Measuring mask ventilation: capnography first, effort second

What the paper says

Difficult facemask ventilation has never had a robust definition. The Han scale grades it by the adjuncts and operators needed, but it is descriptive and has not been tested against an outcome.⁶ Wünsch and colleagues from Hamburg set out to build an objective, data-driven classification, using the same approach as their VIDIAC score for videolaryngoscopy.¹

The study design:

• 400 adults having elective ear, nose and throat or maxillofacial surgery were enrolled at a single centre.
• After induction, facemask ventilation was delivered by the ventilator in pressure-controlled mode (15 cmH₂O, rate 10, no PEEP), before any neuromuscular blocking drug was given.
• An independent observer recorded eight possible indicators.
• The primary outcome was a difficult facemask ventilation alert entered in the health record by the airway operator. This was based on clinical judgement rather than predefined criteria.
• Difficult facemask ventilation occurred in 43 patients (10.8%).

Five indicators were selected:

• a two-handed grip
• an oral airway
• jaw thrust
• tidal volume of 2 ml/kg or less
• a fall in SpO₂ of 10% or more

Each scores one point. A score of 2 flags "impaired" facemask ventilation (sensitivity 0.95, specificity 0.86). A score of 3 flags "difficult" facemask ventilation (sensitivity 0.91, specificity 0.90). The AUROC was 0.94 for the score and 0.96 for the full model. A senior consultant taking over, conversion to manual ventilation and leak fraction were not selected. Even large leaks were often compatible with adequate tidal volumes. Capnography was not among the indicators tested. End-tidal CO₂ was used only to define impossible facemask ventilation.

The correspondence

Nielsen and Lim, from Concord in Sydney, are the authors of the capnography scale.^2,4 They make four points:

• Three of MASCAN's five points are routine techniques, not difficulty. An anaesthetist who routinely uses two hands and jaw thrust will score "impaired" in every patient, and "difficult" if they add an oral airway, even when ventilation is easy and effective.
• The score weights process over outcome.
• Desaturation is a late and non-specific endpoint after preoxygenation.
• MASCAN omits capnography, which recent guidelines and the ATOM core outcome set endorse as the endpoint for facemask ventilation.^7,8

Petzoldt and colleagues reply firmly:³

• The capnography scale has never been prospectively studied.
• Its grades rely on eyeballing idealised waveforms.
• End-tidal CO₂ is confounded by leak, cardiac output, lung function and the mode of ventilation.
• Grades C and D reduce to an arbitrary threshold of 10 mmHg.
• In their study, the adjuncts were rescue manoeuvres, not routine, and they are "unaware of any established prophylactic concepts of this kind".

They do concede that capnography "may be a promising addition" to composite scores, and they call for a move from "eminence-based proposals" to evidence-based classifications.

What is valuable

• The exchange puts the definition of difficult facemask ventilation firmly on the agenda, and both sides now agree that capnography belongs in it.
• MASCAN is a serious, prospective attempt to replace a descriptive grade with recordable findings. Its inclusion of tidal volume confirms that outcome, not effort, is what matters.
• The finding that leak alone did not predict difficulty is useful. A leaking mask can still ventilate, and only an outcome measure will show it.
• Nielsen and Lim's visual scale remains the simplest outcome-based definition we have. It works at any bedside with a capnograph, in theatre, the emergency department, intensive care or retrieval, whether ventilation is by hand or by machine.

What to bear in mind

• The validation is internal only. MASCAN comes from a single centre, with 43 events and no external validation yet. The high AUROC is likely to fall in other settings. The group's own recent systematic review of videolaryngoscopy classifications makes the same point about other tools.
• The "objective" score is anchored to a subjective outcome. It predicts a clinician's free decision to issue an alert. Three of its five predictors are the very manoeuvres that would prompt that decision.
• It was measured before neuromuscular blockade, without PEEP and at a fixed pressure. Ventilation often improves after a relaxant, and many anaesthetists ventilate by hand. Ventilator-measured tidal volume is not available during manual ventilation. The authors acknowledge these limitations.
• The confounding argument applies at least as strongly to MASCAN. Cardiac output and lung function affect SpO₂ just as they affect end-tidal CO₂, and desaturation comes much later.
• The capnography scale needs prospective study. Its 10 mmHg threshold was chosen pragmatically. That is a reason to study it, not to set it aside.

My commentary

This debate is close to my heart. In 2021, Craig Lyons and I wrote a BJA Education review of facemask ventilation.⁵ We argued that capnography should be used whenever ventilation takes place, to provide an objective assessment of whether it is working. We also argued that the definition of difficult and impossible facemask ventilation should rest on the objective evidence of the capnograph, and should include whether additional personnel, adjuncts and neuromuscular blocking drugs were used. Impossible facemask ventilation, in our view, is the absence of lung movement and of any end-tidal CO₂ trace despite optimised efforts. We recommended the Lim and Nielsen scale for exactly that reason. I still hold that view, and this exchange strengthens it.

