INTRODUCTION:

   Laryngeal mask airway (LMA) is an alternative technique for airway management during  administration of General Anaesthesia. Due to its ease of application and its association with lower complication rates, it is increasingly used during elective surgery, resuscitation, and emergency scenarios involving airway complications

In the realm of anesthesia and airway management, the appropriate selection of LMA is pivotal for ensuring optimal patient outcomes during surgical procedures. Traditionally, LMA sizing has relied heavily on factors such as patient demographics, manufacturer’s recommendation based on ideal body weight, and even clinical experience of the anesthesiologist. While these methods have been employed with some success, they often lack precision and may result in suboptimal device selection. Achieving an optimal fit of the LMA remains a critical concern and  improper sizing can lead to complications such as airway leaks, inadequate ventilation, and increased risk during anaesthesia.

The traditional physical examination methods have limitations in airway assessment. Point-of-care ultrasound (POCUS) has emerged as a promising tool for airway management due to its familiarity, accessibility, safety, and non-invasive nature. It can assist physicians in identifying relevant anatomy of the upper airway with objective measurements of airway parameters, and it can guide airway interventions with dynamic real-time images. To date, ultrasound has been considered highly accurate for assessment of the difficult airway, confirmation of proper endotracheal intubation, prediction of post-extubation laryngeal edema, and preparation for cricothyrotomy by identifying the cricothyroid membrane^[1]

A few of the Ultrasonographic airway parameters used so far in predicting difficult airway and intubation are hyomental distance, tongue thickness, anterior neck soft tissue thickness and thyromental distance. Assessment of the airway with POCUS may be helpful to the emergency physician when the clinical airway assessment parameters fail to predict difficult laryngoscopy as most patients requiring intubation are uncooperative. Assessment of the above parameters can prove to be a promising tool for predicting difficult laryngoscopy in the emergency scenario.^[2]

A previous study demonstrated that ultrasonographic measurement of one of  the  upper airway anatomy parameters of hyomental distance, the distance between hyoid bone and tip of the chin, may be considered a predictor for LMA size in adults.^[3]

This thesis aims to extrapolate the correlation found so far between ultrasound airway parameters in predicting difficult airway and difficult intubation onto predicting the LMA size in patients undergoing elective surgeries under general anaesthesia. Through this exploration, we aspire to contribute to the refinement of clinical practice guidelines, ultimately enhancing patient safety and procedural outcomes in the field of anaesthesia and airway management

AIMS AND OBJECTIVES:-

AIM- Assessing utility of ultrasonographic airway parameters viz Tongue volume and thickness, hyomental distance and anterior neck soft tissue thickness) for LMA size selection in adult patients undergoing elective surgery.

PRIMARY OBJECTIVE:-

Ø  To measure the Ultrasound Guided (USG) airway parameters and its correlation with appropriate LMA size

SECONDARY OBJECTIVES:-

Ø  To identify the independent factors associated with  determination of  LMA size.

Ø  To develop a regression equation to predict LMA size using USG based airway parameters along with age and weight or body mass index

MATERIALS AND METHODS :-

STUDY DESIGN- A Prospective observational study.

STUDY SETTING – SGPGIMS, OT areas.

INCLUSION CRITERIA:

1.     Patient who have given written informed consent to enrol in this study.

2.     Patients of both the genders will be included.

3.     Patients in the age group of 18-65 years.

4.     Patients undergoing elective surgery under General anaesthesia where LMA can be used

EXCLUSION CRITERIA :-

1.     Patient refusal to enrol in the study.

2.     Pregnant patients

3.     Patients with high risk of regurgitation; h/o GERD, hiatus hernia.

4.     Patients with potential difficult airway; Mouth opening <2 fingers, edentulous patients, limited neck extension, cervical spine pathology and obesity (BMI > 30Kg/M²)

5.     Patients with h/o COPD or other pulmonary pathologies.

METHODOLOGY: After obtaining approval from the institute ethics committee of SGPGIMS, the study will be conducted on consenting adults about to undergo elective surgery under General Anaesthesia with LMA. There is no scope of randomization or blinding due to the nature of the study. The duration of study is going to be about 18 months.

In the pre-operative area, the patient’s airway will be assessed by conventional method (Inter-incisor distance, MPG scoring, and Thyromental distance). The ultrasonic airway parameters will be assessed as per domains suggested by Bhargava et al in their metanalysis of 33 studies.^[4] The oral space domain (OSD), anatomical position domain [APD] and the anterior neck soft tissue thickness domain (TTD). For OSD tongue thickness, tongue volume, hyomental distance in APD domain and in TTD, skin to hyoid, epiglottis and anterior commissure distance will be measured.

Patients will be placed in supine sniffing position with a pillow under the occiput to achieve optimum head extension and neck flexion Assessment will begin using a 2–6-MHz curvilinear transducer.

1.     Tongue thickness and volume^[5]: transducer will be placed at the submandibular area in the sagittal and transverse planes. In the sagittal plane in the midline, the following images will be visualized, the tongue with the patient’s head in a neutral position and the mentum and hyoid bone. Tongue thickness and cross-sectional area, measured (cm²) automatically in the sagittal scans by tracking the borders of the tongue muscles, will be taken here. In the transverse plane, the submandibular area will be scanned mid-way, the tongue with the patient’s head in a neutral position visualised. Tongue width (centimeters) will be distance measured in transverse scans in the midsection of the tongue. Tongue volume (cm³) will be derived from multiplication of the midsagittal cross-sectional area by the tongue width.

2.     HYOMENTAL DISTANCE ^[3,5]: In sagittal scans, above the tongue the hyoid bone is visualised as a narrow hyperechoic curved structure that casts an acoustic shadow. Distance (cm) from the upper border of the hyoid bone to the lower border of the mentum of the mandible will be measured.

3.     ANTERIOR NECK SOFT TISSUE THICKNESS:^[6,7] A 5–14 MHz linear probe will be used in transverse plane for this assessment.

Skin to hyoid: At hyoid bone level, hyoid bone is visible as a superficial hyperechoic inverted U-shaped linear structure with posterior acoustic shadowing. The minimal distance from the hyoid bone to skin surface will be measured.

Skin to epiglottis: At the level of thyrohyoid membrane, epiglottis is visible as a hypoechoic curvilinear structure. Its anterior border is demarcated by the hyperechoic pre-epiglottic space and its posterior border by a bright linear air mucosal interface. The distance from skin to epiglottis midway between the hyoid bone and thyroid cartilage will be measured. Identification of the epiglottis can be facilitated by tongue protrusion and swallowing, when it becomes visible as a discrete mobile structure inferior to the base of the tongue

Skin to Anterior commissure: At the level of thyroid cartilage, vocal cords are seen forming an isosceles triangle with a central tracheal shadow. During phonation, the vocal cords oscillate and move towards the midline. The minimal distance from skin to anterior commissure will be obtained.

Inside the Operation Room (OR), subjects will be placed in supine position and standard ASA monitors will be attached. Patient will be pre-oxygenated with 100% O2 for 3 min while  keeping the ventilator on manual mode. Injection midazolam 0.03mg/kg,  and  fentanyl 2ug/kg will be given. Induction of Anaesthesia will be done with propofol titrated to loss of response to command. Once the patient is unresponsive, mask ventilation will be started with APL valve closed to 10- 20 mmhg Ensuring the ability to mask ventilate, skeletal muscle relaxant (0.1mg/kg vecuronium or 0.5 mg/kg atracurium depending on patient’s renal function) will be given. After 3 minutes of mask ventilation, LMA (sized according to the manufacture’s recommendation as per patient’s ideal body weight) will be placed by an experienced anaesthesiologist.

The ventilator will be set at PCV, at an inspiratory pressure of 14 cm H20, respiratory rate of 12-14 per minute, inspiration to expiration ratio of 1:2, and 3 litres of fresh gas flow. Appropriate sized LMA will be determined by ventilatory efficacy, Ease of placement , adequate sealing. Ventilation efficacy will be determined based on the tidal volume(Vt) as follows: >8 ml/kg - excellent , 4-8 ml/kg as acceptable and < 4cc/kg as low. The ease of LMA placement scored as 1) Easy: successful placement by once effort, 2) Relative: successful placement by twice efforts and 3) Difficult: more than twice efforts and/or neck repositioning requirement.^[8] Laryngeal mask sealing will be  justified  by absence of noise/leak heard through the LMA or felt on palpating the neck. Ventilatory Leak fraction will be calculated by following formula (Vt _insp- Vt _exp ) / Vt _insp,.^[9] Oropharyngeal leak pressure (OLP) will be measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 litre min^–1, and noting the airway pressure on screen at which leak was audible.^[10] POGO scoring (Percentage of Glottic opening)^[11] will be done using a fiber-optic scope passed through the LMA, to a position just proximal to its opening and the view will be scored as follows: 4, only cords seen; 3, cords plus posterior epiglottis seen; 2, cords plus anterior epiglottis seen; 1, cords not seen, but function adequate; 0, failure to function (< 4ml/kg tidal volume) and cords not seen fiber-optically. Functionality is not relevant for scores 4 to 2 because the vocal cords are visible and any failure to function is not due poor positioning.

In any case of non-acceptable ventilation or leak with the LMA placed, repositioning of LMA will be done once and if the problem persists its size will be changed. If despite there is persistent leak, endotracheal intubation will be done and such patients will be considered drop outs from this study.

At end of surgery all patients will be extubated and shifted to PACU. Incidence of conversion to endotracheal intubation and other complications like trauma to Larynx ( blood stain on LMA),  incidence of Laryngospasm and incidence of sore throat and dysphagia at 2 hour postoperative period will be noted.

SAMPLE SIZE ESTIMATION AND STATISTICAL   ANALYSIS:  We have assumed the average correlation coefficient between LMA size and USG parameters to be 0.75 (≥0.6 to 0.79 is considered good correlation) and null hypothesis of the correlation coefficient to be 0.6. Taking minimum two-sided 95% confidence  interval and 80% power of the study, estimated sample size will be 103. As we will take more  than one USG parameter to evaluate the correlation with LMA size and considering the possible variation in the correlation coefficient, we will be targeting at least 150  patients. Sample size was estimated using software Power analysis and sample size version-16 (PASS-16, NCSS).

Continuous variables will be presented in Mean and standard deviation (SD) or median (interquartile range) depending on the normality status. Categorical variables will be presented in number (%). Spearman correlation coefficient will be used to test the correlation between the variables / measures and LMA size and  Poisson regression analysis to identify the independent  factors associated with LMA size. Further, regression equation will be developed for the  possible  estimation of LMA size using the USG measures, age, and body mass index /body weight Statistical analyses will be performed using SPSS software for windows, version 23.0  (SPSS, Chicago, IL). P value less than 0.05 to be considered as statistically significant.

CASE REPORT FORM

Cr NO:                       Age-                          Gender -                 Wt (Kg)/ HT(cm)-

BMI(kg/m2)-            Inter-incisor distance-                               MPG-

Thyro-mental distance in cm-

USG PARAMETERS OF AIRWAY ANATOMY:-

LMA size based on weight –                                      Ease of LMA placement- 1/2/3

VENTILATORY PARAMETERS:-

Efficacy of ventilation – excellent /acceptable/ low

OLP =

Leak fraction =

POGO Score =

COMPLICATIONS (IF ANY):-

Blood stain on  LMA -        Y/N

Laryngospasm -                  Y/N

Throat pain -                       Y/N

Dysphagia -                         Y/N

REFERENCES:-

1)    Lin J, Bellinger R, Shedd A, et al. Point-of-Care Ultrasound in Airway Evaluation and Management: A Comprehensive Review. Diagnostics (Basel). 2023;13(9):1541.

2)    Pillai, A., Arora, P., Kabi, A. et al. The diagnostic accuracy of point-of-care ultrasound parameters for airway assessment in patients undergoing intubation in emergency department—an observational study. Int J Emerg Med. 2024 Jan 29;17(1):12.

3)    Xia wang,zhi hang tang,wuhua ma.Hyomental distance measured by ultrasound for size selection of laryngeal mask airway in female patients: a randomized controlled study. Research square; 2021. DOI: 10.21203/rs.3.rs-152376/v1.

4)    Bhargava V, Rockwell N.A. Tawfik D, Haileselassie B, Cristina P, Su E. Prediction of Difficult Laryngoscopy Using Ultrasound: A Systematic Review and Meta-Analysis. Critical Care Medicine.2023; 51(1):p 117-126.

5)    Andruszkiewicz, P., Wojtczak, J., Sobczyk, D., Stach, O. and Kowalik, I.Effectiveness and Validity of Sonographic Upper Airway Evaluation to Predict Difficult Laryngoscopy. Journal of Ultrasound in Medicine,2016; 35: 2243-225.

6)     Wu J, Dong J, Ding Y, Zheng J. Role of anterior neck soft tissue quantifications by ultrasound in predicting difficult laryngoscopy. Med Sci Monit. 2014 Nov 18;20:2343-50. 

7)    Kundra P, Mishra SK, Ramesh A. Ultrasound of the airway. Indian J Anaesth. 2011 Sep;55(5):456-62.

8)    Aghadavoudi O, Shetabi H, Saryazdi H, Babayi S. Assessment of Neck Characteristics for Laryngeal Mask Airway Size Selection in Patients Who Underwent an Elective Ocular Surgery; A Cross-Sectional Study. Bull Emerg Trauma. 2022 Apr;10(2):77-82.

9)    Mohamed Ibrahim, Ashraf Ragab, Hossam ElShamaa. I-gel vs cuffed tracheal tube during volume controlled ventilation in elective laparoscopic cholecystectomy. Egyptian Journal of Anaesthesia, 2011;27;1:7-11.

10)   C. Keller, J. Brimacombe, Mucosal pressure and oropharyngeal leak pressure with the ProSeal versus laryngeal mask airway in anaesthetized paralysed patients,  British Journal of Anaesthesia, 2000; Volume 85, Issue 2, : 262–266.

11)   Brimacombe J, Berry A. A proposed fiber-optic scoring system to standardize the assessment of laryngeal mask airway position. Anesth Analg 1993; 76(2):p 457.

12)   Singh S, Ohri R, Singh K, Singh M, Bansal P. Comparison of Different Ultrasound Parameters for Airway Assessment in Patients Undergoing Surgery under General Anaesthesia. Turk J Anaesthesiol Reanim. 2021 Oct;49(5):394-399.

13)   Srinivasarangan M, Akkamahadevi P, Balkal VC, Javali RH. Diagnostic Accuracy of Ultrasound Measurements of Anterior Neck Soft Tissue in Determining a Difficult Airway. J Emerg Trauma Shock. 2021 Jan-Mar;14(1):33-37.

14)   Osman, A., Sum, K.M. Role of upper airway ultrasound in airway management. J of intensive care, 2016; 4, Article number: 52.