There is a really smart anesthesiologist out there called Nicholas Chrimes. He along with his mate Peter Fritz invented the Vortex Approach to Airway Management. He also runs a blog called Clinical CrEd.
He did a post advocating the Mapleson B Circuit as the Ultimate Preox Device
What is the Mapleson B? The Mapleson circuits were used for anesthetics in the good old days. At least in the US, we have move to bigger, and arguably better designs for our operative patients. Many would have thought this device would have been consigned to the trash heap, but seemingly not.
My Recommended Approaches
I recommend two approaches to preox: standard and shunt physiology strategies. I outlines these strategies in the paper Rich Levitan and I wrote.
Standard: NRB @ >=15 lpm and NC @ 10-15 lpm for 3 minutes
Shunt Physio: Choose 1
- BVM with PEEP Valve & NC @ 10-15 lpm
- NIPPV Ventilator with NIPPV Mask or BVM Mask & NC @ 10-15 lpm
Nick makes a number of arguments as to the superiority of the Mapleson circuit over these standard techniques. His points are excellent, but I disagree with pretty much all of them–I think it becomes a question of perspective.
Yes, using the same device for reox and preox makes sure the reox device is there and hooked up, but this for me is an inadequate argument to dispense with NRB/NC set-up.
Multiple BVM Masks
We don't have these readily available in any ED or ICU I've worked in. We have neonate, peds, and adult. Our masks also are not inflatable.
PEEP is good, Mapleson may or may not be a good way to provide this for the reasons I've mentioned in the wee, but a BVM with a PEEP valve or a vent are at least as good.
Mapleson may provide this better than BVM, but not as well as a NC, which should be on during any intubation.
No advantage of Mapleson
Maybe this matters, as soon as you put on the PEEP, I can't imagine this difference persisting
Room Air Entrainment
Release your seal for even one breath and you have blown denitrogenation. Always, always use a strapped system if possible=NRB/NC, NIV mask, or BVM mask with OR straps.
This is the real area in which Nick and I differ. Nick makes the point that a good seal in preox guarantees a good seal in reox–this may be true, but it is unimportant. What I care about is does a bad, one-handed seal in preox mean I won't be able to reox with the BVM–this is entirely untrue. If I did to an awake patient what I will do to them when asleep and desaturating, they would, quite rightfully, punch me in the face.
Anesthesiologists should use Mapleson B/C; ED/ICU should only use BVM +/- PEEP Valve with two hands and oral airway and a rocking triple maneuver (that no pt should experience if they are conscious) otherwise they should be NIV mask with straps or (BVM mask with straps).
This is the same reason I tell my residents to just train with Macintosh blades.
Primary and secondary leaks are the main thrust of Nick's love for the old-timey circuits. But all of us have appreciated this easily by squeezing the bag-valve-mask: Easy-squeezy or Hard Squeezy
ETCO2 with a monitor you can see
Is he holding or squeezing?
I can feel compliance with a BVM if I squeezed it, but I don't unless the pt needs it during reox. But are they squeezing the Mapleson? If they are, they may be doing damage. This study (Anesthesiology 2014;120:326) talks about the myths of Gentle Facemask Ventilation:
>15 cmH20 may be entraining gas into the stomach via the LES (in some patients, even 10 cmH20 may be a problem)
UES will withstand at least 20 cmH20 until NMB at which point again 15 seems to be the number (The latter is why we don't bag during apnea unless we have to)
Two hands ALWAYS on the mask
Recently, I spent 2 weeks intubating 10-15 patients per day. One hand mask skills got better and better–all for naught.
Train how you want to Fight
BVM with a PEEP valve solves equipment issues entirely
ventilator or oxylator
Lower possible Vt and restriction of Inspiratory Flow Time (Maybe a peds bag is the answer–thanks, Peter. Anaesthesia. 2011 Jul;66(7):563-7 and Resuscitation 1999;43(1):31) and Vt of 500 seems the way to go (Crit Care Med. 1998 Feb;26(2):364-8.)
or Use Ventilator or Use an Oxylator
Now on to the wee…
- EMCrit 278 – Labors of Trauma – Blunt Edition (Part 1) - July 24, 2020
- EMCrit 277 – COVID Pulmonary Physiology with Martin Tobin - July 9, 2020
- EMCrit 276 – The Rapid Code Status Conversation with Kei Ouchi - June 25, 2020