A patient with myasthenia gravis testing with edrophonium. Which of the following should be present at bedside?

Appeared in: PGIMER NO - 2020

Explanation

Edrophonium (Tensilon) is a short-acting acetylcholinesterase inhibitor used to diagnose myasthenia gravis.
It works by increasing acetylcholine levels, which can lead to a cholinergic crisis, an adverse effect characterized by excessive muscarinic stimulation.
Symptoms of a cholinergic crisis include severe bradycardia, bronchospasm, and increased secretions.
Atropine is a muscarinic antagonist that acts as a specific antidote to reverse these life-threatening cholinergic effects.
Due to the risk of severe adverse reactions, it is a critical safety standard to have atropine immediately available at the bedside during an edrophonium test.

Option A: Pyridostigmine is a long-acting acetylcholinesterase inhibitor used for the routine treatment of myasthenia gravis. Administering it during a Tensilon test would worsen a potential cholinergic crisis.
Option B: Adrenaline (epinephrine) is a potent adrenergic agonist used for conditions like anaphylaxis or cardiac arrest. It does not specifically counteract the muscarinic effects of a cholinergic crisis.
Option D: Neostigmine is another acetylcholinesterase inhibitor, similar to pyridostigmine. Giving it would increase acetylcholine levels further and exacerbate a cholinergic crisis.

Clinical Relevance

Nursing practice connection: Use the key finding related to Pharmacological safety during diagnostic testing for Myasthenia Gravis to guide bedside assessment, documentation, and the next nursing action.
The nurse's primary role during a Tensilon test is patient safety, which includes preparing the antidote (atropine), continuous monitoring of vital signs (especially heart rate and respiratory status), and being ready to intervene immediately.
Recognizing the difference between a myasthenic crisis (too little medication) and a cholinergic crisis (too much medication) is crucial. Worsening weakness after edrophonium signals a cholinergic crisis.
What if? If the patient develops severe bradycardia (e.g., heart rate drops to 40 bpm) and respiratory distress immediately after edrophonium administration, the nurse must stop the test, administer the pre-drawn atropine as per protocol, provide respiratory support, and call for immediate medical assistance.

How to Approach the Question

First, identify the drug in the question: edrophonium (Tensilon).
Recall its purpose: a diagnostic test for myasthenia gravis.
Understand its mechanism of action: it's a short-acting acetylcholinesterase inhibitor, which increases acetylcholine.
Anticipate the primary adverse effect: an excess of acetylcholine can cause a cholinergic crisis (overstimulation of the parasympathetic nervous system).
Think about the antidote for a cholinergic crisis. The key symptoms are muscarinic (bradycardia, bronchospasm, salivation). Therefore, a muscarinic antagonist is needed.
Evaluate the options: Pyridostigmine and Neostigmine are also cholinesterase inhibitors and would worsen the crisis. Adrenaline is not the specific antidote. Atropine is the classic muscarinic antagonist used for this purpose.

Concept Tested & Keywords

Concept Tested: Pharmacological safety during diagnostic testing for Myasthenia Gravis.
Stem keywords: myasthenia gravis, edrophonium, bedside
Lead-in keywords: Which of the following
Negative lead-in flag: false

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E6 Pharmacology Nursing Lilley 11e Part 2 p. 17-19

E6 Pharmacology Katzung 16e p. 183-185

Practise the full PGIMER NO - 2020

Attempt every question from this paper in a timed mock, then review the full solution for each one.