Airway

Expert Commentary: Troubleshooting Hypoxia on the Vent

In emergency medicine education, we tend to focus on establishing the airway but spend less time discussing the aftercare and managing the ventilator.  While we have spent more time on this recently, thanks to Brian Fuller and his research on the importance of low tidal volume ventilation in the ER (see EM Journal club summary and podcast from February 2014),  most of us are still more comfortable putting the ET tube in than managing the vent.

Luckily for us, here at WashU we have some EM-Critical Care wise guys who can teach us a thing or two, and today we share with you Brian Fuller's method for trouble-shooting hypoxia on the vent, forwarded to us by PGY-3 Brendan Fitzpatrick:

>>From: Fitzpatrick, Brendan
>>To: Fuller, Brian
>>Subject: vent desats

Dr. Fuller,

Good working with you last night. I was trying to recall how you broke down desats on the vent last night, but somewhere between little sleep and my kids' halloween parade, I've lost the finer points.

In all your free time, would you mind jotting down what you told me so I can review it?

thanks,

Brendan

 

>From: "Fuller, Brian"
>To: "Fitzpatrick, Brendan"
>Subject: RE: vent desats


For the purposes of acute deterioration (in the form of hypoxia) on the ventilator, we are gonna talk about two airway pressures: peak pressure and plateau pressure. As an aside, mean airway pressure is the average pressure over one cycle of inspiration and expiration. It is largely governed by PEEP and I:E ratio. It really governs oxygenation- higher it is, more you open up stiff alveoli in sick vented patients.


Peak pressure is the summation of pressure generated from: 1) tidal volume and compliance; 2) resistance and peak inspiratory flow; and 3) PEEP
 

Plateau pressure is a reflection of compliance. Think "how stiff the lungs are"; or "how much transalveolar stretch is occurring".
Compliance is ∆ volume/∆pressure. Specifically, tidal volume/(plateau pressure - PEEP)




So the first thing I do when somebody becomes acutely hypoxic on the ventilator is to look at their peak airway pressure:

1. If decreased: you have an air leak or the patient is hyperventilating/tugging hard and therefore pulling the airway pressures down. Air leak would be something like: bronchopleural fistula, the chest tube you just put in has a leak in the system, your ETT has migrated or cuff has a leak and air is escaping.

2. If increased: see above- this could either be primarily a compliance or resistance problem. So your next step is to look at the plateau pressure to figure out where the problem lies.

If no change in plateau, you therefore have a bigger difference between the peak pressure and the plateau pressure than existed before the hypoxic event. See above for what governs these pressures, so you can tell that this is therefore a resistance problem. Think: airway obstruction from bronchospasm, clogging of the ETT with secretions, kinking of the ETT.


If plateau pressure is also increased, you now have a situation where the peak and plateau pressures both increased. See above for what governs these pressures, so you can tell that this is therefore a compliance problem. Think: pulmonary edema, abdominal distention, pneumothorax, atelectasis, etc.

3. If no change: think "Something made my patient hypoxic but didn't change my airway pressures." Not a lot of stuff does that. Think: pulmonary embolism, PFO.

Sometimes it is difficult to figure out "Is the ventilator and my ventilator settings the problem, or is this a patient problem?" If you remove the patient from the ventilator, and therefore take that out of the equation, bag them and they get better, it is probably a ventilator problem. If you bag them and they stay bad, it is probably a patient problem.

Hope this helps. Hit me back with questions PRN.

Feel free to share with others.

Be good man.
B



For those of you who like pictures, here is a visual representation of the algorithm:

Want to do a little more reading or watching about this? Life in the Fast Lane had a nice review of Pulmonary Mechanics.  I recommend the second Eric Strong video on pulmonary pressures as a supplement to understanding the above material (and hell, it only takes 9 minutes to watch).

Expert Commentary by Brian Fuller
Visual aids by Maia Dorsett (@maiadorsett), PGY-3 
Expert inquiry, sharing skills and parenting by Brendan Fitzpatrick, PGY-3.

#FOAMed Digest No. 6: Ain't Nobody Got Time For That

Welcome back, FOAMheads! My apologies for the delay this week. I ended up being a bit busier than I expected, which not coincidentally brings me to the theme for today's entry.

