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Year : 2020  |  Volume : 3  |  Issue : 2  |  Page : 60-65

Role of ultrasonography for assessing optimal placement of supraglottic airway devices: A review of literature

Department of Onco-Anaesthesia and Palliative Medicine, Dr BRAIRCH, All India Institute of Medical Sciences, New Delhi, India

Date of Submission10-Apr-2020
Date of Acceptance05-May-2020
Date of Web Publication30-Aug-2020

Correspondence Address:
Dr. Rakesh Garg
Room No. 139, First Floor, Department of Onco-Anaesthesia and Palliative Medicine, Dr BRAIRCH, All India Institute of Medical Sciences, Ansari Nagar, New Delhi - 110 029
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ARWY.ARWY_11_20

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Supraglottic airway devices (SADs) have revolutionised perioperative airway management. These devices have contributed significantly to airway management, especially in the context of anticipated or unanticipated difficult airway, thereby decreasing airway-related morbidity. The use of these devices is now accepted even for positive pressure ventilation due to better seal and modifications (such as a double cuff or cuff material) preventing gastric insufflation with lesser chances of regurgitation. The quality of seal depends on how accurately the cuff matches the dimensions of the laryngeal inlet. Various methods and techniques are used for confirming the optimal placement of SADs with variable success rate. Evaluation based on conventional clinical tests is most commonly used for assessing the correct placement of SADs. However, clinical tests have been associated with limited outcome as they may not definitely be able to detect improper placement of SAD. Malpositioning may increase the incidence of complications such as altered airway dynamics, gastric insufflation, regurgitation and aspiration of gastric contents. The accuracy of these tests to identify malposition has been questioned by recent studies where fibreoptic evaluation of position of SAD identified many unacceptable placements which had been considered acceptable on the basis of clinical tests. Another limitation of these tests is that they fail to provide anatomic evidence of optimal SAD placement. Thus, other methods are required to confirm SAD position to avoid adverse events related to the airway. This review elaborates on the use of ultrasound to assess the optimal placement of supraglottic airway devices.

Keywords: Laryngeal mask airway, malposition, supraglottic airway device, ultrasonography

How to cite this article:
Rustagi K, Garg R. Role of ultrasonography for assessing optimal placement of supraglottic airway devices: A review of literature. Airway 2020;3:60-5

How to cite this URL:
Rustagi K, Garg R. Role of ultrasonography for assessing optimal placement of supraglottic airway devices: A review of literature. Airway [serial online] 2020 [cited 2021 Apr 16];3:60-5. Available from: https://www.arwy.org/text.asp?2020/3/2/60/293956

  Introduction Top

Supraglottic airway devices (SADs) are increasingly being used for airway management during anaesthesia. Clinical assessment is most commonly used to identify correct placement of SADs. Clinical methods vary with the type of SADs. Clinical tests such as protrusion of bite block, suprasternal notch test, soap bubble test, elevated peak pressures during ventilation or inability/difficulty to pass catheter through drain tube identify malpositioning.[1],[2],[3],[4],[5],[6] Many malpositions of SADs have been reported in literature. Malposition with ProSeal laryngeal mask airway (LMA) includes folding over of mask tip with imperfect mask position, incomplete insertion of mask or insertion of mask tip into the glottis. It has been observed that clinical methods may miss many cases of inappropriate placement of the SAD.

The other tools for assessing correct placement of SADs include use of fibreoptic bronchoscope or videoendoscope.[6] The gold standard for the assessment of placement is fibreoptic evaluation of glottic view through the airway lumen of SADs.[6] Although it is an important skill-based assessment tool that may not be routinely available, it does not provide real-time assessment of placement of SAD. New methods are needed to assess both the laryngeal size and visualise the SADs in situ.[1],[2],[3],[4],[5] Applications of ultrasound in anaesthesia have widened considerably in the last few years. In addition to its routine use during central venous cannulation, arterial cannulation and regional blocks, it has been found to be useful during airway management. Sonographic assessment of upper airway anatomy emerges as a widely available, practical and non-invasive tool for airway assessment and management. Recently, a few reports have emerged wherein ultrasonography has been used for confirmation of SAD placement before, during and after SAD introduction.[7],[8],[9] This manuscript is written with an aim to review the published literature related to the use of ultrasonography for assessing placement of SADs.

