The current enthusiasm
for apnoeic oxygenation has been based
more on physiologic plausibility & wishful thinking rather than any real science from good
quality RCT’s.
One always needs to be a bit skeptical of physiologic
plausibility. Of course it is an essential ingredient for assessing causality, but it is far from the only requirement. To be sure,
I would imagine that one could think of a physiologic reason why we could fart
ourselves to the moon.
Now we have the largest
RCT investigating the efficacy of apnoeic oxygenation. A whole 150
patients.
Inclusion criteria
were adults requiring intubation in a single medical
ICU in Nashville, Tennessee. The intubator was a “pulmonary and critical care medicine fellow.” (This is probably about a PGY-4 doctor)
There
were some exclusion criteria that
probably meant that some of the sicker patients were not enrolled.
The study protocol was pragmatic and simulated “real world”
ICU practice. Therefore it governed only the provision of supplemental oxygen during apnoea. All other decisions about
medications, devices, etc. were made by the clinical team.
Both groups could get pre-oxygenation. The patients randomized to apnoeic oxygenation got a
high-flow nasal cannula set to 15L/min flow of 100% oxygen before induction and
kept in place until the intubation was complete. The control group received no nasal cannula oxygen.
The primary outcome was the lowest pulse oximetry reading
between induction and 2 minutes after successful intubation. Some might argue
this is not the most patient oriented outcome but at least it is practical and easy to measure.
Results? There
was no statistical difference between
the two groups. The median lowest sat in the apnoeic oxygenation group was 92%
vs. 90% (95% CI for the difference -1.6%-7.4%) in the control arm. Just for
interest, they had only 2/3 success in first pass intubation rate.
This study was powered to have an 80% probability of
detecting a 5% difference in the primary outcome if one truly existed in the population. All of the trends favoured the apnoeic
oxygenation group and it is possible that the study was underpowered. However,
one might question if such smaller differences are clinically meaningful.
Probably not.
Limitations were several, but overall this was a well
conducted study. Consider lack of blinding, single centre study, perhaps lack of
intubator experience, issues of external validity, disease oriented outcome
measure and some others.
So what are we to
conclude? I don’t think this study is going to change anyone’s minds. True
believers will still believe. But it certainly emphasizes the lack of good
quality evidence to support the practice of apnoeic oxygenation. I personally
don’t bother with it. But at the same time we should not have
polarized views until better quality evidence provides us with some answers.
Covering:
Semier MW,
Janz DR, Lentz RJ, et al. Randomized Trial of Apneic Oxygenation during Endotracheal
Intubation of the Critically Ill. Am J Respir Crit Care Med 2016;193:273-80.
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