Sometimes you have a lot on your plate and may not be able to set aside a large chunk of time to watch/listen to a 30-minute-plus podcast. But that doesn't mean you don't have time to get your learn on! This time around, we'll highlight some of the best FOAMed sources of short-and-sweet educational pearls. Easily digestible for the highly-distractible mind of the EM trainee.

There is no moment like the present -- let's get started!




Three Stars:

1. The Glasgow Coma Scale was first introduced 40 years ago. It's past time we started assessing it properly. "GCS 12" doesn't cut it any more. What are the deficits? How do you score for eye-opening if the patient's eyes are swollen shut from trauma? What does "abnormal flexion" even mean, anyway? Ian Miller at TheNursePath provides us an excellent infographic-style breakdown of the "new" GCS.

2. The EMS 12-Lead blog, edited by EMT-P and prehospital resuscitationist extraordinaire Tom Bouthillet, is an excellent resource of EKG cases. This week's case provides an excellent example of why a resuscitationist must always treat the patient, not the monitor. Review the EKG and develop your interpretation first, then read the conclusion.

3. I don't know that a FOAMed segment has ever been more appropriately titled. "Positively Painful Private Parts" is a four-part series published by Brad Sobolewski on his PEM Blog, focusing on the evaluation of acute testicular and scrotal pain. There is a pediatric focus, not surprising given the nature of the blog, but Dr. Sobolewski does include information on "adult" diagnoses like epididymitis as well. Each part is succinct and high yield.
Part 1: Focused H&P
Part 2: Testicular torsion
Part 3: Pathology of the appendix testis
Part 4: Epididymitis

Oldie But Goodie:

An excellent case from The Blunt Dissection, in which Dr. Chris Partyka lays out everything you need to know when you must intubate a crashing neonate.

F(FN)OAMed:

Via your EMRA membership, you now have access to all of the resources from the EMedHome website. Go to the site and explore for yourself the wealth of resources available -- everything from taped lectures from prior EM conferences, the EMCast podcast hosted by Amal Mattu, weekly clinical and radiology pearls, and other vodcasts and presentations.

This week, check out the clinical pearl describing some of the changes in the new 2014 AHA/ACC guidelines for management of patients with NSTEMI.  Ryan Radecki at EM Lit of Note also published his take on the new guidelines this week; well worth the quick read.

(As always, if you need help getting access to any of these resources, please contact your friendly neighborhood Social Media Committee member.)

The Gunner Files:

1. Reinforce the take-home points from the EM Lyceum piece on DKA management with this bullet-pointed breakdown by Adaira Landry on emDocs.

2. In case you've been off the grid for the past week, ebola is here. Triage and isolation protocols are coming to an ED near you any day now. Luckily for all of us Daniel Cabrera at the Mayo EM Blog published for your review the CDC infographic Algorithm for Evaluation of the Returned Traveler.

3. So the latest installment of the Skeptic's Guide to Emergency Medicine will take you about half an hour to listen to, but it's well worth the time. Drs. Milne and Swaninathan analyze the Ottawa Aggressive Protocol for ED cardioversion and discharge of patients presenting with AFib.
This piece really highlights the interconnectedness of the FOAMed world, as it references back to last week's FOAMCast on AFib (as seen in FOAMed Digest #5), and a recently-published research letter (containing data from the largest-ever study on this topic) in JAMA calling into question the safety of cardioverting AFib patients presenting with >12 hours of symptoms.
This research letter was analyzed in depth by Rob Orman on the latest episode of his ERCast.
We're all in this together, folks.

4. I don't want to think too hard about having a cricket or other insect lodged in my ear canal, but it is probably in our best interest to know what to do if we're presented with it. Mitchell Li at ALiEM has us covered. (Great tip for getting out plastic beads, too!)

5. When you do get a little extra time, don't miss the September installment of the Annals of Emergency Medicine podcast. Covered topics include pigtail catheters for pneumothorax, acute stroke care, age-adjusted D-dimer cutoffs, and the HINTS exam (authored by our very own Dr. Brian Cohn!) You can download the podcast directly here.
(And be sure to check out Cohn's paper!)