  Methods Top

The Participants, Intervention, Comparisons and Outcomes study design was followed for making the research question and subsequent review of literature. The research question for this review was 'What is the usefulness of ultrasound for assessment of optimal placement of laryngeal mask airways/supraglottic airway devices in patients requiring general anaesthesia as compared to conventional tools (clinical, fibreoptic endoscope) for assessment?' The explorative search was done from January 2000 to March 2020 from various search engines including PubMed, Cochrane Library, Google Scholar and Embase databases. The search terms used included 'ultrasound OR ultrasonography OR ultrasonographic AND airway OR laryngeal mask airway OR supraglottic airway devices'. Manual search was also done from the bibliography of the retrieved manuscripts for any missing manuscript. The retrieved manuscripts were tabulated and contents assessed for possible inclusion in the review.

  Results Top

The search revealed 23 manuscripts related to ultrasound use for airway management for SADs. However, only five manuscripts (four observational studies and one case description) were included for final review [Table 1]. Rest of the manuscripts described other aspects of the role of ultrasound during use of SADs rather than the primary objective of assessing its placement. Due to the paucity of studies with similar objectives and heterogeneity, the assessment of bias, systematic review or pooled analysis/meta-analysis was not feasible.
Table 1: Published literature describing ultrasonographic assessment of placement of supraglottic airway devices

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  Discussion Top

A thorough knowledge of sonoanatomy of the upper airway is of immense help to anaesthesiologists. Besides being safe, quick, portable and repeatable, ultrasonography allows uninterrupted airway management. Previously limited to airway assessment, it now finds application in real-time dynamic airway management.[7],[8] Ultrasonography for the confirmation of placement of airway devices remains unaffected in conditions such as cardiac arrest, low cardiac output or bronchoconstriction and conditions where use of continuous waveform capnography may be inappropriate to detect the position of the airway device.

Conventionally, the position of SADs is confirmed clinically by checking for adequate lung ventilation without gastric insufflation during controlled ventilation and examining the device for ideal location of the drain tube. Other techniques such as fibreoptic evaluation and ultrasound evaluation have also been described in literature to identify correct anatomical placement of the airway device.[7],[8],[9] However, the role of ultrasonography in the assessment of position of SADs has not been adequately evaluated. The exact technique and the diagnostic criteria have not been standardised to identify correct and optimal placement using ultrasonography. In the last few years, various studies have been performed where ultrasonographic confirmation of position of SADs has been evaluated and compared with other methods and found that it is an appropriate tool for confirmation of SAD placement.[10],[11],[12],[13],[14] Our review reveals that there is no robust evidence at present for definite use of ultrasonography for assessment of placement of SADs. However, existing literature is reassuring for its use in future.

The use of ultrasound was initially reported for placement of AuraOnce™ or AuraFlex™ disposable LMAs.[10] The placement of the LMA was assessed by ultrasound of neck and fibreoptic laryngoscopy (FOL). The authors proposed that when the LMA is correctly placed within the laryngopharynx, the caudal half of cuff of the LMA attains a contour described as 'reverse hanging drop' contour. However, the cranial half of the cuff of the airway device lies in the glossoepiglottic fold where the weight of the large epiglottis or large amount of fat in the pre-epiglottic space may distort the shape of the cuff. This distortion in the LMA cuff may be variable as it is affected by the anatomy of the surrounding airway. Hence, they hypothesised that ultrasound may be used to visualise the cranial half of the cuff of the LMA in the oral cavity and proposed a grading system according to the distortion of the cuff by the epiglottis/pre-epiglottic space. The grading system ranged from grade 1 'tent' view where normal contour of cuff is seen similar to that of shape of an igloo with minimal compression from the epiglottis/pre-epiglottic space, to grade 4 'no tent' view where cuff is completely distorted by the epiglottis/fat in pre-epiglottic space. They found a positive correlation (r = 0.92; P < 0.0001) between these ultrasound views and the intra-LMA fibreoptic laryngoscopic views. They explained that a large or bulky epiglottis or the large amount of fat in pre-epiglottic space results in varying degrees of obstruction of the laryngeal inlet and hence affects performance of the LMA. However, this study has several limitations. The sample size is small for the validation of results in clinical practice. Moreover, there was no blinding of investigators performing ultrasonography and fibreoptic evaluation. The grading system was also subject to the discretion of the investigators.

