Abstract
Objective
This study aimed to review and appraise the evidence regarding airway ultrasound assessment
in predicting difficult laryngoscopy in adult patients.
Design
A systematic review of the literature was conducted according to the Cochrane collaboration
guidelines and the recommendations for the systematic review and meta-analysis of
diagnostic studies. Observational studies that evaluated the diagnostic performance
of airway ultrasound for the prediction of difficult laryngoscopy were included for
consideration.
Setting
Literature searches were performed in 4 databases (PubMed (Medline), Embase, Clinical
Trials, and Google Scholar) to identify all observational studies using any ultrasound
technique to assess difficult laryngoscopy. The search terms included “sonography,”
“ultrasound,” “airway,” “difficult airway,” “difficult laryngoscopy,” “Cormack,” “risk
factors,” “ultrasound at the point of care,” “difficult ventilation,” “difficult intubation”
and others, combined with sensitive filters. The search was done for studies performed
in the last 20 years in English or Spanish.
Participants
Adult patients older than 18 years old under general anesthesia for an elective procedure.
Evident anatomical airway abnormalities, obstetric populations, those using an alternative
imaging method besides ultrasound, and animal studies were excluded.
Interventions
Pre-operative bedside ultrasound measuring distances and ratios from the skin to different
reference points, such as the ratio of the hyomental distance in a neutral position
and in extension (HMDR), the hyomental distance in a neutral position (HMDN), and
the skin-to-epiglottis distance (SED), the pre-epiglottic area, and tongue thickness
among others.
Measurements & Main Results
Twenty-four studies evaluated the prediction of a difficult laryngoscopy using airway
ultrasound. The diagnostic performance and the number of ultrasound parameters reported
in the studies were variable. Meta-analysis was performed for three measurements consistently
included in most studies. Skin-to-epiglottis distance (SED) and the hyomental distance
ratio (HMDR) presented a sensitivity of 75% and 61%, respectively, and a specificity
of 86% and 88%, respectively. The ratio of the pre-epiglottic distance to the epiglottic
distance at the midpoint of the vocal cords (Pre-E/E-VC) presented the best performance
for predicting a difficult laryngoscopy (sensitivity: 82%, specificity: 83%, diagnostic
odds ratio: 22.2).
Conclusion
With the currently available evidence, the three commonly utilized POCUS measures
used to identify difficult laryngoscopy (SED, HMDR, and Pre-E/E-VC) showed better
sensitivity and similar specificity to clinical measures. Future studies and more
data may change our confidence in these conclusions, given the wide variability of
measurements noted in studies.
Keywords
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