Airway Ultrasound as Predictor of Difficult Direct Laryngoscopy

Mismanaging the airway can cause a lot of harm and death, and an unanticipated difficult intubation could be fatal during anaesthesia. In clinical practise, several bedside screening tests are used to identify patients at risk of having a difficult airway. Despite the fact that their accuracy and utility have been well established in the literature and in clinical practise, a small proportion of patients classified as having an easy airway may present an unexpected difficulty. Predicting a "difficult airway" in all patients is not a simple process. 1–7: Numerous structures and functional units contribute to the pathogenesis of a difficult airway, which is a dynamic process that is highly dependent on the operator's experience. For many years, ultrasounds have been used in conjunction with other diagnostic tools to predict difficulty with airway management, both qualitatively and quantitatively. Recently published systematic review and meta-analysis tried to determine whether preoperative upper airway ultrasound (UA-US) can accurately predict difficult airway in adult patients undergoing elective surgery under general anaesthesia who do not have obvious anatomic evidence of a difficult airway on standard clinical examination..

From their beginning through December 2020, the authors searched Medline, Scopus, and Web of Science databases. Adults who needed tracheal intubation for elective surgery under general anaesthesia without obvious anatomic anomalies indicating difficult laryngoscopy were included in the study sample. For the quantitative analysis of summary receiver operating characteristic data, fifteen studies were analysed (SROC). Sensitivity values for the distance between the skin and the epiglottis (DSE), the distance between the skin and the hyoid bone (DSHB), and the distance between the skin and the vocal cords (DSVC) were 0.82 (0.74–0.87), 0.71 (0.58–0.82), and 0.75 (0.62–0.84, respectively. DSE, DSHB, and DSVC had a specificity of 0.79 (0.70–0.87), 0.71 (0.57–0.82), and 0.72 (0.45–0.89), respectively. The area under the curve (AUC) values for DSE, DSHB, DSVC, and the ratio of the depth of the pre-epiglottic space to the distance between the epiglottis and the vocal cords (Pre-E/E-VC) were 0.87 (0.84–0.90), 0.77 (0.73–0.81), 0.78 (0.74–0.81), and 0.71 (0.67–0.75, respectively. Patients undergoing difficult direct laryngoscopy have significantly higher DSE, DSVC, and DSHB values than patients undergoing easy direct laryngoscopy, with a mean difference of 0.38 cm (95 percent confidence interval [CI], 0.17–0.58 cm; P =.0004), 0.18 cm (95 percent CI, 0.01–0.35 cm; P =.04), and 0.23 cm (95 percent CI, 0.08–0.39 cm; P =.00.

This is the first systematic review and meta-analysis of diagnostic test accuracy aimed at elucidating the US's capacity to predict difficult laryngoscopy in this clinical context and elucidating the tool's potential relevance in clinical practise. Among the numerous UA-US index tests examined in the literature, we demonstrated that DSE had an AUC-SROC of 0.87 (95 percent CI, 0.84–0.90) for predicting difficult laryngoscopy in this cohort. Despite its high sensitivity and specificity, DSE is probably most effective in identifying patients who will not present with a difficult airway in the absence of a positive result (when the test is negative, the chance of a simple laryngoscopy is around 95%–97%). DSE was determined by inserting a linear probe into the transverse plane and determining the thickness of the pre-epiglottic gap at the midline. We feel that DSE >2 to 2.5 cm may play a role in determining possible issues in the absence of other frequently used tests. While a difficult airway may be clearly detected when many conventional tests are positive or when obvious anatomical abnormalities are present, a "grey zone" of doubt may persist when just a few clinical indicators of difficulty are seen. DSE may assist to properly rule out a difficult airway in this context if the result is negative or may suggest a smart strategy if the result is positive.

This research reveals that airway ultrasound index tests vary considerably between individuals who have simple vs difficult direct laryngoscopy, and the DSE is the most investigated index test for predicting difficult direct laryngoscopy in the literature. However, no clear conclusion is yet feasible. Additional research is required to improve the uniformity of ultrasound assessment in order to eliminate all potential causes of variation.

Reference –

Carsetti, Andrea MD*,†; Sorbello, Massimiliano MD‡; Adrario, Erica MD*,†; Donati, Abele MD, PhD*,†; Falcetta, Stefano MD† Airway Ultrasound as Predictor of Difficult Direct Laryngoscopy: A Systematic Review and Meta-analysis, Anesthesia & Analgesia: April 2022 - Volume 134 - Issue 4 - p 740-750

doi: 10.1213/ANE.0000000000005839