Never stop learning,
Sam Smith, PGY-3

#FOAMed Digest No. 3: You Need Me On That Wall

Emergency Medicine physicians practice in a unique environment. We must synthesize plans for  diagnosis, management, and disposition while utilizing input from almost every subspecialty, and the ED is the ultimate proving ground for diagnostic tests and treatment modalities of every sort. Unsurprisingly, a fair deal of controversy and debate exists regarding the optimum management of patients. (For reference, see any Trauma Case Conference featuring Drs. Schuerer and Aubin.) The “best evidence” is often poor evidence. We in Emergency Medicine retain the rebellious spirit of our founders, and are always looking for new and innovative techniques. Some physicians are too quick to jump on the bandwagon, and others lag behind the curve when it comes to adopting new practices.

The selections this time around are not meant to tell you the best way to do things. The algorithms and practice patterns suggested are not universally adopted, written in textbooks, or taught as part of any standard curriculum. They are meant to promote thought, to prompt you to read the primary literature for yourself, to encourage you to seek the opinions of other experts on the subject, and to form your own conclusions. Hopefully they will inspire you to suggest new ideas to your seniors and attendings during your next shift – or even question ideas you think are unsound. Maybe, just maybe, they will even inspire a new research or QI project. FOAMed is by design perfectly adapted to assist you in this quest.

Ramblers, let’s get ramblin’.

Three Stars:

1. Ken Milne at the Skeptic’s Guide to Emergency Medicine pretty much sets the bar when it comes to FOAMed of the latest EBM topics. He asks his clinical questions in the PICO format, he applies a rigorous quality checklist when analyzing the available literature, and includes in his discussion other FOAMed experts (including on occasion our very own Chris R. Carpenter, a.k.a. “Captain Cranium”). This episode he turns his skeptical eye to a topic sure to generate heated discussions for years to come: tPA for stroke.

2. If there’s anyone that looms larger in the ED Critical Care world than Weingart, it’s Resuscitationist Extraordinaire Cliff Reid. His lecture from the SMACC Gold conference hit resuscitation dogma like an A-bomb, leaving irradiated bits of unfounded practice patterns strewn about the Outback countryside.
(EXTRA CREDIT: Reid’s talk from the original SMACC conference, “Making Things Happen,” should be required viewing for anyone wanting to be a Trauma Senior someday.)

3. If pediatric surgeons have come to accept ultrasound as a stand-alone diagnostic method for appendicitis, maybe there’s hope that someday ultrasound can also be used as a radiation-sparing technique for diagnosis of small bowel obstruction. Academic Life in EM has an excellent run-down of the technique and comparative research studies.
(EXTRA CREDIT: The book Evidence-Based Emergency Care, authored in part by our own Captain Cranium Chris R. Carpenter, has a chapter dedicated to the inferiority of plain films for SBO diagnosis. You can read it for free online via Becker Library.)

Oldie But Goodie:

I think here in a few more years this will reach “accepted standard practice” level, and maybe even “textbook” level, but it’s not there yet. It should be: there’s good evidence to show kayexelate doesn’t work, and may even cause harm. Let Weingart and the PaperChase fellows from EM:RAP give you the ammunition you need to stand up to any pesky floor seniors.

F(FN)OAMed:

In a very enlightening segment from this month’s EM:RAP, Rob Orman interviews a community ED practitioner, Dr. Cameron Berg, regarding his hospital’s new Accelerated Diagnostic Protocol for low-risk chest pain. While his exact algorithm hasn’t been externally validated and probably isn’t ready for prime-time at our shop, the evidence-based and pragmatic approach is certainly worth considering. And he provides links to almost all of his references in the show notes!

The Gunner Files:

1. The “Research & Reviews” segment on Life in the Fast Lane is worth checking out every week. A group of some of the brightest minds in the FOAMed world get together and spoon-feed us summaries some of the most relevant, practice-changing, or downright strangest papers in the EM literature.

2. Josh Farkas over at PulmCrit wrote an excellent piece laying out his argument for super-high-flow NC (think 30-45L!) as an acceptable method of preoxygenation before RSI. It’s also got a good rundown of apneic oxygenation using NC (which we all should be doing every time), and an enlightening counterpoint from the grand maester of ED Critical Care, Scott Weingart.

3. Pediatric EM expert Sean Fox provides an excellent summary of the neonatal ALTE on his blog Pediatric EM Morsels.

4. Two EM airway heavyweights, Rich Levitan and Reuben Strayer, slug it out in the ultimate Direct Laryngoscopy vs Video Laryngoscopy debate, posted to the Prehospital and Retrieval Medicine podcast hosted by Minh Le Cong.

