A bit of a 2 for 1 job this month as we discussed two papers touching on similar themes; namely what’s the best “non-invasive” option to manage acute onset, non-cardiac, respiratory failure?
Have a read of the comments below and feel free to add your own!
Re paper 1
Hope you all enjoyed the paper!
I do really like this one as it’s a pragmatic, real world study answering a important question that every ICU has to deal with; namely what’s the best way to improve oxygenation in a hypoxemic pneumonia patient…….
The take home message is that High Flow Nasal Oxygen (HFNO) improves survival and reduces intubation rates in severely hypoxemic patients (a paO2 ratio less than 200mmHg) when compared to non rebreathe masks delivering cold dry gas (no suprise there you might say) AND non-invasive ventilation (NIV)….
Now that is a surprise as NIV has been the mainstay of our “rescue” therapy for hypoxemia until now and is something that is still probably standard practice.
So why is there a mortality difference?
I’m sure compliance and patient comfort may be a factor (dyspnoea rates were lower in the NHFO group) plus if the sickest patients (ie the most hypoxemic) in that cohort are avoiding ventilation then, again, their outcomes are likely to be better as well.
However could it be something else? Something that we maybe should have thought of all along but didn’t because the patient is on NIV rather than being intubated…..
Have a look at the paper again and see if you notice what the Tidal Volumes were in the NIV group.
I’m not going to say anything else except please read May’s paper then feel free to comment!”
Re paper 2
Hope you enjoyed this cheeky little paper!
I know it’s a small, single centre study etc. but you have to admire their audacity at thinking up the concept.
The fact that NIV doesn’t seem to improve outcomes in pneumonia (or other new onset, non-cardiac acute respiratory failures) has always been a bit of a puzzle but this group have pointed out that the answer is potentially very simple and in keeping with what we already know.
They wondered if it had something to do with “excessive” tidal volumes (TV) as in NIV it’s extremely difficult to control TV’s as they are due to both the ventilator’s positive inspiratory pressure and the patient’s own negative inspiratory pressure drive (which in acute respiratory failure is going to be high).
So they measured TV’s……
What they found was that excessive TV’s (>9.5ml/kg) were independently associated with failure of NIV particularly in the more severely hypoxemic patients.
Why would that be?
The most simple answer is that the excessive TV’s lead to ventilator induced lung injury (VILI), worsening the respiratory failure, leading to the need for intubation.
I also can’t help but wonder whether the fact that this effect was more pronounced in the moderate to severe hypoxemic patients was because their respiratory drive was higher; further contributing to the excess TV.
So what implications might there be for our clinical practice?
Personally I think I’m going to stick with HFNO rather than NIV when I want to try and improve oxygenation in pneumonia patients.
Also maybe we need to think about whether in patients with severe hypoxemia prior to commencing respiratory support (as measured by the PaO2/FiO2 ratio) we just go straight for intubation as then we can be sure that we are controlling the TV. However that is a bit more of a grey area as I don’t think the evidence is out there yet one way or the other. Hmmm I feel an audit coming on…….
Let me know what you think.”