Wee – What the heck is a Mapleson B Circuit and Why You Probably Shouldn’t Care


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.

Mapleson Circuit
from anesthesia 2000

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.

Automatic Checking

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

Low resistance

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.

Troubleshooting Leaks

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

Hands free

BVM with a PEEP valve solves equipment issues entirely

ventilator or oxylator

Better BVMS

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…

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  1. says

    Scott your plan has worked! I don’t have time for my usual manifesto – but you’ll pay for it with a protracted verbal rant at smaac!

    As you know from our face-to-face discussions, our areas of agreement actually far outweigh our areas of disagreement. I will say this though. Whilst I agree 100% re 2 handed face mask technique (and the use of the “thumb grip” rather than the “classical grip”), I disagree that the benefits of the collapsible bag on the Mapleson are negated by using two hands.

    I also think that it’s worth delineating the issues with FMV into two categories:

    1. Problems with Seal
    2. Problems with Obstruction

    The additional “painful” measures you describe implementing post induction (head tilt, jaw thrust, oral airway, etc) are largely directed at relieving obstruction, they won’t change your ability to get a seal. I maintain that if you can’t get a seal pre-induction (in a cooperative patient) you are unlikely get one afterwards.

    I also could not agree more with the premise of “train how you fight”. Perhaps you should change some aspects of the way you fight though.

    See you on the Gold Coast.


    • says

      Hi Nick,

      Having reasonable familiarity with both self-inflating ventilators and the Mapleson circuit I certainly can appreciate the greater tactile and visual feedback you get with the latter that I (or the patient is) achieving adequate ventilation via the mask. But from a practical viewpoint how would you alter your strategy if you felt prior to induction that you were likely to enter a can’t ‘ventilate’ scenario. Would you more likely to ‘vortex’ to LMA rather than trying a mask seal if you had trouble intubating?

  2. Sean Marshall says

    Hey Scott,
    I debated a bit with Nic and Minh about this a while back, frankly I’m still somewhat on the fence. I found you kind of jumped all over the place in the wee, comparing Mapleson to BVM, NRB mask, NC and ventilators as it suited you. If you take nasal prongs and 2 hand mask seal as a given in both scenarios, the comparison between BVM and Mapleson is simpler:
    -Mapleson does PEEP like a vent, better than a PEEP valve. That’s why we use flow inflating bags in grunting, indrawing newborns, they just need a bit of PEEP.
    -The Mapleson will show you there’s a leak by becoming a complete pain in the ass. I can tell with a BVM too without the frustration.

    At the end of the day, you can do everything just as nicely by replacing your BVM with a Mapleson but since they are not commonly available for adults where either of us work, it becomes an academic argument. We just need to be proficient at the kit we have, it works just fine.

    • says

      Sean, I refuse to have to pick just BVM vs. NRB/NC for the simple reason that I don’t use just one. The debate Nick set up is use of mapleson B for everything vs. Rich’s and my strategy of NRB/NC unless shunt and then a PEEP-capable device. You’ve got to accept the bundle b/c that is how it is done on pts. Mapleson doesn’t do PEEP like a vent the BVM with a PEEP valve does (low-flow CPAP), in some ways the Mapleson does it better than a vent (high-flow CPAP). However, if the NC cannula is there, then all of the devices become high-flow CPAP.

      If you dichotomized the debate to no nasal cannula, no NRB/NC option, just straight up BVM/PEEP/No-NC vs. Mapleson B, then the latter device wins–it is a better stand-alone device, no argument here.

  3. Jane RT says

    Don’t bring one to a code either.
    1. I’ve already started preoxygenating before anesthesia gets arrives.
    2. The middle of a code is not the time to introduce new equipment to the team.

    I also want a peep valve on every single bm that I use you never know when that patient is going to need to peep.

