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

Reason from what makes the exhaled carbon dioxide trace climb suddenly: in almost every case it signals a surge in metabolic carbon dioxide production, that is, a hypermetabolic state, provided the lungs are still perfused well enough to carry that carbon dioxide to the alveoli. Now screen the four options. Malignant hyperthermia is the textbook hypermetabolic catastrophe of anaesthesia; its earliest and most sensitive sign is a rapidly rising end tidal carbon dioxide as the muscles pour out heat and carbon dioxide, so it fits. Thyroid storm, especially plausible during thyroid surgery, is a thyroid-driven hypermetabolic crisis with fever and soaring oxygen use and carbon dioxide output, so it fits. Neuroleptic malignant syndrome likewise produces rigidity, fever, and elevated carbon dioxide generation, so it fits. The misfit is anaphylaxis. Severe anaphylaxis brings on vasodilation, profound hypotension, and a fall in cardiac output, together with bronchospasm; the drop in pulmonary blood flow enlarges alveolar dead space and pulls the end tidal carbon dioxide down, not up. Therefore the one condition that does not explain a sudden rise in end tidal carbon dioxide is anaphylaxis. $Anaphylaxis$ is the exception.\[\boxed{\text{Anaphylaxis}}\]