Evaluation of ultrasound guided airway parameters for placement of ProSeal LMA- An observational study

Airway management is a core component of anaesthesia care. In any procedure that requires general anaesthesia, anaesthesiologists need to control the patient‟s airway in order to maintain adequate ventilation and oxygenation. This can be a high-risk task and can lead to patient morbidity and mortality, due to inadequate/impossible ventilation, and/or intubation. Therefore, it is essential to optimize methods to anticipate a difficult airway and ensure the necessary means to intervene.

As per American Society of Anaesthesiologists (ASA) 2022 guidelines, a difficult airway includes the clinical situation in which anticipated or unanticipated difficulty or failure is seen by an experienced anaesthesiologist during facemask ventilation, laryngoscopy, ventilation using a supraglottic airway, tracheal intubation, extubation or invasive airway. Difficult supraglottic airway ventilation is defined as when it is not possible to provide adequate ventilation because of difficult supraglottic airway placement, supraglottic airway placement requiring multiple attempts, inadequate supraglottic airway seal, excessive gas leak, or excessive resistance to the ingress or egress of gas. Inability to anticipate difficult airway and thereby poor planning for airway management remains the primary cause of airway related complications for anaesthesiologists. Difficult airway is a potential risk in few patients which is associated with serious morbidity and mortality and poses a challenge for anaesthesiologists. There have been many techniques devised to assess difficult airways like modified mallampati test, thyromental distance, hyomental distance, inter incisor distance, neck movements and neck circumference. All these methods are subjective to the observer and require mandatory actions to be performed by the patients which decrease its application especially in unconscious patients. Also they have less sensitivity and specificity with a limited predictive value. Despite using all the available clinical parameters of airway assessment, in many cases a difficult airway may be undiagnosed preoperatively and we may land up in a situation of can’t intubate, can’t ventilate during intubation and anaesthesia.

During the last few years ultrasound has been widely used in the operating room for ultrasound-guided procedures such as nerve block or central venous access. Ultrasound provides quick, relatively easy, and accurate information, with diagnostic and therapeutic relevance. For some considerable time ultrasound has not been taken into consideration as a tool for the evaluation of the airway or as a predictor of difficult laryngoscopy. Pre-operative ultrasound measurement of the anterior neck soft-tissue thickness at different levels, combined with the commonly used screening tests and risk factor assessment for difficult laryngoscopy might improve the ability to predict difficult laryngoscopy.

The ASA has included ultrasound in pre-operative airway assessment in its guidelines for management of difficult airway 2022 and parameters included were skin-to-hyoid distance, tongue volume, and distance from the skin to the epiglottis. So, Ultrasonography is emerging as a new technique for difficult airway assessment as it is simple, convenient and non- invasive, has no risk of radiation exposure, and because it is portable, it can be used to assess airway bedside along with clinical parameters. Some studies are available to assess the usefulness of pre-operatively measured ultrasonographic airway parameters to predict difficult laryngoscopy and difficult tracheal intubation. A metanalysis had concluded that hyomental distance in neutral head position was the most consistent pre-operative ultrasound measured airway parameter to predict difficult laryngoscopy and difficult tracheal intubation.