Comparison of physical with ultrasound measurements of the windpipe in predicting difficulty in management of breathing tube under anaesthesia in patients undergoing surgeries under general anaesthesia

Not yet recruiting

• Conditions: predicting difficult airway

• Registration Number: CTRI/2018/11/016390
• Lead Sponsor: Dr Usha R Sastry

Brief Summary

Introduction

 Examination of  the airway is an essential component of the anesthesiologist‘s pre-operative assessment. It enables to predict the ease of visualizing theglottis and to perform intubation.(1). The preintubation clinicalscreening tests (mallampatti classification, interincisorgap,thyromentaldistance, testing neck mobility)to assess for difficult laryngoscopy have poorto moderate sensitivity(4). Despite the availability of multipleairway assessment methods, unexpected difficult intubations occur with afrequency of 1-8%(2).

The Cormack lehane classification isfrequently used to describe the best view of the larynx seen duringlaryngoscopy. Although it is one of the most used classification, one majordrawback is that it cannot be applied for predicting difficult trachealintubation in patients undergoing intubation for the first time.(3)

Ultrasound imaging is a safe, simple,painless and non invasive modality through which soft tissues can be visualizedand identified.(3)

There is limited literature available that comparesthe ultrasound parameters of the airway to the CL grade and physicalparameters. This study will be undertaken to compare the utility of the  physical with ultrasound parametersof theairway in  predicting difficult airway.

  Review of literature

1.    Anobservational study was done by Preethi et al in 2016 on various parametersmeasured by ultrasonography of neck: anterior neck soft tissue thickness at thelevel of the hyoid (ANS-Hyoid), anterior neck soft tissue thickness at thelevel of the vocal cords (ANS-VC) and ratio of the depth of the pre-epiglotticspace (Pre-E) to the  distance from theepiglottis to the mid-point of the distance between the vocal cords(E-VC)in  comparison with Mallampati (MP)class, thyromental distance (TMD) and sternomental distance (SMD)   in 100 patients undergoing generalendotracheal anaesthesia to predict CL grade during intubation.  The incidenceof difficult intubation was 14%. An ANS-VC >0.23 cm had a sensitivity of85.7% in predicting a CL Grade of 3 or 4, which was higher than that of MPclass, TMD and SMD. However, the specificity, PPV and accuracy were lower thanthe physical parameters. The NPV was comparable. They concluded that ultrasoundis a useful tool in airway assessment. ANS‑VC >0.23 cm is a potentialpredictor of difficult intubation. ANS‑Hyoid is not indicative of difficultintubation. The ratio Pre‑E/E‑VC has a low to moderate predictive value.

2.    CM hui et al hypothesised that sublingual ultrasound provides additionalinformation to predict a difficult airway with greater success than traditionalmethods. They recruited 110 patients to perform sublingual ultrasound onthemselves following brief instructions in 2014. Ability to view the hyoid boneon sublingual ultrasound, mouth opening distance, thyromental distance, neckmobility, size of mandible and modiï¬ed Mallampati classiï¬cation were recordedand assessed for ability to predict a difï¬cult intubation based on the grade oflaryngoscope. Visibility of the hyoid using ultrasound was associated with alaryngoscopic grade of 1–2 (p< 0.0001), and (p < 0.0001) had a positivelikelihood ratio of 21.6 and a negative likelihood ratio of 0.28. Each of theother methods had considerably lower positive likelihood ratios and lowersensitivity. Their results suggest that sublingual ultrasound is a potentialtool for predicting a difï¬cult airway in addition to conventional methods.

3.    Anobservational study was done on 72 ASA I -III patients undergoing generalanaesthesia requiring endotracheal intubation by Gupta et al  in 2012 who obtained the followingmeasurements  with the oblique –transverse view  of the ultrasound :(a)the distance from the epiglottis to midpoint of the distance between thevocal folds,(b)the depth of the pre-epiglottic space, (c) the total time takenby the operator to achieve the ultrasound images. The data was then comparedwith the Cormack – Lehane classification on direct laryngoscopy and theultrasound modification of the CL grading was developed .They found that theprediction of CL grades can be adequately made by the ratio of Pre -E and E-VCdistances. The average time to complete the ultrasound examination of theairway was 31.7+\_12.4 seconds.

