P02 Lidocaine infusion in a patient on ecmo and monitoring levels

Background A 12-year-old patient was admitted to the cardiac intensive care unit (CICU) due to cardiogenic shock along with dilated cardiomyopathy. Whilst on CICU, the patient continuously experienced episodes of bigeminy, ventricular arrhythmias and bradycardia. Due to clinical deterioration, the patient was initiated on veno-arterial extracorporeal membrane oxygenation (VA ECMO). Following initiation of VA ECMO, the patient experienced episodes of torsades de pointes requiring electrolyte corrections, amiodarone infusions and boluses, lidocaine boluses and electrical cardioversion. Due to the patient’s bradycardia, esmolol infusions were not recommended and amiodarone boluses were avoided with plans to wean the infusion therefore a lidocaine infusion was trialled. Despite this infusion the patient continued to experience episodes of torsades de pointes and therefore the clinical team wanted to take lidocaine levels to ensure optimisation of therapy. However, lidocaine levels are uncommon and are not conducted by many centres.

Pharmacist Contributions Firstly, as lidocaine infusions are not commonly used, the clinical team needed to be directed to the British National Formulary for Children for advice on how to prescribe this as careful loading is required.¹ For the maintenance dose, careful consideration needed to be given as there is no set dosing instructions past 24 hours for lidocaine infusions. Lidocaine is a lipophilic molecule and evidence has shown that lipophilic molecules are more likely to bind to ECMO circuits leading to sub therapeutic levels.^{2 3} Therefore, to ensure adequate control, a higher infusion rate of 0.8 mg/min was chosen. As many centres do not undertake levels, it required liaising with our internal laboratories to determine where levels could be sent. It was deduced that levels could be sent to a laboratory in Belfast for them to sample. 2 mL of blood would be required for analysation as agreed by Belfast and our internal laboratories. Additionally, a literature search was conducted to determine what levels should be targeted and what might be deemed to be toxic. Through literature, it was found that target levels of 1.5 mg/L are required for adequate control of ventricular arrhythmias. On the opposite end of the spectrum, levels of 5 mg/L and above are associated with side effects such as vertigo, paraesthesia, and slurring of speech.⁴ Literature is based off levels conducted in adults however, as this patient was 12 years old and weighed 43 kg, the literature could be extrapolated to be applicable for use in this patient.

Outcome The patient was listed as super urgent on the heart transplant waiting list and therefore received a transplant before the lidocaine levels were returned and were no longer required.

Learning Points As the patient was on ECMO, they are not at risk of sudden cardiac arrest due to the heart being fully supported by the ECMO circuit. Additionally, whilst in CICU, the patient would have close ECG monitoring and therefore rather than sending levels of lidocaine which take a significant time to return, it may be more appropriate to monitor the patient for side effects alongside monitoring ECG changes and titrating the dose as necessary.

References

1. Lidocaine hydrochloride: indications and dose. In: Joint Formulary Committee. British National Formulary for Children [Internet]. London: British Medical Association and Royal Pharmaceutical Society of Great Britain: https://bnfc.nice.org.uk/drugs/lidocaine-hydrochloride/ (Accessed 4 July 2023).

2. PubChem [Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; 2004-. PubChem Compound Summary for CID 3676, Lidocaine: https://pubchem.ncbi.nlm.nih.gov/compound/lidocaine (Accessed 4 July 2023).

3. Cheng V, Abdul-Aziz MH, Roberts JA, Shekar K. Optimising drug dosing in patients receiving extracorporeal membrane oxygenation. Journal of Thoracic Disease. 2018;10(Suppl 5):S629.

4. Wong BY, Hurwitz A. Simple method for maintaining serum lidocaine levels in the therapeutic range. Archives of Internal Medicine 1985;145:1588–1591.