- 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
| Download (.pdf) | Print
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 |
- 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
| Download (.pdf) | Print
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 |
Related posts:
Full access? Get Clinical Tree
