Just another intoxicated head injury

At the start of another busy weekend nightshift in a rural ED you receive a handover from the day team.

A 31 year old female was brought in by police after an assault. Agitated, with a previous history of traumatic brain injury and intravenous drug use, the young lady is restrained and procedural sedation is required to perform the head CT scan.

The sedation was challenging, as a result of Withnail levels of tolerance to benzodiazepines. Following 30mg IV Midazolam and two doses of Droperidol 10mg IM, and 10mg IV, the patient is still fighting and needs further sedation with Ketamine.

Following confirmation of no intracranial bleed on CT brain the patient drifts into a sleeping-beauty style slumber and she is returned to the ED cubicle to sleep off the nights events.

In the early hours of the morning her nurse approaches you stating the young lady has an odd rhythm on her telemetry. She’s still sleeping soundly, bar from the occasional obligatory swear word. An ECG is performed:

+ Describe the ECG

• Sinus bradycardia
• Three multifocal ventricular ectopic beats
• Large r-wave amplitude in V4-V6 suggesting left ventricular hypertrophy
• Broad and deep t-wave inversion in aVR and V1, biphasic t in V2 and broadly peaked t-waves in the lateral leads.
• QT prolongation 528, QTc 505

You scratch your head and mumble “I wonder whats happened here?”. There are no previous ECGs for comparison and her medical notes are scant and littered with ‘Did not wait’ notifications only.

A review of her medication chart reveals a long list of drug boluses administered during the sedation. You take a seat and start to look through them. Whilst deep in thought the telemetry lead catches your eye…

+ Describe the ECG trace

• Sinus bradycardia
• Prolonged QT
• “R on T” preceding a short run of polymorphic VT: “torsades de pointes”

She is whisked to resus, pads are on and the nurses are looking at you expecting some useful suggestions….

+ What is the diagnosis?

Prolonged QT interval secondary to droperidol. Possibly this patient has a congenital long QT which has been exacerbated, but this dose has the potential to cause this on its own.

+ What is the immediate management?

• Check electrolytes
• Load with Magnesium, 10 mmol over 1-2 minutes followed by a slower infusion of a further 20 mmol over the next 6 hours.
• Consider increasing the ventricular rate (to reduce the QT) using isoprenaline or overdrive pacing
• Correct abnormality of any electrolyte and aim for upper limit of normal K+, Mg2+, Ca++

+ What are the potential causes?

• Droperidol induced prolongation of the QT interval resulting in polymorphic ventricular tachycardia – or in this context “torsades de pointes”.

+ What happened next?

• Magnesium, potassium and calcium were administered.
• Regular ectopics persisted with 2-3 second runs of tdp every minute
• Commenced on an isoprenaline infusion to a rate >90bpm which resolved the ectopic beats and no further torsades.
• Uneventful full recovery.

+ Take home points

Be aware of the risk of antipsychotics causing QT prolongation, and then VT. Especially when large doses are used in the context of the sedation of an agitated patient.

If the patient is in a chemically induced unconscious state make sure they have adequate monitor-ing in place.This type of patient may not have old medical notes to look at and wont tell you (or wont know) their medical history, so think of the worst case scenario when you approach cases like this!

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