Understanding Alveolar Physiology & Ventilation in the COVID Era. #FOAMed #FOAMcc


First watch this:

Now that should be a good start point to realize that there is something most physicians, even those who routinely ventilate patients, overlook. The time constant required to recruit. One can easily picture the rapid derecruitment, then re-recruitment – known as atelectrauma for the novices- which will result not only in only temporary success with recruitment maneuvers (RMs), but likely also contribute to ongoing lung injury. Now in less severe cases of ALI, we “get away with it” and the patient gets better anyway. But when the rate of healing is less than the rate of VILI, we get in trouble. Only – just like aggressive fluid resuscitation – we can be blissfully unaware of the unwitting iatrogenic contribution and feel like “the patient succumbed despite everything we did.” Perhaps, but then again perhaps because as well.

In our shop, with conservative fluid management and aggressive de-resuscitation, ARDS has been seldom seen in the last 10-15 years (versus my first years of practice where I encouraged aggressive resuscitation in the ICU and to my ED colleagues), hence ventilation had become rather uninteresting… But with COVID now I’ve had to dust off my “fancier” ventilation strategies and have been using inverse ratio and APRV (not all our vents can do APRV). It would be fun if it wasn’t for the mortality…

So, what can that little rat lung video teach us?

First, the concepts of pressure-time integral (PTI) and alveolar surface area, things we do not routinely use as mental constructs. As we can see in the video, time is required for the pressure to move into the distal airways and recruit. That is why RMs often run in the 30-60 second range at anywhere from 30 to 40 cm/h2o. We all know that they work, but only transiently, and yes, a higher PEEP is usually used post RM, but this may not represent a sufficient PTI to prevent de-recruitment and continued atelectrauma.

Second, the visual example of heterogeneity. Though the Baby Lung analogy and lung protective concepts still hold, that heterogeneity highlights how a relatively low VT and respecting plateau pressure limits may not sufficiently protect certain more distended alveoli. Indeed, as compliance increases with recruitment, the stress is more evenly distributed across alveoli rather than preferentially in the ones that remain open. Hence a strategy that prevents de-recruitment becomes paramount.

This is where APRV comes in. I used it a bunch a few years ago when working in a center where we received commonly enough and had a bit more ADRS than commonly in my shop.  APRV stands for airway pressure release ventilation, and requires one to completely wipe the mind’s dry-erase board of ventilatory parameters and really just start thinking in terms of pressure-time integral.

APRV is essentially a bilevel ventilation mode over which a patient can take spontaneous breaths, analogous to a CPAP mode with occasional pressure release that allows for ventilation. Though APRV has been around for a long time, the work of APRV guru Nader Habashi and his APRV network have done tremendous work fine tuning their system of time-controlled adaptive ventilation (TCAV) which is a way of setting APRV appropriately to the patient’s physiology. I highly encourage reading their work and resources available – which includes mentoring. APRV isn’t a plug-and-play mode, it is paramount to understand the physiology behind it.

So we need to set P hi, P lo (it’s supposed to be 0 so an easy one), T hi and T lo – and yes FiO2 (at least one familiar one!). So basically you determine how much time the patient spends (this largely determines your respiratory rate) at a certain level of pressure, generally between 20-30 depending on severity of ALI and lung compliance, and how long an expiratory phase they get (really short).  That’s actually the one that needs understanding, because that’s the TCAV sweet spot, how you prevent as much VILI as possible.

You need to think of peak expiratory flow rates (PEFR – yup just like in outpatient asthma!), and adjust the T lo to 75% of the PEFR. This provides what Nader himself describes as the air cushion that remains in the lungs and prevents the alveoli from taking the brunt of the next positive pressure burst, particularly those at the most fragile end of the spectrum.

You need to remember the concept of functional residual capacity (FRC) as this is what we aim for to avoid recruitment-derecruitment.

So, caught your attention? If you have a physiologist’s soul (and if you’re resuscitating patients you really should!), and were not yet using TCAV-APRV, I hope you are thinking about it because it makes sense. And in these COVID patients we may not have the usual margin of safety to do our usual ventilation.

