Preoperative airway ultrasound assessment in the sniffing position: a prospective observational study

Abstract Background: Clinical airway screening tests intend to predict difficult airways, but none have a high predictive value. Recent systematic reviews correlate ultrasound with difficult laryngoscopy. This study aimed primarily to correlate ultrasound measurements of anatomical upper airway structures in the sniffing position with difficult direct laryngoscopy. The secondary aim was to observe gender-based differences. Methods: This prospective, cross-sectional, single-center observational study included 209 patients requiring general anesthesia for elective surgery. Preoperatively, we performed six clinical airway assessments and three ultrasound measurements, which were the Distance from Skin to the Hyoid Bone (DSHB), to the Epiglottis (DSE), and to the anterior commissure of the vocal cords (DSAC) in a sniffing position. Benumof's criteria for the "best view at the first attempt" for direct laryngoscopy assessed the difficulty of laryngoscopy. Results: The distance from skin to the epiglottis was the best predictor of direct difficult laryngoscopy (defined as Cormack-Lehane grade > 2b) with a minimum thickness cut-off at 2.70 ± 0.19 cm (sensitivity 91.3%; specificity 96.9%). The skin to the hyoid bone distance cut-off was 1.41 ± 0.30 cm with moderate correlation (sensitivity 80.4%; specificity 60.1%). No correlation was found for the distance to the anterior commissure of the vocal cords. In women compared to men, the skin to the epiglottis distance was more sensitive (92.3% vs. 90.9%) and specific (98.8% vs. 95.2%). Conclusions: DSE in the sniffing position is the most reliable parameter for preoperative airway ultrasound assessment in the Caucasian population, with higher sensitivity and specificity in women, and might be considered as an independent predictor for direct difficult laryngoscopy.

Inducción inhalatoria y anestesia tópica de la vía aérea guiada por videolaringoscopio C-MAC pala d-Blade en un paciente con miastenia gravis y vía aérea difícil / Inhaled induction and topical anesthesia of the airway guided with C-MAC d-Blade videolangyscope in a myasthenia gravis patient and difñcult airway

Se describe el caso de un paciente, diagnosticado de miastenia gravis, con factores predicto-res de intubación y ventilación difícil, al que se practica cirugía de eventroplastia y resección intestinal de urgencia, que fue intubado dormido, sin relajación neuromuscular, de forma exitosa con un videolaringoscopio C-MAC y pala específica para intubación difícil (d-Blade), tras inducción inhalatoria y anestesia tópica de la vía aérea. Destacamos la utilidad clínica de la videolaringoscopia en pacientes con predictores positivos para intubación difícil, la aplicabilidad del sevoflurano para el mantenimiento de la ventilación espontánea en un paciente dormido, así como el empleo de sugammadex para revertir el uso de relajantes neuromusculares en un paciente miasténico.

This is a case of a patient diagnosed with myasthenia gravis and clinical predictors of difficult intubation and ventilation undergoing emergency surgery for eventroplasty and bowel resection. The patient was successfully intubated asleep, with no neuromuscular relaxation, using a C-MAC video laryngoscope and difficult intubation d-Blade, following inhaled induction and topical anesthesia of the airway. We do want to stress the clinical value of video laryngoscopy in patients with positive predictors of difficult intubation, the applicability of Sevoflurane for the maintenance of spontaneous ventilation in a patient asleep, as well as the use of Sugammadex for reversal of neuromuscular block in a myasthenia patient.