manual hyperinflation and airway pressures

[Martin345]

me again

the school of thought about NOT doing MHI tends to be leaning less towards consideration of peak inspiratory airway pressures and more towards mean or plateau airway pressures. but what's too high?

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[Martin345]

thought i'd bump this back up to the top

reading a bit about ards and sepsis and so on... the general rule for ventilating seems to be to keep plateau pressures below 30cmh2o. would anyone not bag if they were higher than this?

[shane246]

Your question is fascinating and I hope inspires people to think about pathophysiology and why we as physios apply certain techniques as part of our treatment strategies.
I guess from my perspective it would depend on the mode of ventilation in use, what the underlying ventilatory problem was and why it was felt necessary to apply MHI. If a patient is on PCV for example then I would question the role of disconnecting the pt from the ventilator to apply a manual technique (MHI) that is historically a volume cycled manoevre.
Even with a manometer in the MHI circuit you are still only provided with a peak pressure as a point of feedback - I think that to limit the peak pressure to 30cmH2O during MHI may result in a MHI technique that may not be effective and undoubtably delivering a volume that is lower than the Vt from the ventilator from a plateau pressure of 30. What does this add to patient care?
To answer your question I think, on a case by case basis, it would be useful to look at any variation in peak and plateau pressures along with their absolute values and Vt delivered to gain an appreciation of the lung compliance before deciding if MHI has a role. This of course assumes that there is an indication such as airway clearance or decreased ventilation that you wish to target.
If for argument sake, the decision is to provide MHI in someone with plateau pressures of about 30, do we still provide MHI within the historical constraints of keeping peak pressure below 40cmH2O?

[Martin345]

this is getting slightly off the original topic, but...

i was always brought up with the idea that you don't use mhi with patients on pcv. shane as you know, this doesn't always have to apply and there are times when we do it anyway. i've found more often in recent times that i will. what i always do first is examine why they're on pcv. then i switch the mode to volume-controlled simv and look at what their peak pressures are. if they're appropriately low enough, i'll use mhi if there's a good indication. it's multifactorial of course... what is their fio2, their peep etc etc.

to answer your last question - yes i think the peak of 40cmH2O should still apply for the same reasons of old. i don't think a limit of 30 would be beneficial.

recent case to ponder:

a 50yo man with a drug overdose and nasty aspiration pneumonia who collapsed both bases quite markedly within 24 hours of intubation. he wasn't being sedated but his gcs was quite low after 3-4 days.
his ventilatory pattern was a bit all over the place on simv and so he was put on pcv - peep was 10, ps +10 and pc needed to be 20 to keep his tidal volumes down! tidal volumes were 500-700. his pf ratio improved when just this was changed (and no physio done overnight).

however, when put on psv (not simv) his peak pressures were around 26-28, but his tidal volumes were about 1100-1400. his ventilatory pattern was almost cheyne-stokes like with significant apnoeic periods. you could argue this was a decent enough treatment in itself as he was getting great big tidal volumes, with nice breaks in between sets! combined with manual techniques and suction you could have a complete treatment.

would you use mhi with peep in this case? any other suggestions for changes to ventilation mode/settings? for the record, fio2 went from 0.5 to 0.75 over the first four days, with pao2 kept within normal limits with this increase.