So, please register at the APRV Network, read all their free guideline documents which are great but I will not post as they require you to register (its free), and here are a couple of must-reads by Nader and his group:

dynamic alveolar physiology

history of APRV

And of course Scott has some awesome discussions with Dr. Habashi himself.

Oh yes and as per our Webinar last week, Josh Farkas has been using APRV on his COVID patients with success!


please share your COVID ventilation experience!

…and no offense, but please, though open, this is a blog intended for clinicians, not a forum for lay questions or comments. I simply do not have the time to answer them and will not, and I feel rude deleting them (but will do so) but clinical readers need concise information packaging, so please feel free to read or listen in e-silence. Again, I apologize for this recent necessity.





COVID-19 Webinar: Respiratory Management #FOAMed #FOAMcc


So I had an awesome time talking and learning from some of the smartest and most progressive thinkers I know, some of the usual suspects at H&R, and some amazing docs from Italy and NYC who are at the front lines of this COVID war.


  • HFNC & NIV – do we dare use them? 
  • when do we intubate?
  • how do we ventilate? prone ventilation routine or rescue?
  • Adjuncts: suction, bronchoscopy
  • When do we wean?
  • Q&A if time allows.


Dr. Laura V. Duggan MD FRCPC (Anesthesiology and Pediatrics), Associate Professor, Department of Anesthesiology and Pain Medicine, University of Ottawa, Canada @drlauraduggan. www.airwaycollaboration.org

Dr. Marco Garrone, MD, ED doc from Mauriziano Ospedale, Torino, Italy. @drmarcogarrone.

Dr. Cameron Kyle-Sidell, MD, ED-ICU, Maimonides Hospital, New York. @cameronks

Dr. Josh Farkas, ICU, University of Vermont, Creator, The Internet Book of Critical Care (IBCC), @pulmcrit.

Dr. Adam Thomas, ED doc & CC Fellow, University of British Columbia, co-author, The Internet Book of Critical Care, @adamdavidthomas.

Dr. Philippe Rola, ICU, Santa Cabrini Hospital, Montreal, Quebec. @thinkingcc

Dr. Rory Spiegel, ED-CC doc, Washington Hospital Center, Washington, DC. @emnerd

Dr. Scott Weingart, ED-CC doc, Creator, EmCrit.org, Stony Brook Hospital, New York. @emcrit

Here is the audio, am working on editing the video and should have it up soon.

I realize many questions came from the audience regarding L and H phenotypes, a concept which was rapidly assimilated by those reading and discussing day and night to stay at the cutting edge of the understanding of COVID physiology, so I am including the Gattinoni paper which is the source. For those still thinking of this as ARDS, understand that the single most published author and pre-eminent authority on that disorder states “this is not ARDS,” even if the H type, for those who progress to it – or evolve towards it due to initial management strategies, is fairly similar.

Gattinoni COVID

A huge thanks again to my all star cast for making this happen and for their continuing efforts to learn and teach. Please refer to Josh and Adam’s IBCC covid page which is constantly evolving, and Scott’s emcrit.org for ongoing info.

Webinar Audio:


Webinar video


There were a lot of comments and questions, many very interesting, will try to address them in the next webinar likely in a week or so.


cheers and stay safe



COVID-19 – Respiratory Management: A Physiological Approach. #FOAMed, #FOAMcc, #COVID19


So we’ve got a pretty good lineup of docs who have been taking care of COVID patients for the last few weeks assembled, including one who had pretty much seen it all from the Italian battlefront. We’ve got anaesthesia, critical care and emergency medicine representatives. As usual, we’ll be trying to bring highly physiological and practical approaches to managing the respiratory failure of this new disease we are all facing.

So this is #FOAMed, but I just found out that the max meeting size is 500. So I guess it is first come first served. Asking everyone who is not a panelist to stay muted please, those not adhering to this will be promptly booted out as it completely ruins audio quality. It should be recorded if the cloud doesn’t fail and will be available on this blog.

Questions can be sent on twitter to @ross_prager who will set us up, please use #thinkingcovid.

Join the Webinar here!


8pm EDT (GMT-4) Welcome panelists & intro

  • HFNC & NIV – do we dare use them? 
  • when do we intubate?
  • how do we ventilate? prone ventilation routine or rescue?
  • Adjuncts: suction, bronchoscopy
  • When do we wean?
  • Q&A if time allows.


