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.

Ecografía de vía aérea: en busca de la membrana cricotiroidea / Airway ultrasound: in search of the cricothyoid membrane

Resumen: La ecografía forma parte activa de las herramientas clínicas que tenemos en nuestro arsenal para la valoración de pacientes, y en el manejo de la vía aérea puede permitirnos localizar y marcar la membrana cricotiroidea previo al manejo de un paciente con posible vía aérea difícil (VAD). En manos adiestradas permite identificar la anatomía para poder realizar una cricotiroidotomía con rapidez y precisión en tan sólo 24.3 segundos. En este artículo se muestra una sistemática visual y de rápida localización ecográfica de la membrana cricotiroidea con tiempo estimado inferior a un minuto. Para la exploración se debe usar una sonda lineal de alta frecuencia (5-14 MHz), ya que es probablemente la más adecuada para evaluar estructuras superficiales (dentro de 0-5 cm por debajo de la superficie de la piel). La colocación del operador y del ecógrafo van a depender de la posición del paciente, así en pacientes sentados el operador se coloca detrás de éste y el ecógrafo enfrente de ambos, y en pacientes en decúbito supino el operador se coloca a la cabecera del paciente y el ecógrafo a nivel del codo derecho del mismo.

Abstract: Ultrasonography is an active part of the clinical tools that we have in our arsenal for the evaluation of patients, and in the management of the airway, it can allow us to locate and mark the cricothyroid membrane prior to the management of a patient with a possible Difficult Airway. In trained hands allows the anatomy to be identified so that a cricothyroidotomy can be performed quickly and accurately in just 24.3 seconds. In this article, we show a rapid and visual systematic ultrasound localization of the cricothyroid membrane with an estimated time less than one minute. A linear high-frequency probe (5-14 MHz) should be used for exploration, as it is probably the most suitable for evaluating surface structures (within 0-5 cm below the skin surface). The positioning of the operator and the ultrasound scanner will depend on the patient's position, so in seated patients the operator is placed behind him and the ultrasound scanner in front of both, and in patients in a supine position, the operator is placed at the bedside of the patient and the ultrasound at the level of the right elbow.