In another study, following LMA insertion, its placement was assessed by clinical evaluation, ultrasound and fibreoptic viewing.[11] The position was classified as acceptable or unacceptable based on clinical evaluation which includes symmetric bilateral chest movement without volume leak, and noted the intracuff pressure, cuff volume and oropharyngeal leak pressure. In their study protocol, they analysed the position of the LMA in three aspects - tip of LMA in relation to oesophagus, edge of cuff in longitudinal and transverse plane around base of tongue for rotation of LMA. The first plane for tip of cuff was visualised using the linear transducer placed transversely over trachea below the cricoid cartilage. The second plane was obtained by placing the transducer parallel to the midline to visualise folding of cuff in the longitudinal plane. The third plane was obtained by placing the transducer in the transverse plane around the base of the tongue. The glottic view was ranked based on the established system as suggested by Campbell where grading is based on the percentage of glottis covered by epiglottis. If the percentage of glottic aperture covered by epiglottis as seen with FOB is <25%, it was considered acceptable. The placement was confirmed as acceptable based on clinical tests, fibreoptic assessment and ultrasound evaluation in 89.1%, 59.4% and 67.2% patients respectively. Based on clinical assessment, the position of the LMA was assessed to be acceptable in 57 patients. Of these, 40.4% were considered unacceptable by FOB and 26.3% were deemed unacceptable by ultrasound evaluation. In patients with high oropharyngeal leak pressures, they found no difference between clinical and ultrasound assessment (P = 0.092), but the number of patients identified to be acceptable by ultrasound assessment was greater than that identified by fibreoptic evaluation (P = 0.034). The authors suggested that ultrasound evaluation is superior as compared to the other techniques for confirming the appropriate placement of the LMA.

Kim et al. reported the utility of ultrasonographic evaluation of Classic disposable LMA in 100 children.[12] Following induction of anaesthesia, ultrasonography was done twice, once before and once after insertion of LMA for the glottic image with transducer placed anteriorly on the neck in the midline. Then fibreoptic evaluation was done on the basis of glottic aperture and structures visualised and rotation of LMA noted. In the ultrasonographic image obtained after placement of device, the symmetry of the arytenoid cartilages was compared with the ultrasound image prior to device insertion. A vertical line joining anterior to posterior commissure was divided into three equal parts by 4 horizontal lines. Symmetry of the arytenoid cartilages was further categorised as 0–3 based on disproportionate elevation of an arytenoid cartilage when compared with the opposite cartilage and the glottic midline. Grade 0 denoted horizontal arytenoids at the same level and grades 1, 2 and 3 referred to elevation of the arytenoids to lower, middle and upper 1/3 of the vertical line, respectively. They evaluated the diagnostic performance of each test by analysing its sensitivity, specificity, positive and negative predictive value. The incidence of asymmetrical elevation of arytenoids as evaluated by ultrasonography was 50%. The LMA was misplaced based on disproportionate elevation in 78% and rotated in 43% of patients based on fibreoptic evaluation. The incidence of LMA rotation was similar (P = 0.395), while the malposition rate was higher with fibreoptic bronchoscopy (P < 0.0001). Ultrasound arytenoid grade did not correlate with fibreoptic bronchoscopic LMA grade (P = 0.611), but showed a significant correlation with LMA rotation grade (P < 0.0001). The authors hence reported that for detection of a rotated LMA in children, ultrasound had a sensitivity and specificity of 93% and 82% with accuracy of 87%.

In 2014, Wojtczak and Cattano assessed the use of ultrasound for evaluation of position of LMA Supreme and LMA Unique size 4 in three scenarios: when immersed in water bath, around larynx of pigs and non-embalmed tracheal specimen of human cadavers.[14] They used three different agents for cuff inflation; air, saline and saline with contrast agents such as sonicated albumin and optison. They concluded that when ultrasonography was used for assessment of position of LMA, inflation of the cuff with saline and sonicated agents provided better visualisation of images of the airway device. Air in the airway or cuff attenuates the ultrasound beam, causing shadowing artefacts, an image dropout and a reverberation. On the other hand, saline used for inflation of cuff allows the transmission of ultrasound beams through the cuff without any reflection from air-mucosal interfaces, thereby allowing identification of the surrounding tissues or structures. Then in 2016, Song et al. reported an observational study on 58 patients undergoing surgery under general anaesthesia with LMA Supreme.[13] They used ultrasound in three different planes to assess the position of the LMA; the pharynx, the larynx and in the midline along the craniocaudal axis. The clinical assessment was done on the basis of leakage at 20 cm H2O as suggested by Kundra et al.[15] The leakage was graded as follows: grade 1 being without any leak, grade 2 being minimal leak with satisfactory ventilation possible, grade 3 being significant leak with inadequate ventilation and grade 4 resulting in inability to ventilate. Fibreoptic examination was then performed to categorise placement either as optimal or suboptimal. Placement was optimal when epiglottis and vocal cords were visible and epiglottis did not intrude into airway and tip of airway device was lying behind arytenoids. Other views on fibreoptic examination were labelled as suboptimal. The analysis showed good agreement between the scoring systems-leakage grade and ultrasound grade. They suggested the criteria for reinsertion should be an ultrasound examination score equating to grade 3 in the leakage test and it is associated with a sensitivity and specificity of 85.7% and 94.1%, respectively.[13]

