Difficult Mask Ventilation
Last updated 15th Jan 2018 - Tom Heaton
Mask ventilation is a core anaesthetic skill.
In particular, it is a fallback skill to allow oxygenation and ventilation of the patient when other methods have failed.
Difficult mask ventilation is less well researched than difficult intubation, perhaps because of the difficulty in clearly defining it.
In particular, it is a fallback skill to allow oxygenation and ventilation of the patient when other methods have failed.
Difficult mask ventilation is less well researched than difficult intubation, perhaps because of the difficulty in clearly defining it.
Definition
The American Society of Anaesthesiology (ASA) define it as:
It is not possible for the anaesthetist to provide adequate ventilation due to one or more of the following problems:
There are a number of signs that the ASA list which may indicate this:
Han et al described a grading system to allow clear communication about the level of difficulty.
Grade 0 - Not attempted
Grade 1 - Ventilated by mask
Grade 2 - Ventilated by mask with adjunct
Grade 3 - Difficult mask ventilation (2 person, unstable, inadequate)
Grade 4 - Unable to mask ventilate
It is not possible for the anaesthetist to provide adequate ventilation due to one or more of the following problems:
- inadequate mask seal,
- excessive gas leak,
- or excessive resistance to the ingress or egress of gas.
There are a number of signs that the ASA list which may indicate this:
- Absent/inadequate chest movement
- Absent/inadequate breath sounds
- Absent/inadequate spirometric measures of gas flow
- Absent/inadequate CO2 measurement
- Auscultatory signs of severe obstruction
- Dropping oxygen saturations/cyanosis
- Gastric air entry/distension
- Haemodynamic changes
Han et al described a grading system to allow clear communication about the level of difficulty.
Grade 0 - Not attempted
Grade 1 - Ventilated by mask
Grade 2 - Ventilated by mask with adjunct
Grade 3 - Difficult mask ventilation (2 person, unstable, inadequate)
Grade 4 - Unable to mask ventilate
Epidemiology
Difficult to have precise values due to the challenging definition.
Incidence of difficult MV is probably 1.4%
Impossible MV has an incidence of around 0.15%
Incidence of difficult MV is probably 1.4%
Impossible MV has an incidence of around 0.15%
Risk Factors
Anaesthetic factors:
Patient Factors
Often the biggest contributing factor and there can be many:
- Inadequate depth of anaesthesia
- Inadequate (or no) muscle relaxation
- Improperly sized equipment (mask, adjuncts)
- Inexperienced provider
Patient Factors
Often the biggest contributing factor and there can be many:
- Obesity (BMI as low as 26 may increase risk)
- Male
- High neck circumference (>40cm)
- Increasing age
- Beard
- Edentulous
- Mallampati grade 3 or 4
- Mandibular protrusion
- Laryngospasm
- Bronchospasm
- Tonsillar hypertrophy
- Epiglottis
- Large tongue
- Airway oedema
- Airway tumours
- Neck radiotherapy
- Foreign body
- Pneumothorax
Anaesthetic Implications
Assessment
Assessment for difficult MV should be a part of every airway assessment.
Reviewing previous anaesthetic charts can provide very useful information on the ease of MV.
Some mnemonics may help assessment
MMMMASK
OBESE
The consideration of these risk factors should allow formulation of an appropriate airway management plan.
If there are adverse features for both MV and intubation, then awake fibre optic intubation may be the most appropriate airway management option.
If intubation is likely to be easy, then a rapid sequence induction of anaesthesia may be considered.
Management
Preparation is important in predicted difficult MV.
The principles will be to:
Preparation to reduce risk factors can include:
Increasing safety factors can include:
Unanticipated difficulty is challenging because of the time critical nature.
The difficult airway society has useful guidance on the management of can’t intubate, can’t oxygenate scenarios (CICO).
Key steps will include:
There has been some debate about the role of muscle relaxants in difficult MV.
Whilst it may reduce the resistance to flow provided by certain muscle tone (most importantly laryngospasm) there are worries that the loss of airway tone could make it worse.
The NAP4 by the RCOA recommended that muscle relaxants should be given in cases of difficulty prior to surgical airway rescue, to see if it provides benefit
If these interventions have been unsuccessful, then a situation of impossible MV is likely.
Help is needed, and planning must begin for the next steps of management.
Options will include:
Assessment for difficult MV should be a part of every airway assessment.
Reviewing previous anaesthetic charts can provide very useful information on the ease of MV.
Some mnemonics may help assessment
MMMMASK
- Male
- Mask seal affected by beard or edentulous
- Mallampati 3 or 4
- Mandibular protrusion
- Age
- Snoring/OSA
- Kg i.e. weight
OBESE
- Obesity (BMI >26)
- Beard
- Edentulous
- Snoring
- Elderly (>55)
The consideration of these risk factors should allow formulation of an appropriate airway management plan.
If there are adverse features for both MV and intubation, then awake fibre optic intubation may be the most appropriate airway management option.
If intubation is likely to be easy, then a rapid sequence induction of anaesthesia may be considered.
Management
Preparation is important in predicted difficult MV.
The principles will be to:
- Remove/reduce modifiable risk factors
- Increase Safety factors
Preparation to reduce risk factors can include:
- Shaving beard
- Keeping dentures in
- Weight loss
Increasing safety factors can include:
- Clearly planned and articulated airway management plan
- Optimal preoxygenation
- Ramped position
- Attainment of adequate expired O2 concentration (>80%)
- Apnoeic oxygenation
Unanticipated difficulty is challenging because of the time critical nature.
The difficult airway society has useful guidance on the management of can’t intubate, can’t oxygenate scenarios (CICO).
Key steps will include:
- Optimising positioning
- Considering airway adjuncts
- Ensuring adequate depth of anaesthesia
- Reduce/remove any cricoid pressure
- Considering muscle relaxants if not given
- Multiple person mask technique
There has been some debate about the role of muscle relaxants in difficult MV.
Whilst it may reduce the resistance to flow provided by certain muscle tone (most importantly laryngospasm) there are worries that the loss of airway tone could make it worse.
The NAP4 by the RCOA recommended that muscle relaxants should be given in cases of difficulty prior to surgical airway rescue, to see if it provides benefit
If these interventions have been unsuccessful, then a situation of impossible MV is likely.
Help is needed, and planning must begin for the next steps of management.
Options will include:
- Waking the patient up (not always possible)
- Intubation
- Ventilation via a supraglottic airway
- Surgical airway (rescue technique)
Complications
- Hypoxic insult
- Hypoxic brain injury
- Myocardial ischaemia
- Hypoxic brain injury
- Airway trauma
- Eye trauma
- Gastric insufflation
Links & References
- Holland, J. Donaldson, W. Difficult mask ventilation. Anaesthesia tutorial of the week. 2015. https://www.aagbi.org/sites/default/files/321%20Difficult%20mask%20ventilation.pdf
- Difficult airway society. https://www.das.uk.com/guidelines
- 4th National Audit Project (NAP4). Royal College of Anaesthetists. 2011. https://www.rcoa.ac.uk/nap4