Dr. Laura V. Duggan MD FRCPC (Anesthesiology and Pediatrics), Associate Professor, Department of Anesthesiology and Pain Medicine, University of Ottawa, Canada @drlauraduggan. www.airwaycollaboration.org

Dr. Marco Garrone, MD, ED doc from Mauriziano Ospedale, Torino, Italy. @drmarcogarrone.

Dr. Cameron Kyle-Sidell, MD, ED-ICU, Maimonides Hospital, New York. @cameronks

Dr. Josh Farkas, ICU, University of Vermont, Creator, The Internet Book of Critical Care (IBCC), @pulmcrit.

Dr. Adam Thomas, ED doc & CC Fellow, University of British Columbia, co-author, The Internet Book of Critical Care, @adamdavidthomas.

Dr. Philippe Rola, ICU, Santa Cabrini Hospital, Montreal, Quebec. @thinkingcc

Dr. Segun Olusanya, Anaesthesia-ICU, Reading, England. @iceman_ex

Dr. Rory Spiegel, ED-CC doc, Washington Hospital Center, Washington, DC. @emnerd

Dr. Scott Weingart, ED-CC doc, Creator, EmCrit.org, Stony Brook Hospital, New York. @emcrit

COVID Clinical Discussion w/Cameron Kyle-Sidell: NYC ED/ICU doc in the trenches. #FOAMed

Dr. Cameron Kyle-Sidell is an ED-ICU Doc at Maimonides in New York, currently under the COVID fire. He put up an inflammatory tweet yesterday which caused a lot of different reactions, because it clearly challenged the widespread even if only recent belief that one should intubate the COVID patients quite early, usually much earlier than one would in typical respiratory failure:

So here you go:


Please share your thoughts and experiences – my comments in bold!

Korbin Haycock:

Very interesting. My experience is zero cases so far with COVID-19. Just some thoughts for what it’s worth from someone with no experience with COVID: Hypoxia is due to V/Q mismatch, diffusion, hypoventilation, low pO2 (altitude), shunt, low cardiac output (as more O2 is extracted off HgB and mixed venous O2 is low), and finally hemoglobin problems (whether by poisoning or defective HgB).

It was pointed out to me by Brett Berliner tonight in a paper (via twitter) that SARS CoV-2 appears to disrupt the beta chain of HgB to take up O2. I’d never heard of this, but if this is the case, exchange transfusion makes sense as a therapy for hypoxia as long as one is past the stage of illness where the viral levels are low. If this is a hemoglobinopathy, no amount of increase in mean airway pressure or FiO2 will fix the hypoxia.

Perhaps people out there with actual experience with COVID-19 can shed additional light on how the hypoxia tends to respond to positive pressure or increases in FiO2, or more importantly a lack of expected response, that would indicate the mechanism of hypoxia (such as a hemoglobinopathy).

It is very interesting that the hypoxic patients described in the post don’t appear to be very symptomatic in terms of SOB, nor do they attempt to compensate for the ding to DO2 from low O2 sats (O2 content) with an increase in HR to drive up CO. Normally DO2/VO2 ratios are around 4-5, so either the illness suppresses the normal physiological response to a decrease in the ratio, or the VO2 is suppressed somehow (seems unlikely). In any event, perhaps we should revisit the idea to intubate early if hypoxic, unless the patient actually looks really bad.

Summer Allen:

I’m Pulm/cc. This was fascinating and sparked some ideas. But, I need someone smarter than me to take it forward. The first thought is this is not what we know. It’s a different beast. Stop trying to make it fit what we know.

Why are people not short of breath or tachycardic? I suspect most of this is that compliance is high and there is no issue with expiratory flow limitation, hence WOB is more or less normal… And once hypoxia is corrected with O2, they feel fine.

Does the virus hide hypoxia from the body? Maybe it turns off normal feedback that would make us short of breath and tachycardic. The body doesn’t compensate because it doesn’t know it’s hypoxic. That’s why people are being found dead at home because they didn’t know they were slowly suffocating. Maybe it’s not affecting kids because their feedback mechanisms are more heightened already because of growth. Trying to think outside of the box after listening to this. I definitely agree that treating these patients like normal pneumonia with vent/pressors/fluids isn’t the answer.