  Limitations of Airway Assessment Using Ultrasound Top

Sonographic imaging of airway may sometimes be difficult as the lumen of the airway is filled with air. Being a poor conducting medium for ultrasound waves, air offers high acoustic impedance resulting in poor images. Hence, ultrasonography may be used to visualise structures that are anterior or lateral in relation to the air in the airway, while the rest of the structures which are located posterior to the air are obscured and difficult to visualise using ultrasonography. Furthermore, the cuff of the airway devices is generally filled with air and hence they generate multiple echoes and ultrasound artefacts.[7] Ultrasound waves are poorly propagated through the thyroid cartilage. Thus, ultrasound waves get attenuated quickly by the thyroid cartilage. Air-mucosal interface creates acoustic shadowing and poses various artefacts, thus interfering with the use of ultrasound in airway management. Their use may be further affected in elderly patients whose cartilages are calcified due to the normal ageing process and hence make ultrasonographic visualisation of structures related with the airway difficult. In view of these limitations, a particular plane for ultrasonographic scanning has not been validated till today. A thorough knowledge of sonoanatomy of airway is required for correct interpretation of images obtained from ultrasonography. Otherwise, abnormal findings may be missed or results may be falsely understood. SADs have different shapes and contours. Hence, the effect of each SAD on the surrounding structure will be different. Further studies are required for identifying specific criteria for assessing the optimal placement of the various available SADs.

In a nutshell, ultrasonographic evaluation of the position of SADs is a novel technique and offers a promising role when compared with conventional techniques of clinical evaluation and fibreoptic assessment of position of the device. However, ultrasonographic evaluation of the position of SAD has not been extensively studied and requires further research for validation. The basic principle behind the use of ultrasonography for confirmation of position of SADs is to identify the surrounding structures that provide indirect evidence regarding the exact anatomical position of the device. The spatial orientation and contact of the cuff of the SAD with the surrounding laryngeal structures aids in confirmation of correct placement of the SAD.[10],[11],[12],[13] Most studies have used the transverse view between thyroid and hyoid cartilages to visualise cuff shadows. This technique may be applied for all types of SADs irrespective of whether they are single lumen or double lumen devices. However for the double lumen devices, the cuff may be evaluated on the basis of the suction tube in oesophagus and its relation to the cuff. Based on this hypothesis, the cuff should be examined at other sites also; namely, the tip of the cuff with respect to the oesophagus at the level of suprasternal notch and edge of cuff in parasagittal plane. However, as ultrasonographic evaluation is highly subjective, there is an urgent need for developing and validating a standard scoring system to avoid and minimise observer bias. It has been suggested that use of contrast agents and saline to inflate cuff results in better visualisation of the device with ultrasonography. However, their clinical application is limited as the manufacturers recommend air to be used for cuff inflation to avoid accidental rupture of cuff and fluid spill into the airway.

Ultrasound has been used for identification of correct placement of SADs with inflatable cuff such as the LMA Supreme, and AuraFlex and AuraOnce devices, but has not been used for devices with non-inflatable cuff such as i-gel and devices such as ProSeal LMA which are frequently used to secure airway in routine practice.

  Conclusion Top

Ultrasound offers a promising role in evaluation of placement of SADs. Ultrasound is a noninvasive, fast, repeatable and reliable technique that allows uninterrupted ventilation during assessment. It has the ability to detect correct placement of SADs similar to fibreoptic evaluation and to predict inappropriate placement and identify the need for reinsertion. The identification of sonoanatomy is better with saline filled cuff rather than air filled cuff in SADs. Furthermore, use of ultrasound in transverse view between thyroid and hyoid cartilages to visualise cuff shadows has been studied mostly. However, prospective randomised studies are required to confirm its applicability for assessing the correct placement of SADs. Further, its utility across various types of SADs also needs to be evaluated.

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  References Top

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O'Connor CJ Jr., Borromeo CJ, Stix MS. Assessing ProSeal laryngeal mask positioning: The suprasternal notch test. Anesth Analg 2002;94:1374-5.  Back to cited text no. 5
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