10 to 20 mmol (child: 0.4 mmol/kg up to 20 mmol) intravenously over 1 to 2 hours, every 2 to 4 hours as required. Use a premixed solution of the appropriate intravenous fluid1. resuscitation for poisonings - QRS widening
Serum alkalinisation is effective in treating QRS widening caused by tricyclic antidepressants, local anaesthetics and flecainide, but some drug poisonings do not respond (eg lamotrigine, chloroquine, propranolol). If there is inadequate response to serum alkalinisation, urgently seek advice from a clinical toxicologist.