Written by Jonathan Brewer
Upper airway ultrasound (UA-US) may eventually help us predict if a patient will have a difficult laryngoscopy. However, this is not ready for ED use, and more studies are needed.
Why does this matter?
Difficult tracheal ventilation comprises approximately 5-8% of airways in the emergency department, and knowing how to manage these is critical for the emergency provider. Currently, many utilize anatomical prediction models such as the Mallampati score or upper lip bite test. However, these are not perfect and being able to accurately and consistently predict if a patient will have a “difficult airway” would benefits patients.
The power of POCUS
This was a meta-analysis of fifteen studies that included adults who required tracheal intubation for elective surgery under general anesthesia without clear anatomical abnormalities that would suggest difficult laryngoscopy.
Each study included in this meta-analysis underwent preoperative UA-US with a variety of scans, such as distance from skin to epiglottis (DSE), distance from skin to hyoid bone (DSHB), and distance from skin to vocal cords (DSVC). Patients with difficult DL had higher DSE, DSVC, and DSHB values than patients with easy DL, with a mean difference between easy and difficult of 0.38 cm, 0.18 cm, and 0.23 cm, respectively. Sensitivity for predicting difficult laryngoscopy for these measures ranged from 71-82%, and specificity from 71-79%.
DSE appears to have the most promise, but largely only as a rule-out test in the case of a negative result (NPV 95-98% vs PPV 30-49%). We also have to consider that these studies were conducted in a controlled, operative setting with elective surgeries and not in the emergent environment that we are used to. Additionally, they lacked standardization of the ultrasound assessment (i.e. head positioning), making them subject to heterogeneity. And while the VL vs DL debate is still ongoing, these studies only utilized DL, so keep that in mind. While POCUS is promising, more data will be needed before a conclusive statement is made. I’ll be watching for this closely though!
Have you seen The NNT’s summary of difficult airway predictors?
Airway Ultrasound as Predictor of Difficult Direct Laryngoscopy: A Systematic Review and Meta-analysis. Anesth Analg. 2022 Apr 1;134(4):740-750. doi: 10.1213/ANE.0000000000005839.