  4. Erik says

    Hi Scott,
    You know I love your podcast and look forward to hearing it. I agree with most of what you say, except on airway issues where I often disagree considerably. Case in point: your friend is correct here. The Mapleson D set-up is vastly superior to BVM and there are only two reasons not to use it for initial airway management: you don’t have one or you don’t know how to use it. I suspect in the ED the issue is both, in which case one can use a BVM with PEEP valve, although it should be of the newer variety that allow for spontaneous ventilation and variable PEEP (not the static single PEEP levels). As far as this fascination with using nasal cannula and something else like non-rebreather….uhhh… ok, whatever.

    There seems to be this fascination outside the anesthesiology community with endotracheal intubation as the “goal” of airway management. The “goal” of airway management should be the maintenance of ventilation and oxygenation to keep the patient alive. Period. If it involves an ET tube so be it, but that should not be the goal. Mask ventilation, if done correctly, can be your best friend. If you can bag the patient you can keep him/her alive. Importantly, it buys time. Assuming you haven’t traumatized the airway (sometimes an issue in the ED 😉 ), you can bag the patient all day if you have to: call for help, get necessary airway equipment, sometimes alleviate the patient’s condition without having to instrument them. One-handed masking is admittedly a learned skill, but it is arguably a more important and easily transferable skill than endotracheal intubation. To bag a patient, all I need is a bag and an oxygen source.

    Now for the Mapleson bags – we use the Mapleson D so I can’t really comment on the Bs, but same idea: They allow the intimate ability to assess a patient’s respiratory status (not all patients need a tube- see above) and one can support their efforts as little or as much as they need. I constantly adjust the PEEP valve within the breath cycle to ensure that patients are moving air adequately and I know exactly how much gas is being exchanged. It’s very difficult to do this with a simple BVM. Unfortunately, it is a learned skill. I’ve seen folks who’ve been “involved” with airway management for 20 years who still can’t properly mask ventilate a patient; they push the mask onto the patient’s face rather than bring the face to the mask. So without proper technique I suppose a BVM is superior, because at least the bag inflates so something might be reaching the patient. Other options you suggested include BiPAP, which is ok, IF you know how much I and E they require. However, in a dynamic situation this may change from breath to breath. Nasal cannulae (and OG and NGs, etc) interfere with proper mask seal, get in the way, and don’t provide any benefit if proper mask ventilation is performed so I don’t use them. End thoughts: if I were king everyone would be trained extensively in mask ventilation instead of endotracheal intubation. I think patients would do better. However, I’m not and if one can’t properly use a Mapleson it makes sense to try other modalities. In the end it’s better to be really good at a sub-standard approach than to suck at an optimal approach.

  5. Somnath Chatterjee says

    Hi Scott,
    Being an Intensivist of anaesthetic background and having worked and trained in the UK, I enjoyed your podcast greatly.
    The Mapleson C and not B as suggested here is used extensively in UK in anaesthetic practice. The difference between the Mapleson C and Mapleson B is that the Mapleson C is devoid of the long tubing between the valve and the bag and therefore easier to handle than the Mapleson B.
    The big advantage with these is that you can see the bag move and therefore have a rough idea of the increasing tidal volume and rate. This is of great importance in the recovery period. Lot of British anaesthetists still swear by it.
    Agree with you that there is no great advantage of the Mapleson B (or Mapleson C) over the BVM (Love the idea of using a nasal cannula with the high flow oxygen. Just cannot see the tidal ventilation … can see the chest moving.

    • says

      fantastic comment. you will however see the BVM bag moving with spont resps, just as you do with the Mapleson–for both of them of course, this is reliant on a tight mask seal

  6. says

    Hi Nick,

    Having reasonable familiarity with both self-inflating ventilators and the Mapleson circuit I certainly can appreciate the greater tactile and visual feedback you get with the latter that I (or the patient is) achieving adequate ventilation via the mask. But from a practical viewpoint how would you alter your strategy if you felt prior to induction that you were likely to enter a can’t ‘ventilate’ scenario. Would you more likely to ‘vortex’ to LMA rather than trying a mask seal if you had trouble intubating?


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