I hadn’t noticed that the patient was sunburned until we started positioning. The oximeter had fallen off the finger and the assistant was leaning on the BP cuff whilst tucking in the warming blanket. All you would need is the nurse to ring from recovery to ask for a mod for the parturient with a BP of 100 and everything would be completely normal.
The title of the post rather gives it away, but at the start of a crisis it can often be difficult to realise that it is even happening. The thing that made me reach for the adrenaline was that I noticed that the ETCO2 was low.
Here is a portion of the anaesthetic record, reproduced with permission. The jagged parts are artefact.

The ETCO2 is the gray filled area at the bottom, with units in mmHg. Initially the patient was mask ventilated, which is why the trace has gaps in it. The green line is the plethysmograph amplitude. You can see that by 8 minutes after induction both the CO2 and the plethysmograph amplitude are dropping. The purple syringes are doses of adrenaline. The CO2 immediately rose with the first dose. Just as I was giving the adrenaline the trace was starting to show bronchospasm—which went away immediately.
The agent responsible was found to be rocuronium. Apparently the rate of rocuronium anaphylaxis has increased since COVID, which the allergy specialist thinks might be a result of greater use of cough suppressants.
The important take away messages are:
- Anaphylaxis rash may look like a sunburn
- If you see a low CO2, think low cardiac output
BT_PO 1.27 Discuss West’s zones of the lung
I am not brave enough to suggest that this is the only possible reason, but…
Low cardiac output states can cause hypocapnoea in a ventilated patient because:
- Pulmonary hypotension increases anatomical shunt
- Pulmonary hypotension increases West zone 1
- Pulmonary hypotension increases West zone 3
- Systemic hypotension increases the relative proportion of bronchial artery blood flow
- Systemic hypotension decreases CO2 carriage in the blood
Answers can be found in Nunn 8th ed Cap 7.
Do you have the height, weight and ASA…
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