, 8 tweets, 5 min read
1/ [ 5th AMIB-ESICM Symposium]:
I talked about the physiological rationale of the #HFNC for hypercapnic ARF.
So not all hypercapnic ARF are the same. There are those due to Central hypoventilation / neuromuscular disorders & those due to V/Q mismatch
@israelmaia16 @RENOVATEtrial
2/ In the V/Q mismatch category, airway diseases such as #COPD commonly presents a mismatch due to ⬆️Vd/Vt. And how that happens can be easily appreciated in these two slides:
3/ Dead space (Vd) is composed by:
- anatomical dead space (fixed)
- alveolar dead space (which can vary)

When we think on the potential effect of the HFNC for hypercapnic ARF, it´s probable that the greatest benefits will b seen on hypercapnia due to ⬆️Vd/Vt, and the reason is:
4/ #HFNC clears nasopharynx dead space, changing the Vd/Vt ratio - reducing CO2 rebreathing, reducing the WOB related to it :
5/ Some simulations with COPD pts on Low Flow O2 vs 30L/min HFNC show what clearing nasopharynx dead space + some mild PEEP can do:

PS: Effects are dependent on flow, so 60L/min is more efficient than 45L/min that more efficient than 30L/min
6/ Robust clinical evidence on the effect of HFNC on hypercapnic AE-COPD is lacking. We hope #RENOVATEtrial fill this gap. AE-COPD is one of 4 ARF subgroups to be recruited in our study.
In order to take the most out of a treatment effect in a subgroup,
7/ #RENOVATEtrial data will be analysed using a dynamic hierarchical mixture model w effect sizes´ shrinking and borrowing - the more the subgroups behave alike, the more borrowing. Non-inferiority and superiority Hxs are nested and thus will be tested simultaneously
RENOVATE´s statistical analyses provided us the capacity to take the most out of subgroups´effect size - taking the most out of the resources put into the project: money, pt enrollment. I´m so excited about it!

Soon preparing for publication:
study protocol & SAP
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