Bala Totapally

Looks like these pts have severe V/Q mismatch without abnormalities in respiratory mechanics. Almost like a cyanotic heart condition. I agree if the mechanics are not worsening we may not achieve a lot by early intubation except to prevent sudden deterioration, if anything. HFNC with 100% will be the right choice. Has anyone tried nitric oxide before intubation? Might work to improve V/Q mismatch and reduce RV strain.

I am definitely planning to look at RV function and use inhaled vasodilators both for the VQ and for RV function. 

Richard Harper:

Great talk and very fascinating points. Short of hyperbaric chambers for everyone, I think keeping everyone on high flow for as long as possible seems very reasonable. Given the ongoing reports I’m seeing regarding the pathophysiology regarding COVID-19 related lung disease, including your shared observations, it seems like using stress index on intubated patients would be the best measure of appropriate PEEP in this setting without “trashing” the lungs. If our understanding is correct regarding the atelectatic, high compliance Sars-cov-2 lung is correct, then the PEEP table is not going to accurately predict the proper settings and the stress index measured once a day would solve the problem of too much PEEP.


stay safe!



COVID Clinical Discussions: An Update w Dr. Garrone. Sharing CPAP??? #FOAMed

Incredible discussion with front-line italian ED doc Marco Garrone (@drmarcogarrone – follow him on twitter for great covid POCUS cases). Chilling for those of us not yet in the storm, but very interesting stuff, especially the use of NIV-sharing – two patients simultaneously on CPAP.

Here is the audio:


For more on vent sharing and references, please see Josh’s post here!

stay safe



COVID-19 Clinical Discussions – Dr. Blair Schwartz. #FOAMed

Tonight I had a chance to chat with Dr. Blair Schwartz, intensivist at the Jewish General Hospital in Montreal, Canada, one of the ministry-designated COVID centers, in part due to their ICU which was designed with pandemics in mind and able to physically be divided in sealed-off halves. Impressive stuff.

Here is our chat:

So thus far, the small Montreal experience parallels what we have heard from the Chinese and Italian experiences: they crash fast, so intubate them early, then deal with a high compliance ARDS that is difficult to oxygenate, and prone them. Oh yeah and the critically ill are not the very elderly at least so far…

Oh yes and I also questioned Blair on whether they were re-using N95s or staying completely protected for the day – seems to have been a practice in some of the dedicated areas in China, but so far, given “only” 3 patients they are keeping the general unit “clean” and disposing of all PPE between patients.

We’ll keep tabs on the evolution of the critically ill cases and try to share anything useful.

Here are my other COVID links: POCUS & COVID and Clinical Discussions.

Scott has a great video on COVID preox here:

And if you are running out of vents be sure to check out Josh Farkas’s post here on increasing your patient to ventilator ratio!

Jonny Wilkinson’s fantastic COVID page.


wash your hands & stay safe




POCUS and COVID: Practical & Clinical Applications. #FOAMed

So I’ve yet to take care of any COVID patients, but we are ramping up, and it’s just a matter of time. In the meantime, practical issues such as where we will cohort patients and how we protect non-COVID patients and HCPs are happening, and one of the challenges in infection control is imaging, which is a staple of severe respiratory illness.

Evidence has been steadily coming out that lung ultrasound is carving itself a pivotal role in the diagnosis and management of COVID infection. Here are some of the things I’ve gathered and I think are worth sharing. I will be adding to this as I collect from others and eventually generate a COVID POCUS database and experience.

a. Lung US is more sensitive than CXR for interstitial patterns, small effusions and subpleural thickening. 

b. COVID seems to have some particular ultrasound features:


Full article: COVID LUS

c. POCUS can be used to detect worsening or improvement of disease – by personal communication of Italian and Chinese ER/ICU docs. No published data yet, but several self-scanning infected physicians corroborate clinical improvement with resolution of POCUS lung findings.

d. POCUS can also detect the usual pathologies!  Pneumothorax is not a rare occurence in ventilated patients, and there may be an increased rate related to the parenchymal damage resulting in the unusually high compliance respiratory failure.



