Sun21November0420PM 5

A 72-year-old man is scheduled for an awake fibre-optic diagnostic bronchoscopy. Prior to the procedure he is given 400mcg hysocine hydrobromide intramuscularly as an anti-sialogogue. The procedure is uneventful, during which a total of 100mg topical lidocaine is used.

One hour after the procedure he becomes confused and agitated. The pulse rate is 110 beats per minute, blood pressure 170/80mmHg and SpO2 96% breathing air.

Which of the following drugs is most appropriate for treatment of the change in mental status?

(Please select 1 option)

Neostigmine

Midazolam Incorrect answer selected

Physostigmine This is the correct answer

Flumazenil

Fentanyl

Explanation

Hyoscine hydrobromide is an anticholinergic drug acting on muscarinic cholinergic receptors.

The receptors are found at the following sites:

M1 -central nervous system and stomach

M2 -heart and lungs

M3 -central nervous system, heart, airway smooth muscles, glandular tissues

M4 and M5 -central nervous system

Administration of hyoscine can lead to widespread effects, and these are:

Enhancement of vagal tone

Bronchodilatation

Inhibition of gastric secretion

Inhibition of gastrointestinal peristalsis

Inhibition of bronchial secretions

Mydriasis

Prevention of motion sickness

Sedation

Amnesia

Being a tertiary amine it can cross the blood-brain barrier and give rise to central anticholinergic syndrome (CAS), much more likely in elderly patients. This patient has symptoms suggestive of CAS.

It can be caused by hyoscine and, to a lesser extent, atropine. Glycopyrrolate is a quaternary amine and does not cause central cholinergic syndrome.

Symptoms range from restlessness and hallucinations to somnolence and coma.

It is secondary to blockade of muscarinic cholinergic receptors in CNS.

Treatment is with intravenous physostigmine 15 - 60 mcg/kg. Physostigmine is also a tertiary amine and crosses the blood-brain barrier.

It cannot be reversed with edrophonium, neostigmine, or pyridostigmine as they are quaternary amines.

Physostigmine is an anticholinestrase and is the treatment of choice. Midazolam might be helpful to control agitation. Neostigmine will not cross the blood-brain barrier and flumazenil may make matters worse as an inverse agonist for GABAA receptors.

Answer Statistics

1

30%

2

19%

3

49%

4

3%

5

2%

Times answered: 283