Question 9

• Mechanical circulatory support- V-A ECMO- maintains organ perfusion and can maintain perfusion pressure.

Marks were allocated more for specific management strategies than general resuscitation. Drug doses were not required.

Mention of Lipid Sink therapy essential to score greater than 4 marks

Discussion

Expected pattern of deterioration

• This patient will, at some stage (soon), have a cardiac arrest if she is not treated appropriately. 50 × 180 = 9,000mg, which is a very high dose. For comparison, in a study of 65 case of sustained-release verapamil toxicity, the lowest dose associated with death was 4800mg and the highest dose associated with survival was 14,400mg.
• The other clinical features to expect will be:
  • Common cardiovascular effects for all calcium channel blockers:
    • Hypotension
    • Prolonged PR interval
    • Heart blocks, usually 1st degree
  • Metabolic effects:
    • Hypoinsulinaemia (insulin release is regulated by calcium entry into islet beta cells via L-type channels)
    • Insulin resistance
    • Hyperglycaemia (in contrast to hypoglycaemia of beta-blocker overdose) is a marker of severity
    • Impaired cardiac fatty acid metabolism - CCBs force a switch to the use of carbohydrates
  • Other extracirculatory effects
    • Constipation
    • Hyperkalemia
    • Acute lung injury

Specific management

• Decontamination, even though this is well past the usual 2 hour window, might still have a role to play because (judging by the fact that the patient is still not dead) complete absorption has not yet occurred. 1g/kg of activated charcoal should be the immediate treatment, followed by repeated 0.5g/kg doses if there is still evidence of ongoing absorption.
• Direct and indirect antidotes:
  • Intravenous calcium is the direct antagonist, and classically you infuse these people full of calcium, but it may turn out to be remarkably ineffective. Generally speaking, people infuse about 0.2mmol/hr in order to avoid severe hypercalcemia.
  • High dose insulin euglycaemic therapy  seems promising, as animal studies have found ti to be superior to atropine, adrenaline, glucagon and calcium (Engebretsen et al, 2011).
• Enhanced clearance
  • Haemoperfusion is the only recourse for this highly protein-bound drug
  • Lipid emulsion: among systematic reviews of intravenous lipid emulsion as a rescue therapy, verapamil is listed as an indication (Cave and Harvey, 2009).

General supportive management

• Intubation is rarely indicated, as CCBs do not tend to cause coma, or even aspiration-inducing nausea for that matter.
• Mechanical ventilation may be required if there is pulmonary oedema, but again this is rarely an issue.
• Vasopressors and inotropes  may be useful in some cases, and from a mechanistic point of view it seems to make sense. However, usually there is little benefit. For instance, animal studies of nifedipine-poisoned pigs found that phenylephrine did not add anything to the effects of high-dose insulin (Engebretsen et al 2011).
• Milrinone has been used in the past, but unfortunately it causes too much peripheral vasodilation to be useful.
• Levosimendan, a calcium channel sensitiser, has been used to some effect in several case series (eg. Varpula et al, 2009)
• Transvenous pacing may be possible, but the ventricle may not capture. Bradycardia, but not hypotension, can be managed in this way.
• IABP has been used in cases where nothing you do seems to help, and particularly in case where there has been a beta blocker co-ingestion (in one case report from 2009, the authors were unaware of the CCB poisoning story until well into the course of treatment for an unexplained complete heart block and cardiogenic shock).
• ECMO may be the only answer to a complete failure of the circulation.