5. All of us will be the bearer of the -07 phone at some point, and that means you better have your act together when discussing decision-making capacity. Bill Johnston, EMT-P and author of the excellent blog Prehospital Wisdom, shares his fundamentally sound and no-bullshit method for determining capacity in the field.

In the words of Ken Milne: “Meet ‘em, greet ‘em, treat ‘em, and street ‘em!”

Sam Smith, PGY-3

#FOAMed Digest No. 2: Breathless Love

Welcome back! Fresh new FOAMy goodness for you, this time with an emphasis on airway and pulmonary care. Let’s do it!

Three Stars:

1. No way around it: “Delayed Sequence Intubation” is the new hotness. If you want to be one of the cool kids, you better get on board. I’ll let the more graphically-minded folks at EMCurious lay it all out for you with a prototypical case. Don’t miss the links – more excellent FOAMed resources on DSI.
(And Weingart’s seminal paper on the subject is required reading at this point.)
(And, oh yeah, ketamine does NOT increase ICP. Let’s use these two systematic reviews 1 & 2 to stop the foolishness already.)

2. Someday you will need to perform a cricothyrotomy. Accept it as reality, and do everything you can to prepare for it. Start here, with Weingart’s lecture on the surgical airway delivered at the SMACC Gold conference last fall. This page from the EMCrit blog has compiled all sorts of great surgical airway resources from around the FOAMed world all in one spot, including can’t-miss stuff about the scalpel-finger-bougie technique and Weingart’s pre-intubation checklist. You should probably add it to your favorites list now.

3. Wouldn’t be a FOAMed Digest without getting a little off-topic, and Rick Body’s recent contributions over at St. Elmyn’s regarding ACS & “low-risk” chest pain in the ED are too good to pass up. Great post analyzing his recent paper, which concluded ED physicians simply aren’t capable of ruling out ACS in chest pain patients with an acceptable accuracy using only the clinical exam. Dr. Body also gives you a run-down of how to properly utilize high-sensitivity troponin in his talk from SMACC Gold.
(Link to Body's paper here.)

Oldie But Goodie:

By the end of our Ultrasound rotation, we can all diagnose pneumothorax with ultrasound at the bedside. It’s time to take it next-level. A-lines, B-lines, pneumonia vs edema…the experts at the Ultrasound Podcast help you figure it all out in a two-part 1 & 2 podcast.

F(FN)OAMed:

Sanjay Arora and Mike Menchine, hosts of the PaperChase segment on EM:RAP, summarize the current literature about how terrible we are at adequately sedating patients after RSI. Roc lasts longer than Sux – the patients won’t be able to tell us they need sedation!
(Links to relevant papers in the show notes.)

The Gunner Files:

1. Brett Sweeny at EMDocs provides an exhaustive review of FOAMed resources regarding permissive hypotension in trauma. Great lectures and podcasts from some of the brightest minds in EM & trauma surgery.

2. We’re seeing it already – asthma cases are starting to pile up over on the SLCH side. Luckiliy for you, Pediatric EM rockstar Andy Sloas just published an excellent podcast on the evaluation and management of asthma in the Peds ED.

3. Next time you’re consulting Ortho or Plastics for a hand injury, sound like you know what you’re talking about. The folks over at EMin5 hit you with the quick rundown on the neuro exam of the hand.

4. Last week, St. Elmyn’s helped the rooks get up to speed when it came to dealing with the dyspneic patient in the ED (and I bet the seniors learned a thing or two as well). This time, get your mind right when faced with a syncopal patient.

5. Who doesn’t love infographics? And if they actually help us learn something about managing septic patients, that’s just a bonus! Very well done by EMCurious, with embedded links to the relevant studies!

6. New podcast from R.E.B.E.L.EM, summarizing the results of a meta-analysis just published this month in Annals which concluded prehospital application of NIPPV in patients with severe respiratory distress regardless of cause reduced need for intubation (NNT 8) and in-hospital mortality (NNT 18). 
w00t prehospital medicine!
(Original pub here.)

That’s all, folks! Go get your learn on!

Sam Smith, PGY-3