Predicting Difficult Mask Ventilation and Intubation

Predicting Difficult and Impossible Mask Ventilation

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Overall incidence of difficult mask ventilation (DMV) is 1.4% with impossible mask ventilation (IMV) 0.15%
Obesity, snoring, and lack of teeth can probably be overcome with simple airway maneuvers, which is why they are not risk factors for IMV:
- Lack of teeth actually makes DL and intubation easier
Neck circumference (> 50 or 60 cm at the level of the cricoid cartilage) is the most predictive factor of IMV
Patients with three or more risk factors have a much higher likelihood of being IMV (odds ratio 8.9)
Most patients (75%) who are IMV will be easy to intubate

Risk Factors Associated with Difficult versus Impossible Mask Ventilation

Difficult mask ventilation	Impossible mask ventilation
Neck circumference	Neck circumference
Male sex	Male sex
Sleep apnea	Sleep apnea
Mallampati class 3 or 4	Mallampati class 3 or 4
Beard	Beard
BMI >26
Snoring
Lack of teeth

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Overall incidence of difficult intubation (DI) is 5.2% (obstetric: 3.1%, obese: 15.8%) with failed tracheal intubation 0.15%
A combination of tests tends to be a better predictor of DI than individual tests

Reliability of Different Characteristics Associated with Difficult Intubation

Characteristics associated with difficult intubation	Definition	Sensitivity (%)	Specificity (%)	Positive predictive value or positive likelihood (PL)
Interincisor gap	<4 cm	30	97	28
Range of neck extension	Head extension ≤80°	10	93	18
Retrognathia	>90°	7	99	20
Thyromental distance	<6.5 cm	48	79	9.4 (<4 cm)
Mentohyoid distance	<4.5 cm	16	91	6
Sternomental distance	<12.5 cm	44	87	11
Neck circumference	>43 cm	92	84	37
Mallampati classification	Grade 3 or 4 view	49	86	3 (PL)
BMI	>30	83	50	14
Indirect laryngoscopy	Grade 3 or 4 view	69	98	31
Upper lip bite test	Class 3 (lower incisors cannot bite upper lip)	8	97	8