Question

A 35 year old female was undergoing thyroid surgery under general anaesthesia during which there was a sudden rise in end tidal carbon dioxide. It can be due to all of the following EXCEPT:

• A. Anaphylaxis
• B. Malignant hyperthermia
• C. Thyroid storm
• D. Neuroleptic malignant syndrome

Hint:

Three are hypermetabolic states; which one drops EtCO2 by causing circulatory collapse?

Answer 1

The Correct Option is A

Step 1: This is a negative question. A sudden rise in end tidal carbon dioxide usually reflects a hypermetabolic state with greatly increased carbon dioxide production. We must find the option that does NOT raise end tidal carbon dioxide.
Step 2: Malignant hyperthermia is the classic cause: a hypermetabolic crisis triggered by volatile agents/succinylcholine, producing a steep, often the earliest, rise in end tidal carbon dioxide. So it can cause it.
Step 3: Thyroid storm is a hypermetabolic emergency with hyperthermia and increased oxygen consumption and carbon dioxide production, so it too can raise end tidal carbon dioxide, and it is highly relevant in thyroid surgery.
Step 4: Neuroleptic malignant syndrome is also a hypermetabolic state with rigidity, hyperthermia, and raised carbon dioxide production, so it can raise end tidal carbon dioxide.
Step 5: Anaphylaxis, by contrast, causes circulatory collapse, hypotension, and reduced cardiac output along with bronchospasm. Reduced pulmonary perfusion increases dead space and lowers, rather than raises, end tidal carbon dioxide. Hence anaphylaxis is the exception.
Conclusion: The exception is anaphylaxis (option 1), matching the printed key.