Here is a good example from Marco Garrone with COVID B line pattern on the left, along with pleural thickening and small sub-pleural consolidations, note also the clustering of B lines, compared to the left, B lines of CHF with a relatively smooth and even pleural line:

This is a great article by Yi et al, a Chinese radiology group, with some great CT/POCUS comparative images:

LUS covid study



This makes it important that all physicians and probably also PAs and nurses pick up basic LUS skills. At our shop we are making sure all first line providers can screen for lung POCUS abnormalities.



Lung ultrasound modules have been made open access at USABCD!

here are some excellent first steps by Jacob Avila:

How I perform the Lung Ultrasound Exam

B Lines




COVID-19 Clinical Discussions with Dr. Marco Garrone & Dr. Peng Zhiyong. #FOAMed

COVID19 has made for a rough start to 2020 for humans. Now ramping up in Canada, we can only hope that lessons learnt in China and Italy by governments and medical teams can be applied in a timely enough fashion to flatten the curve and allow our already stretched-thin healthcare system to absorb it without dire consequences for both COVID and non-COVID patients.

At my shop we have started our (re)organizational plan for the potential storm that may hit us.

So here is my chat with Marco (@drmarcogarrone)

And here is the vidconf audio with Dr. Zhiyong


I apologize for the prolonged ending there were technical difficulties and we ended up losing Dr. Zhiyong’s connection at the end.

Some clinical points from these and other discussions:

high compliance ARDS

– needs peep, but avoid hi peep as seems to have high risk of pneumothorax. This may make sense given high compliance may reflect alveolar wall elastic fiber damage.

avoid NIV including HFNC unless negative pressure room to prevent aerosolization.

may need to use N95 for entire duration of rounds in hot zone ICU to save stock

– personally, I would/will consider early proning or modified proning for spontaneously breathing patients (not on NIV either, just face mask).

LUS for screening dx and f/u (see below)


Other COVID resources:

Splitting ventilators for multiple patients https://emcrit.org/pulmcrit/split-ventilators/

Covid effects on cardiovascular system https://www.nature.com/articles/s41569-020-0360-5.pdf

Chinese experience with LUS: https://link.springer.com/article/10.1007/s00134-020-05996-6

My friend Jonny Wilkinson (@wilkinsonjonny) put together a great page with a ton of resources here at criticalcarenorthhampton.

My EMCrit Teammates Josh and Scott have put together some great clinical points as well, especially some practical tips for respiratory support setups and airway management.

IBCC a super comprehensive chapter on COVID.

EMCRIT on airway management.

And here are some excellent documents on hospital preparedness, ethics, a ventilatory support infographic from our italian colleagues as well as some kindly shared clinical notes and tips.


italian_triage_ethics (1)

ESICM info

SIAARTI – Covid-19 – Airway Management rev.1.1

COVID notes March 11 (1)

Also, as this will undoubtedly be a time for stress for HCPs caring for COVID patients, a respirologist friend of mine shared a link to a wellness/meditation tool, the coronavirus survival guide which has been made freely available to us. Now I have not tried it yet but I trust Andy.

Comment from anaesthetist Dr. Marco Vergone who is on the front line in Turin, Italy:

We are using prone positioning in almost all of our patients that require invasive mechanical ventilation, we’re trying alternate lateral position for patients on CPAP (helmet), and personally I find very promising prone positioning for patients in spontaneous breathing during weaning from CPAP, before discharge from the ICU.
I can confirm that diagnostic (CT and XR) is really burdensome when you have many isolated ICU patients, so lung US becomes paramount for bedside daily evaluation.
We’re working on standardized protocols for different levels of expertise of colleagus (pro level, basic skills, beginners).
For intubation procedures, we perform rapid sequence with ketamine + rocuronium or fentanil+propofol+rocuronium and ALWAYS videolaryngoscope. We always clamp the tube before disconnections and we always sop gas flow before removing helmets of masks. Apart from correct use of PPE, it is paramount to reduce aerosolization and contamination of the environment.
Get prepared ASAP, and stay strong!
Best, M

hope some of this can help other HCPs in these trying times.