PONE-D-20-07172

Measurement of subglottic diameter and pre-epiglottic space thickness Among Chinese adults

PLOS ONE

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Reviewers' comments:

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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This manuscript addresses the feasibility of ultrasonography in predicting difficult intubation among Chinese adults. A prospective, observational study was conducted to measure the ultrasonographic subglottic diameter and the “pre-epiglottic (PES) thickness” among healthy Chinese adults. The authors describe that the size of subglottic diameter and “PES thickness” is smaller compared to western populations.

In addition, they compare their results with previous reports and highlight that a smaller size of endotracheal tube should be selected in the Chinese population.

Unfortunately there are some fundamental concerns with the experimental design and, most critically, with the analysis and literature review.

1. The authors define pre-epiglottic thickness (PES) as the distance between the skin and the midpoint of the epiglottis. In fact, that is the measurement of the distance from the skin to the epiglottis as performed and written by other authors. The authors should speak in distance from skin to epiglottis (DSE) instead of PES. The title and manuscript should be revised accordingly to reflect the distance measured.

2. In addition, in ultrasound measurements of the anterior neck soft tissues the amount of pressure applied by the ultrasound probe can cause a difference in values and may alter the results. That fact is not stressed in the study limitations.

3. The authors revised literature between 1957 and 2019, not until 2016 as stated, and compared it with their results. Literature review and data comparison presented in, particularly in Table 3, has pitfalls:

a. The authours compare ultrasonography measurements with CT scan measurements [Kamel et al. (2009); Prasanna Kumar et al. (2014), Tai et al. (2016)].

b. In addition, Tai et al (2016) performed CT scans in Caucasian and Chinese patients, not only in Chinese patients as stated.

c. Pinto et al (2016) evaluated the distance from skin to epiglottis (DSE) in a sample of Portuguese population and not in American patients.

d. Hall et al (2018) measured accurately the pre-epiglottic space from the anterior surface of the epiglottis to the anterior surface of the strap muscles. The BMI presented in the table is the BMI range in Hall’s study, not the comparison between male and female BMI.

e. The study of Yadav et al (2019) measured the distance from skin to hyoid bone, skin to the thyrohyoid membrane and maximum tongue thickness, not the pre-epiglotic space.

4. The authors should clarify the comparison with previous reports among caucasion samples (L202-204): “… Comparing with previous reports among Caucasian samples [22, 23, 25], a relatively smaller subglottic diameter and a thinner PES were noted among Chinese …”

a. Kamel et al. (2009) studied the morphometry of human trachea by CT scans and did not include subglottic diameter measurements (Reference # 23)

b. Kumar Prasanna and Ravikumar (2014) studied an Indian population not Caucasian (Reference # 25).

5. References are not formatted according to PLOS reference style.

a. References must be carefully confirmed and reviewed.

b. The same reference is cited thrice and is presented with different formats:

i. 16. KE Y-T. Point-of-care ultrasound (POCUS) of the upper airway. Can J Anaesth. 2018 Apr;65:473-84.

ii. 21. You-Ten KE, Siddiqui N, Teoh WH, Kristensen MS. Point-of-care ultrasound (POCUS) of the upper airway. Can J Anaesth. 2018;65(4):473-84. Epub 2018/01/20. doi:10.1007/s12630-018-1064-8. PubMed PMID: 29349733

iii. 27. You-Ten KE, Siddiqui N, Teoh WH, Kristensen MS. Point-of-care ultrasound (POCUS) of the upper airway. Can J Anaesth. 2018;65:473-84.

Further specific points:

1. Consider revising L37-39. “The prospective study aims to investigate the sonographic subglottic diameter and the pre-epiglottic thickness among healthy Chinese adults”

2. Consider revising L59-60. “An endotracheal tube (ETT) or a supraglottic airway device delivers a high concentration of oxygen, referring as initial methods of managing the airway [1].”

3. The authors should also consider that the distance of the skin to the epiglottis combined with the modified Mallampati score, for example, improves the predictive power in a decision tree over either test alone.

4. In Figure 1 A: the probe is transversely positioned in a higher location than the subglottic region.

5. Consider revising Table 1: Height, Kg and BMI Kg/m2 to kg and kg/m2, respectively.

6. The authors should revise the language to improve readability.

Reviewer #2: This Manuscript represents a prospective study that analyzed the diameter of the subglottic and pre-epiglottic space in healthy Chinese adults in order to establish the average values for this ethnicity and compare it with standard measures of Caucasians. As the Authors have established average values among their patients’ population, they believe that this information could contribute to the proper choice of the size of endotracheal tube and predict difficult intubation in patients.

Overall, this study is interesting and presents current relevance. However, there are some issues that should be addressed prior to publication.

Abstract

1. The thickness of the pre-epiglottic space (PES) among normal individuals are still limited.

Please rephrase this sentence in order to explain more clearly the problematic regarding the thickness of PES.

2. A smaller size of subglottic diameter and PES thickness were noted among Chinese.

Please rephrase this sentence and indicate to what patients’ population you compared your results with.

Introduction

3. A definite airway could provide effective oxygenation and ventilation rather than a bag-mask device.

I would rephrase this sentence, indicating more clearly that in all airway emergencies, a secured airway brings advantages for patients’ ventilation over a bag-mask device

4. Moreover, it could negatively impact on glottis mobility, ventilation and even quality of life

Rephrase glottis mobility into a vocal fold motility

5. But controversies were reported by investigators in Hong Kong [26].

Please indicate these controversies and present the problematic.

Results

6. The PES in Western countries, such as the United States, was thicker than that in Asian countries (India and China).

Please present the data to support your statement.

Discussion

7. The “size” of an ETT refers to its internal diameter. ETTs with the size of 7.5 and 8.5 are recommended for female and male patients, respectively [30].

Please specify that these measurements refer to adult patients.

8. In addition, there is possibly a higher risk of laryngeal edema or inflammation in real patients when she/he needs intubation.

I suggest you to omit the use of the term ‘real’ when referring to the patients;

9. Please emphasize and integrate into the Discussion section the literature data that support the fact that the subglottic space diameter is a predictor of a correct ETT size

10. I would integrate the difficulties in performing an US airway evaluation in emergency as well, as there is rarely time, often the airway is obstructed by blood or there is laryngeal fracture, all factors that could make this measurement harder

11. ‘it would be validated in future multi-center and international studies’

I would add prospective to multi-center and international studies.

12. The manuscript would benefit from an English native speaker revision

13. It would be interesting to conduct in the future the same measurement preoperatively on patients with laryngeal or neck morbidity and to compare the measurements with current results, as well to correlate these measurements with the Cormack score.

14. Integrate, if data available, the incidence of subglottic /tracheal stenosis or intubation related injuries among Chinese

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Reviewer #1: No

Reviewer #2: No

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Measurement of subglottic diameter and distance to pre-epiglottic space among Chinese adults

PONE-D-20-07172R1

Dear Dr. Lien,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Jorge Spratley, MD, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Thank you for your careful revision of paper PONE-D-20-07172R1. The manuscript has much improved in readability and consistency.

One of the weaknesses of the study is that US in the neck, as in many other body regions, is strongly dependent from examiner to examiner. Therefore, harmonization of results is often times difficult to perform.

Despite this, your article has been accepted for publication at PlosOne.

Good luck!

Reviewers' comments: