Elsevier

Journal of Critical Care

Volume 33, June 2016, Pages 26-31
Journal of Critical Care

Imaging
Predicting difficult laryngoscopy using ultrasound measurement of distance from skin to epiglottis

https://doi.org/10.1016/j.jcrc.2016.01.029Get rights and content

Abstract

Background

Unpredicted difficult intubation can have severe consequences, and it is a significant source of morbidity and mortality. Although recent studies indicate that specific ultrasonography (US) measurements may be predictors of difficult laryngoscopy, their use is still limited, and its quantification is missing. The purpose of this prospective observational study is to evaluate the use of US-measured distance from skin to epiglottis (DSE) for difficult laryngoscopy prediction.

Methods

In a double-blind study, standard preintubation, screening tests, and DSE were obtained from 74 adult patients requiring endotracheal intubation. The relationship between difficult laryngoscopy and DSE was evaluated using a t test. A comparative analysis of its predictive performance with common clinical preintubation screening tests was performed using bootstrapping.

Results

We found that increasing DSE is strongly associated with difficult laryngoscopy (P < .001, 2-sided t test). We showed that a cutoff value of 27.5 mm was able to predict difficult laryngoscopy with an accuracy of 74.3%, a sensitivity of 64.7%, and a specificity of 77.1%.

Conclusions

Our work demonstrates that the DSE can be effectively used to predict difficult laryngoscopy. Moreover, combining DSE with the modified Mallampati score in a decision tree significantly improves the predictive power over either test alone.

Introduction

Airway management is one of the main concerns for anesthesiologists, and unpredictable difficult airway intubation remains one of the most important challenges in routine practice. Adverse outcomes and severe complications related with difficult airway are rare but may have catastrophic consequences to the patient [1].

Airway assessment can help to provide an appropriate management of an expected difficult airway. Prescreening airway evaluation can include consultation of previous medical history, physical examination, and performing additional bedside tests. Presently, bedside tests such as Mallampati test, thyromental distance (TMD), sternomental distance, neck circumference, and interincisor distance (IID), are used in daily clinical practice to predict difficult intubation. Most of these common tests, however, have limited predictive value when used on their own [2]. This is partially due to lack of standardized measurements, subjectivity, and lack of agreed-upon cutoff values. To overcome this, some multivariable risk scores have been proposed [2] to improve the predictive capability of bedside tests. However, these composite scores tend to be time consuming and difficult to use in clinical practice.

Advances in airway devices, patient monitoring, clinical protocols, and education have reduced the risks associated with an unpredicted difficult airway, but not the incidence of unexpected difficult airway [3], [4], [5], [6]. Ultrasound (US) has recently emerged as a simple, portable, noninvasive, and safe method for rapid airway assessment and management in the operating room, emergency department, and intensive care unit [7], [8].

Recent studies suggest that US-based airway assessment may be a useful adjunct to clinical methods of bedside airway assessment [9], [10], [11], [12]. In morbidly obese patients, anterior soft neck tissue was an independent predictor of difficult laryngoscopy [9]. Another pilot study [11] analyzed three US-based measurements including the distance from skin to epiglottis (DSE) for difficult laryngoscopy prediction. The results suggested that DSE gives good predictive results, but no useful cutoff for clinical practice was validated. Although these results are promising, more systematic studies are needed before US measurements can be validated for reliable use in routine clinical practice [2].

In this regard, our main objective was to evaluate the capability of DSE in predicting difficult laryngoscopy and whether it can be used, alone or combined with other standard clinical preintubation screening tests, in daily clinical practice.

Section snippets

Materials and methods

This prospective double-blind study was conducted in Hospital Center Tondela-Viseu, Portugal.

Results

The goal of this study was to determine the feasibility of including an US-based measurement—the DSE—as a standard variable in prescreening tests for predicting difficult laryngoscopy. The 74 patients involved in the study were divided in 2 groups—easy and difficult laryngoscopy—by an anesthesiologist performing the intubation (using the Cormack-Lehane grade; see “Materials and methods” section). Using these 2 groups, we asked which variables were associated with difficult laryngoscopy (see

Discussion

Here, we have proposed methods to predict difficult laryngoscopy using DSE, a US measurement (DSE, a measure of anterior soft neck tissue width at the level of thyrohyoid membrane). We showed that this measure can significantly improve the predictive power of current standard preintubation screening tests when combined with the standard modified Mallampati score in a simple easy-to-implement decision tree.

Previous studies have used anterior soft neck tissue width at the level of thyrohyoid

Conclusions

This study demonstrated that the sonographic measurement of DSE can be used as a stand-alone screening test to predict a difficult laryngoscopy. Furthermore, combined with Mallampati score in a decision tree algorithm, it can considerably improve difficult airway prediction. The proposed models are also easy to understand and use, making them a useful tool for clinical practice in airway management.

Acknowledgments

The authors thank Nuno Ribeiro, MD (Department of Imagiology, Hospital Center Tondela-Viseu, Portugal), for his suggestions and support and CI&DETS - Polytechnic Institute of Viseu for the financial support.

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