Difficult Mask Ventilation

Introduction

• Mask ventilation is one of the most basic yet also most essential skills in airway management.
• It can provide initial ventilation before endotracheal intubation or the placement of an alternative airway device.
• Importantly, it serves as a rescue strategy when intubation is unsuccessful or unexpectedly difficult, thereby preventing hypoxemia, which is the leading cause of airway-related mortality.¹
• Effective mask ventilation is a key branch point in difficult airway management algorithms.
• The ASA defines DMV as inadequate ventilation due to a poor mask seal, excessive gas leak, or increased airflow resistance.²
• This definition is partly subjective, as perceptions of difficulty vary significantly with clinician experience and training.

Clinical Signs of Inadequate Ventilation

• Disclaimer: No single sign is completely reliable, as some are nonspecific, late, or misleading (e.g., gastric insufflation may occur even with effective ventilation), so clinicians must interpret findings in combination, especially in settings with limited monitoring.
• Waveform capnography should be checked before the induction of anesthesia.³
• Audible pulse oximetry tones should be enabled before induction of anesthesia.³
• Continuous, uninterrupted waveform capnography should be used throughout all phases of airway management.
• Early indicators: Absent or inadequate chest rise, inappropriate bag compliance when squeezing the reservoir bag (too easy with a leak/poor seal or unusually stiff with obstruction), lack of visible fogging in the mask (unreliable and environment dependent), and lack of exhaled CO2 return on capnography (when available)⁴
• Late indicators: falling oxygen saturation (delayed with preoxygenation), cyanosis, and hemodynamic changes (tachycardia, arrhythmias). These are delayed indicators of inadequate mask ventilation and should be avoided if at all possible.

Estimated Incidence

• The reported incidence of DMV differs depending on study design and patient population.
• A large retrospective review of 50,000 anesthetics found DMV in 2.2% of patients and impossible mask ventilation in 0.15%.⁵
• In contrast, a smaller prospective study in 90 obese patients reported DMV rates as high as 38.9%.⁶
• A recent meta-analysis of 20 observational studies involving over 335,000 patients found a pooled incidence of 6.1% in the general surgical population and 14.4% among patients with obesity.¹

Anticipation and Documentation

• Anticipating DMV is key to creating a safe airway plan, though unanticipated DMV remains common.
• Reviewing prior anesthetic records is a simple, reliable method to identify past difficulties.
• Standardized grading systems for mask ventilation improve consistency and communication among clinicians and may help to avoid unnecessary risk.

Anesthetic Factors Influencing Mask Ventilation

• Certain elements of general anesthesia can contribute to DMV.
  • High-dose opioids, inadequate anesthetic depth, and insufficient muscle relaxation may cause chest wall rigidity and reduced compliance.⁹
• Opioid-induced rigidity is not observed in patients with a tracheostomy, suggesting that resistance may stem from vocal cord closure, which improves after muscle relaxant administration.
• Muscle relaxants may facilitate mask ventilation by relieving rigidity and laryngospasm.
  • Clinicians should not delay administration of neuromuscular blockade to check facemask ventilation.³

Predictors of DMV

• Neck radiation, increased neck circumference, and obstructive sleep apnea are among the strongest independent predictors of DMV.¹
• Many factors approximately double the odds of DMV, but only a few (neck radiation, neck circumference, obstructive sleep apnea) increase the risk 3–5 fold.
• Risk is cumulative. Patients with ≥3 predictors may have DMV rates exceeding 30%.¹⁰
• Preoperative airway assessment should consider combinations of predictors rather than single factors, since risk is cumulative.

Management of DMV

• DMV management can be categorized as anticipated (allowing preparation) or unanticipated (requiring immediate corrective maneuvers).

Anticipated DMV

• DMV risk should be anticipated and minimized whenever possible.
• Mask seal should be optimized. Management of facial hair, keeping dentures in place until intubation, and selecting an appropriately sized mask can all improve ventilation.¹¹
• Proper positioning, such as the ramped position in obese patients, enhances both preoxygenation and ventilation efficiency.
• Airway adjuncts should be prepared in advance, with supraglottic devices and rescue equipment readily available.
• Continuous positive airway pressure may help maintain airway patency after induction and reduce the likelihood of collapse.
• Thorough preoxygenation is critical in high-risk patients, as it extends safe apnea time and provides a buffer for intervention.

Unanticipated DMV

• When DMV is encountered unexpectedly, corrective maneuvers should be initiated without delay, the difficulty should be clearly announced to the room, and help should be sought immediately.
• Initial steps include optimizing mask seal, inserting an oropharyngeal or nasopharyngeal airway, and adjusting head and neck positioning.
• Switching operators or employing a two-person mask ventilation technique may improve effectiveness.
• If difficulty persists, deepening anesthesia or giving a neuromuscular blocker can relieve laryngospasm or opioid-induced rigidity and facilitate ventilation.
• If ventilation remains inadequate, discontinuation of anesthetics and an attempt to awaken the patient should be considered, though this may not always be safe or feasible if hypoxemia is imminent.¹¹
• In cases of impossible mask ventilation, either tracheal intubation by direct laryngoscopy or placement of a supraglottic airway device is a reasonable next step; the choice depends on urgency and oxygen saturation.¹¹
• If oxygen desaturation continues despite these interventions, the situation has progressed to a Can’t Intubate, Can’t Oxygenate (CICO) emergency.
  CICO requires immediate front-of-neck access with either a cannula cricothyrotomy or surgical cricothyrotomy; 11 a complete discussion of this topic is beyond the scope of this summary. The authors recommend reviewing the latest Difficult Airway Society Guidelines for the management of unanticipated difficult intubation in adults. Link

DMV in the Broader Airway Algorithm

• The ASA Task Force highlights that if difficult intubation is anticipated in combination with DMV, aspiration risk, or poor tolerance of apnea, awake intubation should be strongly considered.²
• Thus, accurate recognition of potential DMV not only guides immediate corrective maneuvers but also influences whether an awake versus postinduction pathway is chosen.