Capnography answers the question that matters most: did gas reach the alveoli and come back? Chest movement, bag feel and mask fogging are reassuring but unreliable. Tidal volume shows that gas moved, but not where it went. Saturation is a late signal after good preoxygenation, and by the time it falls by 10% the problem has been there for some time. A sustained CO₂ trace is real-time, specific evidence of alveolar ventilation, breath by breath. That is why capnography is a standard monitor for every general anaesthetic. Australasian airway teaching has also long placed oxygenation, rather than any particular device or technique, at the centre of airway safety. The Vortex, for example, treats a sustained capnograph trace as the marker of successful alveolar oxygen delivery.⁹

The criticism that the Concord scale is subjective "eyeballing" deserves a direct answer. Reading a capnograph is not a fringe skill. It is what every anaesthetist does at every induction, every intubation and every emergency. The question the scale asks is simple. Is there a plateau? Is there a trace? Is there any CO₂ at all? Recognising a trace, its shape and its absence is among the most reliable judgements we make, and the four grades map directly onto the decisions we face. A visual scale that every clinician can apply in seconds, at any bedside, is a strength, not a weakness. The 10 mmHg threshold may be pragmatic, but so is every threshold until it is tested. The scale was endorsed by the Difficult Airway Society and the ATOM consensus because it measures the right thing.^7,8 That is not eminence; it is physiology.

It is also worth being clear about what the Concord scale actually is. It is not simply a reading below 10 mmHg. It grades the capnograph from A to D, and it records the optimisation that produced that trace: one or two hands, an oropharyngeal or nasopharyngeal airway, and whether a neuromuscular blocking drug had been given.⁴ In other words, it already combines outcome with effort, with the outcome first. That is exactly the composite the Hamburg group now says future research should explore.

On the question of routine technique, Nielsen and Lim again have the better of the argument. Jaw thrust is part of almost every facemask ventilation I see, not a rescue manoeuvre. Many anaesthetists also use a two-handed grip or an oropharyngeal airway as part of a first, optimised attempt. Our own review noted that the two-handed grip is generally preferred because it improves both the mask seal and airway patency, and that some clinicians use oral airways universally. Facemask ventilation with two hands and an oral airway can be entirely easy if it produces a good airway that any competent colleague could reliably reproduce. Once MASCAN leaves the study that produced it, a reader cannot tell whether those manoeuvres were rescue or routine. A score that counts effort as difficulty will label easy patients as difficult, and a false alert is not harmless. It erodes trust in the alerts that matter.

Effort still matters, but it belongs second. A grade A trace achieved with two operators, an oral airway and full neuromuscular blockade tells the next anaesthetist something different from a grade A trace with one hand. That is the same point I made about videolaryngoscopy in a recent commentary. Classify consistently, record the outcome objectively, record what it took, and describe it properly when it fails. For facemask ventilation, that means:

• the capnograph grade as the primary outcome, with tidal volume where it is available
• the optimisation used, and whether it was planned or a rescue
• whether a neuromuscular blocking drug had been given
• an honest appraisal of whether it was easy, moderate or difficult, judged by whether others could reliably reproduce it
• a short description whenever the best attempt produced a grade C or D trace

Wünsch and colleagues have produced the first data-driven score for facemask ventilation, and they deserve credit for it. But Nielsen and Lim identified the right endpoint a decade ago. The next study should build on it: the capnograph grade as the outcome, the MASCAN manoeuvres as the record of effort, tested prospectively across centres and in manual as well as mechanical ventilation. Both groups now seem to agree that capnography belongs in the answer. I would go further. It should be where the answer starts.

References

1. Wünsch VA, Bommes H, Piltan M, et al. Prospective development and validation of an objective classification for difficult facemask ventilation: the MASCAN score. Anaesthesia 2026; 81: 1349–57. doi:10.1111/anae.70262
2. Nielsen JR, Lim K-S. Measuring mask ventilation: capnography is better. Anaesthesia 2026. doi:10.1111/anae.70400
3. Petzoldt M, Schäfersküpper V, Wünsch VA. Classifying mask ventilation: current evidence supports the MASCAN score, not capnography. Anaesthesia 2026. doi:10.1111/anae.70402
4. Lim KS, Nielsen JR. Objective description of mask ventilation. Br J Anaesth 2016; 117: 828–9. doi:10.1093/bja/aew368
5. Bradley WPL, Lyons C. Facemask ventilation. BJA Educ 2022; 22: 5–11. doi:10.1016/j.bjae.2021.09.002
6. Han R, Tremper KK, Kheterpal S, O'Reilly M. Grading scale for mask ventilation. Anesthesiology 2004; 101: 267.
7. Ahmad I, El-Boghdadly K, Iliff H, et al. Difficult Airway Society 2025 guidelines for management of unanticipated difficult tracheal intubation in adults. Br J Anaesth 2026; 136: 283–307. doi:10.1016/j.bja.2025.10.006
8. Hansel J, Fuchs A, Cornwell B, et al. A core outcome set for airway management research. Anaesthesia 2026; 81: 373–82. doi:10.1111/anae.70026
9. Chrimes N. The Vortex approach to airway management. vortexapproach.org

Related commentary: Classifying videolaryngoscopy: standardise it, but describe the failure

This commentary is my own professional opinion, written for anaesthetists and other professional readers. It does not represent Alfred Health, ANZCA or any other organisation with which I am associated, and it is not individual medical advice. The original articles are the work of their authors and are linked above.