- Design
- Single-centre retrospective cohort
- Population
- 185,455 adults having noncardiac surgery under general anaesthesia, 2010-2020
- Primary outcome
- In-hospital mortality
- Effect
- aOR 1.63 (95% CI 1.36 to 1.86) per 5 mmHg decrease in mean ETCO2 from the median
This retrospective cohort included 185,455 adults having noncardiac surgery under general anaesthesia with mechanical ventilation at one tertiary centre between 2010 and 2020. In-hospital mortality was 0.85%. The question was whether low end-tidal CO2, previously linked to death, simply reflects hypotension or over-ventilation.
It did not appear to. Lower mean intraoperative ETCO2 was associated with higher mortality in a non-linear way: each 5 mmHg fall from the median carried an adjusted odds ratio of 1.63 (95% CI 1.36 to 1.86), after accounting for minute ventilation and the severity and duration of hypotension. There was no interaction with hypotension, and sensitivity analyses gave similar results.
This is association. Low ETCO2 may mark low cardiac output, high dead space or frailty rather than cause harm, so the study does not show that ventilating to a higher ETCO2 improves survival. What it supports is treating an unexplained low ETCO2 as a signal worth explaining, not a number to ignore.
- Look for a cause when ETCO2 is persistently low despite normal ventilation settings: low cardiac output, embolism, high dead space.
- Avoid unnecessary hyperventilation during routine anaesthesia.
- Record low ETCO2 episodes alongside hypotension in the anaesthetic chart.
- Consider low intraoperative ETCO2 a marker of higher postoperative risk when planning the level of postoperative care.
Why it matters
Hypotension gets most of the intraoperative attention; this suggests ETCO2 carries separate prognostic information.
Don't overread it
This is observational; it cannot show that targeting a higher ETCO2 would reduce mortality.
The statistics, in plain English
An adjusted odds ratio of 1.63 means the odds of in-hospital death were about 60% higher for each 5 mmHg lower ETCO2 below the median. Because death was rare (under 1%), the absolute increase is small for any one patient. Large datasets make associations precise, but not causal.
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