4.    Aobservational study on 51 patients undergoing elective surgery was done by  Srikar Adhikari et al in 2011. The ultrasound(US) measurements of tongue and anterior neck soft tissue were obtained. Thelaryngoscopic view was graded using Cormack and Lehane classiï¬cation byanesthesia providers on the day of surgery. The sonographic measurements ofanterior neck soft tissue were greater in the difï¬cult laryngoscopy groupcompared to the easy laryngoscopy group at the level of the hyoid bone andthyrohyoid membrane . No signiï¬cant correlation was found between sonographicmeasurements and clinical screening tests. They concluded  that sonographicmeasurements of anterior neck soft tissue thickness at the level of hyoid boneand thyrohyoid membrane can be used to distinguish difï¬cult and easylaryngoscopies. Clinical screening tests did not correlate with USmeasurements, and US was able to detect difï¬cult laryngoscopy, indicating thelimitations of the conventional screening tests for predicting difï¬cultlaryngoscopy.

5.    Arandomised study was done on 50 morbidly obese patients undergoing bariatricsurgery by T. Ezri et al in 2003. They  quantified the neck soft tissue from skin to anterior aspect of tracheaat the vocal cords using ultrasound . Thyromental distance less than 6cm,mouthopening less than 4cm,limited neck mobility,mallampatti score more than 2,abnormal upper teeth, neck circumference >45 cm, and sleep apnoea wereconsidered predictors of difficult laryngoscopy. Of the nine (18%) difficultlaryngoscopy cases, seven had obstructive sleep apnoea history; whereas, only 2of the 41 easy laryngoscopy patients did have. Difficult laryngoscopy patientshad larger neck circumference [50 (3.8) vs. 43.5 (2.2) cm; and morepre-tracheal soft tissue. . Soft tissue values completely separated difficultand easy laryngoscopies. None of the other predictors correlated with difficultlaryngoscopy. Thus, an abundance of pretracheal soft tissue at the level ofvocal cords is a good predictor of difficult laryngoscopy in obese patients.(5)

Though of late,ultrasound is used as a new modality for airway assessment, there are very fewstudies with large patient numberdescribing the utility of ultrasound scan ofthe airway routinely. Hence we would like to do the study.

  Justification andneed for the study

Ours is atrauma centre, a tertiary referral teaching hospital and we deal with lotof  patientswith different build andsizes who can present with unanticipated difficult airways. Since the epresently available physical parameters have high interobserver variability, anobjective measurement of the airway using a non invasive simple bedsideinstrument would help in being prepared for any unanticipated difficultscenarios and reduce morbidity and mortality considerably.

 Outcome measure

a.    Anteriorsoft tissue thickness at the level of the hyoid -ANS – hyoid

b.    Anteriorsoft tissue thickness at the level of the vocal cords – ANS VC

c.     Ratioof depth of the preepiglottic space (Pre-E )to the distance from the epiglottisto the mid point of the distance between the vocal cords.(E- VC)

d.    Thetotal time taken by the operator to achieve the final ultrasonic image

The above parameters will be measured andcompared with the physical parameters such as

a.  malampatti class,

b. thyromental distance

c. sternomental distance

d.  neck circumference

Theincidence of difficult intubation will be identified by direct laryngoscopy byan experienced anesthesiologist (>5yrs )and graded according to the Cormacklehane grading. Both physical and ultrasound parameters will be compared withincidence of difficult intubations and plotted.

Detailed Description

Not available

Study Timeline

• Study Start: 2018-01-12
• Last Update Posted: 2018-11-16

Recruitment & Eligibility

• Status: Not Yet Recruiting
• Sex: All
• Target Recruitment: 100

Inclusion Criteria

ASA I or II or III patients undergoing surgery under general anesthesia with endotracheal intubation.

Exclusion Criteria

Patient refusal Pregnant and lactating mothers Anticipated difficult airway Patients requiring rapid sequence intubation or fibreoptic intubation with cervical spine pathology or head and neck anatomical pathologies or un cooperative patients.

Study & Design

• Study Type: Observational
• Study Design: Not specified

Primary Outcome Measures

Name	Time	Method
To compare the anatomical with ultrasound parameters of the airway in predicting difficult airway	1 In the preoperative room before induction of general anaesthesia | 2 During direct laryngoscopy for endotracheal intubation after administration of general aanesthesia

Secondary Outcome Measures

Name	Time	Method
A To identify an objective parameter in assessment of airway	B To identify airway anatomy by ultrasound in detail

Trial Locations

Locations (1)

OT 2nd floor Operation Theatre Complex; 🇮🇳 Bangalore, KARNATAKA, India

OT 2nd floor Operation Theatre Complex

🇮🇳Bangalore, KARNATAKA, India

Dr Usha R Sastry

Principal investigator

9611713971

urs22984@gmail.com